Ferreira Matheus L, Vedovatto Marcelo, P Siqueira Isabelle, Marcon Hiam, Dos Reis Bárbara R, Silva Junior Ronaldo G, Chinaglia João V, Renno Luciana N, Edwards Ashley K
Hill Farm Research Station, Louisiana State University, Homer, LA, 71040, USA.
Dean Lee Research and Extension Center, Louisiana State University, Alexandria, LA, 71302, USA.
J Anim Sci. 2025 Jan 4;103. doi: 10.1093/jas/skaf280.
This study evaluated the effects of providing or not providing maternal access to shade and chromium (Cr) propionate supplementation for beef cows under heat stress conditions on cow-calf performance, thermotolerance, and physiological responses. Seventy-two Angus-cross cows were stratified by body weight (BW; 566 ± 5.38 kg) and body condition score (BCS; 6.3 ± 0.5) and allocated to 1 of 12 bermudagrass pastures (3 to 5 ha pastures/5 to 7 cows per pasture). Treatments were randomly assigned to pastures in a 2 × 2 factorial arrangement: shade and Cr (SCr), no shade and Cr (NSCr), shade and no Cr (SNCr) and no shade and no Cr (NSNCr), from day 0 to 180 (on average 150 ± 20 d prepartum and 30 ± 10 d post-partum). Chromium propionate was added to the mineral mix at a rate of 1.8% of the total mineral mixture on a weight basis (Cr target intake of 6.3 mg/cow/d). Data was analyzed on SAS as a 2 × 2 factorial design with pasture considered the experimental unit. The SCr cows showed greater BW on days 90 and 120 compared to all other treatments (P = 0.04). Shaded cows had greater BCS on days 30, 60, and 120 (P < 0.001). Supplementation of Cr increased Cr liver concentration of cows (P = 0.05), but not in calves (P = 0.14). Calves born from no-shaded cows showed lower vigor score at birth (P < 0.02) and were lighter at birth and weaning (P < 0.001). Shaded cows had reduced respiration rate (RR) on days 45, 75, and 90, but cows supplemented with Cr showed increased RR on these days (P < 0.01). Shade reduced cows' overall body temperature and rectal temperature (P < 0.001). Shade reduced overall intravaginal temperature (IT), but NSCr cows showed the greatest IT from 0900 to 1800 hours between treatments on days 60 and 90 (P ≤ 0.04). No-shade cows tended to have increased glucose concentrations on days 30, 90, and 120 (P < 0.0001), and increased non-esterified fatty acids concentrations on days 90 and 120 (P < 0.01). Cows supplemented with Cr had reduced total proteins, globulins, and creatinine (P ≤ 0.03) and tended to have reduced glucose concentrations (P = 0.10). NSCr cows had greater serum urea N concentrations on days 30 and 60 compared to NSNCr (P < 0.001). Total protein, globulins, and IgG tended to be greater for calves born from shaded cows (P ≤ 0.10). Shade improved dam performance, thermotolerance and calf vigor, immunity, and growth. Chromium enhanced pre- and postpartum BW, but only when shade was provided. Chromium supplementation did not improve thermotolerance but enhanced physiological responses.
本研究评估了在热应激条件下，给肉牛母牛提供或不提供遮荫以及补充丙酸铬对母牛-犊牛生产性能、耐热性和生理反应的影响。72头安格斯杂交母牛按体重（BW；566±5.38千克）和体况评分（BCS；6.3±0.5）进行分层，并分配到12个百慕大草牧场中的1个（每个牧场3至5公顷，每牧场5至7头牛）。处理以2×2析因设计随机分配到各个牧场：有遮荫和铬（SCr）、无遮荫和铬（NSCr）、有遮荫和无铬（SNCr）以及无遮荫和无铬（NSNCr），从第0天至180天（平均产前150±20天，产后30±10天）。丙酸铬以占总矿物质混合物重量1.8%的比例添加到矿物质混合物中（铬目标摄入量为6.3毫克/头/天）。数据在SAS上作为2×2析因设计进行分析，牧场被视为实验单位。与所有其他处理相比，SCr组母牛在第90天和120天时体重更大（P = 0.04）。有遮荫的母牛在第30天、60天和120天时体况评分更高（P < 0.001）。补充铬增加了母牛肝脏中的铬浓度（P = 0.05），但犊牛中未增加（P = 0.14）。无遮荫母牛所生的犊牛出生时活力评分较低（P < 0.02），出生时和断奶时体重较轻（P < 0.001）。有遮荫的母牛在第45天、75天和90天时呼吸频率（RR）降低，但补充铬的母牛在这些天呼吸频率增加（P < 0.01）。遮荫降低了母牛的总体体温和直肠温度（P < 0.001）。遮荫降低了阴道内总体温度（IT），但在第60天和90天的处理中，NSCr组母牛在0900至1800小时之间IT最高（P≤0.04）。无遮荫的母牛在第30天、90天和120天时血糖浓度往往增加（P < 0.0001），在第90天和120天时非酯化脂肪酸浓度增加（P < 0.01）。补充铬的母牛总蛋白、球蛋白和肌酐降低（P≤0.03），血糖浓度往往降低（P = 0.10）。与NSNCr组相比，NSCr组母牛在第30天和60天时血清尿素氮浓度更高（P < 0.001）。有遮荫母牛所生犊牛的总蛋白、球蛋白和IgG往往更高（P≤0.10）。遮荫改善了母牛的生产性能、耐热性以及犊牛的活力、免疫力和生长。铬提高了产前和产后体重，但仅在提供遮荫时。补充铬并未改善耐热性，但增强了生理反应。
