Reproductive and Nutrition Management for Bulls

One of the most important, and often overlooked, areas of cow/calf herd management is the reproductive and nutritional management of bulls in the herd, according to the Beef Cattle Handbook, a publication from the Extension Beef Cattle Resources Committee.

"Too often the range bull's breeding capacity is taken for granted, and the actual care and management of this bull during the non-breeding season is considered an inconvenience rather than an important part of a herd management system," the report states. "Each bull is expected to impregnate from 15 to 40 females during the breeding season in a typical cow/calf operation and, thus, the fertility of that bull actually is of considerably greater consequence than the fertility of an 'individual' cow."

Fertility Factors
Semen quality can play a major role in the productivity of a cow/calf operation. Studies have been performed to find out how important the reproductive soundness of bulls actually is to a cow/calf operation. In one study, the pregnancy rates in mated cows averaged 91.5 percent from bulls that were classified as having semen with 80 percent or more normal sperm. This compares to 86 percent conception rate for 26 randomly selected bulls. Factors affecting fertility include semen score, semen density, and sperm motility.

Scrotal circumference may be the best single criteria to use when determining the fertility of young bulls, the report states. Desirable scrotal circumference has been linked to several good traits including early onset of sex ual maturity in bulls, early onset of puberty in daughters and the early onset of pregnancy in daughters. Factors affecting scrotal circumference include heritability and breed difference.

Health Management
Health management is another important part of caring for bulls both in and out of the breeding season. Newly purchased bulls need to be vaccinated according to the herd management plan being used for the cow/calf operation.
The total cost of the vaccines is minor when compared to the cost of the diseases, the report states. Booster shots are also recommended if the bull has not been vaccinated prior to purchase.

Pasture management
The right bull to cow ratio needs to be kept in the pasture during breeding season. According to a recent USDA study, the average bull to cow ratio was 1:19 for yearling bulls and 1:29 for mature bulls.

In a Georgia study, bulls were exposed to 25 or 40 cows during a 90-day breeding season in a one bull per pasture mating scheme. The results showed no difference in pregnancy rates.

A ratio of 1:25-30 for yearling bulls and 1:40 for mature bulls appear to be realistic, if the bulls have been properly evaluated prior to the breeding season, according to the research.

Nutritional Development
rowth and avoid excessive body condition, the report says. During the post-weaning period, both under nutrition and over nutrition can have a negative impact.

Conditioning prior to the breeding season is important. Both yearling and mature bulls need to be considered for a pre-breeding conditioning plan.

"There is limited potential for special nutrition management for bulls during the breeding season," the report says. "Thus, it is critical that the nutritional management of the bull occur prior to the breeding season."

The nutritional management of the bull after breeding season will depend on the age of the bull and how much weight it lost. If mature bulls come out of the season in fairly good condition, they can be maintained on an all-roughage diet during winter. However, young bulls need to continue gaining after the breeding season to help reach their optimum size upon maturity.

"The general goals in the development of a beef bull are to have a bull that is capable of breeding cows as a yearling, is capable of producing quality semen, is physically able to seek out cows and heifers in heat, and is physically able to breed those females," the report says. "A proper evaluation, including semen quality and physical soundness prior to the breeding season, should be a routine practice on all bulls.

Extension personnel who contributed to this report include Larry R. Corah of Kansas State University, Harlan Ritchie of Michigan State University and Glenn Selk of Oklahoma State University