ABSTRACT
Many influences on variations in fertility have been identified including nutritional factors, diseases, environmental stress, and genetic factors. Information was gained on the incidence of defective ovulations and functional sterility and also on the effect of high-level feeding on fertility problems. The slowing down of reproductive rate, when feed level and body condition or growth rate is reduced, is a natural survival mechanism. The reproductive hormones, their levels and interactions, and reciprocal effects of these hormones on their target organs vary continually not only between female animals, but within the same female from cycle to cycle and almost from day to day within the same cycle. Cystic follicles were preceded by short cycles, and while apparent recovery was recorded in some cases, it might be accepted that short cycle lengths and follicular cysts are symptoms of greatly reduced fertility in cows and heifers. Calving problems in both dairy and beef cattle present a formidable challenge to breeders and their advisers.
