Heritability Estimation and Correlation Analysis of Longevity and Milk Yield of Holstein Cattle in Xinjiang Region

Milk production and longevity are important traits in dairy cattle breeding. In recent years, the high milk yield has been pursued in dairy cattle breeding, while longevity has been declining. With the development of balanced breeding, the longevity traits were gradually included into the comprehensive selection index of dairy cows in developed countries. The purpose of this study was to explore the relationship between milk yield and longevity of dairy cows, and to provide the reference for Xinjiang region to develop the comprehensive selection index of Holstein dairy cows in China, so as to achieve balanced breeding and high-quality healthy development of dairy industry.

The production records of three large-scale dairy farms in Xinjiang from 1997 to 2020 were collected, and the herd life and production life were calculated. The longevity records of 7 206 dairy cows and first parity 305 d milk yield of 15 218 first fetuses were obtained. A total of 18 183 pieces of pedigree information from three generations of individuals were collected, including 903 bulls and 20 883 cows. Firstly, the GLM process of SAS 9.2 software was used to analyze the effects of field, birth year, birth season and age at first calving on the herd days, productive life and first parity 305 d milk yield of Chinese Holstein cattle in Xinjiang region, and the least square mean values of the herd days, productive life and the first parity 305 d milk were calculated. SPSS 19.0 software was used to calculate the Pearson correlation coefficient between the number of herd days, production life and first parity 305 d milk yield of Chinese Holstein cattle in Xinjiang. Secondly, the genetic variance and covariance of herd days, productive life and first parity 305 d milk yield of Holstein dairy cows in Xinjiang were estimated by using AI-REML in DMU software combined with EM algorithm and multi-trait animal model, and the genetic correlation between herd days, productive life and first parity 305 d milk yield was calculated. Finally, the breeding values of the herd days, productive life and first parity 305 d milk yield of Chinese Holstein cattle in Xinjiang region were estimated by animal model BLUP method, and the genetic trend chart was drawn.

The results of basic statistical analysis on the days in the herd days, productive life and first parity 305 d milk yield of Chinese Holstein cows in Xinjiang showed that the average herd days of Chinese Holstein cows in Xinjiang was 1 754.7 days, the average production life was 937.33 days, and the average first parity 305 d milk yield was 9 362.94 kg. GLM program analysis showed that the effects of different fields, birth year, birth season and age at first calving had significant effects on herd days, productive life and first parity 305 d milk yield (P<0.01). The heritability of herd days, productive life and first parity 305 d milk yield of Chinese Holstein cattle in Xinjiang was 0.11 (0.03), 0.11 (0.03) and 0.33 (0.03), respectively. The genetic and phenotypic correlations between herd days span and productive life span were 0.99 and 0.98, respectively. There was a positive correlation between first parity 305 d milk yield and the phenotypes of herd days and production life, with correlation coefficients of 0.079 and 0.077, respectively, while genetic correlation was negative, with correlation coefficients of -0.18 and -0.20, respectively. The genetic trend chart of the herd days, the productive life and the first parity 305 d milk yield of Holstein in Xinjiang showed that the breeding values of the herd days and the productive life changed greatly with the increase of the number of cattle tested, and the overall trend decreased. The first parity 305 d milk yield of Holstein cattle in the first foetus also changed greatly with the increase of the number of cattle tested, but showed an overall upward trend.

Therefore, the longevity of dairy cows should be considered while improving milk yield, so as to avoid the decline of longevity of dairy cows with the increase of milk yield.