Impact of dry period heat stress on milk yield, reproductive performance and health of dairy cows
Two studies were performed to determine the effects of heat stress during the dry period on subsequent lactation yield, occurrence of health disorders, and reproductive performance. In experiment 1, cows were dried off 60 d before calving and assigned to cooling (CL, n=250) or heat stress (HT, n=250). CL cows were housed with sprinklers, fans and shade, whereas the HT group had fans and shade. All cows were cooled postpartum. Rectal temperature (RT) and respiration rate (RR) were recorded during the dry period. BCS was recorded weekly during the dry period and at d 7 and 33 postpartum. Milk yield was recorded monthly. Occurrence of postpartum disorders was evaluated during the first 60 DIM. Reproductive performance included metritis check (MC), days to first breeding (DTAI) and pregnancy rates. In experiment 2, records of 147 multiparous cows over 5 years that were under cooling (n=73) or heat stress (n=74) during the dry period were analyzed. In those studies, HT cows did not have fans or soakers. Traits analyzed were 305 d milk production, number of breedings, and occurrence of postpartum health disorders. In experiment 1, relative to HT, CL cows had lower RT (39.0 vs. 39.1 °C; P = 0.03) and RR (51 vs. 59 breath/min; P < 0.01) when dry. BCS during the dry period and postpartum , DTAI and MC33 did not differ between treatments. CL cows tended to have a greater incidence of metritis at d 7, but no other differences in postpartum health disorders were observed. Milk yield for the first 2 months of lactation did not differ. In experiment 2, HT cows had higher RT (39.0 vs. 39.4°C; P < 0.001) and RR (48 vs. 76 breath/min; P = 0.02) than CL cows. Additionally, CL cows produced 5.3 kg/d more milk (P= 0.01) than HT cows. BW and BCS after calving did not differ between treatments, but CL cows gained more BW and increased BCS during the dry period versus HT cows. Reproductive performance did not differ between treatments. CL cows had a higher incidence of ketosis, and tended to have a higher incidence of metritis and retained placenta versus HT cows. Cooling dry cows during the dry period improves subsequent lactation performance, but the severity of heat stress is a significant influence on the response.
heat stress, dry period, lactation