日粮不同钴水平对奶牛泌乳性能、营养物质消化率和血液生化指标的影响

本研究旨在确定日粮中添加不同水平碳酸钴对奶牛泌乳性能、营养物质消化率和血液生化参数的影响。试验选用30头泌乳中期荷斯坦奶牛，随机分为5组，分别饲喂基础日粮（对照组）和试验日粮（4个试验组），试验日粮为在基础日粮中以碳酸钴（CoCO₃）的形式，分别添加钴0.15、0.30、0.75和1.50 mg·kg^-1 DM。试验期56 d，其中适应期14 d，正试期42 d。测定每日采食量和产奶量，并采集奶样测定乳成分含量，采集饲料和粪样测定营养物质表观消化率，采集血样测定血液生化指标。结果表明，与对照组相比，日粮中添加不同水平的碳酸钴后，奶牛干物质采食量（DMI）和乳成分含量均无显著差异（P>0.05）。但添加钴0.30和0.75 mg·kg^-1 DM提高了产奶量（P<0.05）；与对照组相比，添加钴0.75 mg·kg^-1 DM组显著提高了酸性洗涤剂纤维（ADF）和粗蛋白（CP）的消化率（P<0.05）。此外，添加钴1.50 mg·kg^-1 DM组的血浆葡萄糖含量和谷草转氨酶（AST）活性降低（P<0.05），日粮添加钴0.75 mg·kg^-1 DM降低了谷丙转氨酶（ALT）和碱性磷酸酶（ALP）的活性（P<0.05）；红细胞（RBC）、血红蛋白（HGB）含量和红细胞压积（HCT）随日粮碳酸钴水平升高而升高且呈二次曲线变化（P<0.05）。综上，泌乳中期的荷斯坦奶牛日粮Co水平推荐在0.30~0.75 mg·kg^-1 DM，最适添加水平是0.73 mg·kg^-1 DM。

Effect of Dietary Cobalt Levels on Lactation Performance,Nutrient Digestibility and Plasma Biochemical Parameters in Lactating Dairy Cows

The aim of this study was to determine the effects of different dietary cobalt (Co) supplemental levels on lactation performance, nutrient digestibility and plasma biochemical parameters in lactating dairy cows. Thirty mid-lactation Holstein dairy cows were blocked and randomly divided into 5 groups which were fed with basal diet (control group) and experimental diets (4 experimental groups), and the experimental diets were supplemented with Co of 0.15, 0.30, 0.75 and 1.50 mg·kg^-1 DM as CoCO₃, respectively. The experiment was conducted for 56 d, including 14 d of adaptation and 42 d of trial period. Dairy feed intake and milk yield were recorded every day, milk samples were obtained for component determination, feed and fecal samples were collected for apparent nutrient digestibility determination, blood samples were taken for biochemical parameters determination. The results showed that there was no significant effect on dry matter daily intake (DMI) or milk contents at all Co supplemental levels compared with control group (P>0.05). However, the milk yield was increased by adding cobalt of 0.30 and 0.75 mg·kg^-1 DM (P<0.05). Acid detergent fiber (ADF) and crude protein (CP) digestibility increased significantly at 0.75 mg·kg^-1 DM group compared with control group (P<0.05). Co supplemental level of 1.50 mg·kg^-1 DM resulted in the decrease of plasma glucose and aspartate aminotransferase (AST) activity (P<0.05), while 0.75 mg·kg^-1 DM group decreased the activity of alanine aminotransferase (ALT) and alkaline phosphatase (ALP) (P<0.05). Red blood cells (RBC), hemoglobin (HGB) concentration and hematocrit (HCT) were quadratically increased (P<0.05). The recommended level of dietary Co for mid-lactation Holstein dairy cows is between 0.30 to 0.75 mg·kg^-1 DM, the optimal level is 0.73 mg·kg^-1 DM in this study.