本试验旨在研究日粮中添加吡啶羧酸铬对热应激下泌乳前期奶牛生产性能、血液生化指标和激素浓度的影响及其机理。选用24头泌乳前期的荷斯坦奶牛（产后15-24 d），随机分为对照组A和吡啶羧酸铬试验组B、C、D。对照组A饲喂基础日粮，试验组B、C、D在此基础上分别添加铬3.6、7.2和10.8 mg/(头·d)，饲养试验时间为9周。试验期内白天平均温湿度指数（THI）高于79，形成严重的热应激环境。试验结果表明：补铬可以显著提高热应激下奶牛的干物质采食量（P<0.05），添加铬7.2和10.8 mg/(头·d)可以显著提高泌乳量、血糖浓度、胰岛素样生长因子-Ⅰ（IGF-Ⅰ）及胰岛素的活性（P<0.05）。此外添加铬7.2和10.8 mg/(头·d)可以显著提高发情后第1天黄体生成素（LH）浓度和发情后第10天孕酮（P4）和LH浓度（P<0.05）。补铬使各试验组奶牛产后发情天数分别缩短1.85、4.00和3.84 d（P>0.05），添加铬7.2和10.8 mg/(头·d)可以改善奶牛第一情期受胎率（P>0.05）。由此可知，添加铬7.2和10.8 mg/(头·d)能显著提高热应激下泌乳前期奶牛的生产性能，改善机体代谢及调节生殖激素的浓度。

The objective of this article was to study the effects of dietary supplementation with chromium-picolinate on production performance, blood biochemical indexes and hormone levels of dairy cows and their mechanism under heat stress. Twenty-four dairy cows (15-24 days after parturition) were randomly divided into four groups which were randomly allocated to one of the four treatment diets (A, B, C and D). Diet A was basal diet, and diets B, C and D were added with chromium at the level of 3.6, 7.2 and 10.8 mg chromium/(head·day) based on diet A, respectively. The feeding trial lasted for nine weeks. Averaged THI was above 79 units during day period, which indicated that dairy cows were under serious heat stress. Results showed that chromium supplementation could improve the production performance of dairy cows under heat stress. The dry matter intake of dairy cows was significantly increased by adding chromium-picolinate (P<0.05). The milk yields, concentrations of blood glucose and IGF-Ⅰ, and the activities of insulin were increased significantly by adding 7.2 and 10.8 mg chromium/(head·day) (P<0.05). The concentrations of luteinizing hormone （LH） at the first day after oestrus, progesterone （P4） and LH at the tenth day after oestrus were significantly increased by adding 7.2 and 10.8 mg chromium/(head·day) (P<0.05). Compared with control group (group A), the days from parturition to oestrus of groups B, C and D were shortened by 1.85, 4.00 and 3.84 days, respectively (P<0.05), and conception rate in the period from parturition to oestrus was both improved by adding 7.2 and 10.8 mg chromium/(head·day). In conclusion, adding 7.2 and 10.8 mg chromium/(head·day) could significantly increase production performance of early-lactation cows under heat stress, improve the metabolism and regulate the reproduction hormone levels.［Chinese Journal of Animal Nutrition, 2010，22（2）:380-385］