Weiss W P
Department of Animal Sciences, Ohio Agricultural Research and Development Center, Ohio State University, Wooster 44691, USA.
J Dairy Sci. 1998 Sep;81(9):2493-501. doi: 10.3168/jds.S0022-0302(98)70141-9.
Knowledge about vitamins has evolved greatly since they were discovered < 100 yr ago, but the quantitative determination of the vitamin requirements of dairy cows has been difficult. Current requirements are based on data that are at least 20 yr old and, in some cases, > 50 years old. The response variables in those studies were the prevalence of overt signs of deficiency, level of milk production, reproductive performance, and vitamin concentrations in blood and tissues. Since those studies were conducted, milk production per cow has increased substantially, and the feeding and management of cows have changed (less pasture, less forage, and more total confinement). More refined measures of vitamin adequacy have been developed. Immunocompetence may be a useful tool for determining the requirements of some vitamins. Requirements that are based on measures of immune function are usually higher than those that are based on production or reproduction. The current requirements for vitamin D appear to be adequate, but the requirement for vitamin A should be increased by approximately 50% because of differences in bioavailability between beta-carotene and retinyl esters. Based on health data, the vitamin E requirement should be increased at least 500% and perhaps as much as 700% for dry cows and lactating cows.
自从维生素在不到100年前被发现以来，人们对它们的认识有了很大的发展，但确定奶牛维生素需求量的定量测定一直很困难。目前的需求量是基于至少20年前的数据，在某些情况下，甚至超过50年的数据。这些研究中的反应变量是明显缺乏症状的发生率、产奶量、繁殖性能以及血液和组织中的维生素浓度。自进行这些研究以来，每头奶牛的产奶量大幅增加，奶牛的饲养和管理方式也发生了变化（牧场减少、草料减少、完全圈养增多）。已经开发出了更精细的维生素充足性测量方法。免疫能力可能是确定某些维生素需求量的有用工具。基于免疫功能测量的需求量通常高于基于生产或繁殖的需求量。目前对维生素D的需求量似乎是足够的，但由于β-胡萝卜素和视黄酯之间生物利用度的差异，维生素A的需求量应增加约50%。根据健康数据，干奶牛和泌乳奶牛的维生素E需求量应至少增加500%，甚至可能高达700%。
