| In recent years,calf mortality has become an increasingly prominent problem and there is a trend of increasing calf mortality year by year in several countries,and calf survival is not only related to animal welfare but also helps to avoid huge losses of economic and genetic material due to calf mortality,therefore,improving calf survival is crucial in dairy breeding.In this study,the causes of calf culling were analyzed,descriptive statistics were performed,and the main causes of culling(respiratory diseases and digestive disorders)were estimated to be genetically related to different growth stages of calves(2-750 d,2-30 d,31-60 d,61-180 d,181-360 d,361-450 d and 451-750 d),and non-genetic factors(birth season,farm,calving ease score,dam parity and single or twin birth)on calf survival,and estimated the genetic power and genetic correlation of calf survival at different growth stages of calves.The main results were obtained as follows:1.Respiratory diseases and digestive disorders are the main reasons for culling calves in the first 6 months after birth;respiratory diseases,digestive disorders and stunting are the main reasons for culling calves at 6-12 months of age;reproductive disorders and stunting are the main reasons for culling after 12 months.2.Calf survival was significantly(P<0.001)affected by season of birth,number of calves born,ease of calving,singleton and twin calves,and the farm to which the calves belonged.Calves born in the fall,calves born in the 3rd parity,calves born naturally,singleton calves and calves with better farm management were more likely to survive.3.Four models were used to estimate calf survival heritability,with the sire model calculating heritability ranging from 0.062～0.084(451-750 d～2-30 d),the single-trait animal model calculating heritability ranging from 0.087～0.110(451-750 d～31-60 d),the Logit model calculating heritability ranging from 0.093～0.143(2-750 d～181-360 d),and the heritability range calculated by the Probit model was 0.014～0.041(451-750 d～181-360 d).The results obtained indicated that calf survival was a low heritability trait.4..High genetic and phenotypic correlations were found between calf survival at adjacent growth stages,and thereafter correlations decreased with increasing time intervals,especially phenotypic correlations,with the lowest genetic and phenotypic correlations between 2-30 d for all later growth stages,with the lowest genetic and phenotypic correlations between 2-30 d and 451750 d,indicating that different genes control early and late postnatal survival traits.The lowest genetic and phenotypic correlations were found between 2-30 d and 451-750 d,indicating that different genes control survival traits in early and late postnatal stages.5.Genetic correlations between calf survival at 2-750 d and digestive disorders(-0.657)and respiratory disease(-0.457)were moderate to low,with calves genetically susceptible to digestive disorders having lower survival rates,and calves genetically susceptible to digestive disorders at 61-180 d(-0.875)and calf survival at 451-750 d(-0.707)was genetically susceptible to digestive disorders and respiratory disease,respectively,and direct and indirect selection should be combined when genetically selecting for calf survival.This study was conducted to analyze Holstein calf survival in large-scale dairy farms in Ningxia region,to estimate the effects of culling causes and non-genetic factors on calf survival,and to estimate genetic parameters for calf survival,which provides a reference for improving calf survival in terms of both feeding management and genetic breeding. |
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