The effect of varying levels of nutrition on growth, development, and fertility of beef bulls

The statement, a bull is half the herd, has been made by many people associated with the beef cattle industry; yet, there is an absence of scientific papers appearing in the literature concerning the development of herd sires. The majority of performance testing programs reported for beef bulls have been progeny tests. Progeny tests are useful In predicting a bull\u27s prepotency, but are time consuming and expensive. Not only does the bull have to reach sexual maturity, he must then sire adequate numbers of progeny for purposes of evaluation. A program Is needed which will test a bull\u27s performance under various conditions during his developmental period In order to provide an early Indication of his productive potential. A large majority of post-weanlng performance tests which have been designed for beef cattle have emphasized that the best way to evaluate the gaining and feed utilization ability of an animal Is to feed a maximum amount of grain for a period of approximately 140 days. It has generally been accepted that the performance of beef cattle during this 140-day period of consuming large quantities of high-energy feeds Is indicative of future productive ability; these data have been extensively used as criteria for the selection of breeding stock. Beef cattle have the unique ability, with the assistance of rumen microorganisms, to convert low-cost roughages Into a popular high-priced commodity. Since there is an abundance of nutritious, low-cost feeds available in the Southeastern portion of the United States, it is economically sound to incorporate large quantities of roughages into beef cattle rations. Since it has been established that high-roughage rations are economical for beef cattle, it seemed appropriate that a program be considered which utilizes an optimum amount of roughage during the developmental period of beef bulls. In order to acquire the amount of finish desired by the consumer, a steer must possess the ability to gain in the feed lot as well as on high-roughage rations. Likewise, a pro-spective herd sire should not only have the ability to gain on a high-roughage ration, but he should also demonstrate a high productive potential in the feed lot. Since the level of feeding during the growing period may have an effect on future reproductive performance, a program for the development of bulls must consider first the effects on the future fertility of the bull. In order to obtain more data on methods of developing bulls, a Record of Performance Test was initiated by the Animal Husbandry- Veterinary Science Department at the University of Tennessee. In the initial report Anderson (1962) concluded that the most desirable program of those tested for developing bulls consisted of three periods: 1. A 140-day wintering period in which the basic ration consisted of a full-feed of corn silage, 2 lb. of alfalfa hay, and 5.5 lb. of concentrates. 2. A pasture period of approximately 90 days in which the bulls were allowed to consume daily an average of approximately 1 lb. of grain per 100 lb. of body weight. 3. A 98-day full-feed period. Since bulls wintered on 5.5 lb. of concentrates were in a highly satis-factory condition at the conclusion of the test, the question of whether lower amounts of concentrates could be fed during the wintering period naturally arose.. Therefore, the present work was designed to determine the effects on growth rate, productive performance, and fertility of reducing the amounts of concentrates from 5.5 lb. to 2.5 lb. during the winter period and feeding silage and hay as in previous tests