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ARS Home » Midwest Area » West Lafayette, Indiana » Livestock Behavior Research » Research » Publications at this Location » Publication #282759
Title: Pre-natal heat load affects bacterial levels and innate immunity in neonatal calves

Author
item PAN, D - Purdue University
item LEE, C - University Of Hawaii
item Rostagno, Marcos
item Eicher, Susan

Submitted to: Veterinary Immunology and Immunopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2015
Publication Date: N/A
Citation: N/A

Interpretive Summary: Heat stress suppresses immunity, making animals more susceptible to bacterial infections. Additionally, field observations suggest that calves have greater morbidity and mortality when they are born after a heat event. However, scientific evidence is still lacking, limiting the development of targeted interventions. Therefore, a study was conducted with the objective of determining effects of pre-natal seasonal heat load on bacterial levels and innate immunity in neonatal calves. Calves born in late winter (February and March) and summer (June to August) of 2010 on 2 commercial dairies (dairy 1 and 2) located in Hawaii were studied. Hide and udder swabs from dams on dairy 1 were taken shortly after calving. Rectal and nasal swabs from calves on the dairy 1 were taken 1, 2, and 3 week after birth. Total aerobes (total bacteria) and total coliforms (suggesting fecal contamination) were determined for all samples. Jugular blood samples from calves on dairy 2 were collected on week 1, 2, 3, and 4 after birth to determine blood leukocyte RNA expression of a cell surface protein involved in detection of bacteria, toll-like receptor 4, and an inflammatory protein, tumor necrosis factor-alpha. Colostrum samples from dams on both dairy farms were collected within 48 hours after parturition, and bacterial population and antibody concentration were determined. Compared to the winter cows, summer cows had greater hide and udder total aerobe counts, but coliform counts did not differ. Both aerobes and coliforms in colostrum samples did not differ between winter and summer cows. Winter calves had fewer nasal aerobe counts than summer calves at week 1 and 3, but no differences were found in rectal aerobe counts between winter and summer calves. Winter calves had greater nasal coliform counts at week 2. Rectal coliform counts in winter calves were also greater than in summer calves throughout the 3-week sampling. The greater heat load did not affect colostrum antibody concentrations. No difference in toll-like receptor 4 expression was detected between winter and summer calves. However, tumor necrosis factor-alpha expression in summer calves was less at week 2 compared to winter calves. Initial activity and oral behaviors were least for the summer calves, but were greatest for summer calves by the end of the study. The reverse was true for lying behavior. These results support recent recommendations for cooling of dry cows in summer months, but also demonstrate areas to focus change to improve profitability of dairies by improving calf morbidity and mortality rates.

Technical Abstract: Heat stress suppresses immunity, making animals more susceptible to bacterial infections. Additionally, field observations suggest that calves have greater morbidity and mortality when they are born after a heat event. However, scientific evidence is still lacking, limiting the development of targeted interventions. Therefore, a study was conducted with the objective of determining effects of pre-natal seasonal heat load on bacterial levels and innate immunity in neonatal calves. The study was undertaken in late winter (February and March) and summer (June to August) of 2010 on 2 commercial dairies (dairy 1 and 2) located in Hawaii. Fifty-three neonatal Holstein calves were used, 27 born in winter and 26 born in summer. Hide and udder swabs (100 cm2) from dams on dairy 1 were taken shortly after calving. Rectal and nasal swabs from calves on the same farm (n = 15 for each) were taken 1, 2, and 3 week after birth. Total aerobes and total coliforms were determined for all samples. Jugular blood samples from calves on dairy 2 (n = 12 and 11 for winter and summer, respectively) were collected at week 1, 2, 3, and 4 after birth to determine blood leukocyte RNA expression of toll-like receptor 4 (TLR4) and tumor necrosis factor-alpha (TNF-a). Colostrum samples from dams on both dairy farms were collected within 48 hours after parturition, and bacterial population and IgG concentration were determined. All data were transformed and analyzed using the MIXED procedure of SAS with season and time as fixed effects. Compared to the winter cows, summer cows had greater hide (P < 0.001) and udder (P < .001) total aerobe counts, but coliform counts did not differ. Both aerobes and coliforms in colostrum samples did not differ between winter and summer cows. Winter calves had fewer (P < 0.001) nasal aerobe counts than summer calves at week 1 and 3, but no differences were found in rectal aerobe counts between winter and summer calves. Winter calves had greater (P < 0.001) nasal coliform counts at week 2. Rectal coliform counts in winter calves were also greater (P < 0.001) than in summer calves throughout the 3-wk sampling. The greater heat load did not affect colostrum IgG concentrations. No difference in TLR4 expression was detected between winter and summer calves. However, TNF-alpha expression in summer calves was less (P < 0.01) at week 2 compared to winter calves. Initial activity and oral behaviors were least for the summer calves, but were greatest for summer calves by the end of the study. The reverse was true for lying behavior. These results show that seasonal pre-natal heat load affects bacterial populations, decreased TNF-alpha expression of neonatal calves, and behavior showed early lethargy suggesting increased susceptibility to infections. These data show areas where producers can focus attention during summer months to improve calf morbidity and mortality rates.