Effects of month and parityon raw milk composition and related traits of Chinese Holstein Cows in the North of China

摘要

Introduction Factors influencing the composition of milk includeextemal factorsand cow factors (Fox and McSweeney,1998) (Cao et al.,2010).For external factors,higher percentages of fat and protein were shownin the evening milking,but season has more significantlyaffectedon composition of milk than the milking-to-milking variation(Quist et al.,2008).As a cow factor,gene impacts on the composition of milk directly (Khatib et al.,2008),but it is difficult to quantify the role of genes.Therefore,season and parity may be the major external and cow factors affecting milk composition and may be the primary sources of variation of raw milk composition.This study investigatedeffects of calendar month and parityon composition of raw milkand analyzed correlationswith milk traits.A few models were also developed to quantify the effects of seasonal variation on milk composition.