Davidson B D, Dado-Senn B, Ouellet V, Dahl G E, Laporta J
Department of Animal Sciences, University of Florida, Gainesville 32608.
Department of Animal and Dairy Sciences, University of Wisconsin, Madison 53706.
JDS Commun. 2021 Mar 12;2(3):165-169. doi: 10.3168/jdsc.2020-0069. eCollection 2021 May.
Youngstock such as nulliparous pregnant dairy heifers are not typically considered for active cooling, as they are thought to be more heat tolerant than mature cows. Recently, the benefits of heat stress abatement in pregnant heifers were studied, but the effect of in utero hyperthermia on the calf is still unknown. Herein, we aimed to investigate the effects of late-gestation heat stress in nulliparous heifers on the growth, immune, and thermoregulatory responses of their calves. Pregnant nulliparous dams were randomly selected for either active cooling (CL; fans and soakers; n = 15) or heat stress (HT; n = 16) 60 d before expected calving. After birth, respiration rate, rectal temperature, skin temperature, and sweating rate were obtained from their heifer calves at 24 h and on d 14, 28, 42, and 56. Blood samples and body weights were both collected for measurement of total protein and hematocrit and calculation of average daily gains, respectively. Gestation length was shorter in HT heifers (272 vs. 276 ± 1.28 d) relative to CL heifers. Birth weights, weaning weights, body weights up to d 56, and average daily gain from birth to weaning were not different between in utero HT (IUHT; n = 13) and in utero CL (IUCL; n = 12) calves. Apparent efficiency of absorption of immunoglobulin G tended to be lower in IUHT calves (26.3 vs. 42.7 ± 9.0%), and serum IgG concentrations from birth to d 56 were significantly lower in IUHT calves relative to IUCL calves (22.0 vs. 32.4 ± 4.47 g/L). Postnatal respiration rate, rectal temperature, sweating rate, total protein, and hematocrit were not different between in utero treatments. There was a tendency for IUHT calves to have lower skin temperature at 24 h (34.9 vs. 36.9 ± 1.05°C), and skin temperature tended to be elevated in IUHT calves at d 56 (29.6 vs. 27.9 ± 1.05°C). In summary, the lack of heat stress abatement during late gestation reduces gestation length of nulliparous heifers. Additionally, providing active cooling to nulliparous heifers during the prepartum period confers immune benefits to their offspring, although it does not translate to growth improvements.
诸如未产怀孕奶牛小母牛之类的幼畜通常不考虑进行主动降温，因为它们被认为比成年母牛更耐热。最近，对减轻怀孕小母牛热应激的益处进行了研究，但子宫内热应激对犊牛的影响仍不清楚。在此，我们旨在研究未产小母牛妊娠后期热应激对其犊牛生长、免疫和体温调节反应的影响。在预期产犊前60天，将怀孕的未产母畜随机分为主动降温组（CL；风扇和喷淋；n = 15）或热应激组（HT；n = 16）。出生后，在24小时以及第14、28、42和56天，从它们的小母牛犊牛身上获取呼吸频率、直肠温度、皮肤温度和出汗率。分别采集血样和体重，用于测量总蛋白和血细胞比容以及计算平均日增重。与CL组小母牛相比，HT组小母牛的妊娠期较短（272天对276 ± 1.28天）。子宫内热应激（IUHT；n = 13）组和子宫内主动降温（IUCL；n = 12）组犊牛的出生体重、断奶体重、至第56天的体重以及出生至断奶的平均日增重没有差异。IUHT组犊牛免疫球蛋白G的表观吸收效率趋于较低（26.3%对42.7 ± 9.0%），并且从出生到第56天，IUHT组犊牛的血清IgG浓度相对于IUCL组犊牛显著较低（22.0 g/L对32.4 ± 4.47 g/L）。子宫内处理对产后呼吸频率、直肠温度、出汗率、总蛋白和血细胞比容没有影响。IUHT组犊牛在24小时时皮肤温度有降低的趋势（34.9°C对36.9 ± 1.05°C），并且在第56天IUHT组犊牛的皮肤温度有升高的趋势（29.6°C对27.9 ± 1.05°C）。总之，妊娠后期缺乏热应激缓解会缩短未产小母牛的妊娠期。此外，在产前为未产小母牛提供主动降温对其后代有免疫益处，尽管这并没有转化为生长改善。
