March 2018 Articles

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Management of Beef Bulls

Management of Beef Bulls Jason E. Holmes - LSU AgCenter When purchasing bulls, genotype and phenotype are important factors in bull selection. However, information about health and environment should also be considered. Breeding Soundness Examination (BSE) Only purchase bulls that have been classified as Satisfactory Potential Breeders following a complete BSE. Purchase only virgin bulls to avoid introducing venereal diseases. Although there are tests for venereal diseases such as Trichomoniasis, they are not 100% in determining that a bull is not a carrier. Testing for other diseases should be considered and discussed with the herd veterinarian and negotiated with seller. Purchase bulls from local sources or environmentally similar to their eventual destination. Bulls reared in dry, cool climates may require months of adaptation if moved to warmer, more humid climates. This period of adaptation is often accompanied by a drop in fertility. In some instances, this decrease is dramatic and may last several months. Purchase bulls developed on a forage-based diet. Concentrate diets can lead to infertility. Quarantine bulls for 4 weeks prior to introducing to native bulls or cows. If bulls are not tested for diseases prior to purchase, test while in quarantine. Health Maintenance of Bulls: ● BSEs (a uniform method of assessing a bull’s likelihood of accomplishing pregnancy in an appropriate number of open, healthy, cycling cows or heifers in a breeding season) should be completed each year 2-3 months before breeding season. This is critical as spermatogenesis (development of new sperm) takes place over a 60 day period. This leaves time to recheck questionable bulls (now having a new generation of sperm) and locate replacements if necessary. BSEs consist of a 1) physical exam of the feet, legs, testicles and other reproductive organs; 2)scrotal circumference measurement {at least 32cm for 2-year-old bulls and at least 34cm for mature bulls}; 3)semen evaluation with a goal of at least 70% normal sperm and 30% motile sperm. ● A BSE does not evaluate a bull’s libido or actual mating ability, nor does it ensure that a bull will remain a satisfactory potential breeder the entire breeding season. Therefore, it is important to observe bulls closely throughout the breeding season for libido, mating ability, health and injuries. ● Breeding bulls are overlooked in many cow herd feeding programs. Unfortunately, in some cases this results in lower than desirable fertility and libido. Over the last several decades, there has been a shift from purchasing 2-year-old bulls to purchasing yearling bulls. This has increased the importance of feeding programs for adequate bull development on most cow-calf operations. ● In the southeastern U.S., heat stress is a major cause of bull infertility and decreased libido. High temperatures, especially combined with high humidity and high nighttime temperatures, are especially detrimental to bull health and fertility. Disease Prevention: ● A comprehensive health plan for bulls should be developed with the herd veterinarian and include purchasing decisions (health status of the herd of origin), vaccinations, deworming and nutrition. ● Vaccinate bulls at least annually for all five serotypes (5-way Lepto) of leptospirosis and for campylobacter (Vibrio).  Vaccinations for BVD, IBR, PI3 and other viral diseases could also be recommended, but producers should consult their veterinarian for specific recommendations for diseases prevalent in their area. Bull:Cow Ratio: A number of factors influence the optimal bull:cow ratio, such as: ● Terrain, water availability and stocking rate.  In rugged country and areas with low stocking rates, the number of bulls per 100 cows should probably be slightly higher than in smaller pastures. In pastures with numerous water sources, the ratio should be higher because in pastures with only a few water sources, bulls often congregate around the water sources enabling them to breed cows without excessive travel. If numerous water sources are available, bulls must travel to find cows in heat requiring more bulls per 100 cows. ● Age of bulls.  Mature bulls breed more cows than yearling bulls. The following table shows some guidelines for bull:cow ratios with yearling and mature bulls in different management scenarios. These recommendations are based on using bulls that are in good condition at the start of the breeding season, have passed a BSE and have demonstrated good libido and ability to mate.
Age of Bull & Management Scenario Recommended Ratio Yearling bulls 1:18 Yearling bulls, natural service with estrous synchronization 1:15 Mature bulls 1:40 Mature bulls on rugged terrain or in low stocking rate 1:35 Mature bulls used for clean-up following artificial insemination 1:60
Another bull:cow ratio rule of thumb is a bull can handle the same number of cows as his age in months. So an 18-month-old bull could feasibly breed 18 cows, 24-month-old could feasibly breed 24 cows, and a mature bull would max out at 40 cows. Again, these general numbers are based on bulls in good condition. Nutrition: Bulls can nutritionally be classified into one of three categories: 1) Mature bulls in good body condition — BCS 5 or 6 ¨ Mature bulls can subsist on a 100% forage-based diet of moderate quality (7-10% crude protein and 50% TDN). They will consume approximately 2% of their body weight in dry matter daily. 2) Mature bulls that need to gain weight — BCS 4 or less¨ Mature bulls that need to gain weight will require forage plus potentially a grain supplement. Their diet will need to consist of 8-10% crude protein and 55-65%TDN. The greater the weight gain needed, the greater the energy (TDN) concentration needed in the diet. 3) Young bulls (yearlings and 2-year-olds)¨ Young bulls should be targeted to be about 75% of their mature body weight at two years of age. Young bulls need to gain up to 2.5 pounds per day from weaning to 15 months. Growth should continue at 2.0 to 2.5 pounds per day until three years of age. Supplemental feed should be fed to young bulls during breeding season if necessary to maintain adequate body condition. Managing Social Dominance in Bulls — Put young bulls with young bulls, and mature bulls with mature bulls. Mixing the ages will result in the mature bull dominating the younger bull completely, and in some instances causing a serious injury. Considering the cost of yearling bulls, it is crucial to use them in a way that allows them to contribute genetics to the herd. One way is to rotate bulls during the breeding season; use the mature bulls first, and follow with the yearling bulls in the last third of the breeding season. In this way, the young bulls will have fewer cows to breed, and will be 1 - 2 months older when they start breeding.