Effect Of Heat Stress On The Production Traits Of Holstein In Beijing

This study aims was to quantify the impact of heat stress in Beijing on the performance of dairy cows through analysis of dairy cow production data in Beijing.Data on DHI(1 190 158),reproductive mating data(256 568),and veterinary treatment data(194 907 articles)from 1993 to 2017 were collected.Using Wood model to obtain the individual’s lactation curve and milk yield parameters,The effect of calving season(heat stress)on the parameters of the lactation curve was analyzed using the MIXED module in SAS 9.2.The GLM of SAS 9.2 was used to analyze the effect of sampling season and calving season on traits such as milk fat ratio,milk protein ratio,and somatic cell score(SCS).The logistic model was used to analyze the effect of the season on dairy cows’ health traits,and multi-trait animal models were used to estimate the genetic parameters of the health traits.The logistic regression model was used to analyze the effect of calving season on the first fertilization rate,and the effect of calving season on the number of pregnancies was analyzed using the SAS 9.2 GLM module.(1)Calving season had a significant effect on Wood’s lactation curve parameters,secondary parameters(initial milk yield,peak rate of rise,peak rate of decline,lactation peak,and estimated 305 days of milk production).Calving season has no significant effect on lactation persistence.The lactation curve of calving in summer was lower than that of other calving seasons,and the higher the parity,the more obvious the differences were.The 305-day milk yield for the first parity and calving in the summer is 274.33-490.17 kg lower than for the other calving seasons.305 days milk production in summer with multiple parity is 440.76-930.68 kg lower than that in other calving seasons.The milk fat ratio and milk protein ratio were 0.36 and 0.24 lower in June to August than in November to January,respectively.In August,the number of somatic cells was 39 000/ml higher than that in October.(2)The odds ratio of relative risk in the summer(OR)was 4-7 times that of the autumn,and the odds ratio of risk of the spring(OR)was 2-3 times that of the autumn(except for the hoof disease).The estimated range of heritability of healthy traits was from 0.0088 to 0.0379,and the heritability of health traits in different seasons was different.The genetic correlation range of health traits in different seasons ranged from 0.4707 to 0.9798.There were environmental and genetic interactions between the three common diseases in different seasons.(3)The frequency of insemination was significantly different in different calving months.The number of inseminations of calving in March,April and May was significantly higher than that of calving in August,September and October(0.5 times,P<0.05).The rate of first-time insemination pregnancy for calves produced in August,September and October is higher,and August is 3 times of January.The reason for the difference in reproductive efficiency in different calving months is whether or not the month of insemination is during heat stress.Heat stress affects the production traits of dairy cows in Beijing.The results of this study provide theoretical support for the efficient management of Holstein in Beijing and the reduction of heat stress.Reveal for the first time the genetic and environmental interactions in the traits of cows in different seasons.It provides data for the comprehensive breeding of dairy cows to improve their production performance and their ability to resist heat stress.