Menta P R, Machado V S, Piñeiro J M, Thatcher W W, Santos J E P, Vieira-Neto A
Department of Veterinary Sciences, Texas Tech University, Lubbock 79409.
Department of Animal Sciences Texas A&M AgriLife Extension Service, Texas A&M University, Amarillo 79106.
J Dairy Sci. 2022 May;105(5):4474-4489. doi: 10.3168/jds.2021-21185. Epub 2022 Mar 10.
Objectives of this retrospective cohort study were to determine the association of heat stress (HS) exposure during the periparturient period with production, health, reproduction, and survival during the first 90 d postpartum in dairy cows. A total of 5,722 Holstein cows (2,324 nulliparous and 3,397 parous) were categorized into environmental condition groups based on average temperature-humidity index (THI) exposure as thermoneutral (TN) or HS during the prepartum (PRE) and early postpartum (POST) periods into TN-TN (THI: PRE = 57.9 and POST = 63.7), TN-HS (THI: PRE = 68.2 and POST = 72.0), HS-TN (THI: PRE = 71.4 and POST = 65.6), and HS-HS (THI PRE = 72.2 and POST = 72.7). Nulliparous and parous cows were analyzed separately. In nulliparous cows, exposure to HS during the PRE, POST, or both PRE and POST periods was associated with a 1.7 kg/cow per day reduction in milk yield compared with TN-TN. Postpartum HS was associated with increases of 4.4 percentage points in incidence of retained placenta, 18.1 percentage points in incidence of metritis, and 2.0 percentage points in incidence of mastitis, but a reduction of 5.3 percentage points in pregnancy at first AI, and an increase of 4.5 percentage points in pregnancy loss compared with POST TN. Exposure to HS during PRE and POST periods was associated with increased removal from the herd. In parous cows, exposure to HS during PRE, POST, or both PRE and POST was associated with a 2.4-kg/cow per day reduction in milk yield when compared with TN-TN. There was an interaction between HS exposure PRE and POST and incidence of retained placenta, because POST HS was associated with an increase in incidence of 5.8 percentage points within PRE HS cows, whereas no difference was found within PRE TN cows. Postpartum HS was associated with an increase of 6.3 percentage points in incidence of metritis and tended to be associated with an increase of 1.9 percentage points in mastitis incidence compared with POST TN. There was an interaction between HS exposure PRE and POST and pregnancy per AI because POST HS was associated with reduced pregnancy incidence by 10.6 percentage points within PRE TN cows, whereas no difference was found within PRE HS cows. Removal from the herd increased in cows exposed to HS during the PRE or POST or PRE and POST. These data suggest that POST HS is associated with performance losses to a greater extent than prepartum HS and that nulliparous and parous cows are prompt to losses associated with exposure to HS during the transition period. The results corroborate findings from manipulative experiments that showed improved milk production and reproduction in cows under HS provided with heat abatement but adds insights to the associations between HS and health.
这项回顾性队列研究的目的是确定围产期热应激（HS）暴露与奶牛产后前90天的生产、健康、繁殖和存活之间的关联。总共5722头荷斯坦奶牛（2324头初产牛和3397头经产牛）根据产前（PRE）和产后早期（POST）的平均温度湿度指数（THI）暴露情况分为环境条件组，即热中性（TN）或HS，分为TN-TN（THI：PRE = 57.9，POST = 63.7）、TN-HS（THI：PRE = 68.2，POST = 72.0）、HS-TN（THI：PRE = 71.4，POST = 65.6）和HS-HS（THI PRE = 72.2，POST = 72.7）。初产牛和经产牛分别进行分析。在初产牛中，与TN-TN相比，产前、产后或产前和产后均暴露于HS与日产奶量降低1.7千克/头有关。产后HS与胎盘滞留发生率增加4.4个百分点、子宫炎发生率增加18.1个百分点、乳腺炎发生率增加2.0个百分点有关，但与产后TN相比，首次人工授精时的妊娠率降低5.3个百分点，妊娠损失增加4.5个百分点。产前和产后暴露于HS与牛群淘汰率增加有关。在经产牛中，与TN-TN相比，产前、产后或产前和产后均暴露于HS与日产奶量降低2.4千克/头有关。产前和产后HS暴露与胎盘滞留发生率之间存在交互作用，因为产后HS与产前HS奶牛中发生率增加5.8个百分点有关，而产前TN奶牛中未发现差异。与产后TN相比，产后HS与子宫炎发生率增加6.3个百分点有关，并且倾向于与乳腺炎发生率增加1.9个百分点有关。产前和产后HS暴露与每次人工授精的妊娠情况之间存在交互作用，因为产后HS与产前TN奶牛中妊娠率降低10.6个百分点有关，而产前HS奶牛中未发现差异。产前、产后或产前和产后暴露于HS的奶牛被淘汰出牛群的比例增加。这些数据表明，产后HS比产前HS在更大程度上与生产性能损失有关，并且初产牛和经产牛在过渡期容易受到HS暴露相关的损失。这些结果证实了操纵性实验的结果，即给处于热应激下的奶牛提供降温措施可提高产奶量和繁殖性能，但也为HS与健康之间的关联提供了新的见解。
