Genetic Analysis of Stayability in Dairy Cattle―A Review.

Abstract

The present review on stayability or herd life of dairy cattle discusses different measures of stayability and methods of genetic analysis of stayability using linear models, thresh hold models and non -linear regression methods (Cox and weibull proportional hazard models)stayability is a composite survival trait with significant impact on the overall profitability of dairy cows. higher the stayability , higher would be the number of mature cows in the herd leading to lower replacement rates .the liner models are not optimal for genetic analysis of non linear longivity data with certain degree of skewness . the effect of various genetic(sires and breeds) and non genetic factors (herds,seasons, year/periods) on measors of stayability having waeussed. the heritibility of stayability differed according to methods used and ranged from zero to moderate. however, estimates of heritability using proportional hazard models of survival analysis were reported to be more consistent as compared to the estimates obtained from linear models . the proportional hazard model had the advantage of inclusion of censored records during the analysis of data . the phenotypic and genetic correlations of stayability with early production , reproduction and titrates revealed that it is difficult to predict sataybility in herds where involunatary culing is practiced . however , comparatively higher geentic correlation of stayability with first lactation milk yield has been reported in strature . higher genetic correlation along with moderate estimate of heritability of both the traits would lead to higher correlated response in stayability as better producing cows tends to live longer in the herd .Hence, indirect selection can be done for this trait on this basis of first lactation milk yield.