|Do Amaral, Bruno|
Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/2010
Publication Date: 1/1/2011
Publication URL: http://hdl.handle.net/10113/48735
Citation: Do Amaral, B., Connor, E.E., Tao, S., Hayen, J., Bubolz, J., Dahl, G. 2011. Heat Stress Abatement During the Dry Period Influences Metabolic Gene Expression and Improves Immune Status in the Transition Period of Dairy Cows. Journal of Dairy Science. 94:86-96. Interpretive Summary: Heat stress dramatically depresses milk production during lactation and cooling cows during late pregnancy (the dry period) increases milk production in the subsequent lactation. The effects of heat stress on liver function and immunity of dairy cattle prior to calving are not known. This study was undertaken to evaluate expression of genes in liver and immune cells of cows prior to calving, which were exposed to either heat stress or were cooled during the dry period of late pregnancy. The results indicated that cooling cows during the dry period may improve liver metabolic function, contributing to increased milk yield in the subsequent lactation, and may improve immune function of dairy cows. Heat stress abatement during late pregnancy is a promising management strategy to improve transition into lactation; however, studies on the effect of cooling during the entire dry period on the incidence of periparturient diseases are needed to confirm the practical application of these findings.
Technical Abstract: Heat stress (HT) and photoperiod affect milk production and immune status of dairy cows, especially during the transition period. Management strategies to improve the transition into lactation will impact subsequent cow health and milk production. The objective of the study was to evaluate the effects of HT abatement prepartum under controlled photoperiod on hepatic metabolic gene expression and cellular immune function of periparturient Holstein cows (n = 21). Cows were dried off 46 d before expected calving date and assigned to treatments by mature equivalent milk production. The treatments were: 1) Heat stress (HT) and 2) Cooling (CL), both imposed during a photoperiod of 14L:10D. Rectal temperature was measured twice daily, whereas respiration rate was measured 3×/wk at 1500h during the entire dry period. After calving, cows were housed in a free-stall barn with cooling, and milk yield was recorded daily up to 140 DIM. Liver samples were taken at dry off, -20, +2, and +20 d relative to calving by biopsy. Under a similar schedule, neutrophil function was measured in blood of cows on HT (n = 12) and CL (n = 9). Blood samples were taken at -46, -32, -18, 0, +14, +28, and +42 d relative to calving for measurement of metabolites and were collected twice daily from -7 to +2 d relative to calving for prolactin (PRL) analysis. The HT cows had greater concentrations of PRL at 0 d relative to calving (150 vs. 93 ng/mL), produced less 3.5% FCM (30.8 vs. 35.5 kg/d), and had higher afternoon rectal temperatures (39.4 vs. 39.0°C) and elevated respiration rates (78 vs. 56 respirations/min) during the prepartum period compared with CL cows. Relative to HT cows, CL cows had greater expression of PRL-R and SOCS-2 mRNA postpartum. In addition, CL cows had greater hepatic mRNA expression of PPAR-A and CPT1-A relative to HT cows. Neutrophil phagocytosis was greater in CL cows relative to HT cows at +2 d (61 vs. 42%) and at +20 d (62 vs. 49%) relative to calving, and oxidative burst was greater 60 in CL cows at +2 d (47 vs. 33%) and +20 d (52 vs. 36%) relative to calving compared with HT cows. Humoral response, as measured by IgG secretion against ovalbumin challenge, was greater for CL cows at -32 d (0.44 vs. 0.33 OD) and -21 d (0.60 vs. 0.50 OD) relative to calving compared with HT cows. These results suggest that HT abatement during the dry period increases milk production, improves innate and acquired immune status as measured by neutrophil function and immunoglobulin secretion against ovalbumin challenge, and alters hepatic metabolic gene expression in the subsequent lactation.