Reconception in grade and pedigree Africander cows of different sizes - postpartum factors influencing reconception

Abstract

The influence of postpartum mass, bodymass gain from calving to the end of the bulling season and month of calving was studied in I 975 grade and 440 pedigree Africander cows that were classified into six size categories according to postpartum mass. Approximately half the number of each breed received protein rich supplements for bodymass maintenance in winter; the others were not fed. Reconception is negatively related to month of calving. The probability of reconception declined markedly as the month of calving advanced from September to April. In order to reconceive, medium and large size cows (456 - > 645 kg) could gain little or even lose mass after calving and still conceive, whereas small cows ( < 455 kg) had to gain considerably in mass. Postpartum mass and postpartum mass gain are negatively related (r=-0,7; P< 0,01). Regression models obtained through stepwise procedures, revealed that postpartum mass, postpartum mass gain, month of calving and age of dam are in that order the most important factors influencing reconception. Reconception appears to be a function of postpartum mass per se and the effect of postpartum mass gain in the statistical models is entirely due to its strong negative relationship with postpartum mass.