Published online by Cambridge University Press: 02 September 2010
Reproductive data of 139 Simmentaler heifers, previously subjected to different levels of winter and summer nutrition, over a 3-year period, were analysed. Pregnancy rates of 77% and 96% were achieved during the first and second seasons for the two groups of heifers, respectively. Winter and summer nutritional levels affected the number of heifers culled, but had little effect on conception. There were no significant differences in the weight at mating between the heifers that conceived and those that failed to conceive. Mean date of conception was within 30 days and 20 days of the commencement of the breeding season for the first and second season, respectively. Post-weaning nutrition played a relatively minor role in affecting the time of conception. Birth weights of the progeny were not affected by treatment. Calf birth weight was however, significantly (P < 0·05) correlated with the weight of the dam at mating. Sixty-three % of the heifers produced three calves in 3 years, 35% produced two calves in 3 years and only two heifers produced one calf in 3 years. The data supported the original hypothesis that the emphasis, when heifers are bred at 2 years of age, should be shifted away from a physiological base to one where management and grazing strategy are more important in rendering the enterprise economically viable.