Final answer:
The question discusses the importance of selecting top proven A.I. sires for use with heifers in breeding practices, emphasizing the assumed higher fertility and pregnancy rates of heifers over cows. It highlights the significance of well-established pedigrees and the effects of natural selection and inbreeding in animal breeding strategies.
Step-by-step explanation:
The question pertains to artificial insemination in animal breeding and the prioritization of top proven A.I. sires for heifers over cows. The idea is that using sexually mature males, who are well built, well nurtured, coming from a strongly established pedigree with high fertility rates, can be significantly beneficial. It is suggested that this practice is especially important for heifers, which are young female cattle that have never borne a calf, presumably because their fertility rates and potential for successful pregnancy are higher than those of cows that have previously calved. However, this statement might be misleading as fertility rates can vary based on multiple factors.
Considering the longevity and health of animal breeds, it is acknowledged that through natural selection, individuals not capable of sustaining pregnancy would not survive, while those capable of mating and having successful deliveries would pass their genes to the next generation, as observed in female elk. Retaining the constant presence of a male throughout the offspring rearing process may contribute to higher survival rates and healthier offspring.
Furthermore, breeding strategies in domesticated animals tend to avoid inbreeding to maintain genetic diversity and reduce the occurrence of inherited disorders, even though animals might not naturally be selective in their mating choices. Breeding practices are designed to enhance positive traits within domesticated populations, leading to healthier and more productive animals over generations.