Effects of late-gestation heat stress independent of reduced feed intake on colostrum, metabolism at calving, and milk yield in early lactation of dairy cows

摘要

The objective of this study was to differentiate theeffects of acute heat stress (HS) from those of decreaseddry matter intake (DMI) during the prepartum periodon metabolism, colostrum, and subsequent productionof dairy cows. Holstein dairy cows (n = 30) with similarparity and body weight were randomly assigned to 1 of3 treatments on 45 d before calving: (1) cooled (CL, n= 10) conditions with ad libitum feed intake, (2) HSconditions with ad libitum feed intake (n = 10), and(3) pair-fed cooled (CLPF, n = 10) with reduced DMIsimilar to the HS group while housed under cooled conditions.The reduction in the amount of feed offered tothe CLPF cows was calculated daily as the percentagedecrease from the average DMI of HS cows relative tothe CL cows. For CLPF and CL cows, barns providedshade, sprinklers, and fans, whereas the HS cows wereprovided only with shade. Cows in all groups receivedindividually the same total mixed ration. Cows weredried off 60 d before the expected calving. Cows in theHS group and, by design, the CLPF cows had reducedDMI (~20%) during the experiment. Heat stress decreasedgestation length, first colostrum yield, and calfbirth weight compared with CL and CLPF cows. Milkyield decreased 21% (5 kg) in the HS and 8% (2 kg) inCLPF cows, indicating that reduced feed intake duringlate gestation accounted for 60% of the total reducedmilk yield. The CLPF cows exhibited an elevated NEFAconcentration compared with the CL and HS cows. TheHS cows had a greater mRNA abundance of HSP70 inthe peripheral blood leukocytes at 21 d prepartum comparedwith the other groups. At calving, the mRNAabundance of HSP70 was greater in HS cows, followedby CLPF, compared with the CL cows. In conclusion,HS during the late gestation period caused metabolismand production differences, which were only partiallyattributed to reduced feed intake in dairy cows.