Evaluation of the prevalence and onset of lung lesions and their impact on growth of lambs

Joseph A. Daniel Department of Animal and Range Sciences, College of Agriculture and Biological Sciences, South Dakota State University, Brookings, SD 57007.

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Jeff E. Held Department of Animal and Range Sciences, College of Agriculture and Biological Sciences, South Dakota State University, Brookings, SD 57007.

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Denise G. Brake Department of Animal and Range Sciences, College of Agriculture and Biological Sciences, South Dakota State University, Brookings, SD 57007.

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Duane M. Wulf Department of Animal and Range Sciences, College of Agriculture and Biological Sciences, South Dakota State University, Brookings, SD 57007.

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William B. Epperson Department of Veterinary Science, College of Agriculture and Biological Sciences, South Dakota State University, Brookings, SD 57007.

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Abstract

Objective—To determine the prevalence and temporal onset of lung lesions in lambs and the impact of lung lesions on growth of affected lambs.

Animals—259 crossbred wether lambs from a single flock in the upper Midwestern United States.

Procedure—An observational study was conducted. Lambs born in the spring and fall were slaughtered at finished weight or at a predetermined time point. Lungs of each lamb were examined and classified as normal, moderate lesions (consolidation > 5% but ≤ 50% of any lobe), or severe lesions (consolidation > 50% of any lobe). Data were examined to detect effects of prevalence or severity of lung lesions on growth and carcass traits.

Results—57 of 89 (64%) spring-born lambs had lung lesions characterized by consolidation of lung tissue. A small number of lambs had pulmonary adhesions or active abscesses. In contrast, only 31 of 108 (29%) fall-born lambs had lung lesions. Severe lung lesions were associated with a significant reduction in average daily gain. Severe lung lesions were not detected until the middle of the finishing period and were associated with culture of Mannheimia haemolytica or Pasteurella multocida.

Conclusions and Clinical Relevance—Analysis of results indicates that the prevalence of severe lung lesions can be quite high in lambs. Severe lung lesions can lead to greatly decreased growth performance of lambs.

Abstract

Objective—To determine the prevalence and temporal onset of lung lesions in lambs and the impact of lung lesions on growth of affected lambs.

Animals—259 crossbred wether lambs from a single flock in the upper Midwestern United States.

Procedure—An observational study was conducted. Lambs born in the spring and fall were slaughtered at finished weight or at a predetermined time point. Lungs of each lamb were examined and classified as normal, moderate lesions (consolidation > 5% but ≤ 50% of any lobe), or severe lesions (consolidation > 50% of any lobe). Data were examined to detect effects of prevalence or severity of lung lesions on growth and carcass traits.

Results—57 of 89 (64%) spring-born lambs had lung lesions characterized by consolidation of lung tissue. A small number of lambs had pulmonary adhesions or active abscesses. In contrast, only 31 of 108 (29%) fall-born lambs had lung lesions. Severe lung lesions were associated with a significant reduction in average daily gain. Severe lung lesions were not detected until the middle of the finishing period and were associated with culture of Mannheimia haemolytica or Pasteurella multocida.

Conclusions and Clinical Relevance—Analysis of results indicates that the prevalence of severe lung lesions can be quite high in lambs. Severe lung lesions can lead to greatly decreased growth performance of lambs.

Although negative impacts of atypical pneumonia on lamb growth are known,1 interest in assessing the importance of lung lesions in ruminants at slaughter has only recently emerged. Initial studies2,3 examined the prevalence and effects of lung lesions on performance of cattle. Those investigators concluded that lung lesions in cattle can be reliably diagnosed by observation at slaughter and are associated with decreased performance and product quality.4 In a study5 conducted in New Zealand, the prevalence of lung abnormalities in lambs was as high as 80%, and severe lung lesions were associated with a reduction in daily gain of 5% to 10% during the last month of the finishing period.5 The purpose of the study reported here was to determine the prevalence of lung lesions in lambs, impact of lung lesions on lamb growth, bacterial agents associated with lung lesions, and temporal onset of lesion formation.

Materials and Methods

Animals and animal care—Two flocks maintained at the sheep unit of South Dakota State University were used in the study. Each flock had a separate lambing season (1 flock lambed in the spring, and the other flock lambed in the fall). With exception of lambing season, management of the sheep was as similar as possible. Animal care and use was reviewed and approved by the South Dakota State University Institution Animal Care and Use Committee.

Before ewes were bred, they were vaccinated against abortion-causing agents (Chlamydia psittaci, Campylobacter fetus jejuni, and Campylobacter intestinalis). Approximately 4 to 6 weeks before lambing, ewes were vaccinated against campylobacteriosis, Clostridium perfingens types C and D, Clostridium tetani, and Escherichia coli. Ewes lambing in the spring were sheared approximately 8 weeks before lambing, whereas ewes lambing in the fall were sheared in April prior to the breeding season.

Both flocks of ewes lambed in 73 × 22-m pole-frame construction barn. Windows and doors were adjusted to maintain adequate ventilation and temperature. Ewes and lambs were maintained in 1.5 × 1.5-m pens for approximately 24 hours after lambing. Ewes and lambs were subsequently moved to larger pens and housed together until weaning. At weaning, lambs were separated from the ewes, weighed, sorted on the basis of sex, and returned to pens in the barn, whereas ewes were moved to outside drylots. Spring-born lambs were maintained in pens in the barn until slaughter. Fall-born lambs were moved to another pole-frame construction barn on the farm approximately 1 week after weaning and were maintained there until slaughter.

Diets for the lambs consisted of a pelleted feed (20% protein) available as creep feed until approximately 2 weeks before weaning, at which time the feed was switched to a grower ration that consisted of 62.5% cracked corn, 25% commercially available pelleted feed supplement formulated for growing lambsa (pellets containing 16% protein, vitamins, and minerals), and 12.5% oats. When lambs weighed approximately 45 kg, the diet was changed to a finisher diet that consisted of 72.5% cracked corn, 15% commercially available pelleted feed formulated for finisher lambsb (pellets containing 13% crude protein, vitamins, and mineral), and 12.5% oats.

Sick lambs were identified and treated, and treatments were recorded. Lambs that died were submitted to an animal disease diagnostic laboratoryc for necropsy.

Experiment 1—Lung lesions were assessed in springborn lambs. In spring of 2002, all crossbred wethers were monitored. Dams were Finn-Dorset-Targhee crossbred ewes, and sires were Hampshire or crossbred Dorper (3/4 Dorper, 1/8 East Friesian, and 1/8 Corriedale) rams. Lambs were born during a 28-day period (February 14 to March 14, 2002). Lambs were weaned at 58 to 95 days of age (mean, 77 days) and allowed ad libitum access to the ration.

Hampshire-sired lambs were slaughtered at a target weight of 54 kg, and Dorper-sired lambs were slaughtered at a target weight of 50 kg. Lambs were slaughtered in 2 groups (group 1 comprised 42 lambs slaughtered on July 18, 2002, whereas group 2 comprised 47 lambs slaughtered on August 22, 2002). Lambs were 133 to 187 days old (mean, 160 days) at time of slaughter.

Live weight of each lamb was determined the day before slaughter (designated as finished weight). After slaughter, lungs were visually examined by a single investigator (WBE). Area of consolidation was estimated for each lung lobe, and active abscesses or pleural adhesions in lungs were recorded. Lambs were considered to have normal lungs when ≤ 5% of any lobe was consolidated. Lambs were considered to have moderate lung lesions when > 5% but ≤ 50% of any lobe was consolidated. Lambs were considered to have severe lung lesions when > 50% of any lobe was consolidated. Consolidation was defined as an extremely firm confluent purple area devoid of air. In preliminary experiments, sections of consolidated areas were examined microscopically and found to contain pyogranulomatous inflammation, which confirmed that these areas were abnormal and not postmortem artifact. Pleural adhesions were also categorized (P1, mild pleuritis lesions with adhesions confined to only 1 lobe; P2, pleuritis lesions that extended from 1 lobe to another lobe or from 1 lobe to the thoracic wall; and P3, pleuritis lesions of such severity that an affected lobe or lobes were not removed with the other internal organs during slaughtering but remained in the chest cavity). Carcass data (fat thickness at the 12th rib, body wall thickness, and rib eye area) were collected after carcasses were chilled overnight at 4°C. Carcass data collected by the commercial slaughter facility (hot carcass weight and USDA yield grade6) were also recorded.

Experiment 2—Lung lesions were assessed in fall-born lambs. In fall of 2002, all crossbred wethers were monitored. Dams were Finn-Dorset-Targhee crossbred ewes, and sires were Polypay or Dorper crossbred rams. Lambs were born during a 36-day period (September 5 to October 11, 2002). Lambs were weaned at 55 to 91 days of age (mean, 78 days) and allowed ad libitum access to the ration.

Lambs were slaughtered at a target weight of 50 kg. Lambs were slaughtered in 2 groups (group 1 comprised 66 lambs slaughtered on February 11, 2003, whereas group 2 comprised 42 lambs slaughtered on March 10, 2003). Live weight was determined for each lamb on the day before slaughter (designated as finished weight). After slaughter, lungs were visually examined and assessed for lung lesions by use of the same criteria described for experiment 1. All assessments were performed by a single investigator (WBE).

Experiment 3—Time of onset of lung lesions in springborn lambs and causative agents associated with lung lesions were assessed. In spring 2003, Dorper-sired wethers were allocated to 3 slaughter groups before the lambs were weaned. Lambs were born during a 32-day period (February 4 to March 8, 2003). Lambs at weaning were 58 to 90 days of age (mean, 78 days).

Lambs were slaughtered the day after weaning (weaning group, n = 21) or allowed ad libitum access to the ration and slaughtered subsequently (20 lambs comprised a midfinishing group and were slaughtered 50 days after weaning, whereas 21 lambs comprised a finished group and were slaughtered 71 days after weaning). Live weight was determined for each lamb on the day before slaughter (designated as slaughter weight). After slaughter, lungs were visually examined and scored for lung lesions as described in experiment 1; all assessments were performed by a single investigator (WBE).

For all lambs, samples of lung tissues were aseptically collected from affected areas or from the ventral portion of the right cranial lung lobe of unaffected lungs. Samples were submitted to an animal disease diagnostic laboratoryc for culture of Mycoplasma spp and aerobic bacteria by use of standard techniques.

Carcass traits and weights of the triceps brachii, biceps femoris, semitendinosus, infraspinatus, and lumbar longissimus dorsi (the portion of the longissimus muscle from the last thoracic to the last lumbar vertebrae) muscles were recorded. Flank streaking and marbling were scored as follows: 100, practically devoid; 200, trace amount; 300, slight amount; 400, small amount; 500, modest amount; 600, moderate amount; and 700, slightly abundant. A portion of the longissimus muscle was allowed to age for 14 days. It was subsequently frozen, thawed, and cooked for analysis of cooking shrink and shear force.7 An additional portion of the longissimus muscle was frozen at −20°C until assayed by use of ether extract to determine the percentage of fat.

Statistical analysis—Data from experiment 1 were analyzed by use of a general linear modeld to determine the effect of prevalence and severity of lung lesions on average daily gain, finished weight, age at slaughter, and carcass traits (hot carcass weight, fat thickness at the 12th rib, body wall thickness, rib eye area, and USDA yield grade). When the main effect was significant (P < 0.05), separation of means was performed by use of least significant difference procedures.eEffect of breed of sire on the prevalence of lung lesions in experiment 1 was tested by use of categoric data analysis.fEffect of season of birth (experiment 1 [spring] vs experiment 2 [fall]) on prevalence of lung lesions was tested.f In experiment 3, effect of slaughter group on prevalence of lung lesions was tested,f and differences among groups were determined by use of contrast statements. Effect of lung lesions (prevalence and severity) on carcass traits in experiment 3 was determined for each slaughter group by use of a general linear model.d When the main effect was significant (P < 0.05), separation of means was performed by use of least significant difference procedures.e

Results

Experiment 1—Of 89 lambs, only 7 (8%) required treatment for respiratory tract disease. However, 34 of 89 (38%) lambs had severe lung lesions, and 57 of 89 (64%) lambs had moderate or severe lung lesions. Few (4/89) lambs had pleural adhesions, and only 1 lamb had an active abscess. Growth performance from weaning to finish was significantly (P = 0.005) lower (34 g/d [10.2%] less) for lambs with severe lesions, compared with values for lambs with moderate lesions or normal lungs (Table 1). Dorper-sired lambs had a greater prevalence of severe lung lesions (56%), compared with the prevalence for Hampshire-sired lambs (36%), but the difference was not significant (P = 0.10). However, severe lesions resulted in reduced average daily gain regardless of the breed of sire for the lambs. Lung lesions did not have a significant impact on age at slaughter or any of the carcass traits examined.

Table 1—

Mean ± SEM effect of lung lesions* on growth after weaning and carcass traits for lambs born in the spring (experiment 1).

VariableNormalModerate lesionsSevere lesions
No. of lambs322334
Average daily gain (kg/d)0.33 ± 0.01a0.34 ± 0.01a0.30 ± 0.01b
Age at slaughter (d)162 ± 3163 ± 4158 ± 3
Hot carcass weight (kg)28.5 ± 0.4828.9 ± 0.5328.2 ± 0.44
Fat thickness at 12th rib (cm)0.5 ± 0.030.5 ± 0.040.5 ± .03
Body wall thickness (cm)2.4 ± 0.083.0 ± 0.712.3 ± 0.08
Rib eye area (cm2)16.4 ± 0.316.2 ± 0.416.0 ± 0.3
USDA yield grade2.2 ± 0.12.4 ± 0.12.5 ± 0.1

Lung tissues were categorized as follows: normal, ≤ 5% consolidation of any lobe; moderate, > 5% but ≤ 50% consolidation of any lobe; and severe, > 50% consolidation of any lobe.

Within a row, values with different superscript letters differ significantly (P = 0.005).

Experiment 2—The prevalence of lung lesions in fall-born lambs was significantly (P < 0.001) less than the prevalence in spring-born lambs, despite the fact that lambs were of similar breeds and raised on the same farm (Figure 1). Only 7 of 108 (7%) lambs had severe lung lesions, and 31 of 108 (29%) lambs had moderate or severe lung lesions. A similar proportion of fall-born lambs required treatment for respiratory tract problems (6%), compared with the proportion of springborn lambs that required treatment (8%).

Figure 1—
Figure 1—

Percentage of lambs born in the spring or fall that had moderate (> 5% but ≤ 50% of any lobe was consolidated; gray bars) or severe (> 50% of any lobe was consolidated; black bars) lung lesions at time of slaughter. *Prevalence of lung lesions differs significantly (P < 0.001) from the prevalence of lung lesions for spring-born lambs.

Citation: American Journal of Veterinary Research 67, 5; 10.2460/ajvr.67.5.890

Experiment 3—Lambs in the weaning group had no severe lung lesions, and only 1 lamb had moderate lung lesions. Lambs in the midfinishing and finished groups had a significantly (P = 0.003) greater prevalence of lung lesions, compared with the prevalence for lambs in the weaning group (Figure 2).

Figure 2—
Figure 2—

Percentage of lambs with moderate (gray bars) or severe (black bars) lung lesions when slaughtered at 1 day after weaning (78 days of age; weaning group), 50 days after weaning (midfinishing group), or 71 days after weaning (finished group). *Prevalence of lung lesions differs significantly (P= 0.003) from the prevalence of lung lesions for lambs in the weaning group.

Citation: American Journal of Veterinary Research 67, 5; 10.2460/ajvr.67.5.890

Mycoplasma spp were not isolated from any lung samples. Mannheimia haemolytica or Pastuerella multocida or both were cultured from lambs with moderate or severe lung lesions but not from lambs with normal lung tissues (Table 2).

Table 2—

Proportion of lambs in experiment 3 with lung lesions* on the basis of results of microbial culture.

OrganismNormalModerate lesionsSevere lesions
Mycoplasma spp000
Mannheimia haemolytica02/15 (13)8/12 (67)
Pasteurella multocida03/15 (20)6/12 (50)
M haemolytica and P multocida01/15 (7)4/12 (33)
M haemolytica or P multocida04/15 (27)10/12 (83)

Values reported are No. of lambs from which microbial organisms were cultured/No. of lambs with lesions (percentage).

See Table 1 for remainder of key.

Prevalence or severity of lung lesions did not significantly affect any carcass traits examined in lambs in the midfinishing slaughter group. Lambs with severe lung lesions had a higher mean ± SEM marbling score (388 ± 7), compared with scores for lambs with normal lungs (325 ± 29) or scores for lambs with moderate lung lesions (334 ± 13); however, these values did not differ significantly (P = 0.090). In finished lambs, detection of lung lesions resulted in lambs that had a significantly smaller rib eye area and semitendinosus muscle that weighed less, compared with lambs that did not have evidence of lung lesions (Table 3). Furthermore, lambs with lung lesions had biceps femoris and infraspinatus muscles that weighed less, but not significantly so (P = 0.100), when those lambs were slaughtered at finishing, compared with muscle weights for lambs with normal lungs.

Table 3—

Mean ± SEM effect of lung lesions on carcass traits of lambs slaughtered at various time points* after weaning in experiment 3.

VariableMidfinishFinished
Normal lungsLung with lesionsNormal lungsLungs with lesions 
No. of lambs515912
Slaughter weight (kg)47.9 ± 3.548.1 ± 1.353.6 ± 1.550.1 ± 2.1
Hot carcass weight (kg)26.1 ± 2.226.5 ± 0.730.1 ± 0.927.7 ± 1.2
Fat thickness at 12th rib (cm)0.43 ± 0.090.51 ± 0.060.49 ± 0.060.50 ± 0.07
Rib eye area (cm2)14.14 ± 1.4115.19 ± 0.3417.24 ± 0.37a15.69 ± 0.51b
Body wall thickness (cm)2.29 ± 0.272.21 ± 0.082.85 ± 0.122.54 ± 0.15
Flank streaking score§632 ± 46603 ± 32671 ± 26656 ± 31
Marbling score§332 ± 34349 ± 11364 ± 13397 ± 18
Muscle weight (g)
  Semitendinosus111 ± 10115 ± 3139 ± 5a116 ± 4b
  Lumbar longissimus dorsi290 ± 25312 ± 10350 ± 11319 ± 15
  Biceps femoris307 ± 20322 ± 6366 ± 5339 ± 12
  Triceps brachii234 ± 19253 ± 10262 ± 10257 ± 12
  Infraspinatus142 ± 11153 ± 4190 ± 12167 ± 6
Fat in longissimus muscle (%)2.63 ± 0.302.56 ± 0.122.82 ± 0.173.14 ± 0.20
Cooking shrink (%)37 ± 0.739 ± 1.132.4 ± 0.834 .4 ± 0.8
Shear force (kg)2.82 ± 0.232.53 ± 0.142.38 ± 0.152.59 ± 0.24

Lambs in the midfinish group were slaughtered 50 days after weaning, whereas lambs in the finished group were slaughtered 71 days after weaning.

Lungs were categorized as normal when lesions occupied ≤ 5% of any lobe.

Lungs were categorized with lesions when lesions occupied > 5% of any lobe.

Scored as follows: 100, practically devoid; 200, trace amount; 300, slight amount; 400, small amount; 500, modest amount; 600, moderate amount; and 700, slightly abundant.

Within a row, values with different superscript letters differ significantly (P < 0.05).

Discussion

The low prevalence of lung lesions in fall-born lambs, compared with the prevalence in spring-born lambs of similar genetics and that were raised on the same farm, suggests the prevalence of lung lesions was influenced by unmeasured environmental factors. Analysis of data from the National Climatic Data Center station in Brookings, SD, indicated that the spring-born lambs were raised in a period with a higher ambient temperature (mean monthly temperature, 10.2°C) and more precipitation (18.9 cm), compared with temperature and rainfall (−1.1°C and 16.1 cm, respectively) for the fall-born lambs. However, the high prevalence (64%) of lung lesions in spring-born lambs of experiment 1 does not appear to be anomalous because the prevalence of lung lesions at finishing for experiment 3 the following spring was similar (57%). Furthermore, high prevalence of lung lesions does not appear to be limited to lambs raised in the upper Midwestern United States because lambs in New Zealand also have a high prevalence of lung lesions and pneumonia.1,5

A high prevalence of lung lesions is not limited to lambs because a prevalence of lung lesions of 33% to 72% has been observed in steers.2–4 Similar to lambs, the percentage of steers affected with lung lesions is much greater than the percentage of steers receiving treatment for respiratory tract disease.2 Lung lesions are a result of subclinical respiratory tract disease and appear to be a widespread problem in domestic ruminants.

The observation of a much higher prevalence of lung lesions in spring-born lambs than in fall-born lambs is intriguing. There was a similar observation5 in lambs in New Zealand in which prevalence of lung lesions and pneumonia varied from 6% to 80% on the basis of time of year and location in which lambs were raised. It has been suggested5 that the increase in severity and prevalence of lung lesions may be attributable to a qualitative or quantitative change in cumulative exposure to risk factors and pathogens as lambs age. Because lambs from experiments 1 and 2 (born in the spring and fall) were raised under similar management and slaughtered at approximately the same age, a change in quantitative exposure (intensity) seems to be a more likely possibility. Perhaps most importantly, variability of the prevalence of lung lesions between springand fall-born lambs indicates that the prevalence of lung lesions can be reduced by use of an appropriate management system. However, lambing in the fall requires overcoming the natural physiologic processes of sheep, which favor lambs being born in the spring. Additionally, although we observed a large reduction in prevalence of lung lesions in fall-born lambs, relative to the prevalence for spring-born lambs, factors other than season of birth may have influenced the prevalence of lung lesions.

We observed a decrease of 10% in average daily gain of lambs with severe lung lesions during the finishing period after weaning. This is consistent with reduction (72 g/d) in daily weight gain observed during the month before slaughter in lambs with > 20% of the lung surface area affected by lesions in another study.5 Furthermore, steers with lung lesions also had a reduction in average daily gain that ranged from 6% to 11%.2,4

In cattle, lung lesions have been associated with carcasses that weigh less, have less internal fat, and have lower marbling scores as well as higher values for shear force of the longissimus muscle.4 Although none of the carcass traits examined in experiment 1 was altered by prevalence or severity of lung lesions, lambs with lung lesions at finishing in experiment 3 had smaller rib eye areas and semitendinosus muscles that weighed less, which would indicate an overall decrease in deposition of lean tissue. Contrary to lower marbling scores and higher shear force for the longissimus muscle in cattle with lung lesions,4 we were unable to detect changes in quality measures (flank streaking, marbling, and shear force) associated with prevalence or severity of lung lesions in finished lambs. However, the limited number of samples from finished lambs in the study reported here resulted in a low power of the test to detect meaningful differences in quality measures of interest (ie, by use of the observed variance and sample size, power of the test was calculated to be 0.43, 0.65, and 0.29 for flank streaking, marbling, and shear force, respectively).

Interestingly, spring-born lambs slaughtered 1 day after weaning did not have any lung lesions. Analysis of these data suggests that lung lesions develop after weaning, although events before weaning could predispose lambs to development of lung lesions. Alternatively, the stress of weaning or waning of colostral antibodies could increase the susceptibility of lambs to agents that cause lung lesions. Prevalence of lung lesions increased dramatically by 50 days after weaning. At 71 days after weaning, there was a shift toward more lambs having severe lung lesions and fewer lambs having moderate lung lesions. This is interpreted to indicate that as time passes, lung lesions become progressively more severe in affected lambs.

Mannheimia haemolytica and P multocida, which are pathogens capable of inducing consolidative lesions and mild illness without clinical signs of disease, have been commonly detected in lambs with lung lesions.8–10 Mycoplasma spp were not recovered from any samples in the lambs of the study reported here. Analysis of our findings suggests that these common respiratory tract pathogens are found in lung lesions, although they may not be the initiator of such lesions. Mannheimia haemolytica and P multocida can be a primary cause of disease, but often they are secondary invaders that follow viral infection.11 A poorly understood balance between pathogen and host is apparently in play in lambs affected with lung lesions, and it is unclear as to the factor or factors that limit progression of respiratory tract disease in these lambs and the reasons that apparent fatalities attributable to respiratory tract disease are low. These organisms may represent targets for future studies aimed at limiting prevalence of lung lesions in lambs.

Lambs appear to have a high prevalence of lung lesions that negatively impact growth performance. Furthermore, lambs with lung lesions have reduced deposition of lean tissue mass. As indicated by the apparent change in prevalence of lung lesions on the basis of season, it is clear that environment has a major impact on formation of lung lesions and that lung lesions in lambs could be reduced by modification of the environment, thereby enhancing lamb growth and deposition of lean tissue. The association of lung lesions with culture of M haemolytica and P multocida suggests a role of these common respiratory tract pathogens and also suggests that efforts aimed at mitigating these pathogens deserve study in an attempt to reduce prevalence of lung lesions in lambs.

a.

Big Gain lamb grower pellets, Big Gain Inc, Mankato, Minn.

b.

Big Gain lamb finisher pellets, Big Gain Inc, Mankato, Minn.

c.

Animal Disease Research and Diagnostic Laboratory, Brookings, SD.

d.

Proc GLM, SAS, version 8, SAS Institute Inc, Cary, NC.

e.

LSMEANS/PDIFF, SAS, version 8, SAS Institute Inc, Cary, NC.

f.

Proc CATMOD, SAS, version 8, SAS Institute Inc, Cary, NC.

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