Lourenço João Paulo de A, Cappellozza Bruno I, Bertin Rafaela D, Miranda Victor F B, Junior Wilson M C, de Sousa Osvaldo A, Vasconcelos José Luiz M
School of Veterinary Medicine and Animal Science, São Paulo State University (UNESP), Botucatu, SP, Brazil.
Nutricorp, Araras, SP, Brazil.
Transl Anim Sci. 2021 Oct 14;5(4):txab199. doi: 10.1093/tas/txab199. eCollection 2021 Oct.
Heat stress negatively impacts production, reproduction, and health of ruminants and strategies to alleviate these losses are warranted. Therefore, four experiments evaluated different cooling strategies on vaginal temperature (VT) of Holstein × Gir cows. Experiment 1 compared different amounts of water (2- or 4-L) over a 1-hour period from 1000 to 1100 h and 1600 to 1700 h. Experiment 2 evaluated the effects of sprinkling duration (in hours; 1- or 2-H), whereas Experiment 3 evaluated the effects of water amount (4- or 8-L) applied for 1- or 2-H. Lastly, the effects of a cooling strategy on specific hours of the day, starting at either 0700 (T-1) or 1100 h (T-2; Experiment 4), were evaluated. In all experiments, 12 Holstein × Gir cows were used in a 2 × 2 Latin Square Design containing two periods of 6 days each. Temperature and humidity index (THI) were recorded hourly and VT was recorded every 10-min throughout the experiments. As expected, an hour effect was observed for THI ( < 0.0001), which peaked early in the afternoon. In Experiment 1, a treatment × hour interaction was observed ( < 0.0001) for VT, as animals assigned to receive 4-L had a reduced VT at 1100, 1600, 1700, and 2300 h ( ≤ 0.03). During the cooling applications, cows receiving 4-L for 1 h had a reduced VT from 60 to 150 min ( ≤ 0.04). In Experiment 2, a treatment × hour interaction was observed ( < 0.0001) for VT, as animals assigned to receive 4-L of water for 2-H had a reduced VT at 1200 h ( = 0.05). Moreover, during the cooling process, VT was reduced for 2-H cows from 140 to 170 min after the beginning of the cooling process ( ≤ 0.05). In Experiment 3, animals assigned to receive 4-L + 2H had a reduced VT at 1200, 1700, 1800, and 1900 h ( < 0.001). A treatment × hour interaction was observed ( < 0.0001), as VT was reduced for 4-L + 2-H cows from 130 to 180 min after the beginning of the cooling process ( ≤ 0.05). In Experiment 4, by the time when the first cooling cycle of T-1 was applied (0700 h), T-1 cows consistently had ( ≤ 0.05) a reduced VT up to the hottest hours and greatest THI of the day (1400 and 1500 h). This pattern was maintained until the end of the last cooling cycle, whereas T-2 cows had a reduced VT. In summary, 4 L of water over a 5-min cycle for a period of 2 hours twice a day maintained VT of Holstein × Gir cows at lower levels. Moreover, the hour at which the first cooling cycle starts also should be considered when evaluating the efficacy of a cooling strategy for an entire day.
热应激对反刍动物的生产、繁殖和健康产生负面影响，因此有必要采取策略来减轻这些损失。为此，进行了四项实验，评估不同冷却策略对荷斯坦×吉尔牛阴道温度（VT）的影响。实验1比较了在1000至1100时和1600至1700时这1小时内不同的水量（2升或4升）。实验2评估了喷淋持续时间（小时；1小时或2小时）的影响，而实验3评估了1小时或2小时内施加的水量（4升或8升）的影响。最后，评估了冷却策略对一天中特定时间（从0700时开始的T - 1或1100时开始的T - 2；实验4）的影响。在所有实验中，12头荷斯坦×吉尔牛采用2×2拉丁方设计，每个阶段为期6天。实验期间每小时记录温度和湿度指数（THI），每隔10分钟记录一次VT。正如预期的那样，观察到THI存在小时效应（<0.0001），在下午早些时候达到峰值。在实验1中，观察到VT存在处理×小时交互作用（<0.0001），因为分配接受4升水的动物在1100、1600、1700和2300时的VT降低（≤0.03）。在冷却过程中，接受4升水1小时的奶牛在60至150分钟时VT降低（≤0.04）。在实验2中，观察到VT存在处理×小时交互作用（<0.0001），因为分配接受4升水喷淋2小时的动物在1200时的VT降低（=0.05）。此外，在冷却过程中，冷却开始后140至170分钟内，喷淋2小时的奶牛VT降低（≤0.05）。在实验3中，分配接受4升水+2小时处理的动物在1200、1700、1800和1900时的VT降低（<0.001）。观察到处理×小时交互作用（<0.0001），因为冷却开始后130至180分钟内，接受4升水+2小时处理的奶牛VT降低（≤0.05）。在实验4中，到应用T - 1的第一个冷却周期时（0700时），T - 1组奶牛在一天中最热的时段和最高THI时段（1400和1500时）之前，VT持续降低（≤0.05）。这种模式一直保持到最后一个冷却周期结束，而T - 2组奶牛的VT也有所降低。总之，每天两次，每次2小时，以5分钟的周期提供4升水，可使荷斯坦×吉尔牛的VT保持在较低水平。此外，在评估一整天的冷却策略效果时，还应考虑第一个冷却周期开始的时间。
