Some Aspects of yield-Survival Relationship in dairy Cattle

Abstract

The data collected by the institute of Agricultural Research statistics from five organized Indian herds of dairy cattle spread over about is years were processed and analysed in an attempt to study the probability of survival of a cow up to a given lactation and its relationship with first lactation milk yield. An attempt has also been made to study the heritability of survival and its genetic correlation with milk yield in the first lactation. The results pertaining to proportion of cows surviving up to a particular order of lactation, the average milk yield characteristics of the first lactation and of their survivors, the regression of proportion surviving on the progeny test values based on dam daughter records, relative survival coefficient, heritability of survival and genetic correlation co efficient, heritability of survival and genetic correlation coefficient were obtained in each of the five herds of Indian cattle viz, red sindhi (Bangalore), Kanga yam, Tharparkar and kankrej. It was found that proportion of cows surviving to various orders of lactation continues to decrease with the increase in the order of lactation for all the five herds. Judged from 50 per cent survival, the cows in the Tharparkar herd survive longer than in the other herds whereas those in the Kankrej herd survive for a shorter period. The average first lactation yield, average first lactation length and average milk yield per day of lactation of cows surviving to various orders of lactation showed almost an increasing trend with the increases order of lactation in each of the five herds. This point out that cows with a higher initial milk yield tend to survive longer in the herd in the sense that such cows are retained deliberately for several generations. It was observed that on an average the milk yield in the first lactation, as judged by the progeny test values, based on dam-daughter records, significantly affected the chances of survival of a cow in the first few orders of lactation. By and large, the maximum survival was noticed at the 3rd lactation. Quite a large number of negative regression coefficients in later lactation indicated that there were factors other than the first lactation yield which affected the chances of surviving the calling process. The relative survival coefficients showed almost a similar trend as that in regression coefficients. Their values were however, different from those of regression coefficient. Such differences became very prominent in later lactations due to a considerable decrease in the proportion surviving. The heritability of survival was calculated by two different methods; one by using angular transformation and the other by using heterogeneity chi-square. It was observed that for a particular order of lactation, the values of heritability obtained by the two methods did not differ markedly. It was also noticed that, on an average, the estimates of heritability of survival in Tharparkar herd were not that high as noticed in the other herds. The genetic correlation coefficient between milk yields in the ratio and the survival to bad lactation was found to be of use. The genetic relationship of the milk yield in the first with survival to 3rd and subsequent lactations was found to be in magnitude.