Reproduction in Cattle

Cattle are the most common type of large domesticated ungulates. Cattle are raised as livestock for meat (beef and veal), as dairy animals for milk and other dairy products, and as draft animals (oxen or bullocks that pull carts, plows and other implements). Other products include leather and dung for manure or fuel. They are an integral part of animal agriculture in all parts of the world. Demand for some products, such as fat in meat and in milk, has declined in some markets, and in some countries milk production is limited by quotas. Nevertheless, the efficient production of animal protein continues to be of vital importance. Efficient production system can maximize output of meat and milk per unit of feed input per animal. In cattle production as with other livestock systems a high level of reproductive performance is absolutely crucial to efficient production. Efficient reproduction results in optimum calving intervals, which in turn result in optimum production of milk and calves to be reared for beef or replacements. The breeding program may use either artificial insemination (AI) or natural service. AI has been commercially available; it is widely used in dairy cattle but is used much less in beef cattle because of handling and labor costs. AI offers a selection of bulls with known genetic potential, such as measured by estimated breeding values (EBVs) for traits such as ease of calving or growth rates. When nutrition and heat detection are properly managed, satisfactory results are obtained. Failure to detect estrus is the major reason for unsuccessful AI. When cows are properly inseminated with good-quality semen at the proper time, 50%–60% may conceive on first service, the same percentage on second service. In cattle, AI is used primarily for genetic improvement of livestock and to facilitate high health replacement strategies. The worldwide adoption of AI for genetic improvement in dairy cattle was made possible by development of a progeny test system and subsequent use of milk production records as an objective measure of performance on which to select superior bulls, techniques for freezing semen, and liquid nitrogen storage refrigerators. The development of objective systems such as EBVs to measure economic traits in beef cattle (e.g., growth rate, carcass conformation and composition, efficiency of feed conversion) and thus the more accurate selection of sires, as well as control of the estrous cycle, is leading to an increase in use of AI in beef cattle. Processing of frozen semen is a highly specialized technique. In order to manage cattle reproduction and the specific problems that arise, it is important to understand the underlying physiology of the reproductive process.