|Do Amaral, B|
Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 2/21/2008
Publication Date: 7/7/2008
Citation: Do Amaral, B.C., Hayen, J., Connor, E.E., Tao, S., Dahl, G.E. 2008. Heat stress abatement for dry cows: Does cooling improve transition into lactation? [abstract]. Journal of Dairy Science. 91(E-Suppl. 1):379. Abstract 457. Interpretive Summary:
Technical Abstract: Environmental factors, especially temperature and photoperiod, influence health and productivity of dairy cows during lactation, possibly via similar physiological effects. For example, heat stress is a critical component of lowered milk yield during summer. Long days improve yield during lactation, while short days improve health and subsequent performance in dry cows. The objective of the study was to evaluate the effects of heat stress prepartum under controlled photoperiod on lactation performance and hepatic metabolic gene expression of periparturient Holstein cows (n=16). 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 treatments had a photoperiod of (14L:10D). Rectal temperature was measured 2x daily during the dry period. After calving, cows were housed in a free stall barn with cooling, and milk yield was recorded daily up to 42 DIM. Daily DMI was measured from -35 to 42 d relative to calving. Liver biopsies were collected at dry off, -20, +2, and +20 d relative to calving for cows on HT (n=5) and CL (n=4) to measure mRNA expression of prolactin receptor (PRL-R), suppressors of cytokine signaling (SOCS1, 2, and 3), CAV1, IGFII, IGFBP5, a key transcription factor in lipid biosynthesis (SREBP1-c), and enzymes of lipid metabolism (FASN, ACACA, ACADVL, LCAT, CPT1A, and ACOX) by real-time qPCR. HT cows had greater afternoon rectal temperatures (39.2 vs. 38.8°C) and decreased DMI prepartum (12.0 vs. 14.1 kg/d) and milk yield postpartum (25.4 vs. 33.3 kg/d) compared with CL cows. Relative to CL cows, hepatic mRNA expression of SOCS2 and IGFBP5 was down-regulated in HT cows. Expression of ACADVL was up-regulated in CL cows at d +2 but down-regulated at d +20 relative to HT cows. These results suggest that heat stress abatement in the dry period improves subsequent lactation, possibly through SOCS-2 and its regulation of hepatic lipid metabolism.