PEGASE, INRA, Agrocampus-Ouest, 35042, Rennes, France.
Institut de l'Elevage, 49105, Angers, France.
J Dairy Sci. 2018 May;101(5):4554-4569. doi: 10.3168/jds.2017-14043. Epub 2018 Mar 1.
Milk is an important source of Ca in Western diets. Milk Ca is important for the cheesemaking process and could be a useful biomarker of Ca regulation in cows. The objective of this study was to identify and quantify nongenetic factors affecting the variation of Ca content in bovine milk. During the PhénoFinLait program, a survey was performed in 3 major areas of milk production in France. This survey consisted of collecting milk samples, together with information about herd management and cow nutrition, from 924 commercial farms. More than 200,000 individual milk samples were collected, and Ca content was measured by mid-infrared spectroscopy. Each farm was surveyed several times during the year, and 3 to 6 milk samples were collected from each cow. An equation to predict milk Ca content from mid-infrared spectra was developed based on the Ca contents of 292 milk samples, and the milk Ca contents of the 200,000 samples were then predicted. Milk Ca content was lowest in Holstein cows, intermediate in Montbéliarde cows, and highest in Normande cows. For all 3 breeds, milk Ca decreased during the first month of lactation and increased after the fourth month of lactation, with the range between minimum and maximum values largest in Holsteins, intermediate in Montbéliardes, and smallest in Normandes. Milk Ca content also decreased with parity in all 3 breeds. By using multiple factorial analysis, 6 major feeding strategies employed on French dairy farms were characterized based on the data from the survey. Calendar month and cow feeding strategy affected milk Ca content, which dropped in the spring during grazing turnout and was lower when cows were fed fresh and conserved grass rather than corn silage. In conclusion, environmental factors induce variations in milk Ca content in addition to the genetics of the cows, which to date have been identified as a main factor of variation of milk Ca content in dairy cows. In several of the tested conditions, increases in milk production and in the amount of Ca daily secreted in milk were associated with a decrease in milk Ca content as though the mammary gland operated to limit the exportation of Ca when milk production rapidly increased. This result would suggest that milk Ca content could be a biomarker of Ca regulation in dairy cows.
牛奶是西方饮食中钙的重要来源。牛奶中的钙对于奶酪制作过程很重要，并且可以作为牛体内钙调节的有用生物标志物。本研究的目的是确定和量化影响牛奶中钙含量变化的非遗传因素。在 PhenoFinLait 计划期间，在法国的 3 个主要牛奶生产地区进行了一项调查。该调查包括从 924 个商业农场收集牛奶样本，以及有关牛群管理和奶牛营养的信息。收集了超过 200,000 个个体牛奶样本，并通过中红外光谱法测量钙含量。每个农场在一年内被调查几次，每个奶牛采集 3 到 6 个牛奶样本。基于 292 个牛奶样本的钙含量，开发了一个预测牛奶中钙含量的中红外光谱方程，并预测了 200,000 个样本的牛奶钙含量。荷斯坦奶牛的牛奶钙含量最低，蒙贝利亚尔牛的牛奶钙含量中等，诺曼底牛的牛奶钙含量最高。对于所有 3 个品种，牛奶钙含量在泌乳的第一个月最低，在泌乳的第四个月后增加，荷斯坦牛的最低值和最高值之间的范围最大，蒙贝利亚尔牛的范围中等，诺曼底牛的范围最小。牛奶钙含量也随着牛的胎次而减少。通过使用多因素分析，根据调查数据，确定了法国奶牛场使用的 6 种主要饲养策略。日历月份和奶牛饲养策略影响牛奶钙含量，春季放牧时牛奶钙含量下降，当奶牛饲喂新鲜和青贮的草而不是青贮玉米时，牛奶钙含量较低。总之，除了奶牛的遗传因素外，环境因素还会导致牛奶钙含量的变化，到目前为止，这些因素已被确定为奶牛牛奶钙含量变化的主要因素。在测试的几种条件下，牛奶产量的增加和每天在牛奶中分泌的钙量的增加与牛奶钙含量的降低有关，就好像当牛奶产量迅速增加时，乳腺组织会限制钙的输出。这一结果表明，牛奶钙含量可以作为奶牛体内钙调节的生物标志物。
