Brief Communication Communication brève Experimental infection with Mycobacterium avium subspecies paratuberculosis resulting in decreased body weight in Holstein-Friesian calves Gwendolyn L. Roy, Jeroen De Buck, Robert Wolf, Rienske A.R. Mortier, Karin Orsel, Herman W. Barkema Abstract — Fifty calves inoculated at either 2 weeks or at 3, 6, 9, or 12 months of age with either a low or high dose of Mycobacterium avium subspecies paratuberculosis (MAP) were on average 32 and 39 kg lower in body weight, respectively, compared to negative controls at 17 months of age. Résumé — Chute du poids corporel chez des veaux Holstein-Friesian suite à l’infection expérimentale avec Mycobacterium avium sous-espèce paratuberculosis. Cinquante veaux qui ont été inoculés à l’âge de 2 semaines ou à l’âge de 3, 6, 9 ou 12 mois avec soit une dose faible ou élevée de Mycobacterium avium sous-espèce paratuberculosis (MAP) présentaient en moyenne un poids corporel inférieur de 32 kg et de 39 kg respectivement, comparativement aux témoins négatifs à l’âge de 17 mois. (Traduit par Isabelle Vallières)
Can Vet J 2017;58:296–298
M
ycobacterium avium subspecies paratuberculosis (MAP) is the causative agent of Johne’s disease (JD), a gastrointestinal disease in ruminants. Although cattle are in general infected as calves (1), due to JD’s chronic nature, typically older cattle (between 2 and 6 years of age) present with signs. Only a small percentage of MAP-infected animals will have clinical JD; many more are infected, but are subclinical (2). The latter animals may shed MAP intermittently (1), creating an environmental reservoir. Following ingestion, MAP invades the wall of the intestinal tract. Microscopic and macroscopic lesions inhibit absorption of nutrients through the gut lining, particularly in the small intestine. Furthermore, energy must be expended by the animal to mount an immune response (2). Subclinical infection with MAP results in lower milk yields, poor reproductive performance, and reduced value of culled cows, thereby reducing profitability (3). Dairy cows that were milk MAP enzyme-linked immunosorbent assay (ELISA)-positive weighed 10% less at slaughter than milk ELISA-negative cows (4). Furthermore, if the cow was shedding MAP, its weight was on average 15% less compared to non-shedders (4). Subclinical infection with MAP also reduces weight at slaughter of sheep (5), deer (6), and beef cattle (7).
Department of Production Animal Health, Faculty of Veterinary Medicine, University of Calgary, Calgary, Alberta. Address all correspondence to Dr. Herman W. Barkema; e-mail: [email protected] Use of this article is limited to a single copy for personal study. Anyone interested in obtaining reprints should contact the CVMA office ([email protected]) for additional copies or permission to use this material elsewhere. 296
Additionally, calves of strong ELISA-positive beef cows (defined as an S/P ratio . 0.99 or . 3.49 for the Herdcheck and the Paracheck ELISA, respectively), and calves of heavy or moderate MAP shedders had a 21 and 59 kg reduced 205-day adjusted weaning weight compared to calves of ELISA-negative and MAP culture-negative dams, respectively (8). Decreased weight could be due to lower milk yield of the dam and/or a direct effect of MAP infection on the offspring. However, dairy calves are usually separated from their dams shortly after birth, and lower milk yield of the dam would not affect growth of the calf. To our knowledge, there are no reports on the effects of MAP infection on body weight of dairy young stock. The objective of this study, therefore, was to quantify the effect of MAP inoculation on weight in dairy bull calves. The design of the overall study was described by Mortier et al (9) and was conducted under the University of Calgary Health Sciences Animal Care Committee permits M09083 and M09050. Briefly, 56 Holstein-Friesian bull calves were collected on farms with an adult cow serum ELISA prevalence , 5%. To prevent bacterial contamination, newborn calves were collected directly from a MAP ELISA-negative dam without touching the ground. These calves were brought to our research facility, individually housed, and careful biosecurity consistently practiced to prevent cross-contamination. Fifty calves were randomly allocated to 5 MAP-inoculation age groups and 6 calves were not challenged with MAP (i.e., negative controls). Mycobacterium avium subsp. paratuberculosis was cultured from a cow with clinical JD, and was given orally as either a high dose [5 3 109 colony-forming units (CFU)] or low dose (5 3 107 CFU). Groups of 10 calves were each inoculated at either 2 wk or at 3, 6, 9, or 12 mo of age. For each infection group, 5 calves were inoculated with a high dose of MAP; the CVJ / VOL 58 / MARCH 2017
Coefficient SE
Intercept Age at euthanasia (d) Dose Low High Triala
275.8 1.16 232.2 239.3 222.3
P-value 95% CI
173.5 0.66 2424.0 to 272.4 0.33 0.001 0.50 to 1.81 11.5 0.007 255.2 to 29.1 11.5 0.001 262.4 to 216.3 7.1 0.003 236.6 to 28.0
a The
experiment was conducted in 2 consecutive trials. SE — standard error; CI — confidence interval.
600 500
465 451 454 456 445 489
400
B R I E F C O M M U N I CAT I O N
Average weight at necropsy (kg)
Table 1. Final linear regression model for body weight (kg) of 50 Holstein-Friesian steers inoculated and 6 steers not inoculated with Mycobacterium avium subspecies paratuberculosis
300 200 100 0
0.5 3 6 9 12 C
Age at inoculation (months)
other 5 calves were inoculated with a low dose. Inoculation took place on 2 consecutive days. Because of the limited capacity of the research facility, the experiment was conducted with 2 identically conducted consecutive trials of 33 and 23 calves with equal representation of all age groups and negative controls in each trial. The work started in January 2010 and ended in August 2011, for Trial 1, and started in May 2011 and ended in December 2012, for Trial 2. Calves were dehorned under local anesthesia using a cauterizing iron and they were surgically castrated after administration of sedation and local anesthesia. Calves were individually housed on deep bedding (pine shaving substrate). Within 12 h after birth calves were given 6 L of colostrum which had been collected from 7 MAP seronegative and environmental culture-negative Alberta dairy farms and gamma-irradiated. Thereafter, calves were bucket fed 1.5 L of Grober High Performance milk replacer (Grober Nutrition, Cambridge, Ontario) thrice daily for 3 d. They were then given 2 L thrice daily for 3 d, and finally 3 L twice daily until weaning. The milk was fed by a researcher wearing separate coveralls, boots, and gloves for each calf. At 7 to 8 wk of age, calves were weaned using a week-long process, during which they were fed half the milk replacer powder in the same volume of water. Calves were weaned onto a diet of high-quality timothy hay ad libitum and approximately 500 g of concentrate (pelleted mix containing vitamins and trace minerals). The ration increased as the calves aged and the concentrate was doubled on days when the temperature in the barn was below 220°C. All steers had access to water ad libitum. Blood and fecal samples were collected both pre-exposure and at fixed intervals after inoculation (9). The number of preinoculation samples depended on age of inoculation, with every animal sampled at least once before inoculation. Samples were collected at 2 and 4 d after inoculation, then weekly for 4 wk, and finally, monthly until euthanasia. Steers were euthanized at approximately 17 mo of age with an overdose of sodium pentobarbitone (Euthapent; Kyron Laboratories, Johannesburg, South Africa). Immediately after euthanasia, body weight was determined with a spring scale that was raised by a forklift and attached to a hind limb of the carcass. Differences in age-adjusted weight at necropsy between MAP dose groups, age at inoculation, and trials were analyzed using a linear regression model (Stata 12.1, Stata Corp., College Station, Texas, USA). For all analyses, P , 0.05 was considered statistically significant. Stepwise regression with backward elimination was done to identify variables associated with weight at necropsy. CVJ / VOL 58 / MARCH 2017
Figure 1. Average weight at necropsy (corrected for age of necropsy) for the 5 ages at which the cattle were inoculated with Mycobacterium avium subspecies paratuberculosis. Each bar represents the mean 6 standard deviation. Negative controls (labeled C) had a greater average weight (P = 0.006).
The combination of diagnostic tests performed on the inoculated calves demonstrated that most of the calves were indeed infected, with positive fecal shedding in 61% (10), positive antibody ELISA in 42% (11), MAP-positive tissues in 56% and overall 90% of the calves positive by either tissue culture, macroscopic lesions, fecal shedding and/or ELISA (9) and 100% by interferon-gamma release assay (12). Because all calves inoculated with MAP were interferon-gamma positive and the sensitivity of the other tests is relatively low, we decided to include all inoculated calves in the analysis. Steers gained on average 1.16 kg/d, and there was a 22.3 kg difference in weight between the first and second trials (Table 1). Mean weight was not associated with the age at which the cattle were inoculated with MAP (Figure 1). Consequently, inoculation age was not included in the final model. Negative control steers had a higher mean body weight; those inoculated with a low dose of MAP weighed on average 32.2 kg less than control steers, whereas steers inoculated with a high dose weighed 39.3 kg less than control steers (Table 1). Two steers developed clinical JD and were subsequently euthanized early (to mitigate welfare concerns). Inclusion or exclusion of these 2 steers had limited effects on results (inclusion reduced the high-dose group’s average weight by a further 2 kg). Therefore, these 2 animals were ultimately included in the analysis. It is unfortunate that calves were not weighed shortly after birth and more frequently during the experiment. It is unlikely, however, that the difference in weight at necropsy was the result of a difference in birth weight, growth potential between control versus inoculated calves, or differences in feeding or housing, because infection dose was assigned randomly, and treatment and housing were standardized. Control calves were collected randomly throughout the 2 consecutive trials and were individually housed among inoculated calves. Feeding was not done according to MAP status. Including birth weight in the analysis, however, would have made the estimate more precise, and more frequent weighing would have enabled determination of when the decrease in growth after MAP infection started. The difference in body weight in the 2 consecutive trials may have arisen for several reasons. The cattle in the first trial 297
C O M M U N I CAT I O N B R È V E
were slightly older (average = 5.6 d at slaughter); however, age at necropsy was included in the model for the final dose effect. Additionally, the first trial and the second trial ended in different seasons. As the barn was not heated and there were fewer cattle in the second trial, growth rate in the cattle in the second trial may have decreased as the outdoor temperature decreased. Cattle in the first trial may have had compensatory growth after the winter, as the trial ended in the summer (July and August). Finally, feed quality varied over both years. Although high-quality hay was sourced, it was not possible to ensure the hay from both years was exactly equivalent. In 3 US cow-calf beef herds, weaned calves from serum ELISA-positive dams were on average 33 kg lighter than calves from non-positive cows (8). Weight at 205 d of age for calves from ELISA-positive dams was 21 kg less than that of calves of ELISA-negative dams. The difference was even larger comparing calves of moderate or heavy MAP shedders to those of fecal culture-negative dams (59 and 41 kg, respectively). The researchers speculated that the weight loss was either because the dams produced less milk and/or because of direct effects of MAP infection on calves. Quantity and quality of milk was controlled in our study, and body weight at necropsy was lowest in the steers inoculated with the high dose; therefore, we inferred that weight loss in calves in the previous study (8) was due to MAP infection. Worldwide, a high proportion of dairy farms is infected with MAP (13,14), and the proportion of calves already shedding MAP is relatively high in infected dairy farms (15). Lower body weights were not only present in calves inoculated with a high MAP dose, but also in calves inoculated with a low dose, which may be more representative of exposure under field conditions on infected dairy farms. It is therefore likely that economic losses caused by MAP infection are underestimated, as to our knowledge none included decreased weight in calves. Although this was a large challenge experiment, the number of cattle was relatively low in the individual groups, which was probably the reason why no significant difference in weight between the age groups was found. Furthermore, the relatively low sample size made it not possible to exactly predict a weight difference between infected and uninfected cattle. However, the purpose of the study was to determine whether MAP infection impacts cattle growth instead of quantifying the difference. In conclusion, MAP infection in cattle is more costly than previously considered because of a negative effect of subclinical infections on young stock weight. Good management practices with both dairy and beef herds are paramount to reducing JD prevalence. These management practices should be maintained for cattle of all ages, as exposure to MAP, even at 1 y of age, resulted in the same average weight reduction as in cattle exposed at younger ages. Careful management should be used by both dairy and beef producers to ensure that uninfected cattle remain free of MAP.
298
Acknowledgments This work was supported by Alberta Innovates — Bio Solutions, the Alberta Livestock and Meat Agency, Alberta Milk, Dairy Farmers of Canada, the Natural Sciences, Engineering Research Council of Canada, and University of Calgary, Faculty of Veterinary Medicine. The authors acknowledge numerous undergraduate students who collaborated in this experiment and Dr. John Kastelic who edited the manuscript. CVJ
References 1. Mortier RAR, Barkema HW, De Buck J. Susceptibility to and diagnosis of Mycobacterium avium subspecies paratuberculosis infection in dairy calves: A review. Prev Vet Med 2015;121:189–198. 2. Tiwari A, VanLeeuwen JA, McKenna SL, Keefe GP, Barkema HW. Johne’s disease in Canada Part I: Clinical symptoms, pathophysiology, diagnosis, and prevalence in dairy herds. Can Vet J 2006;47:874–882. 3. McKenna SL, Keefe GP, Tiwari A, VanLeeuwen J, Barkema HW. Johne’s disease in Canada part II: Disease impacts, risk factors, and control programs for dairy producers. Can Vet J 2006;47:1089–1099. 4. Kudahl AB, Nielsen SS. Effect of paratuberculosis on slaughter weight and slaughter value of dairy cows. J Dairy Sci 2009;92:4340–4346. 5. Morris CA, Hickey SM, Henderson HV. The effect of Johne’s disease on production traits in Romney, Merino and Merino x Romney-cross ewes. N Z Vet J 2006;54:204–209. 6. Murray HL, Yabsley MJ, Keel MK, Manning EJ, Wilmers TJ, Corn JL. Persistence of Mycobacterium avium subspecies paratuberculosis in endangered Florida Key deer and Key deer habitat. J Wildl Dis 2014; 50:349–353. 7. Elzo MA, Rae DO, Lanhart SE, Hembry FG, Wasdin JG, Driver JD. Association between cow reproduction and calf growth traits and ELISA scores for paratuberculosis in a multibreed herd of beef cattle. Trop Anim Health Prod. 2009;41:851–858. 8. Bhattarai B, Fosgate GT, Osterstock JB, Fossler CP, Park SC, Roussel AJ. Comparison of calf weaning weight and associated economic variables between beef cows with and without serum antibodies against or isolation from feces of Mycobacterium avium subsp paratuberculosis. J Am Vet Med Assoc 2013;243:1609–1615. 9. Mortier RAR, Barkema HW, Bystrom JM, et al. Evaluation of age-dependent susceptibility in calves infected with two doses of Mycobacterium avium subspecies paratuberculosis using pathology and tissue culture. Vet Res 2013;44:94. 10. Mortier RAR, Barkema HW, Orsel K, Wolf R, de Buck J. Shedding patterns of dairy calves experimentally infected with Mycobacterium avium subspecies paratuberculosis. Vet Res 2014;45:71. 11. Mortier RAR, Barkema HW, Negron M, Orsel K, Wolf R, de Buck J. Antibody response early after experimental infection with Mycobacterium avium subspecies paratuberculosis in dairy calves. J Dairy Sci 2014;97: 5558–5565. 12. Mortier RAR, Barkema HW, Wilson TA, Sajobi TT, Wolf R, de Buck J. Dose-dependent interferon-gamma release in dairy calves experimentally infected with Mycobacterium avium subspecies paratuberculosis. Vet Immunol Immunopathol 2014;161:205–210. 13. Barkema HW, Hesselink JW, McKenna SLB, Benedictus G, Groenendaal H. Global prevalence and economics of infection with Mycobacterium avium subsp. paratuberculosis in ruminants. In: Behr MA, Collins DM, eds. Paratuberculosis: Organism, Disease, Control. Wallingford, Oxfordshire, UK: CAB International, 2010:10–21. 14. Wolf R, Barkema HW, De Buck J, et al. High herd-level prevalence of Mycobacterium avium subspecies paratuberculosis in Western Canadian dairy herds, based on environmental sampling. J Dairy Sci 2014;97:6250–6259. 15. Wolf R, Orsel K, De Buck J, Barkema HW. Calves shedding Mycobacterium avium subspecies paratuberculosis are common on infected dairy farms. Vet Res 2015;46:71.
CVJ / VOL 58 / MARCH 2017
Can Vet J 2017;58:296–298
M
ycobacterium avium subspecies paratuberculosis (MAP) is the causative agent of Johne’s disease (JD), a gastrointestinal disease in ruminants. Although cattle are in general infected as calves (1), due to JD’s chronic nature, typically older cattle (between 2 and 6 years of age) present with signs. Only a small percentage of MAP-infected animals will have clinical JD; many more are infected, but are subclinical (2). The latter animals may shed MAP intermittently (1), creating an environmental reservoir. Following ingestion, MAP invades the wall of the intestinal tract. Microscopic and macroscopic lesions inhibit absorption of nutrients through the gut lining, particularly in the small intestine. Furthermore, energy must be expended by the animal to mount an immune response (2). Subclinical infection with MAP results in lower milk yields, poor reproductive performance, and reduced value of culled cows, thereby reducing profitability (3). Dairy cows that were milk MAP enzyme-linked immunosorbent assay (ELISA)-positive weighed 10% less at slaughter than milk ELISA-negative cows (4). Furthermore, if the cow was shedding MAP, its weight was on average 15% less compared to non-shedders (4). Subclinical infection with MAP also reduces weight at slaughter of sheep (5), deer (6), and beef cattle (7).
Department of Production Animal Health, Faculty of Veterinary Medicine, University of Calgary, Calgary, Alberta. Address all correspondence to Dr. Herman W. Barkema; e-mail: [email protected] Use of this article is limited to a single copy for personal study. Anyone interested in obtaining reprints should contact the CVMA office ([email protected]) for additional copies or permission to use this material elsewhere. 296
Additionally, calves of strong ELISA-positive beef cows (defined as an S/P ratio . 0.99 or . 3.49 for the Herdcheck and the Paracheck ELISA, respectively), and calves of heavy or moderate MAP shedders had a 21 and 59 kg reduced 205-day adjusted weaning weight compared to calves of ELISA-negative and MAP culture-negative dams, respectively (8). Decreased weight could be due to lower milk yield of the dam and/or a direct effect of MAP infection on the offspring. However, dairy calves are usually separated from their dams shortly after birth, and lower milk yield of the dam would not affect growth of the calf. To our knowledge, there are no reports on the effects of MAP infection on body weight of dairy young stock. The objective of this study, therefore, was to quantify the effect of MAP inoculation on weight in dairy bull calves. The design of the overall study was described by Mortier et al (9) and was conducted under the University of Calgary Health Sciences Animal Care Committee permits M09083 and M09050. Briefly, 56 Holstein-Friesian bull calves were collected on farms with an adult cow serum ELISA prevalence , 5%. To prevent bacterial contamination, newborn calves were collected directly from a MAP ELISA-negative dam without touching the ground. These calves were brought to our research facility, individually housed, and careful biosecurity consistently practiced to prevent cross-contamination. Fifty calves were randomly allocated to 5 MAP-inoculation age groups and 6 calves were not challenged with MAP (i.e., negative controls). Mycobacterium avium subsp. paratuberculosis was cultured from a cow with clinical JD, and was given orally as either a high dose [5 3 109 colony-forming units (CFU)] or low dose (5 3 107 CFU). Groups of 10 calves were each inoculated at either 2 wk or at 3, 6, 9, or 12 mo of age. For each infection group, 5 calves were inoculated with a high dose of MAP; the CVJ / VOL 58 / MARCH 2017
Coefficient SE
Intercept Age at euthanasia (d) Dose Low High Triala
275.8 1.16 232.2 239.3 222.3
P-value 95% CI
173.5 0.66 2424.0 to 272.4 0.33 0.001 0.50 to 1.81 11.5 0.007 255.2 to 29.1 11.5 0.001 262.4 to 216.3 7.1 0.003 236.6 to 28.0
a The
experiment was conducted in 2 consecutive trials. SE — standard error; CI — confidence interval.
600 500
465 451 454 456 445 489
400
B R I E F C O M M U N I CAT I O N
Average weight at necropsy (kg)
Table 1. Final linear regression model for body weight (kg) of 50 Holstein-Friesian steers inoculated and 6 steers not inoculated with Mycobacterium avium subspecies paratuberculosis
300 200 100 0
0.5 3 6 9 12 C
Age at inoculation (months)
other 5 calves were inoculated with a low dose. Inoculation took place on 2 consecutive days. Because of the limited capacity of the research facility, the experiment was conducted with 2 identically conducted consecutive trials of 33 and 23 calves with equal representation of all age groups and negative controls in each trial. The work started in January 2010 and ended in August 2011, for Trial 1, and started in May 2011 and ended in December 2012, for Trial 2. Calves were dehorned under local anesthesia using a cauterizing iron and they were surgically castrated after administration of sedation and local anesthesia. Calves were individually housed on deep bedding (pine shaving substrate). Within 12 h after birth calves were given 6 L of colostrum which had been collected from 7 MAP seronegative and environmental culture-negative Alberta dairy farms and gamma-irradiated. Thereafter, calves were bucket fed 1.5 L of Grober High Performance milk replacer (Grober Nutrition, Cambridge, Ontario) thrice daily for 3 d. They were then given 2 L thrice daily for 3 d, and finally 3 L twice daily until weaning. The milk was fed by a researcher wearing separate coveralls, boots, and gloves for each calf. At 7 to 8 wk of age, calves were weaned using a week-long process, during which they were fed half the milk replacer powder in the same volume of water. Calves were weaned onto a diet of high-quality timothy hay ad libitum and approximately 500 g of concentrate (pelleted mix containing vitamins and trace minerals). The ration increased as the calves aged and the concentrate was doubled on days when the temperature in the barn was below 220°C. All steers had access to water ad libitum. Blood and fecal samples were collected both pre-exposure and at fixed intervals after inoculation (9). The number of preinoculation samples depended on age of inoculation, with every animal sampled at least once before inoculation. Samples were collected at 2 and 4 d after inoculation, then weekly for 4 wk, and finally, monthly until euthanasia. Steers were euthanized at approximately 17 mo of age with an overdose of sodium pentobarbitone (Euthapent; Kyron Laboratories, Johannesburg, South Africa). Immediately after euthanasia, body weight was determined with a spring scale that was raised by a forklift and attached to a hind limb of the carcass. Differences in age-adjusted weight at necropsy between MAP dose groups, age at inoculation, and trials were analyzed using a linear regression model (Stata 12.1, Stata Corp., College Station, Texas, USA). For all analyses, P , 0.05 was considered statistically significant. Stepwise regression with backward elimination was done to identify variables associated with weight at necropsy. CVJ / VOL 58 / MARCH 2017
Figure 1. Average weight at necropsy (corrected for age of necropsy) for the 5 ages at which the cattle were inoculated with Mycobacterium avium subspecies paratuberculosis. Each bar represents the mean 6 standard deviation. Negative controls (labeled C) had a greater average weight (P = 0.006).
The combination of diagnostic tests performed on the inoculated calves demonstrated that most of the calves were indeed infected, with positive fecal shedding in 61% (10), positive antibody ELISA in 42% (11), MAP-positive tissues in 56% and overall 90% of the calves positive by either tissue culture, macroscopic lesions, fecal shedding and/or ELISA (9) and 100% by interferon-gamma release assay (12). Because all calves inoculated with MAP were interferon-gamma positive and the sensitivity of the other tests is relatively low, we decided to include all inoculated calves in the analysis. Steers gained on average 1.16 kg/d, and there was a 22.3 kg difference in weight between the first and second trials (Table 1). Mean weight was not associated with the age at which the cattle were inoculated with MAP (Figure 1). Consequently, inoculation age was not included in the final model. Negative control steers had a higher mean body weight; those inoculated with a low dose of MAP weighed on average 32.2 kg less than control steers, whereas steers inoculated with a high dose weighed 39.3 kg less than control steers (Table 1). Two steers developed clinical JD and were subsequently euthanized early (to mitigate welfare concerns). Inclusion or exclusion of these 2 steers had limited effects on results (inclusion reduced the high-dose group’s average weight by a further 2 kg). Therefore, these 2 animals were ultimately included in the analysis. It is unfortunate that calves were not weighed shortly after birth and more frequently during the experiment. It is unlikely, however, that the difference in weight at necropsy was the result of a difference in birth weight, growth potential between control versus inoculated calves, or differences in feeding or housing, because infection dose was assigned randomly, and treatment and housing were standardized. Control calves were collected randomly throughout the 2 consecutive trials and were individually housed among inoculated calves. Feeding was not done according to MAP status. Including birth weight in the analysis, however, would have made the estimate more precise, and more frequent weighing would have enabled determination of when the decrease in growth after MAP infection started. The difference in body weight in the 2 consecutive trials may have arisen for several reasons. The cattle in the first trial 297
C O M M U N I CAT I O N B R È V E
were slightly older (average = 5.6 d at slaughter); however, age at necropsy was included in the model for the final dose effect. Additionally, the first trial and the second trial ended in different seasons. As the barn was not heated and there were fewer cattle in the second trial, growth rate in the cattle in the second trial may have decreased as the outdoor temperature decreased. Cattle in the first trial may have had compensatory growth after the winter, as the trial ended in the summer (July and August). Finally, feed quality varied over both years. Although high-quality hay was sourced, it was not possible to ensure the hay from both years was exactly equivalent. In 3 US cow-calf beef herds, weaned calves from serum ELISA-positive dams were on average 33 kg lighter than calves from non-positive cows (8). Weight at 205 d of age for calves from ELISA-positive dams was 21 kg less than that of calves of ELISA-negative dams. The difference was even larger comparing calves of moderate or heavy MAP shedders to those of fecal culture-negative dams (59 and 41 kg, respectively). The researchers speculated that the weight loss was either because the dams produced less milk and/or because of direct effects of MAP infection on calves. Quantity and quality of milk was controlled in our study, and body weight at necropsy was lowest in the steers inoculated with the high dose; therefore, we inferred that weight loss in calves in the previous study (8) was due to MAP infection. Worldwide, a high proportion of dairy farms is infected with MAP (13,14), and the proportion of calves already shedding MAP is relatively high in infected dairy farms (15). Lower body weights were not only present in calves inoculated with a high MAP dose, but also in calves inoculated with a low dose, which may be more representative of exposure under field conditions on infected dairy farms. It is therefore likely that economic losses caused by MAP infection are underestimated, as to our knowledge none included decreased weight in calves. Although this was a large challenge experiment, the number of cattle was relatively low in the individual groups, which was probably the reason why no significant difference in weight between the age groups was found. Furthermore, the relatively low sample size made it not possible to exactly predict a weight difference between infected and uninfected cattle. However, the purpose of the study was to determine whether MAP infection impacts cattle growth instead of quantifying the difference. In conclusion, MAP infection in cattle is more costly than previously considered because of a negative effect of subclinical infections on young stock weight. Good management practices with both dairy and beef herds are paramount to reducing JD prevalence. These management practices should be maintained for cattle of all ages, as exposure to MAP, even at 1 y of age, resulted in the same average weight reduction as in cattle exposed at younger ages. Careful management should be used by both dairy and beef producers to ensure that uninfected cattle remain free of MAP.
298
Acknowledgments This work was supported by Alberta Innovates — Bio Solutions, the Alberta Livestock and Meat Agency, Alberta Milk, Dairy Farmers of Canada, the Natural Sciences, Engineering Research Council of Canada, and University of Calgary, Faculty of Veterinary Medicine. The authors acknowledge numerous undergraduate students who collaborated in this experiment and Dr. John Kastelic who edited the manuscript. CVJ
References 1. Mortier RAR, Barkema HW, De Buck J. Susceptibility to and diagnosis of Mycobacterium avium subspecies paratuberculosis infection in dairy calves: A review. Prev Vet Med 2015;121:189–198. 2. Tiwari A, VanLeeuwen JA, McKenna SL, Keefe GP, Barkema HW. Johne’s disease in Canada Part I: Clinical symptoms, pathophysiology, diagnosis, and prevalence in dairy herds. Can Vet J 2006;47:874–882. 3. McKenna SL, Keefe GP, Tiwari A, VanLeeuwen J, Barkema HW. Johne’s disease in Canada part II: Disease impacts, risk factors, and control programs for dairy producers. Can Vet J 2006;47:1089–1099. 4. Kudahl AB, Nielsen SS. Effect of paratuberculosis on slaughter weight and slaughter value of dairy cows. J Dairy Sci 2009;92:4340–4346. 5. Morris CA, Hickey SM, Henderson HV. The effect of Johne’s disease on production traits in Romney, Merino and Merino x Romney-cross ewes. N Z Vet J 2006;54:204–209. 6. Murray HL, Yabsley MJ, Keel MK, Manning EJ, Wilmers TJ, Corn JL. Persistence of Mycobacterium avium subspecies paratuberculosis in endangered Florida Key deer and Key deer habitat. J Wildl Dis 2014; 50:349–353. 7. Elzo MA, Rae DO, Lanhart SE, Hembry FG, Wasdin JG, Driver JD. Association between cow reproduction and calf growth traits and ELISA scores for paratuberculosis in a multibreed herd of beef cattle. Trop Anim Health Prod. 2009;41:851–858. 8. Bhattarai B, Fosgate GT, Osterstock JB, Fossler CP, Park SC, Roussel AJ. Comparison of calf weaning weight and associated economic variables between beef cows with and without serum antibodies against or isolation from feces of Mycobacterium avium subsp paratuberculosis. J Am Vet Med Assoc 2013;243:1609–1615. 9. Mortier RAR, Barkema HW, Bystrom JM, et al. Evaluation of age-dependent susceptibility in calves infected with two doses of Mycobacterium avium subspecies paratuberculosis using pathology and tissue culture. Vet Res 2013;44:94. 10. Mortier RAR, Barkema HW, Orsel K, Wolf R, de Buck J. Shedding patterns of dairy calves experimentally infected with Mycobacterium avium subspecies paratuberculosis. Vet Res 2014;45:71. 11. Mortier RAR, Barkema HW, Negron M, Orsel K, Wolf R, de Buck J. Antibody response early after experimental infection with Mycobacterium avium subspecies paratuberculosis in dairy calves. J Dairy Sci 2014;97: 5558–5565. 12. Mortier RAR, Barkema HW, Wilson TA, Sajobi TT, Wolf R, de Buck J. Dose-dependent interferon-gamma release in dairy calves experimentally infected with Mycobacterium avium subspecies paratuberculosis. Vet Immunol Immunopathol 2014;161:205–210. 13. Barkema HW, Hesselink JW, McKenna SLB, Benedictus G, Groenendaal H. Global prevalence and economics of infection with Mycobacterium avium subsp. paratuberculosis in ruminants. In: Behr MA, Collins DM, eds. Paratuberculosis: Organism, Disease, Control. Wallingford, Oxfordshire, UK: CAB International, 2010:10–21. 14. Wolf R, Barkema HW, De Buck J, et al. High herd-level prevalence of Mycobacterium avium subspecies paratuberculosis in Western Canadian dairy herds, based on environmental sampling. J Dairy Sci 2014;97:6250–6259. 15. Wolf R, Orsel K, De Buck J, Barkema HW. Calves shedding Mycobacterium avium subspecies paratuberculosis are common on infected dairy farms. Vet Res 2015;46:71.
CVJ / VOL 58 / MARCH 2017
