Factors Associated with Estimated Fertilization and Service Efficiency of Cows

Abstract

Embryonic mortality was estimated by using the difference between percentage of estrous cycles recurring between 18 and 25 days for the cows which were bred at the previous estrous compared with those which were not bred. The study included 6719 calvings carried to term, 668 abortions, and 1915 estimated embryos lost, for a total of 9302 fertilizations. The estimated embryonic loss for all cows was 20.6% and abortion loss was 7.2%. Clinically normal cows averaged 11.4% and clini-cally normal cows and heifers averaged 16.6% embryonic loss. Though fertilizing capacity was equal, normal heifers had a significantly higher embryo loss than cows in their 2d and 3d reproductive periods. Fourth and 5th reproductive period cows had the highest efficiency as determined from the percentage of services carried to term. Fertilizations per service and embryo loss declined markedly with increasing age. Reproductive efficiency was very low for cows with infections of the genital tract and estimated embryo loss exceeded 40%. Losses were equally high for cows with cystic ovaries. Cows having only short estrous cycles averaged 28.8% embryo loss and 24.2% services carried to term. Cows with an abnormal calving from the preceding gestation averaged 14.4% embryo loss and 39.2% services carried to term. Monthly differences in reproductive efficiency were relatively unimportant as compared with yearly differences.