Kertz A F
Purina Mills, Inc., St. Louis, MO 63144, USA.
J Dairy Sci. 1998 Nov;81(11):3075-84. doi: 10.3168/jds.S0022-0302(98)75872-2.
Dairy cows consume feedstuffs from which they derive nutrients to meet their requirements. Water and dry matter intake limit overall nutrient intake. The variability in the nutrient content of forages is recognized by dairy producers and is addressed with a laboratory analysis program. Grains, oilseeds, and by-products vary considerably in nutrient content, most often being below values listed by the NRC. Nevertheless, these ingredients are usually not analyzed prior to delivery or prior to consumption by the lactating dairy cow. Commercial feeds are regulated and must provide certain concentrations of major nutrients and list the ingredients on the feed label. Energy cannot be directly analyzed but has been estimated by in vitro, regression, and summative equations. Conversions from digestibility to metabolizable and net energy are also estimated simply from coefficients or by using empirical models based on the nutritional composition of individual feedstuffs or diets. Storage and handling losses must be accounted for, and variability in feedstuffs must be addressed through the supplier or a check sample laboratory analysis program. Knowledge of ingredients and dietary nutrient content is essential for any method of computing and delivering nutrients to meet the requirements of the lactating dairy cow.
奶牛食用饲料以获取营养来满足自身需求。水和干物质摄入量限制了总体营养摄入量。奶牛养殖户认识到饲料中营养成分的变异性，并通过实验室分析程序来解决这一问题。谷物、油籽和副产品的营养成分差异很大，通常低于美国国家研究委员会（NRC）列出的值。然而，这些成分在交付给泌乳奶牛或奶牛食用之前通常不进行分析。商业饲料受到监管，必须提供一定浓度的主要营养素，并在饲料标签上列出成分。能量无法直接分析，但已通过体外、回归和总计方程进行估算。从消化率到代谢能和净能的转换也只需根据系数或使用基于单个饲料或日粮营养成分的经验模型进行估算。必须考虑储存和处理损失，饲料的变异性必须通过供应商或检查样品实验室分析程序来解决。了解成分和日粮营养成分对于计算和提供营养以满足泌乳奶牛需求的任何方法都至关重要。
