气候变化导致的全球变暖对奶牛养殖来说是一个挑战,特别是在撒哈拉以南的国家。在高温和相对湿度下,泌乳奶牛遭受热应激。这项研究的目的是研究通过温度-湿度指数(THI)测量的热应激(HS)对生理参数,产奶量和组成的影响和关系。坦桑尼亚的潮湿沿海地区。在泌乳的第二个和第三个月中,总共使用了29头泌乳的荷斯坦FriesianxZebu杂交奶牛,其中50%(HF50)和75%(HF75)的荷斯坦Friesian基因水平。根据坦桑尼亚家畜研究所(TALIRI)使用的动物记录系统确定了荷斯坦·弗里西亚人的品种组成,Tanga.收集的数据包括每日温度,相对湿度,每日产奶量,和生理参数(核心体温,直肠温度,呼吸频率,和气喘吁吁的分数)。THI是使用国家研究委员会的方程式计算的。THI值分为三类,即,低THI(76-78),中等THI(79-81),和高THI(82-84)。评估THI对生理参数和产奶量和组成的影响。基因型的影响,平价,哺乳月份,以及这些参数与THI对产奶量的相互作用,牛奶成分,和生理参数也进行了研究。结果表明,THI及其与基因型的相互作用,奇偶校验,泌乳月份对所有参数都有非常显著的影响。THI影响(p=0.05)平均日产奶量和乳脂%,蛋白质%,乳糖%,和固体-非脂肪%。随着THI从中等水平增加到高水平,平均日产奶量从3.49±0.04下降到3.43±0.05L/天,脂肪%从2.66±0.05%增加到3.04±0.06%,蛋白质从3.15±0.02%减少到3.13±0.03%。没有观察到乳糖%的下降,而固体非脂肪%从8.56±0.08%下降到8.55±0.10%,因为THI值从中等增加到高。此外,THI影响生理参数(p<0.05)。核心体温(CBT),直肠温度(RT),呼吸频率(RR)和喘息评分(PS)从35.60±0.01增加到36.00±0.01°C,38.03±0.02至38.30±0.02°C,62.53±0.29至72.35±0.28次呼吸/分钟,和1.35±0.01至1.47±0.09,随着THI从低到高增加。THI与平均日产奶量和脂肪百分比呈弱正相关,而蛋白质,乳糖,固体非脂肪百分比与THI呈负相关(p≤0.05)。CBT,RT,RR,PS与THI呈正相关(p≤0.05)。这些负相关表明,对HS的敏感性与生产水平之间存在拮抗相关性。结论是,基因型,平价,和哺乳月份,随着他们与THI的互动,显著影响牛奶产量,牛奶成分,和泌乳荷斯坦弗氏乳品杂交的生理参数在77至84的THI阈值范围内。
Global warming caused by climate change is a challenge for dairy farming, especially in sub-Saharan countries. Under high temperatures and relative humidity, lactating dairy cows suffer from heat stress. The objective of this study was to investigate the effects and relationship of heat stress (HS) measured by the temperature-humidity index (THI) regarding the physiological parameters and milk yield and composition of lactating Holstein Friesian crossbred dairy cows reared in the humid coastal region of Tanzania. A total of 29 lactating Holstein Friesian x Zebu crossbred dairy cows with 50% (HF50) and 75% (HF75) Holstein Friesian gene levels in the second and third months of lactation were used. The breed composition of Holstein Friesians was determined based on the animal recording system used at the Tanzania Livestock Research Institute (TALIRI), Tanga. The data collected included the daily temperature, relative humidity, daily milk yield, and physiological parameters (core body temperature, rectal temperature, respiratory rate, and panting score). THI was calculated using the equation of the National Research Council. The THI values were categorized into three classes, i.e., low THI (76-78), moderate THI (79-81), and high THI (82-84). The effects of THI on the physiological parameters and milk yield and composition were assessed. The effects of the genotype, the parity, the lactation month, and the interaction of these parameters with THI on the milk yield, milk composition, and physiological parameters were also investigated. The results show that THI and its interaction with genotypes, parity, and the lactation month had a highly significant effect on all parameters. THI influenced (p ˂ 0.05) the average daily milk yield and milk fat %, protein %, lactose %, and solids-not-fat %. As the THI increased from moderate to high levels, the average daily milk yield declined from 3.49 ± 0.04 to 3.43 ± 0.05 L/day, while the fat % increased from 2.66 ± 0.05% to 3.04 ± 0.06% and the protein decreased from 3.15 ± 0.02% to 3.13 ± 0.03%. No decline in lactose % was observed, while the solid-not-fat % declined from 8.56 ± 0.08% to 8.55 ± 0.10% as the THI values increased from moderate to high. Also, the THI influenced physiological parameters (p ˂ 0.05). The core body temperature (CBT), rectal temperature (RT), respiratory rate (RR) and panting score (PS) increased from 35.60 ± 0.01 to 36.00 ± 0.01 °C, 38.03 ± 0.02 to 38.30 ± 0.02 °C, 62.53 ± 0.29 to 72.35 ± 0.28 breaths/min, and 1.35 ± 0.01 to 1.47 ± 0.09, respectively, as the THI increased from low to high. The THI showed a weak positive correlation with the average daily milk yield and fat percentage, whereas the protein, lactose, and solids-not-fat percentages showed negative relationships with THI (p ≤ 0.05). CBT, RT, RR, and PS showed positive relationships (p ≤ 0.05) with THI. These negative relationships indicate that there is an antagonistic correlation between sensitivity to HS and the level of production. It is concluded that the THI, the genotype, the parity, and the lactation month, along with their interactions with THI, significantly influenced the milk yield, milk composition, and physiological parameters of lactating Holstein Friesian dairy crosses at THI thresholds ranging from 77 to 84.