Protein Reserves in the Lactating Dairy Cow

作者：R.L. Botts, R.W. Hemken, L. S. Bull · 发表于：Journal of Dairy Science · 年份：1979 · DOI：10.3168/jds.s0022-0302(79)83263-4 · 被引用次数：125 · 研究领域：Reproductive Physiology in Livestock、Ruminant Nutrition and Digestive Physiology

Protein reserves were measured in a nitrogen depletion-repletion experiment with 15 lactating Holstein cows.At 2 to 3 wk postpartum, cows were fed 14 kg/day of a ration containing 9% crude protein (dry matter).At the end of depletion (8 to 16 wk), animals were assigned randomly to rations containing 14, 18, or 22% crude protein.The amount of nitrogen repleted was measured by nitrogen balance.The animals were fed a complete ration of 60% corn silage and 40% concentrate dry matter.Intake was greater for the 14 and 18% protein groups during repletion.Milk production was greater for the 18% group, 26.5 kg/day compared with 22.8 and 21.9 kg/day for the 14 and 22% protein groups.Nitrogen balance was affected by protein content of the ration.Means were .24,.43,and .60 g nitrogen per day per kg body weight .7s.Urinary nitrogen increased with crude protein; however, fecal nitrogen was not affected.Milk nitrogen output was greater for the 18% group.Apparent means of digestibilities for dry matter and nitrogen were 62.0 and 63.0 for the 14% group, 64.3 and 71.7 for the 18% group, and 67.1 and 75.1 for the 22% group.The groups were repleted for a period of 12.4, 9.6, and 7.4 wk and accumulated 19.7, 29.2, and 31.7 g nitrogen per kg body weight .Ts.There was a greater amount of nitrogen repleted by the medium and high groups com-