Department of Animal Sciences, Isfahan University of Technology, Isfahan 84156 Iran.
J Dairy Sci. 2010 Sep;93(9):4111-20. doi: 10.3168/jds.2009-2568.
The primary objective was to determine pre- and postweaning calf physiological responses to increased Cr supply under high ambient temperatures. In a randomized complete block design, 24 neonate Holstein calves (BW=41.5+/-1.9 kg) were grouped based on sex and randomly assigned to 3 treatments within each group. Treatments included either no supplemental Cr (control), 0.02 mg of supplemental Cr/kg of BW0.75, or 0.04 mg of supplemental Cr/kg of BW0.75. The average temperature-humidity index was 77 during the study. Chromium was provided as a commercial product in whole milk for preweaning calves and in a starter concentrate for postweaning calves. Calves were weaned at 1 kg of daily calf starter intake lasting for 6 consecutive days. A glucose tolerance test was conducted on d 25 postweaning. Treatments had no effects on preweaning dry matter intake, feed conversion ratio, average daily gain, and weaning age. Chromium decreased dry matter intake in postweaning calves; however, it did not affect growth and feed conversion ratio. Chromium lowered respiration rate at wk 5 without affecting fecal score and rectal temperature. Preweaning serum cortisol concentrations were altered by a 3-way interaction of Cr dose with calf sex and age. Preweaning serum glucose showed week-dependent increases by Cr. Serum insulin, urea, albumin, total protein, triiodothyronine, and thyroxin concentrations through weaning were not affected. The increasing Cr doses caused quadratic declines in serum thyroxin on d 21 postweaning, whereas blood triiodothyronine declined only with the higher Cr dose. Serum NEFA remained unchanged, but BHBA decreased by Cr in male calves on d 21 postweaning. The glucose tolerance test revealed linear reductions in area under insulin curve between 0 to 90 and 0 to 120 min after glucose infusion, suggesting improvements in peripheral insulin efficiency. Sex-dependent responses to Cr were observed for serum total protein and albumin concentrations at 21 d postweaning. Overall, results indicate that in summer, increased dietary Cr supply can benefit postweaning insulin metabolism, alter preweaning blood cortisol and glucose levels, and reduce respiration rate and may have only minor effects on calf growth.
本研究的主要目的是在高温环境下，确定增加 Cr 供应对断奶前和断奶后小牛生理反应的影响。在随机完全区组设计中，将 24 头新生荷斯坦小牛（BW=41.5+/-1.9kg）按性别分组，并在每组内随机分配到 3 个处理。处理包括不补充 Cr（对照）、0.02mg/kg BW0.75 的补充 Cr 或 0.04mg/kg BW0.75 的补充 Cr。研究期间平均温湿度指数为 77。Cr 以全脂牛奶的形式提供给断奶前的小牛，以开食料的形式提供给断奶后的小牛。小牛在 6 天连续每天摄入 1kg 犊牛开食料后断奶。断奶后第 25 天进行葡萄糖耐量试验。处理对断奶前干物质采食量、饲料转化率、平均日增重和断奶年龄没有影响。Cr 降低了断奶后小牛的干物质采食量，但对生长和饲料转化率没有影响。Cr 在第 5 周降低了呼吸率，但不影响粪便评分和直肠温度。断奶前血清皮质醇浓度受到 Cr 剂量与小牛性别和年龄三因素相互作用的影响。断奶前血清葡萄糖浓度随 Cr 呈周依赖性增加。血清胰岛素、尿素、白蛋白、总蛋白、三碘甲状腺原氨酸和甲状腺素浓度在断奶期间不受影响。随着 Cr 剂量的增加，断奶后第 21 天血清甲状腺素呈二次下降，而仅在高 Cr 剂量下，血液三碘甲状腺原氨酸下降。血清 NEFA 保持不变，但断奶后第 21 天雄性小牛的 BHBA 因 Cr 而减少。葡萄糖耐量试验显示，在葡萄糖输注后 0 至 90 分钟和 0 至 120 分钟，胰岛素曲线下面积呈线性降低，提示外周胰岛素效率提高。断奶后第 21 天，Cr 对血清总蛋白和白蛋白浓度表现出性别依赖性反应。总体而言，结果表明，在夏季，增加日粮 Cr 供应可以有益于断奶后胰岛素代谢，改变断奶前血液皮质醇和葡萄糖水平，降低呼吸率，并且可能对小牛生长只有很小的影响。
