AgNext, Department of Animal Sciences, Colorado State University, Fort Collins, CO 80523, USA.
Departamento de Ciencias Veterinarias y Salud Pública, Universidad Católica de Temuco, Temuco 4780000, Chile.
J Anim Sci. 2024 Jan 3;102. doi: 10.1093/jas/skae218.
The objective of this study was to assess the effects of the exposure to daily maximum and temperature-humidity index (THI) and to daily THI fluctuations (∆THI = maximum THI-minimum THI) at exposure periods comprising 2 d before birth to birth (-2 d), birth date (0 d), birth to 2 d of age (+2 d), and birth to 7 d of age (+7 d) on serum total proteins (STP), transfer of passive immunity (TPI), and the occurrence of scours and respiratory disease. A total of 841 Holstein heifer calves were retrospectively observed from -2 d until 65 d of age. Colostrum quality was assessed using a colostrometer to ensure a minimum globulin concentration of 52 mg/mL in the colostrum fed to the study calves. Two temperature and relative humidity sensors were installed at the calf yard. Maximum, minimum, and ∆THI values were obtained for each exposure period, and thermal exposure categories were defined as heat stress (HS: maximum THI > 70 units; non-HS: THI ≤ 70 units) and ∆THI (low < 20 units, medium ≥ 20 to ≤30 units, high > 30). The TPI was classified as poor (STP < 5.1 g/dL), fair (5.1 and 5.7 g/dL), good (>5.7 and 6.1 g/dL), and excellent (≥6.1 g/dL). Associations between the thermal exposure categories and the study outcomes were examined using ANOVA, logistic regression, and survival analyses. No differences in STP at -2 d were observed between HS and non-HS calves (6.83 ± 0.05 vs. 6.91 ± 0.05 g/dL), whereas HS-exposed calves at 0 d tended to have lower STP compared with non-HS calves (6.82 ± 0.05 vs. 6.92 ± 0.05 g/dL). Calves exposed to small ∆THI at 0 d had greater STP compared with calves exposed to medium ∆THI (7.00 ± 0.06 vs. 6.75 ± 0.05 g/dL). No association was found between HS, and ∆THI categories and the TPI category. The odds of scours were about 2 times greater in HS calves compared with non-HS calves at all exposure periods. In addition, HS calves were affected by scours between 9 and 15 d earlier than non-HS calves. Furthermore, high ∆THI favored the development of respiratory problems compared with medium and low ∆THI. Assessment of extreme THI values and THI fluctuations provides a research opportunity for assessing thermal stress in dairy heifer calves raised in dry climate.
本研究旨在评估奶牛犊牛在出生前 2 天至出生（-2 天）、出生日（0 天）、出生至 2 天龄（+2 天）和出生至 7 天龄（+7 天）期间暴露于日最高温度和温湿度指数（THI）和日 THI 波动（∆THI=最高 THI-最低 THI）对血清总蛋白（STP）、被动免疫转移（TPI）以及腹泻和呼吸道疾病发生的影响。总共对 841 头荷斯坦奶牛犊牛进行了回顾性观察，从-2 天龄直至 65 天龄。使用乳脂计评估初乳质量，以确保给研究犊牛喂养的初乳球蛋白浓度至少为 52mg/mL。在犊牛场安装了两个温度和相对湿度传感器。获得了每个暴露期的最大、最小和 ∆THI 值，并将热暴露类别定义为热应激（HS：最大 THI>70 单位；非 HS：THI≤70 单位）和 ∆THI（低<20 单位，中≥20 至≤30 单位，高>30 单位）。TPI 被分类为差（STP<5.1g/dL）、中（5.1 和 5.7g/dL）、好（>5.7 和 6.1g/dL）和优（≥6.1g/dL）。使用方差分析、逻辑回归和生存分析检查了热暴露类别与研究结果之间的关系。在-2 天龄时，HS 和非 HS 犊牛之间的 STP 没有差异（6.83±0.05 与 6.91±0.05g/dL），而 0 天龄时暴露于 HS 的犊牛的 STP 倾向于低于非 HS 犊牛（6.82±0.05 与 6.92±0.05g/dL）。0 天龄时暴露于小 ∆THI 的犊牛的 STP 高于暴露于中 ∆THI 的犊牛（7.00±0.06 与 6.75±0.05g/dL）。HS 和 ∆THI 类别与 TPI 类别之间没有关联。在所有暴露期，HS 犊牛发生腹泻的几率是无 HS 犊牛的约 2 倍。此外，与非 HS 犊牛相比，HS 犊牛在 9-15 天龄时更容易发生腹泻。此外，与中、低 ∆THI 相比，高 ∆THI 有利于呼吸道问题的发展。评估极端 THI 值和 THI 波动为评估在干燥气候下饲养的奶牛犊牛的热应激提供了研究机会。
