期刊
JOURNAL OF DAIRY SCIENCE
卷 86, 期 6, 页码 2170-2177出版社
AMER DAIRY SCIENCE ASSOC
DOI: 10.3168/jds.S0022-0302(03)73807-7
关键词
heifer metabolism; N balance; protein-to-energy ratio
Four prepubertal Holstein heifers, average age 146.0 +/- 3.6 d and 152.8 +/- 8.6 kg of body weight (BW), fitted with rumen cannulae were used to evaluate increasing levels of dietary protein with a constant metabolizable energy intake on rumen ammonia N concentrations, N balance, total tract apparent digestibility, and urinary excretion of purine derivatives in a 4 x 4 Latin square design with 20 d periods. Heifers were fed dietary crude protein levels (CP) of 11.9, 16.7, 18.1, and 20.1% CP with similar amounts of metabolizable energy (ME) (2.6 Mcal per kg of dry matter) at 2.0% BW as dry matter intake. Resulting protein to ME ratios (CP:ME) were 45.0, 63.3, 69.4, and 77.3 g of dietary CP per Mcal of ME. Rumen ammonia N and plasma urea nitrogen increased as CP level increased. Rumen pH, volatile fatty acids, and the acetate-to-propionate ratio were not affected with increasing CP levels. Greater urinary N excretion resulted in an increase in total N excretion with increasing CP levels. Apparent dry matter digestibility was similar for all diets, while apparent total tract N digestibility was lowest for the 11.9% CP level. Microbial N calculated from urinary excretion of purine derivatives increased with increasing CP levels. Holstein heifers between 153 and 196 kg consuming a diet at 2.0% BW as dry matter intake containing a CP level of 16.7% achieved a better synergistic relationship of dietary protein to energy (CP:ME of 63.3 g of CP per Mcal of ME) than the diets lower or higher in CP that were studied.
作者
我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。
推荐
暂无数据