Department of Animal Sciences, University of Florida, Gainesville 32611.
Department of Animal Sciences, University of Florida, Gainesville 32611.
J Dairy Sci. 2020 Jan;103(1):325-339. doi: 10.3168/jds.2019-17303. Epub 2019 Oct 31.
The objectives were to evaluate the effects of feeding different amounts of supplemental live yeast (LY) on performance and digestion of cows under heat stress. Sixty Holstein cows, 27 multiparous and 33 primiparous, were blocked by parity and milk yield in the first 20 d in milk (DIM) and randomly assigned to receive 0, 0.5, or 1.0 g/d of LY, resulting in daily intakes of 0, 14.2, and 37.6 billion cells, respectively, of Saccharomyces cerevisiae strain CNCM I-1077 from 30 to 107 DIM. Cows were milked twice daily, dry matter intake (DMI) and milk yield were measured daily, and milk components, body weight, and body condition were measured weekly. Blood was sampled weekly and plasma analyzed for concentrations of glucose, fatty acids, urea N, haptoglobin, serum amyloid A, and acid-soluble protein. Digestibility of nutrients was measured in the last 2 wk of the experiment. Ruminal fluid was collected on 2 consecutive days 6 h after the morning feeding for measurements of pH, concentrations of short chain fatty acids, and NH-N. Feeding behavior was observed for 48 h on experiment d 21 and 63. The mean ambient temperature was 26.8°C, humidity was 83.2%, and the temperature and humidity index ranged from 73 to 81. Treatment did not affect rectal temperature (38.9 ± 0.04°C) or DMI but increased yield of energy-corrected milk (ECM; 35.2 vs. 36.1 vs. 37.2 kg/d for 0, 0.5, and 1.0 g/d, respectively) and efficiency of conversion of DM into ECM (1.70, 1.79, and 1.83 for 0, 0.5, and 1 g/d, respectively). Feeding LY increased digestibility of crude protein (65.1 vs. 68.8 vs. 70.4%) and neutral detergent fiber (NDF; 47.5 vs. 49.2 vs. 55.2%), and concentration of acetate (64.7 vs. 69.1 vs. 72.2 mM), which resulted in increased concentration of total short chain fatty acids in ruminal fluid (110.3 vs. 117.7 vs. 121.4 mM). Mean ruminal pH increased (5.99 vs. 6.03 vs. 6.26), and proportion of cows with pH <5.8 decreased linearly (42.9 vs. 34.9 vs. 7.7%) with increasing inclusion of LY. Concentrations of acute-phase proteins decreased with increasing amount of LY. Some aspects of feeding behavior were altered by LY, and meal size reduced quadratically (3.2, 3.5, and 2.9 kg of DM, respectively), whereas interval between rumination bouts tended to reduce linearly (122, 96.5, and 90.7 min, respectively) with increasing dose of LY. Chewing time per kilogram of NDF tended to increase linearly (71.6, 71.3, and 81.6 min/kg, respectively) with increasing dose of LY. The estimated net energy for lactation of the diet increased 5.2%, from 1.72 Mcal/kg of DM for 0 g of LY to 1.81 Mcal/kg for 1 g of LY. Feeding 1 g of LY/d to cows under heat stress increased yield of ECM and efficiency of feed conversion into ECM, improved diet digestibility, and increased ruminal fluid pH; these responses might be related either to direct effects of LY on ruminal microbial activity or to changes in feeding behavior that improved digestion of cows in heat stress.
本研究旨在评估在热应激条件下，给奶牛饲喂不同水平的补充活酵母（LY）对其生产性能和消化的影响。选择 60 头荷斯坦奶牛，其中 27 头为经产牛，33 头为初产牛，根据产奶量和泌乳天数进行分组，然后随机分为 0、0.5 或 1.0 g/d 的 LY 组，酵母菌株为 Saccharomyces cerevisiae CNCM I-1077，每日摄入细胞数分别为 0、14.2 和 37.60 亿个，从 30 到 107 天泌乳日进行饲喂。奶牛每天挤奶 2 次，每天测量干物质采食量（DMI）和产奶量，每周测量乳成分、体重和体况。每周采集血样，检测血浆中葡萄糖、脂肪酸、尿素氮、结合珠蛋白、血清淀粉样蛋白 A 和酸溶性蛋白的浓度。在实验的最后 2 周测量养分消化率。在第 2 天早晨饲喂后 6 h 连续采集瘤胃液，检测 pH 值、短链脂肪酸浓度和 NH3-N。在实验第 21 天和第 63 天，观察 48 h 的采食行为。平均环境温度为 26.8°C，湿度为 83.2%，温度和湿度指数在 73 到 81 之间。处理对直肠温度（38.9 ± 0.04°C）或 DMI 没有影响，但提高了能量校正乳（ECM）的产量（0、0.5 和 1.0 g/d 组分别为 35.2、36.1 和 37.2 kg/d）和 DM 转化为 ECM 的效率（0、0.5 和 1.0 g/d 组分别为 1.70、1.79 和 1.83）。饲喂 LY 提高了粗蛋白（65.1%比 68.8%比 70.4%）和中性洗涤纤维（NDF；47.5%比 49.2%比 55.2%）的消化率，增加了瘤胃液中乙酸（64.7%比 69.1%比 72.2 mM）的浓度，导致瘤胃液中总短链脂肪酸的浓度增加（110.3%比 117.7%比 121.4 mM）。平均瘤胃 pH 值升高（5.99 比 6.03 比 6.26），随着 LY 添加量的增加，pH 值<5.8 的奶牛比例呈线性下降（42.9%比 34.9%比 7.7%）。急性期蛋白的浓度随着 LY 添加量的增加而降低。LY 还改变了一些采食行为，采食时间呈二次减少（3.2、3.5 和 2.9 kg DM），反刍时间间隔呈线性减少（122、96.5 和 90.7 min）。每千克 NDF 的咀嚼时间呈线性增加（71.6、71.3 和 81.6 min/kg），随着 LY 添加量的增加。添加 1 g/d 的 LY 使日粮的泌乳净能提高了 5.2%，从 0 g/LY 的 1.72 Mcal/kg DM 增加到 1 g/LY 的 1.81 Mcal/kg DM。在热应激条件下给奶牛饲喂 1 g/d 的 LY 可以提高 ECM 的产量和饲料转化为 ECM 的效率，改善日粮消化率，并增加瘤胃液 pH 值；这些反应可能与 LY 对瘤胃微生物活性的直接影响有关，也可能与改善奶牛在热应激下消化的采食行为变化有关。
