Variation characteristics of non-genetic factors and somatic cell score for raw milk composition and related traits of Holstein in Ningxia region

Objective  To clarify the effects of non-genetic factors on the raw milk composition and related traits of Holstein in Ningxia region.

Method  Based on the DHI data of Holstein in Ningxia region, the effects of parity, lactation stage and calving season on nine lactation traits were analyzed by GLM process of SAS 9.2 software, and the variation characteristics of lactation traits in different somatic cell scores were explored.

Result  Parity, lactation stage, calving season, lactation stage × calving season had significant effects (P<0.05) on nine lactation traits. Comparison of different parities showed that milk fat percentage and milk solid content decreased significantly after the second parity (P<0.05), milk protein percentage and peak milk yield decreased significantly after the third parity (P<0.05), daily milk yield decreased slightly after the fourth parity, milk lactose percentage decreased first and then increased, reaching the lowest level of 4.84% in the third parity (P<0.05), somatic cell score increased gradually with the increase of parity, and the day of peak milk yield was the latest in the first parity(94.07 d) and the earliest in the fourth parity (67.33 d). Comparison of different lactation stages showed that daily milk yield and milk lactose percentage gradually decreased with the prolongation of lactation in the second and third parities (P<0.05), while milk protein percentage, milk solid content, somatic cell score and milk fat percentage showed an increasing trend (P<0.05). Comparison of different calving seasons showed that from spring to winter, milk fat percentage of the first parity to third parity and milk solid content of the first parity gradually decreased, while daily milk yield and milk lactose percentage showed an increasing trend for the first parity and were at the lowest level in summer for the second parity and third parity. Milk protein percentage, somatic cell score, the day of peak milk yield and peak milk yield showed a trend of increasing first and then decreasing from the first parity to third parity, and the highest levels of all these traits for different parities were found in summer. With the increase of somatic cell score, milk lactose percentage, daily milk yield and peak milk yield decreased gradually, while milk fat percentage and milk protein percentage increased slowly. Milk solid content and the day of peak milk yield reached the highest level when somatic cell score was 4 and 5, respectively.

Conclusion  The results of this study provide a theoretical basis for improving the lactation performance and fresh milk quality of Holstein in Ningxia.