26 July 2007

3 minute read

Bull breeding soundness exams may be an essential piece of the beef cattle producer's herd fertility puzzle, North Dakota State University Extension Service beef cattle experts say.

"Progressive beef cattle producers focus a great deal of attention on managing their cow herd to improve fertility," says Lisa Pederson, Extension beef quality assurance specialist. "While management of the female is essential, concentrating management entirely on the cows and not worrying about the bulls could be a disaster. The importance of the bull in a cattle breeding program is often underestimated."

A cow is responsible for half of the genetic makeup of one calf per year, while the bull is responsible for half of the genetic make up of 20 to 50 calves per year.

"The bull's ability to detect cows in heat and breed them is clearly vital to a successful breeding program," Pederson says. "One tool producers can use to assure this success is the breeding soundness exam. Examining bulls for breeding soundness before the breeding season will detect most bulls with potential fertility problems."

For the exam to be successful, a veterinarian should evaluate the bulls 30 to 60 days prior to the start of the breeding season, says Charlie Stoltenow, Extension veterinarian. That will give producers sufficient time to replace questionable bulls.

The exam consists of three parts: physical examination of overall appearance, internal and external examination of the reproductive tract and an evaluation of semen for normality and motility, or its ability to move spontaneously and independently. The producer can do the first part; a veterinarian should do the other two exams.

The physical exam includes an evaluation of the feet, legs, eyes, teeth and flesh cover.

"Sound feet and legs are very important because unsound bulls have trouble traveling and mounting cows for mating," Stoltenow says. "Bulls should be in good condition, ideally carrying enough fat cover at the beginning of the breeding season so their ribs appear smooth across their sides." A body condition score of 6 is the target prior to the start of the breeding season. That's on a scale where a 1 is emaciated and 9 is very obese. Stoltenow advises producers to observe their bulls often throughout the breeding season to make sure the bull is capable of traveling and breeding.

The reproductive tract evaluation should include measuring scrotal circumference, palpation of the testes and palpation of the seminal vesicles. The Beef Improvement Federation has adopted the exam guidelines the Society of Theriogenology recommended. The minimum criteria for passing the scrotal circumference and semen evaluation are:

• No chronic infections of the seminal vesicles or testes
  
• Scrotal circumference exceeds the minimum for age: 15 to 18 months, 31 centimeters; 18 to 21 months, 32 cm; 21 to 24 months, 33 cm; and 24 months or older, 34 cm
  
• Sperm motility of 30 percent (fair) or greater
  
• Percentage of normal sperm is at least 70 percent