Repeatability, Heritability and the Effect of Level of Milk Production on the Occurrence of First Estrus after Calving in Dairy Cattle

Abstract

The avg. length of time from calving to first estrus for 472 normal parturitions of 210 cows was 32.1 [plus or minus] 18.6 days. Analysis of the data indicated that individual cows had a tendency to repeat a similar length of time between calving and first estrus at successive parturitions. It appears that one previous observation on a cow would eliminate about 29% of the variance in predicting future performance in respect to the occurrence of heat after calving. Level of milk production accounted for about 0.9% of the variation in time from calving to first heat. Heritability for time interval from calving to first estrus was estimated to be 27% when based on the intra-sire regression of daughter on dam using only the first available records for each animal. When all records were used, the heritability estimate was 32.2%. The correlation between paternal half-sibs indicated a heritability that was too small to be measured when based on single records but was 31.1% when all records were used.