Pneumonia and pleurisy in sheep:

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Pneumonia and pleurisy in sheep:

Studies of prevalence, risk factors, vaccine efficacy and economic impact

Kathryn Anne Goodwin-Ray

2006

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Pneumonia and pleurisy in sheep:

Studies of prevalence, risk factors, vaccine efficacy and economic impact

A thesis presented in partial fulfilment

of the requirements for the degree of Doctor of Philosophy at Massey University, Palmerston North

New Zealand

Kathryn Anne Goodwin-Ray

2006

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Abstract

The objectives of this thesis were to investigate patterns of lamb pneumonia prevalence of a large sample of New Zealand flocks including an investigation of spatial patterns, to evaluate farm-level risk factors for lamb pneumonia, to determine the efficacy of a commercially available vaccine for the disease and to estimate the likely cost of lamb pneumonia and pleurisy for New Zealand sheep farmers.

Data were collected by ASURE NZ Ltd. meat inspectors at processing plants in Canterbury, Manawatu and Gisborne between December 2000 and September 2001. All lambs processed at these plants were scored for pneumonia (scores: 0, <10% or ≥10% lung surface area affected) involving 1,899,556 lambs from 1,719 farms. Pneumonia prevalence was evaluated for spatial patterns at farm level and for hierarchical patterns at lamb, mob and farm levels (Chapter 3). The average pneumonia prevalence in Canterbury, Feilding and Gisborne was 34.2%, 19.1% and 21.4% respectively. Odds ratios of lambs slaughtered between March and May were vastly higher than those slaughtered in other months indicating longer growth periods due to pneumonia. Since pneumonia scores were more variable between mobs within a flock than between flocks, it was concluded that pneumonia scores were poor indicators for the flock pneumonia level due to their lack of repeatability. There was no statistically significant spatial autocorrelation in pneumonia prevalence for any region, hence lamb pneumonia appeared to be largely independent of topographical and geo-climatic factors.

A questionnaire-based case-control study was conducted investigating farm-level factors from a sample of farms with either high (case) or zero (control) pneumonia prevalence at slaughter (Chapter 4). Significant risk factors for case farms were: (1) shearing lambs on the day of weaning, (2) breeding ewe replacements on-farm (3) number of lambs sold (an indicator of flock size) and (4) increased percentage of lambs sold late in the season

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with Vitamin B12 at weaning. In Canterbury, flocks with Romney ewes and other ewes had a higher risk of pneumonia than those with fine wool type ewes (Merinos, Corriedales or Halfbreds).

In a clinical trial, 8,364 lambs from seven commercial sheep farms with a history of lamb pneumonia were vaccinated with Ovipast Plus® or placebo by systematic random allocation within mob and farm. An assessment of the extent of pneumonic lesions was conducted at slaughter and lamb growth rate was monitored through the growth period (Chapter 5). The vaccination trial showed no statistically significant effect of Ovipast®

vaccination on the extent of lung lesions at slaughter or ADG of lambs from the first treatment until slaughter. No significant differences were found between isolation rates of Pasteurella spp and patho-histological classifications from pneumonic lung samples of placebo and vaccinated lambs.

A spreadsheet-based stochastic model was constructed to estimate the cost of lamb pneumonia and pleurisy to New Zealand farmers. The estimate was based on data of the effect of pneumonia on lamb growth rate, distributions of pneumonia severity, prevalence of moderate to severe pneumonia (≥10% lung surface area) and pleurisy prevalence (Chapter 6). The simulated annual average cost of pneumonia was NZ $28.1 million and that of pleurisy NZ $25.1 million. The combined cost of pneumonia and pleurisy to New Zealand farmers had an average of NZ $53.2 million (95% stochastic interval = $32.4–

$78.9 million), or US $31.9 million per annum. This would equate to NZ $2.32 per lamb.

In comparison, animal health, shearing expenses and feed expenses cost NZ $2.37, $2.62 and $1.85 per lamb, respectively.

This research has demonstrated sub-clinical pneumonia to be a widespread disease in the New Zealand sheep farming population while previous research has focussed on case studies of affected farms. The estimated costs of pneumonia and pleurisy to New Zealand farmers ($53.2 million) highlight the financial effects of these diseases and the need for further research. We also found that the commercially available vaccine could neither prevent sub-clinical effects (lamb growth rate) nor clinical manifestations (pneumonic lung lesions) of lamb pneumonia. The case-control study has revealed farm-level factors which, in the absence of effective vaccines, indicated management practices that farmers might perceive as opportunities to control lamb pneumonia. However, it is advisable to evaluate the efficiency of such management changes.

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Pneumonia is aetiologically complex disease involving the interplay of many environmental, host and pathogen factors. It is also a difficult disease to study in the absence of diagnostic tests in live animals. However, further research should focus on the development of management changes until effective vaccines are available. A starting point for this research would be to evaluate the impact of such management changes in reducing the incidence of lamb pneumonia. More specifically, the roles of stress during crowding of lambs for extended periods warrants further investigation. The development of efficient vaccines requires an analysis of pathogens, especially Pasteurella (Mannheimia) haemolytica and Mycoplasma species, the sources of infection, their strain diversity and transmission dynamics.

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Acknowledgements

There are several people to whom I am grateful for their various contributions to this research work and thesis. Firstly, I would like to express my gratification to my supervisors Dr. Cord Heuer and Dr. Mark Stevenson for their invaluable knowledge, input and time into this study. They both have been very approachable and willing to help. I'd also like to extend my appreciation to Colin Brown, Tony Rhodes, Sam McIvor and Mark Aspin for the management of funding, facilitating various industry meetings and overall support. I would like to acknowledge the support of Meat New Zealand who funded this project. Julie Dunlop, Colleen Blair and Simon Verschaffelt have provided valued administrative and computer support. Thank you to Dr. Ron Jackson who provided input through various stimulating discussions, support at industry meetings and encouragement throughout the course of my study. Other EpiCentre staff and students, although not directly involved in my studies have also provided support and friendship throughout my PhD, I thank you all too. Not only does the EpiCentre have a world-renowned reputation professionally, it also has a warm, friendly and supportive atmosphere in which to study.

For data collection, I am indebted to ASURE NZ Ltd. meat inspectors at Canterbury Meat Packers, Lamb Packers Feilding Ltd. and Gisborne Progressive Ltd. lamb processing plants for their efforts outside of regular duties without financial reward. This data has provided most of basis for this thesis. I would also like to thank the lamb suppliers to these processing plants who gave up their time to fill in the extensive questionnaire that was mailed to them. I would like to thank the farmers involved in the vaccination trial for their time, co-operation and enthusiasm. Thanks to Maurice Alley who performed the histopathology of lung samples for the vaccination trial and Anne Midwinter and Lynn Rogers who performed the bacteriology. There were various people who assisted in ear tagging, administering treatments and weighing lambs. These people include; Diane Richardson, Annette Sutherland, Ema Tocker, Andrew Goodwin, Jason McMurray, Andre

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Sutherland, Mike, Troy Sutherland, Ema Tocker, Andre Sutherland, Steven Ray, Stuart Field and Esther Richardson for their help. I would like to extend particular thanks to Annette Sutherland for her involvement throughout the trial with weighing, vaccination, ear tagging, processing plant data collection, sample processing and data entry and last but not least, friendship and support.

I would like to thank my friends and family for their continued support. I dedicate this thesis to the memory of my late father John who passed away in April 2006 and my late mother Betty who passed away in December 1997. Mum and Dad were sheep farmers in South Canterbury. Dad was especially proud that sheep were the focus of my studies. I would like to thank my husband Steve for his help with the vaccination trial but mostly for his tremendous support, love and encouragement.

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List of Figures

Figure 2.1: Average daily pasture growth rates for 50 North Island (♦) and 24 South Island (■) farms per month and 95% confidence intervals (adapted from Dexcel Limited (2005)) ...10 Figure 2.2: Map of New Zealand ...22 Figure 2.3: Isolation of adenovirus (WV 757/75, WV 419/75) and parainfluenza type

3 virus (PI3) in the surveillance group of lambs, nasal isolation of Mycoplasma spp. (Nasal Myco.) and P. haemolytica (Nasal P. haem), average haemaglutinating antibody titres to P. haemolytica (titre to P.

haem) and pneumonia prevalence (prevalence) at slaughter in random groups of lambs (adapted from (Pfeffer et al., 1983) ...34 Figure 2.4: Prevalence of lambs with pneumonia lesions classified as Category 3 or 4

(≥ 10.0% lung surface affected) that were randomly selected for slaughter at monthly intervals (Group I) from Southland ( ), King Country ( ) and Northland ( ) in December (D) 2000; and January (J), February (F), March (M), April (A) and May (My) 2001 (Goodwin et al., 2004)...46 Figure 2.5: Percentage of lambs with pleurisy at slaughter between December and

July 2002/2003 in five regions of New Zealand (ASURE New Zealand Ltd., P.O.Box 1141, Christchurch)...49 Figure 2.6: Percentage prevalence of major pleurisy at slaughterhouses in Timaru

(South Canterbury), Bluff (Southland), Wairoa (Northern Hawkes Bay) and Moerewa (Northland) (Van der Logt, 1996) ...50 Figure 3.1: Map of New Zealand with shaded areas indicating the selected study

areas: (a) Canterbury, (b) Manawatu, and (c) Gisborne. Circles represent areas where farms were selected for the spatial analyses described in the text ...71 Figure 3.2: Pneumonic lesions in lambs slaughtered in three regions of New Zealand,

December 2000 to September 2001. Number of lambs slaughtered per month at the Canterbury, Manawatu, and Gisborne plants ...76 Figure 3.3: Pneumonic lesions in lambs slaughtered in three regions of New Zealand,

December 2000 to September 2001. Mean monthly true pneumonia prevalence (with 95% confidence intervals) for lambs slaughtered at the Canterbury, Manawatu, and Gisborne plants ...80 Figure 3.4: Pneumonic lesions in lambs slaughtered in three regions of New Zealand,

December 2000 to September 2001. Point maps showing the location of case and control flocks in: (a) Canterbury, (b) the Manawatu, and (c) Gisborne ...83

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incidence risk of moderate to severe pneumonia for flocks in: (a) Canterbury, (b) the Manawatu, and (c) Gisborne. In (a) the shaded circular area identifies the location of the significant cluster of case flocks, identified using the spatial scan statistic ...84 Figure 3.6: Pneumonic lesions in lambs slaughtered in three regions of New Zealand,

December 2000 to September 2001. Binned omnidirectional variograms computed using the standardised residuals from the multilevel model for flocks in: (a) Canterbury, (b) the Manawatu, and (c) Gisborne ...86 Figure 4.1: Case-control study of lamb pneumonia in three regions of New Zealand,

December 2000 to May 2001. Path model showing inter-relationships between variables listed in chronological order with significant direct or indirect paths to case or control flock ...107 Figure 5.1: Clinical trial of Ovipast Plus® vaccine in seven commercial lamb flocks

in the lower North Island of New Zealand, 2002/2003. Least square means of ADG (g/day) of lambs in the first growth period (W1 to W2:

0–11 weeks post vaccination 1) by flock and vaccination group (error bars show 95% confidence intervals)...124 Figure 5.2: Clinical trial of Ovipast Plus® vaccine in seven commercial lamb flocks

in the lower North Island of New Zealand, 2002/2003. Least square means of ADG (g/day) of lambs in the second growth period (W2 to W3:

11–23 weeks post vaccination 1) by flock and vaccination group (error bars show 95% confidence intervals)...125 Figure 5.3: Clinical trial of Ovipast Plus® vaccine in seven commercial lamb flocks

in the lower North Island of New Zealand, 2002/2003. Least square means of ADG (g/day) of lambs in the overall growth period (W1 to WS: vaccination 1–slaughter) by flock and vaccination group (error bars show 95% confidence intervals). ...126 Figure 5.4: Clinical trial of Ovipast Plus® vaccine in seven commercial lamb flocks

in the lower North Island of New Zealand, 2002/2003. Least square means () (and 95% CI) of weight gains (g/day) of lambs from vaccination 1 to slaughter according to pneumonia category (Category 0, no pneumonia; Category 1, <5%; Category 2, 5-9.9%; Category 3, 10- 19.9%; and Category 4, ≥20% lung surface area affected).. ...127 Figure 6.1: Stochastic model to estimate the direct annual cost of pneumonia and

pleurisy to New Zealand farmers. Scatter plots, regression equations and the multiple coefficients of determination (R²) of average cost of pneumonia per lamb (AML) for 14 () flocks (Goodwin-Ray and Heuer, 2006) and 7 flocks (–) (Goodwin et al., 2005), according to moderate to severe pneumonia (≥ Category 3) prevalence (% of lambs) for (a) January, (b) February, (c) March and (d) April...141 Figure 6.2: Least square means (■) (and 95% CI) of average daily weight gains

(g/day) of randomly selected lambs in the month prior to slaughter in categories of: 0, no pneumonia; 1, ≤ 5% lung surface area affected; 2, 5- 9.9%; 3, 10-19.9%; and 4, ≥ 20% lung surface area affected ...145 Figure 6.3: Stochastic model to estimate the direct annual cost of pneumonia and

pleurisy to New Zealand farmers. Distributions of true moderate to

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severe pneumonia (≥ 10%lung affected) prevalence (adjusted according to sensitivity and specificity (Table 6.2) based on 1,719 flocks for January (a), February (b), March (c), April (d), May (e) and June (f) (frequency of flocks with 0 prevalence indicated at top of bar (n = number of flocks in category 0)). ...146 Figure 6.4: Stochastic model to estimate the direct annual cost of pneumonia and

pleurisy to New Zealand farmers. Distribution of the estimated annual cost of pneumonia to New Zealand farmers...148 Figure 6.5: Stochastic model to estimate the direct annual cost of pneumonia and

pleurisy to New Zealand farmers. Distribution of the estimated annual cost of downgraded or condemned carcasses due to pleurisy to New Zealand farmers ...150 Figure 6.6: Stochastic model to estimate the direct annual cost of pneumonia and

pleurisy to New Zealand farmers. Distribution of the estimated annual cost of pleurisy and pneumonia to New Zealand farmers. ...151

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List of Tables

Table 2.1: Number of farms with the average and standard deviation of farm size and number of sheep per farm grouped by region (adapted from AgriBase (AgriQuality, 2004))...4 Table 2.2: Average dates of mating, lambing, weaning, ages of lambs at tailing,

weaning and slaughter with each standard deviation (SD, days) and number of flocks in the calculation based on a survey of 313 sheep flocks in Gisborne, Manawatu and Canterbury (refer Chapter 4, this thesis)...8 Table 2.3: Pathogens of sheep pneumonia and their sensitivity to antibiotics, with

study references ...17 Table 2.4: Bacterial isolations from cases of ovine pneumonia ...30 Table 2.5: Mycoplasmal isolations from cases of ovine pneumonia ...32 Table 2.6: Relationship between virus infections and prevalence of pneumonia

(Davies et al., 1980a)...33 Table 2.7: Prevalence of enzootic pneumonia and pleurisy on necropsy in lambs

less than 3 months of age (below slaughter weight) from three New Zealand sheep farms (McGowan et al., 1978)...44 Table 2.8: Prevalence of enzootic pneumonia and pleurisy at time of slaughter in

market lambs from three New Zealand sheep farms (McGowan et al., 1978)...44 Table 2.9: Prevalence of pleurisy at slaughter in market lambs from 3 farms from

the studies of McGowan et al. (1978) and Davies et al. (1980a) ...51 Table 2.10: Pasteurella vaccines commercially available throughout the world...56 Table 2.11: Group mean disease scores and percentage protection of iron regulated

protein vaccines in SPF lambs challenged with P. haemolytica A2 (Gilmour et al., 1991) ...58 Table 3.1: Date, duration and number of lungs sampled for validation of pneumonia

data from Canterbury, Manawatu and Gisborne between May 1^st and June 8^th 2001...77 Table 3.2: Validation sensitivity and specificity (with 95% confidence intervals), of

inspector diagnosis of minor, moderate to severe and total pneumonia in Canterbury, Manawatu and Gisborne...78 Table 3.3: Descriptive statistics of number of mobs, number of lambs, means of

true minor, true moderate to severe and total pneumonia prevalence per flock, grouped by region with 95% confidence intervals...79

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flock-level from Canterbury, Manawatu and Gisborne between December 2000 and September 2001...81 Table 3.5: Number of study flocks selected for spatial analysis supplying lambs to

data collection processing plants, mean (standard deviation) number of lambs supplied per flock, true moderate to severe pneumonia prevalence and true total pneumonia prevalence in Canterbury, Manawatu and Gisborne ...82 Table 4.1: Summary description of variables from a retrospective questionnaire (for

2000/2001 season) mailed to study flocks in 2002 ...98 Table 4.2: Descriptive and univariate statistics of continuous variables grouped by

time period (significant at p ≤ 0.250) for case and control flocks ...99 Table 4.3a: Control and case flock frequency (n) and odds ratios (OR) with 95%

confidence intervals (95% CI) for categorical time independent mating to lambing variables (p ≤ 0.250). ...100, 101 Table 4.3b: Control and case flock frequency (n) and odds ratios (OR) with 95%

confidence intervals (95% CI) for categorical variables from lambing to slaughter (p ≤ 0.250) ...102, 103 Table 4.4: Odds ratios (95% confidence interval, CI) of the final logistic regression

model for flock-level management factors on lamb pneumonia (control flock: 0% moderate-severe pneumonia; case flock: ≥ 3% moderate- severe pneumonia)...104 Table 5.1: Frequency of the number of lambs (placebo, vaccinated and total) for the

planned sample size, those enlisted in the trial (W1) by flock and region, those present at vaccination 2 (W2), those with average daily weight gain (ADG (g/day)) records and those with pneumonia scores and the number of lung lesions cultured and examined for histopathology ...122 Table 5.2: Descriptive statistics of average daily gain (ADG,(g/day)) calculated

from the difference between the weight taken at vaccination 1 (W1) and the final pre-slaughter weight in vaccinated and placebo lambs from 7 commercial sheep flocks ...123 Table 5.3: Number of placebo and vaccinated lamb’s lungs scored at slaughter for

pneumonia and weighted average slaughter dates from seven trial sheep flocks ...128 Table 5.4: Percentages of placebo (n = 2,596) and vaccinated lambs (n = 2,454) in

five pneumonia categories...129 Table 5.5: Adjusted relative risks for the effect of vaccination on moderate to

severe pneumonic lesions ( ≥ 10% lung surface area affected) adjusted for flock of origin and month of slaughter (95% CI = 95% confidence interval) ...129 Table 5.6: Prevalence of isolation of P. haemolytica or P. trehalosi from

pneumonic lung lesions of placebo and vaccinated lambs from five commercial sheep flocks in New Zealand (p = 0.884)...130

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Table 5.7: Histopathology results from samples of lambs from four commercial sheep flocks in New Zealand grouped by placebo or vaccinated lambs (p

= 0.284)...130 Table 5.8: Histopathological classifications of disease from samples of lambs from

four commercial sheep flocks in New Zealand grouped by isolations of P. haemolytica or P. trehalosi from pneumonic lung lesions (p = 0.649) ...131 Table 6.1: Most likely value, standard deviation (SD), minimum, maximum and

assumed distribution of stochastic model variables ...144 Table 6.2: Sensitivity and specificity (with 95% confidence intervals), of inspector

diagnosis of moderate to severe pneumonia for Canterbury, Manawatu and Gisborne processing plants ...147 Table 6.3: Mean pleurisy prevalence (95% CI) from January-June 2001 for

Canterbury, Manawatu and Gisborne processing plants ...147 Table 6.4: Correlation coefficients between model output (total cost of pneumonia)

and sets of sampled input variables (n = 5), ranked according to significance...149 Table 6.5: Correlation coefficients between model output (total cost of pleurisy)

and sets of sampled input variables (n = 5), ranked according to significance...150 Table 6.6: Correlation coefficients between model output (total cost of pneumonia

and pleurisy) and sets of sampled input variables (n = 10), ranked according to significance...152

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CHAPTER 1 Introduction

The need to further investigate lamb pneumonia arose in 1997 through a meeting of epidemiologists, pathologists, industry representatives and farmers. The focus of that meeting was to establish the current knowledge and future requirements for research. A funding application to Meat New Zealand was successful and lead to a Masterate study preliminary to this Doctorate study. The objectives of the Masterate study were to quantify the impact of the disease on lamb live-weight gain. A longitudinal study was conducted involving farms known to have a history of pneumonia. It was shown that pneumonia had a significant impact on lamb growth rate. A reduction in average daily weight gain of up to 50% was evident in the most severe pneumonia cases. A panel of experts finally realised that economic loss due to lamb pneumonia was primarily at sub-clinical level through reduced growth rates and that disease related mortality was rather exceptional and low at population level.

Subsequent to the Masters study, a need arose to estimate total economic loss due to lamb pneumonia, to investigate spatial and temporal patterns of pneumonia prevalence in New Zealand, and to determine on-farm risk factors that might lead to control options and if feasible, to evaluate control. On this basis, the current PhD study was successful in attaining further funding by Meat and Wool New Zealand (MWNZ). The New Zealand sheep industry has guided our research through regular mentor meetings involving representatives from the sheep council, processing plants, MWNZ, researchers from Massey University and AgResearch and farmers. As a result of one of these meetings, the need to determine the efficacy of a commercially available vaccine against pneumonia was voiced leading to one chapter of this PhD. Pneumonia is not routinely recorded at lamb processing plants, so this project was fortunate to have the support of ASURE NZ Meat Inspectors who collected data in addition to their regular duties. Pneumonia scores were

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CHAPTER 2 Review of the literature on pneumonia and pleurisy in lambs

2.1 Introduction

Pneumonia is a respiratory disease arising from an inflammatory response of the bronchioles and alveoli in the lung to infective agents and resulting in the consolidation of lung tissue. It is a common disease of sheep in all major sheep-producing countries. It is regarded as a disease complex, involving interactions between host (immunological and physiological), multiple agents (viral, bacterial, mycoplasmal) and environmental factors.

When a certain threshold dose of microorganisms, host susceptibility and non-specific defence mechanisms are reached, lung defence mechanisms are compromised allowing disease to occur (Bruere et al., 2002). The disease occurs in two main forms in New Zealand sheep: an acute fibrinous pneumonia which occurs in sheep of all ages and a chronic non-progressive pneumonia (CNP) which occurs in lambs and hoggets (Bruere et al., 2002). Extension of pneumonia from the surface of the lung to the lining of the chest cavity results in inflammation of the pleura and the formation of a fibrous adhesion between lungs and the chest wall, known as pleurisy. Ovine progressive pneumonia and Jaagsiekte, (caused by an ovine retrovirus) is exotic to New Zealand (Dalefield and Alley, 1988; Alley, 2002). In lambs pneumonia causes mortality, decreased growth and a predisposition to pleurisy, at considerable cost to the industry, along with animal welfare implications. Due to its sub-clinical nature, detection of CNP is limited to examination of lungs at necropsy or after slaughter. Inability to detect the disease in the live animal and detailed knowledge of the time of onset of lesions severely limits our understanding of the epidemiology of pneumonia in sheep and its effect on productivity. The aim of this review is to give a background of sheep farming in New Zealand and provide an overview of respiratory diseases of sheep and pneumonia and pleurisy in lambs including a critique of relevant scientific trials and literature.

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2.2 Sheep farming in New Zealand

Sheep farming plays an important role in New Zealand’s economy especially with regard to export. In June 2004, there were 39.3 million sheep in New Zealand, comprising 26.7 million breeding ewes, 8.0 million ewe hoggets, 3.1 million wether hoggets and 1.4 million other wethers and rams (MWES, 2004). New Zealand sheep farms are, on average 506 hectares in size and are comprised of around 1,991 sheep (Table 2.1). Cattle are often farmed on the same properties. South Island farms tend to be more extensive than those of the North Island. They are generally larger in size but do not tend to differ in sheep numbers per property.

Table 2.1: Number of farms with the average and standard deviation of farm size and number of sheep per farm grouped by region (adapted from AgriBase (AgriQuality, 2004)).

Region Number of farms (≥ 4 ha, ≥ 20 sheep)

Average (SD) of farm size (hectares)

Average (SD) number of sheep/farm

Lower South Island

5,774 678 (2,195) 2,358 (2,845)

Upper South Island

3,168 532 (1,785) 1,656 (2,040)

Lower North Island

5,236 396 (591) 2,203 (2,735)

Upper North Island

3,746 371 (667) 1,410 (2,365)

Total 17, 924 506 (1,525) 1,991 (2,616)

SD – standard deviation

2.2.1 Sheep Breeds

There are approximately 30 sheep breeds in New Zealand. The six most common are:

• Romney (originally the English Romney Marsh, brought to New Zealand in 1853).

• Coopworth (cross of Border Leicester and Romney).

• Perendale (cross of Cheviot and Romney).

• Merino (originated from North Africa or Spain).

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• Corriedale (British long wool rams - Lincoln and English Leicester mainly - crossed with Merino ewes).

• Halfbred (Merino crossed with Leicester, Lincoln or Romney) (Statistics New Zealand, 1996).

The geographical distribution of breeds tends to reflect regional differences in climate and topography. Merinos predominate in the alpine grasslands of the Southern Alps.

Halfbreds and Corriedales tend to be farmed on the foothills and plains east of the Southern Alps and some drier parts of the North Island. Romneys, Coopworths and Perendales typically are used for meat and wool production on hill country sheep farms elsewhere in New Zealand. Often Texel, Southdown or Suffolk rams are used for market lamb production as they are earlier maturing compared with traditional breeds. In more recent times composite breeds have played a role in breeding programmes. Breeds of higher fecundity and milk production are used in composites, such as Finish Landrace and East Friesian.

2.2.2 Sheep products and markets

Throughout the twentieth century New Zealand has enjoyed a reputation for being largest producer of crossbred wool (wool fibre >31 microns in diameter) throughout the world (MAF, 2004d). Crossbred wool is used for interior textiles such as carpets, upholstery, furnishings, rugs, hand knitting yarn, knitwear and in blankets. Fine wool (<24.5 micron) comprised five percent of export wool volume in 2003/2004 (MAF, 2005) and is used in the clothing industry.

The annual production of lamb meat in New Zealand was approximately 410,000 tonnes in 2004 (MAF, 2005), of which 91% was exported, with the remainder being consumed locally (MIA, 2004). New Zealand sheep meat accounted for 47% of the world export trade of lamb and mutton in 2002(MAF, 2004c). The major markets of sheep meat in are the European Union, United States and Asia. In the year ended September 2004, approximately 19% of New Zealand exported lamb was chilled (contributing 29% of total lamb export revenue) and the remainder frozen (MAF, 2005). Annual mutton production was approximately 107 tonnes in 2004 (MAF, 2005), of which 83% was exported (MIA, 2004).

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2.2.3 Structure of the Industry

Meat and Wool New Zealand is a body funded by livestock producer levies on all sheep slaughtered in New Zealand (MWNZ, 2004a).

Its purpose is to:

• Market New Zealand sheep meat internationally and domestically.

• Maintain and extend trade access for New Zealand red meat.

• Fund research and development to help improve the profitability of New Zealand farmers (MWNZ, 2004a).

Within the wool industry there are other groups involved in marketing, research and development. These are:

• The National Council of New Zealand Wool Interests (provides the forum in which all sectors involved in the New Zealand wool industry work together for the benefit of the industry) (NZTE, 2004).

• The New Zealand Merino Company Ltd (A joint venture between New Zealand Merino woolgrowers and Wrightson Ltd which handles the majority of the merino wool clip. It has developed a number of direct supply linkages where growers are contracted to supply agreed amounts of fibre meeting agreed specifications to particular manufacturers) (MAF, 2004a);

• Wool Interiors Ltd (International marketing of New Zealand wool and products through management of the Wools of New Zealand branding programme) (NZTE, 2004).

• Canesis Network Ltd (Jointly owned by the Wool Research Organisation of New Zealand and Wool Equities Ltd. A grower-owned investment company specialising in wool, sheep research and development on ways of using New Zealand wool, developing innovative wool and wool-blend products) (NZTE, 2004).

In the meat industry, more than 150 New Zealand meat processing companies are licensed to operate slaughter houses, the majority of which produce meat for export. The four largest exporting companies are PPCS Limited, AFFCO New Zealand, ANZCO Foods Limited and the Alliance Group (NZTE, 2004).

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The Meat Industry Association of New Zealand (MIA) represents processing companies that supply sheep meat for export. The MIA provides a forum for consideration of industry-wide commercial, human resource, marketing and sanitary and phytosanitary issues. They convey a collective industry position to government, trade bodies and other agencies and organisations (MIA, 2005).

Sheep meat and wool production in New Zealand is undertaken without the assistance of government subsidies. Agricultural subsidies were removed in the mid-1980s leaving producers and exporters entirely reliant on export market returns (MAF, 2004b). Since then, sheep numbers have decreased from 70 million to 39 million and farmers have diversified, especially into dairying and deer farming. Farm productivity since this time has improved. The average slaughter weight of lambs has increased along with an increase in lambing percentage from 100% to 115%. The processing and marketing companies have moved from exports of whole frozen carcasses to chilled meat which made up 25% of lamb export value in 2004 (MAF, 2005). The current projection for the New Zealand sheep industry to 2008 is promising, with expected increases in sheep meat production, lamb carcass weights and lamb price (MAF, 2005).

2.2.4 Timing of Farm Management Events

Ewes are mated in autumn and lamb in spring (Fleming, 2003a). Table 2.2 shows average dates and ages for mating, lambing, tailing, weaning and slaughter based on a survey of 313 sheep flocks from Gisborne, Manawatu and Canterbury. On average rams are put with ewes in late March for 57 days leading to a lambing start date in late August (Table 2.2).

The average lambing date is 3 September. Lambs are tailed on average at 45 days of age, weaned mid December at 101 days of age and slaughtered 72 days post-weaning. Shearing may be carried out once a year, twice a year (second-shearing) or three times every two years.

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Table 2.2: Average dates of mating, lambing, weaning, ages of lambs at tailing, weaning and slaughter with each standard deviation (SD, days) and number of flocks in the calculation based on a survey of 313 sheep flocks in Gisborne, Manawatu and Canterbury (refer Chapter 4, this thesis).

Variable Number of

flocks Average (SD (days))

Date ram out 296 29 March (23.4)

Number of days ram out 298 57 (24.2)

Start date of lambing 300 22 August (24.6)

Average lambing date 298 3 September (24.4)

Age of lambs at tailing (days) 288 45 (24.2)

Date of weaning 298 13 December (23.1)

Age of lambs at weaning

(days) 297 101 (21.1)

Average slaughter age (days) 296 173 (30.6)

SD – standard deviation

2.2.5 Farming systems

There are two main types of sheep farming systems. These are;

1. Sheep breeding

a. Flocks of breeding ewes with ewe replacements bred ‘on-farm’ and lambs finished to slaughter weight or,

b. Flocks of breeding ewes with ewe replacements bred ‘on-farm’ selling a proportion of lambs as ‘forward stores’ (sale of live lambs not yet at slaughter weight) with the remaining proportion finished to slaughter weight.

2. Sheep finishing

a. Flocks of breeding ewes where no ewe replacements are bred ‘on-farm’.

Ewe replacements are purchased from other properties (often older ewes which are then sold post weaning) and lambs are finished to slaughter weight.

b. No breeding ewes ‘on-farm’. Lambs purchased as ‘forward stores’ and finished to slaughter weight.

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2.2.6 Disease Status

New Zealand is free of foot-and-mouth disease and scrapie, aided by its geographical isolation from affected countries (MWNZ, 2004b). Some of the most relevant health problems in New Zealand sheep are internal and external parasites, facial eczema, footrot, pneumonia, pleurisy, caseous lymphadenitis, scabby mouth, Johnes disease, toxoplasmosis, campylobacteriosis, listeriosis, leptospirosis, brucellosis and salmonella.

2.2.7 Pasture growth and climate

The generally mild temperatures and reliable annual rainfall in New Zealand favours a pasture based livestock production system. Sheep are traditionally grazed on pasture year round, often with supplements of hay or silage in the winter (MAF, 2004c). In the South Island, crops such as Swedes and Brassicas are often grown for winter feeding. Fertiliser is commonly applied and irrigation is used in areas where rainfall is low for pasture production. Pasture growth occurs for 8 to 12 months of the year depending on soil type and location. Based on values from 1971-2000 (for locations having at least 5 complete years of data), the average annual temperature and rainfall for the South Island was 11^oC and 1656 mm and that for the North Island was 13.9^oC and 1166 mm (NIWA, 2001).

Average daily pasture growth rates in the South Island (n = 24 farms) and North Island (n

= 50 farms) are shown in Figure 2.1 by calendar month.

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North Island South Island

0 10

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov D

Av

20 60 70

ec Month

30 40 50

erage pasture growth rate (kgDM/ha/day)

Figure 2.1: Average daily pasture growth rates for 50 North Island (♦) and 24 South Island (■) farms per month with 95% confidence intervals (adapted from Dexcel Limited (2005)).

2.3 Respiratory disease in sheep

2. Chronic non-progressive pneumonia (CNP).

Respiratory disease is common in most livestock around the world. There are several different types recognised in sheep:

1. Acute pneumonia (AP).

3. Ovine progressive pneumonia (OPP) or maedi-visna (MV).

4. Pleurisy.

5. Jaagsiekte sheep retrovirus (JSRV).

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In New Zealand AP, CNP and pleurisy are the only forms of ovine respiratory disease currently recognised.

purulent asal discharge, increased respiratory rate and rales in the anterior thorax (Gilmour and

rring mainly in the cranioventral bes. The remainder of the lung becomes congested and may contain haemorrhages

acute stage may recover, or become chronically

onia, proliferative terstitial pneumonia or enzootic pneumonia.

experimentally induced CNP, Jones et al. (1982) observed laboured breathing or abnormal breathing during the first 14 days post inoculation. During the first 6 weeks post inoculation the majority of the lambs appeared depressed and fever was recorded in 67% of 2.3.1 Clinical and patho-physiological classification

Acute pneumonia (AP)

This type of pneumonia has also been referred to as acute fibrinous pneumonia, acute necrotising pneumonia, acute exudative pneumonia or pneumonic pasteurellosis. Clinical signs of AP include fever, depression, weight loss, isolation from flock, muco

n

Angus, 1983). AP often results in death within 12 hours of the onset of any clinical signs in sheep of any age (Alley, 1991). Mortality rates associated with acute pneumonia vary between 2 and 8% (Bruere et al., 2002).

On post mortem examination fibrinous exudates are present in the thoracic cavity with variable amounts of swollen, dark red consolidation occu

lo

(Alley, 2002). Animals surviving this

affected with reduced lung capacity and reduced weight gain (Brogden et al., 1998).

Chronic non-progressive pneumonia (CNP)

CNP is a subclinical form of pneumonia occurring more commonly in lambs or hoggets between 3 and 10 months of age (Bruere et al., 2002). CNP has also been referred to as atypical pneumonia, summer pneumonia, proliferative exudative pneum

in

CNP has few, if any, clinical signs (Alley, 1987b). Chronic coughing, difficulty in breathing, abnormally fast breathing (best demonstrated by exercise) or a mucopurulent nasal discharge may be present (Jones and Gilmour, 1983).

In

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them. Generally, CNP is associated with high morbidity and low mortality (Bouljihad and

NP and AP are considered to be pathologically different due to the severity and extent of

P. haemolytica erotypes between the two disease forms (Alley, 2002).

eathing and ‘visna’ as wasting.

Leipold, 1995).

Lesions are usually confined to the apical lobes and vary in colour from grey to red-brown.

They may be accompanied by dull red bands of collapsed tissue (Jones and Gilmour, 1983). CNP may last several months but lesions may resolve. Gilmour et al.(1982a) suggest that complete regression of lesions is unlikely in less than 7 months. Lungs may be permanently shortened but consolidated tissue can be re-aerated (Alley, 1991).

C

damage to the alveolar epithelium. In both forms of pneumonia, Pasteurella (Mannheimia) haemolytica is considered to be the main bacterial agent responsible for lung damage where multiple serotypes may be involved (P. haemolytica serotype A1, A2, A6, A7 and A9). However, little is known of the frequency of recovery of

s

Ovine-progressive pneumonia (OPP)

OPP is a lentivirus disease of sheep in North America, which may progress for several months to a year before death occurs. Characteristic signs of disease include severe and progressive weight loss and laboured breathing or pneumonia. In most cases infected animals show no clinical signs. Maedi visna is a disease exotic to New Zealand, caused by a lentivirus closely related physically and biochemically to that causing OPP (Cutlip et al., 1986). ‘Maedi’ translates as difficult br

Clinical signs of OPP seen in animals 2 to 3 years old include laboured respiration, loss of condition, decreased milk production and abortion. Lungs become mottled greyish-blue to greyish-brown, firm and large (2 to 3 times the normal weight). Transmission of the disease is pseudo-vertical through the ingestion of infected colostrum and milk. There is no effective treatment or vaccine available (Bruere et al., 2002).

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Sheep pulmonary adenomatosis

Jaagsiekte sheep retrovirus (JSRV) causes sheep pulmonary adenomatosis (SPA) which is a contagious disease characterised by a tumour in the lungs of adult sheep (Holland et al., 1999). A herpes virus and a retrovirus are often aetiologically associated with the disease.

SPA has been reported in Europe, South Africa, Asia, Britain, Iceland and Israel. The isease is spread mainly by aerosol transmission. The incubation period in naturally rs to be long, which means that the disease is generally only seen in

n rare occasions tumours have been seen in lambs as young as

e dhesions stretch with respiration (Blood and Radostits, 1989). Pleurisy lesions never resolve completely and permanent fibrous scars remain on the lungs and the parietal d

infected sheep appea adult animals. However, o two months old.

Traditionally, classical SPA is diagnosed on the basis of chronic wasting with marked respiratory signs in adult sheep (Sharp, 2000). At necropsy, grey lesions are found in the apical and cardiac lobes of lungs and the lung is 3 to 4 times its normal size. The only method of control is by slaughter of affected animals (Bruere et al., 2002).

Pleurisy

Pleurisy is an inflammation of the pleura resulting in fibrous adhesions between lung and chest wall. It has been commonly accepted that pleurisy is not a separate entity but part of a pleurisy-pneumonia complex of poorly defined aetiology (McGowan et al., 1978; Davies, 1985a; Pfeffer, 1986). Acute pleural adhesions are likely to contain large numbers of the bacteria that caused the pneumonia from which they arose. Chronic fibrous pleurisy of any size may only contain a few of these organisms or be sterile depending on the stage of the disease process (Davies et al., 1986a).

In the early acute stage of pleurisy, contact and movement between the parietal and visceral pleurae causes pain due to inflammation of the pleura. In the second stage, serofibrinous inflammatory exudate collects in the pleural cavity and can cause collapse of the ventral parts of the lungs. This reduces lung capacity and interferes with gas exchange.

In the third stage, fluid is resorbed and adhesions develop, restricting movement of the lungs and chest wall. Interference with breathing is minor and disappears with time as th a

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Animals with subclinical pneumonia and those surviving clinical pneumonia may develop

avies, 1985b; Pfeffer, 1986).

of whether lung damage has occurred or its extent.

ted the use of ultrasonographic examination to detect lung pleurisy. Extension of pneumonia from the surface of the lung to the lining of the chest cavity results in the formation of a fibrous adhesion between lungs and the chest wall.

These lesions persist after the pneumonia resolves and appear to accumulate with successive episodes of pneumonia (D

2.3.2 Diagnosis Diagnosis in live animals

In the case of AP, clinical signs may be present (refer 2.3.1, Acute pneumonia). However, mortality often occurs within 12 hours of the onset of any symptoms.

There are usually no clinical signs with CNP or pleurisy until the disease has reached an advanced state (refer 2.3.1, Chronic non-progressive pneumonia, Pleurisy). Serology of antibodies may indicate exposure to the main pathological agents of pneumonia in the live animal but gives no indication

Two studies have investiga

lesions (Maxson et al., 1996; Scott and Gessert, 1998). Both of these studies, however, highlighted the limitation of this diagnostic technique for use in lungs. This is because air reflects the ultrasonographic beam and prevents the visualisation of structures beneath the aerated lung surface. The study conducted by Scott and Gessert (1998) examined ten ewes with pulmonary disorders and found that abscesses involving the pleura were clearly visible. The extent of SPA (sheep pulmonary adenomatosis) lesions were able to be outlined and they identified secondary abscess formation within the tumour mass, however, no lung abscesses far away from the pleura surrounded by normal aerated lung tissue were identified during the ultrasonographic examinations. The study by Maxson et al. (1996) also found that ultrasound was limited in the detection of hydatid cysts in the lung because air in the peripheral pulmonary parenchyma reflects sound waves and prevents the imaging of deeper structures. Only hydatid cysts, which were adjacent to the chest wall, could be visualised. They reported a sensitivity and specificity of ultrasound examination for detecting hydatid cysts in sheep and goat lungs to be 54.4% and 97.6%.

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Diagnosis at slaughter

eatment

ntibiotics have been shown to have an effect in the treatment of pneumonia. When there have been substantial deaths attributed to AP in the field, antibiotics are used to treat the remainder of the flock to prevent further deaths. They can also be used to reduce the effects of CNP. There has been some degree of resistance of pneumonic pathogens to some types of antibiotic. A number of in vitro, experimental infection and field studies have tested a variety of antibiotics against strains of bacteria and mycoplasmas isolated from sheep pneumonia cases.

In vitro antibiotic studies

Six in vitro studies have measured the susceptibility or resistance of several sheep pneumonia pathogens to different types of antibiotics (Table 2.3). Three of the studies are Turkish (Otlu, 1997; Kaya and Kirkan, 1999; Gurbuz and Sahin, 2003), two are Indian (Umesh et al., 1994; Mondal and Srivastava, 2004) and the remaining study is French (Sanchis and Abadie, 1992). These studies have shown varying results where Gurbuz and Sahin (2003) have suggested that P. haemolytica isolates are 97% sensitive to penicillin and 93% sensitive to streptomycin, but other studies have shown P. haemolytica Biotype A to be resistant to streptomycin and Biotype T to be resistant to penicillin and streptomycin (Sanchis and Abadie, 1992; Kaya and Kirkan, 1999). There are also some conflicting results between Kaya and Kirkan (1999) and Sanchis and Abadie (1992), in the sensitivity of P. haemolytica Biotype A to erythromycin, kanamycin and gentamycin and that of Biotype T to erythromycin and ampicillin. In some of these studies (Umesh et al., 1994;

Gurbuz and Sahin, 2003; Mondal and Srivastava, 2004), there was a limitation of the number of isolates tested, particularly that of Mondal and Srivastava (2004), where only six isolates were tested. In terms of the number of isolates tested in the study of Sanchis and Abadie (1992, n=166) was superior to that of Kaya and Kirkan (1999, n=48) and The most accurate method of detecting chronic pneumonia and pleurisy in sheep is to carefully examine the lungs at necropsy (Alley, 2002). This restricts the establishment of pneumonia status to a single point in the life of a lamb, resulting in limited knowledge of disease development and progress.

2.3.3 Tr A

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oplasma species are susc

Some Myc eptible to an P. haemol

not and vice versa. It would appear based on the dies, that enro o tibiotics that P. haemolytica and Myc In the ab wing which p thogen is the cause of the field, the most su ntibiotic treatment would be that to whic vident.

tibiotics that se in vitro stu

ytica isolates are floxacin and

danofloxacin are the nly two an oplasma spp. are

susceptible to. sence of kno a pneumonia cases

in ccessful a h no resistance is

e

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Table 2.3: Pathogens of sheep pneumonia and their sensitivity to antibiotics, with study references.

Pathogen Antibiotic Sensitivity (Reference)

Sensitive strains (Reference)

Pasteurella haemolytica Danoflaxin 29/29

Enroflaxin 29/29

Erythromycin 24/29

Gentamycin 28/29

Penicillin 28/29

Streptomycin 27/29

Tetracycline 27/29

Kanamycin 26/29

Clavulanic acid-amoxicillin 0/29

P. haemolytica biotype A Penicillin Sensitive (2) 101/219

Ampicillin Sensitive (2) 215/219 Oxytetracycline Sensitive (2)

Erythromycin Sensitive (2) 103/219

Streptomycin Not sensitive (2) 93/217 Kanamycin Not sensitive (2) 199/219

Gentamycin Not sensitive (2) 211/220

Kanamycin Sensitive (6) Streptomycin Sensitive (6)

in 7/43

in 0/18

. ovipneumoniae Enrofloxacin 18/18

17/18

cin 16/18

P. haemolytica biotype T Erythromycin Sensitive (2) 22/42

Kanamycin Sensitive (2) 38/42 Gentamycin Sensitive (2) 42/42 Penicillin Not sensitive (2) 11/42 Ampicillin Not sensitive (2) 40/42

Oxytetracycline Not sensitive (2) 10/40 Streptomycin Not sensitive (2)

P. multocida Tetracycline Not sensitive (6)

Ampicillin Not sensitive (6) Gentamycin Sensitive (6)

Mycoplasma agalactiae Enroflaxin highly sensitive (3) Oxytetracycline highly sensitive (3) Gentamycin highly sensitive (3)

M. arginini Enrofloxacin 42/43

Danofloxacin 40/43

Ampicillin 39/43

Erythromyc Streptomyc M

Oxytetracycline Danofloxa

Ampicillin 16/18

Erythromycin 2/18

Streptomycin 0/18

References:

1 – Gurbuz and Sahin (2003).

2 – Kaya and Kirkan (1999).

3 – Mondal and Srivastava (2004).

4 – Otlu (1997).

5 – Sanchis and Abadie (1992).

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Experimental antibiotic studies

In the UK, long–acting oxytetracycline was administered to specific pathogen free lambs at a dose rate of 20 mg/kg either 24 hours before or 24 hours after exposure to an aerosol of P. haemolytica (Gilmour et al., 1982c). Three groups of 10 lambs with antibiotic treatment 24 hours before exposure, antibiotic treatment 24 hours after exposure and non-treated, exposed lambs were compared. The pre-infection treatment delayed the appearance of clinical signs of pneumonia by 4 days and deaths of 5 lambs for 5 to 6 days. Seven untreated lambs had died by this time. The post-infection treatment resulted in rapid clinical recovery persisting until 6 days post-infection, but 2 treated lambs died 7 days post-infection. The extent of lung lesions in the post-infection treatment lambs was reduced in comparison to untreated lambs. This indicated that oxytetracycline had some effect against P. haemolytica but was more effective when administered post-infection.

(long-acting oxytetracyline and lavulanic acid/amoxicillin) have had an effect on experimentally induced pneumonia.

ield studies investigating the effect of antibiotics have predominantly involved clinical or Three-week old lambs were experimentally challenged with an aerosol of P. haemolytica biotype A serotype 2 (Gilmour et al., 1990). Ten lambs were treated with a clavulanic acid and amoxicillin combination (repeated twice at 24 hour intervals). There was a significant difference in death rate, 1 out of 10 treated lambs died and 7 out of 10 untreated lambs died between 3 and 6 days after treatment. Post mortem examination showed bacteriological evidence of pasteurellosis and the presence of either pleurisy or subacute pneumonia.

These experimental field studies show that antibiotics c

Recent in vitro studies (as described above) have indicated some level of resistance of P.

haemolytica isolates to oxytetracyline and clavulanic acid-amoxicillin (Kaya and Kirkan, 1999; Gurbuz and Sahin, 2003).

Field studies of antibiotic use F

acute pneumonia. The challenge for the treatment of subclinical CNP is the ability to detect the disease in live animals and to correctly identify which animals to treat. In addition, issues involving antibiotic residues in lamb meat, antibiotic resistance and cost effectiveness of such treatments require consideration. In field studies involving acute pneumonia, antibiotic treatment has largely been effective.

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On seven Scottish farms there was a laboratory confirmation of Pasteurella-related deaths in young lambs (Appleyard and Gilmour, 1990). Half of each flock was treated with long- acting oxytetracycline (20 mg/kg intramuscularly). On four of the farms two treatments were given and on the remaining three only one treatment was given. Fewer deaths resulted in the treatment groups where 1 out of 345 (1 treatment) and 0 out of 533 (2 treatments) lambs died compared with the untreated control group where 10 out of 345 and

out of 533 lambs died. The comparison of lamb deaths, between lambs treated both once

cott, 1995). Half of the lambs were treated with a single bcutaneous injection of 10mg/kg tilmicosin (Micotil) and the other half with a single

ates of 1% due to pneumonia, were treated with gentamycin (Sadiek et al., 1993). Treatment

severity of clinical signs (anorexia, pyrexia, congested mucous membranes,

Hungary, tiamulin was used to treat lambs that had experienced pneumonia outbreaks 8

and twice, with the control group was statistically significant (p<0.001). Treatment (both 1 and 2 treatments) was associated with a 94.0% reduction (95%CI 58.5, 99.3%) in the risk of death compared with placebo. Nine control lambs were diagnosed with AP (which responded to long-acting oxytetracycline) and no treated lambs showed any clinical signs of disease.

In the UK, an outbreak of AP caused the death of 8 out of 188 (4%) 5 week old lambs over a period of 1 week (Sargison and S

su

intramuscular injection of oxytetracycline (Engemycin). There was no untreated control group used in this study to make a valid comparison. Treatment improved the clinical condition and daily liveweight gains were improved, but no significant differences occurred between the two treatment groups. Four more lambs died within two days of the treatment but there were no further deaths subsequently.

In Egypt, three flocks of sheep with average morbidity rates of 54% and mortality r 1

reduced the

laboured respiration, bilateral mucopurulent nasal discharge and signs of dyspnoea).

Mortality rates post-treatment were not provided and no control groups were used.

In

associated with adenovirus, pasteurella and mycoplasma spp. infection (Stipkovits et al., 1985). Average weight gains 41 days post treatment were 15.8, 14.7 and 10.4 kg for lambs with tiamulin added to feed (n = 200), lambs injected with tiamulin (n = 200) and control

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difference in pulmonary changes and pneumonia between either of the tiamulin treatment groups and the control group was significant (p < 0.001) but not between treatment groups.

ycoplasmas were isolated from 90% to 100% of nasal swabs prior to treatment and from

is difference was ignificant between all groups of lambs (p < 0.020).

centration of Ronidazole eliminated bacteria nd mycoplasmas from the lungs and gave the greatest suppression of lesions, however, the dose produced signs of toxicity. Although penicillin markedly diminished the severity the lung by M. ovipneumoniae or the d lesions.

his section has described the different forms of respiratory disease present in sheep, their aetiology and their clinical patho-physiological classifications. AP, CNP and pleurisy are the only forms of ovine respiratory disease found in New Zealand.

Accurate diagnosis of CNP and pleurisy is limited to slaughter, which places limitations on the ability to precisely identify the time of onset of disease and the temporal development in affected animals. Serology can provide evidence of infection with micro-organisms, however, this information is of limited use as these pathogens may have either proliferated M

3 out of 20 (15%), 10 out of 20 (50%), 19 out of 20 (95%) nasal swabs post treatment from the feed group, injection group and control group respectively. Th

s

In a study by Alley and Clarke (1980), Ronidazole, oxytetracycline, tylosin and penicillin suppressed in varying degrees the development of lesions and the growth of bacteria and mycoplasmas in the lung. The dose of tylosin did not prevent consolidation of the lungs by M. ovipneumoniae, whereas the highest con

a

of lesions, it did not prevent either colonisation of development of localise

These limited numbers of field trials have shown that antibiotic treatment tends to have positive effects on the surviving animals of AP outbreaks in terms reducing the severity of clinical signs and reducing the development of pneumonic lung lesions. This effect is apparent even though some level of resistance of some pathogens of pneumonia to antibiotics has been observed in vitro. Animals surviving AP either recover completely or go on to develop CNP. Antibiotic treatment reduces the development of lung lesions of surviving animals of AP and it is likely the development of CNP is also suppressed.

Summary T

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in the lung causing pneumonia or been cleared from the respiratory tract through innate defence mechanisms.

Ultrasonography has been trialled as a diagnostic method although it is limited to lesions on the lung surface as air in the lung reflects the ultrasonographic beam

Antibiotics have been used successfully in the treatment of AP and CNP in the field although in vitro studies have indicated resistance of P. haemolytica, P. multocida, M.

arginini and M. ovipneumoniae to some antibiotics. Antibiotic treatment is essentially restricted to the treatment of AP, as in the absence of clinical signs for CNP, no knowledge of which lambs to treat provides difficulties.

2.4 Pneumonia in New Zealand

he earliest estimate of mortality rate attributable to AP in New Zealand lambs was about

tudies as discussed throughout this review.

2.4.1 Prevalence T

five percent in individual flocks (Porter, 1970). Manktelow (1970) proposed AP caused

‘quite severe mortalities on individual farms although no field data was presented to support this proposition. Since then, several other authors have reported lamb mortality rates ranging from 8% to 21% and outbreaks occurring at various locations nationwide (Smith, 1975; Anonymous, 1976; Sorenson, 1976; Anonymous, 1978; Davies, 1986; Orr and Black, 1996; Orr et al., 1998; Clark et al., 2001). From the limited published reports, there appears to be no identifiable trend in AP mortality rates over time or associated with geographical location. A map of New Zealand (Figure 2.2) shows the various regional locations of pneumonia s

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Figure 2.2: Map of New Zealand.

Reports of CNP prevalence have varied between 21% and 93%. In a trial estimating the seasonal incidence of pneumonia in Hamilton (Waikato, Kirton et al. 1976), an average of 60% of the trial lambs showed some evidence of pneumonic lesions at slaughter over a five year period. Thurley et al. (1977) reported CNP prevalence of 78% (n = 27) and 57% (n = 58), recorded at slaughter, in a subsequent season at Wallaceville (Wellington). In the Hawkes Bay and Feilding (Manawatu), McGowan et al. (1978) demonstrated prevalence of 78 to 93% in lambs three months of age when examined post-mortem. The prevalence of lesions measured at slaughter in their older counterparts at suitable market slaughter weights was 35 to 68%.

Between March and April 1996, the prevalence of CNP among 9,400 lambs across seven slaughter plants covering all geographic regions of New Zealand was estimated by Black (1997). The case definition used in this study was lesions with red or red-grey consolidation covering more than a quarter of one anteroventral lung lobe with the presence of fibrinous plural exudates. The prevalence of this definition of pneumonia in Northland was 13% (95%CI 11, 16), Bay of Plenty 6% (95%CI 5, 8), East Coast (corresponds to Eastland in Figure 2.2) 4% (95%CI 3, 5), Wanganui 6% (95%CI 4, 7),

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Marlborough 4% (95%CI 3, 5), Canterbury 4% (95%CI 3, 5) and Southland 5% (95%CI 4,

the pig industry, programs for the utilisation of post mortem data collected at slaughter nt practices. This stry an effective The need for use of this vaccine

of the animal’s life, therefore, is limited. In comparison, ere is no efficacious pneumonia vaccine for lambs at present and only general guidelines 7).

In Southland, the King Country (refer Figure 2.2, Upper Wanganui/Taupo) and Northland the pneumonia prevalence of lambs randomly selected for slaughter was 21.8% (95%CI 20.0, 23.7) in Southland (n = 1,917), 49.2% (95%CI 46.9, 51.5) in the King Country (n = 1,831) and 60.3% (95%CI 57.8, 62.8) in Northland (n = 1,485). The prevalence of lesions in each region was significantly different from each other region (Goodwin et al., 2004).

2.4.2 Feedback to farmers from processing plants

Pneumonia is not routinely recorded by processing plants as there are no associated human health risks or direct effects on lamb carcasses. In flocks with a high incidence risk of subclinical pneumonia, farm managers may be unaware of the extent of the problem due to the lack of feedback from processing plants. Post mortem inspection by veterinarians when AP related mortality occurs on farm is currently the only source of an aetiological diagnosis. However, these are not likely to be conducted unless mortality rates are high.

Pleurisy is routinely recorded by processing plants and reported to producers. Pleurisy affects carcass quality and consequently, carcasses with pleurisy are of reduced value. As pneumonia can be a precursor to pleurisy, records of pleurisy from processing plants may provide some indication of pneumonia levels. The correlation between pneumonia and pleurisy, however, is highly variable, so pleurisy is not an accurate indicator of pneumonia.

In

have been developed to improve disease control measures and manageme includes the collection of pneumonia information. In the pig indu mycoplasma vaccine is often used to control pneumonia.

may be established through feedback of pneumonia levels at slaughter to farm managers.

The main limitation is that pneumonia levels recorded at slaughter only reflect the last four to six weeks of production. The ability to identify significant risk factors for pneumonia occurring through the entirety

th

exist for control of the disease. It is questionable therefore whether feedback of