The objective of this study was to evaluate the influence of supplementing lactating dairy cows with Saccharomyces cerevisiae on milk production and composition, cow behavior, and physiological responses during summer. Twenty primiparous cows were used and two treatments were imposed: (1) control (CON); and (2) probiotic supplementation (PRO; S. cerevisiae, providing 10¹⁰ colony forming units (CFU) per day). Rumen temperature (T_RUM, °C) and pH were obtained via rumen boluses. Rumen temperatures were obtained from all cows (n = 20) at 10-min intervals and ruminal pH were obtained from five cow pairs (n = 10) at 10-min intervals. Ambient temperature (T_A; °C), relative humidity (RH; %), wind speed (WS; m/s), and solar radiation (SR; W/m²) were recorded at 10-min intervals. The temperature humidity index (THI) was calculated using T_A and RH. Cows were milked twice daily. Milk fat (%), protein (%), lactose (%), and somatic cell count (SCC, ‘000) were evaluated on 16 occasions. Cows were observed three times (0800 h; 1200 h; and 1400 h) daily for panting score (PS); respiration rate (RR); posture (standing/lying); shade utilization; and cow activity (eating/drinking/ruminating). Individual PS were used to calculate a mean panting score (MPS) for CON and PRO treatments for each observation. S. cerevisiae did not influence milk yield (P = 0.87), fat (P = 0.82), protein (P = 0.26) or SCC (P = 0.19), although there was a tendency for PRO cows to have higher lactose (P = 0.06). Probiotics did not influence the proportion of cows utilizing shade (P = 0.42); standing (P = 0.41); ruminating (P = 0.72); or drinking (P = 0.40). All cows exhibited an increase in RR (> 24 bpm) at 1200 h and RR showed a steady increase as THI increased (P < 0.0001), regardless of treatment (P = 0.96). Both CON (35.8%) and PRO (40.2%) exhibited an increase in MPS as THI increased from thermoneutral (THI ≤ 74) to very hot (THI ≥ 84.1; P < 0.001). However, PRO cows had lower (2.19 ± 0.09; P < 0.0001) MPS compared with CON (2.54 ± 0.22) cows when THI was categorized as very hot (THI ≥ 84.1). Rumen pH were not influenced by treatment (P = 0.38), however T_RUM of PRO cows were 0.2 °C lower across days (P < 0.0001) and hours (P < 0.0001). These results suggest that supplementing cows with S. cerevisiae may support thermoregulation via decreased T_RUM and MPS; however, further studies are required.

本研究的目的是评估在泌乳奶牛中添加酿酒酵母对夏季产奶量和成分、奶牛行为和生理反应的影响。使用了 20 头初产奶牛并进行了两种处理：（1）对照（CON）；(2) 益生菌补充剂（PRO；S. cerevisiae，每天提供 10 ^{10 个}菌落形成单位 ( CFU )）。瘤胃温度 ( T _RUM ,°C) 和 pH 值通过瘤胃推注获得。每隔 10 分钟从所有奶牛 (n = 20) 获得瘤胃温度，每隔 10 分钟从五对奶牛 (n = 10) 获得瘤胃 pH 值。每隔 10 分钟记录_一次环境温度 ( TA ; °C)、相对湿度 ( RH ; %)、风速 ( WS ; m/s) 和太阳辐射 ( SR ; W/m ^{2 )。}_{使用 T A}和 RH计算温湿度指数 ( THI ) 。奶牛每天挤奶两次。对乳脂肪 (%)、蛋白质 (%)、乳糖 (%) 和体细胞计数 (SCC, '000) 进行了 16 次评估。每天观察奶牛 3 次（0800 小时、1200 小时和 1400 小时）的喘气评分（PS); 呼吸频率（RR）；姿势（站立/躺着）；阴影利用；和奶牛活动（吃/喝/反刍）。单个 PS 用于计算每次观察的 CON 和 PRO 治疗的平均喘气分数 ( MPS )。酿酒酵母不影响产奶量 ( P  = 0.87)、脂肪 ( P  = 0.82)、蛋白质 ( P  = 0.26) 或 SCC ( P  = 0.19)，尽管 PRO 奶牛有较高乳糖 ( P  = 0.06)。益生菌不影响奶牛利用遮荫的比例（P  = 0.42）；站立（P  = 0.41）；反刍（P  = 0.72）；或饮酒（P  = 0.40）。所有奶牛在 1200 小时时的 RR (> 24 bpm) 都表现出增加，并且随着 THI 的增加，RR 表现出稳定的增加 ( P  < 0.0001)，无论处理如何 ( P  = 0.96)。CON (35.8%) 和 PRO (40.2%) 都表现出 MPS 的增加，因为 THI 从热中性 (THI ≤ 74) 增加到非常热 (THI ≥ 84.1; P  < 0.001)。然而，当 THI 被归类为非常热 (THI ≥ 84.1) 时，PRO 奶牛的 MPS 较低 (2.19 ± 0.09; P  < 0.0001) 与 CON (2.54 ± 0.22) 奶牛相比。瘤胃 pH 值不受处理的影响（P  = 0.38），但 PRO 奶牛的 T _RUM在几天（P  < 0.0001）和小时（P < 0.0001)。这些结果表明，用酿酒酵母补充奶牛可能通过降低 T _RUM和 MPS 来支持体温调节；但是，还需要进一步研究。