The Cow-Calf Manager
Livestock Update, June 2002
John B. Hall, Extension Animal Scientist, Beef, VA Tech
Give Your Bull A Job Evaluation
Evaluation of new employees is an important part of ensuring job quality for the future. The same is true of herd bulls whether they are new to the herd or they have been around for several breeding seasons. Just as new employee evaluations occur during the first 30 days of employment, an "on-the-job" bull evaluation should be performed early in the breeding season.
Not a breeding soundness exam
As has been stressed many times, breeding soundness exams are important to breeding success. Bulls passing a breeding soundness exam (BSE) settle an average of 6 to 20% more cows than unexamined bulls. Similarly, watching bulls during the first few days of the breeding season to ensure they are successfully mounting and inseminating cows is important. But those don't qualify as the "on-the-job" evaluation.
Between the 21st and 30th day of the breeding season, the bull and cows need to be checked carefully. The herd does not need to be gathered to make this check, so this exam can be performed from a pick-up, horseback or on foot. The essential parts of the exam are to check:
Results and remedies
Lameness. Lameness or other injuries that prevent the bull from mounting are the main reason for breeding season failure by bulls that pass a BSE. Foot rot in breeding bulls often results in a fever, which will reduce sperm viability for 1 to 2 weeks even if it is treated rapidly.
Remedy: Bulls that are unable to mount or are poorly mobile need to be removed from the herd and replaced, immediately.
Reproductive injury. Bull that receive an injury to the prepuce or penis may be fertile but may not have the desire or ability to service cows. Injuries to the testis may result in inflammation, which decreases sperm viability and fertility.
Remedy: A veterinarian should examine the bull to determine if he can be salvaged. Bulls with reproductive injuries should be replaced.
Low libido. Occasionally bulls start out the breeding season ready to go, but for unknown reasons become disinterested in breeding cows. Some bulls have a limited desire to breed cows from the first day they are turned in. The reasons for low libido are poorly understood but may include unseen injury, over condition, over-dominance by a boss cow, or age. Producers should not accuse a bull of low libido if he breeds a cow once or twice then doesn't bother with her again. Low libido means bulls show no interest in cows that are in heat or doesnąt try to mount cows that are in heat.
Remedy: Occasionally, moving the bull to a new group of cows will increase libido. Often the bull may need to be replaced.
Producers often believe that using multi-sire breeding groups will reduce the impact of injuries, bull reproductive failure or low libido. However, research, using DNA of calves to identify sires, demonstrated that 50% of the bulls breed 80% of the cows (Table 1). Even in age and size matched bulls, there is a dominance hierarchy where the most dominant bull breeds most of the cows. In addition, Dr. Saacke from VA Tech found that sperm from different bulls vary in their ability to fertilize eggs. Even when the cows are inseminated with the same number of sperm from each bull, some bulls will sire more calves. Unfortunately, dominant bulls will often keep the other bulls from breeding cows even if the dominant bull cannot. The result is open cows. This "not my cows" syndrome is often a problem with dominant bulls that have reproductive failure or injury.
Table 1. Effect of dominance on percentage of cows bred in multi-sire pastures
|Bulls per pasture|
|Dominate Bull||66 %||50 %||40 %|
|Subordinate bull A||28 %||31 %||29 %|
|Subordinate bull B||7 %||13 %||19 %|
|Subordinate bull C||6 %||8 %|
|Subordinate bull D||3 %|
Poor bull body condition. Bulls need to be big, lean breeding machines. Bulls should enter the breeding season in body condition score 4 or 5, no fatter and no thinner. However, during the breeding season a 1700-1800 lb. bull has the same nutritional requirements as the lactating 1200 lb. cow he is servicing. Bulls need top quality nutrition. Most of the time high quality pasture will meet the needs of a bull, but remember, on heavy breeding days bulls will spend limited time grazing.
Remedy: If possible young bulls should be supplemented during the breeding season. This is easier said than done, but some producers have come-up with creative ways of supplementing young bulls. Another option is to replace a bull for 2 weeks while you build him up nutritionally.
Over-conditioned bulls. Over-fat bulls have decreased fertility. This appears to be a result of high scrotal temperatures, stress or hormonal imbalances.
Remedy: Bulls need to be hardened off before the breeding season. Allowing over-conditioned bulls to lose some weight during the breeding season may help, but it may be too late.
High percentage of cows cycling after first 21 days. By checking heat on cows for 3 to 5 days between days 21 and 30 of the breeding season, producers can get an idea about general bull and cow fertility. If 20 % or more of the cows are cycling during this 3 5 day period, there may be a bull problem. At the beginning of the breeding season, if cows were thin or many of the cows had calves less than 30 days old then it is probably normal. However, if most of the cows were in good condition and cycling at the beginning of the breeding season, then there could be a bull problem.
Remedy: The simplest solution is to replace the bull. The second option is to have another BSE performed on the bull. The last (and expensive) option is to have a veterinarian pregnancy check the cows with ultrasound at day 40 of the breeding season. The heartbeat of the calf can be detected by day 22 of gestation. Forty days into the breeding season, 50 % to 65 % of the cows should have fetuses that are 22 days old or older.
Giving the herd bull a job evaluation between day 21 and 30 of the breeding season is easy, but it takes time. Bulls with poor performance should be fired immediately! Selling or at least removing a bull during the breeding season is a hard decision to make, but it is much easier to take than more open cows and fewer calves next year.