Range Cattle Research and Education Center, University of Florida, Ona, FL 33865, USA.
Livestock Issues Research Unit, ARS-USDA, Lubbock, TX 79403, USA.
J Anim Sci. 2022 Apr 1;100(4). doi: 10.1093/jas/skac107.
On day 0 of years 1 and 2, 64 Brangus crossbred heifers per year were stratified by initial body weight (BW) and age (mean = 257 ± 20 kg and 271 ± 22 d) and allocated into 16 bahiagrass (Paspalum notatum) pastures (4 heifers per pasture per yr). Treatments were randomly allotted to pastures in a 2 × 2 factorial arrangement of treatments (4 pastures per treatment per yr). Treatments consisted of concentrate dry matter (DM) supplementation at 1.50% of BW from days 0 to 100 (CON) or concentrate DM supplementation at 1.05% of BW from days 0 to 49 and 1.95% of BW from days 50 to 100 (SST). Then, each respective supplementation strategy was added or not with immunomodulatory feed ingredients from days 0 to 100 (OMN; 4 g/45 kg of BW). Heifers were assigned to an estrus synchronization protocol from days 100 to 114. Heifers detected in estrus from days 111 to 114 were inseminated (AI) 12 h after estrus detection. Heifers not detected in estrus were timed AI on day 114. All heifers were exposed to Angus bulls from days 120 to 210 (1 bull per pasture). Effects of supplementation strategy × OMN inclusion × hour were detected (P < 0.0001) only for intravaginal temperature from days 26 to 30, which were the least (P ≤ 0.03) for SST heifers offered OMN supplementation and did not differ (P ≥ 0.17) among all remaining treatments from 0830 to 1600 hours. Effects of supplementation strategy × OMN inclusion and OMN inclusion were not detected (P ≥ 0.12) for any variable, except for the percentage of heifers detected in estrus, which was greater (P = 0.01) for heifers supplemented with vs. without OMN. Total concentrate DM offered from days 0 to 100 and heifer BW on days 0 and 56 did not differ (P ≥ 0.49) between CON and SST heifers, but SST heifers were heavier (P ≤ 0.01) on days 100 and 210 compared with CON heifers. Body surface temperature on day 25 and plasma IGF-1 concentrations on day 75 were greater (P ≤ 0.04) for SST vs. CON heifers. Percentage of pubertal heifers, heifers detected in estrus, and pregnancy to AI did not differ (P = 0.36) between SST and CON heifers but the final pregnancy percentage was greater (P = 0.04) for SST vs. CON heifers. Thus, OMN supplementation decreased the intravaginal temperature of SST heifers but failed to improve their growth and reproduction, whereas the SST strategy improved body thermoregulation, growth, and final pregnancy percentage of heat-stressed Bos indicus-influenced beef heifers compared with a constant concentrate supplementation strategy.
在第 1 年和第 2 年的第 0 天，将 64 头婆罗门杂交奶牛按照初始体重（BW）和年龄（平均值=257±20kg 和 271±22d）分层，并分配到 16 个巴西牧草地（Paspalum notatum）（每个牧草地每年有 4 头奶牛）。处理方法采用 2×2 因子设计随机分配到牧草地（每年每个处理有 4 个牧草地）。处理方法包括从第 0 天到第 100 天每天补充浓缩物干物质（DM）占 BW 的 1.50%（CON）或从第 0 天到第 49 天和第 50 天到第 100 天每天补充浓缩物 DM 占 BW 的 1.05%和 1.95%（SST）。然后，从第 0 天到第 100 天，分别在各自的补充策略中添加或不添加免疫调节饲料成分（OMN；4g/45kg BW）。从第 100 天到第 114 天，奶牛被分配到发情同步方案中。从第 111 天到第 114 天发情的奶牛在发情检测后 12 小时进行人工授精（AI）。未发情的奶牛在第 114 天进行定时 AI。所有奶牛从第 120 天到第 210 天接触安格斯公牛（每个牧草地 1 头公牛）。仅从第 26 天到第 30 天检测到补充策略×OMN 包含×小时的影响（P＜0.0001），即接受 OMN 补充的 SST 奶牛的阴道内温度最低（P≤0.03），并且在 0830 到 1600 小时之间，所有其余处理之间的阴道内温度没有差异（P≥0.17）。除了发情奶牛的百分比，发情奶牛的发情检测和 AI 妊娠没有检测到补充策略×OMN 包含和 OMN 包含的影响（P≥0.12），发情奶牛的发情检测百分比更大（P=0.01）与未接受 OMN 补充的奶牛相比。从第 0 天到第 100 天提供的浓缩物 DM 总量和第 0 天和第 56 天的奶牛 BW 在 CON 和 SST 奶牛之间没有差异（P≥0.49），但 SST 奶牛在第 100 天和第 210 天比 CON 奶牛更重（P≤0.01）。第 25 天的体表面温度和第 75 天的血浆 IGF-1 浓度 SST 奶牛比 CON 奶牛更高（P≤0.04）。青春期奶牛的百分比、发情奶牛的百分比和 AI 妊娠率在 SST 和 CON 奶牛之间没有差异（P=0.36），但 SST 奶牛的最终妊娠率更高（P=0.04）与 CON 奶牛相比。因此，OMN 补充降低了 SST 奶牛的阴道内温度，但未能改善其生长和繁殖性能，而 SST 策略改善了热应激 Bos indicus 影响的肉牛奶牛的体温调节、生长和最终妊娠率，与恒定的浓缩物补充策略相比。
