BREEDING SOUNDNESS EXAMINATION

By Gary Warner, DVM, Elgin Veterinary Hospital, Production Animal Consultation

Bulls have an important economic impact on the cow herd. To have calves with heavier weaning weights, the bulls should get cows pregnant at the beginning of breeding season so their calves can drop early in the calving season. Under the best management conditions, 75-80% of cows bred during a natural service conceive on the first service with highly fertile bulls. A study conducted at the King Ranch evaluated the pregnancy rate of cows serviced naturally by bulls that had a complete BSE compared to cows serviced by a randomly selected group of bulls without a BSE. Cows serviced by bulls that passed a BSE had 5-6% higher pregnancy rates when compared to the herds serviced by bulls without a BSE. Another study conducted in Brazil found that using bulls that passed a full BSE improved calf production 31% and increased weaning weights by 50 pounds.

Research has shown that one in eight to ten bulls are sub-fertile. This can cost the herd a 30% reduction in pregnancies that the sub-fertile bull serviced. In the unfortunate event that the sub-fertile bull is in the dominant position in the herd bull battery, the impact on the herd pregnancy rate could be even greater on ranches with a high-density stocking rate. Other studies have shown the sub-fertile male to cost a producer as much as 4,000 pounds of live calf crop per 35 cows for the production year.

The breeding soundness examination was the result of decades-long research and collaboration by members of the Society of Theriogenology as well as others in the veterinary and animal science communities. The exam is intended to determine the reproductive fitness of bulls. Bulls must pass a physical exam, reproductive organ exam, and semen analysis.

The physical exam pays particular attention to hooves/legs, eyes, oral cavity, body condition, and ensuring that there is no overt evidence of disease. After gross physical examination, the veterinarian will evaluate the underline, particularly the sheath, prepuce, and scrotum. The testicles and associated structures are palpated to appreciate symmetry and consistency. Each teste should feel similar to an orange with the rind on. Scrotal circumference is measured and is especially important when evaluating yearling bulls. At a minimum, the scrotal circumference should be 30 centimeters by 14 months of age and 34 centimeters at 24 months of age. Several studies indicate that a larger scrotal circumference in yearling bulls leads to improved semen quality and early fertility in that bull’s progeny. However, mature bulls with an excessively large scrotal circumference (48 centimeters or greater) may be at an increased risk of trauma during ambulation.

Next, secondary reproductive structures are evaluated during rectal examination. These include the seminal vesicles, ampullae, prostate, and inguinal rings. The seminal vesicles of young bulls are prone to developing infections that spontaneously resolve. Mature bulls can also have an infection of the seminal vesicle but the frequency is much less than the yearling bull and mature bulls are much less likely to resolve the problem on their own or with parenteral antibiotics. During the rectal exam, the veterinarian should massage the pelvic structures to stimulate the bull which can enable an easier collection process.

Most bulls having a BSE in the United States have their ejaculate collected via electrostimulation. The objective is to collect a quality, concentrated sample with the least amount of distress and vocalization. It may take patience and time to collect the sample, and the speed of collection should not be emphasized. Many electroejaculators have automatic settings that provide guidance to the less-experienced practitioner and may decrease bull stress while increasing the quality of the semen sample. During electroejaculation, the bull should exteriorize the penis with a semi-rigid erection for evaluation. If this does not happen, the veterinarian should attempt to evaluate the bull’s penis by manual extension after the semen sample is collected.

Selection of the appropriate probe for the size of the bull is important.

Mature bulls require a larger probe for better contact and response to the procedure.

Next, the semen is protected from adverse temperatures (including during collection) and quickly examined under a microscope to decrease the impact on sperm cell motility (ability of the sperm to move forward in a straight line) and morphology (appropriate cell shape). To start the examination, a drop of semen is placed on a microscope slide to evaluate gross motility. Good motility is described as a profound wave action. Improvements in microscope technology have allowed the practitioner to evaluate progressive, linear movement of individual sperm cells. In the US, at least 30% of the sperm cells should be aggressively motile with a good linear track to pass this portion of the exam; in Canada, 60% motility is the minimum standard for acceptable semen motility.

Either a special stain or a specialized microscope is used to evaluate semen morphology. A minimum of 70% normal cells must be present for a bull to pass this component of the BSE. The veterinary practitioner should have a good staining technique and thorough knowledge of cell defects. Abnormal cells contribute directly to lower conception, either through a lack of fertilization of the egg or through early embryo mortality due to damaged DNA within the sperm cell.

Remember, the breeding soundness examination is just a “snapshot” in time of the bull’s reproductive health and only speaks to his fertility on the day he is tested. Over time, the only assurance the producer has about a bull’s continued reproductive ability is to retest the individual at the beginning of the breeding season. If low conception rates in the herd are being investigated, be aware that the BSE does not incorporate any other diagnostics, such as testing for communicable disease, therefore a frank discussion between the bull owner and veterinarian should occur about ancillary health tests that can be performed while the bull is restrained in the chute.

Lastly, a breeding soundness exam should be performed any time there is an expected sale of a bull as protection for both the buyer and the seller. It is also strongly recommended that bulls be tested after the breeding season to identify injuries and seminal dysfunction in order to allow time to correct any issues before the next season and to prevent expensive maintenance costs during the interim season for those bulls found unsound for breeding.

Dr. Warner grew up in north Louisiana in a family run cow/calf and stocker operation. His dad moved the family to Ferriday, Louisiana, in 1965 where his dad operated an auction barn and continued in the cow/calf business and was also a procurer of replacement cows. Dr. Warner received a BS from the University of Louisiana at Monroe in 1977 and received his DVM degree from the Louisiana State University School of Veterinary Medicine in 1980. Immediately after graduation, Dr. Warner entered clinical practice as a mixed animal associate at Elgin Veterinary Hospital. After two years of employment, he became a partner and developed a primary interest in large animals and eventually, just beef cattle practice. Today, the practice is largely referral based, focusing primarily on lameness and reproductive problems in both the male and female. Dr. Warner has been actively involved with the Professional Bull Riders as a consultant and practitioner for many years, providing for animal welfare and the wellbeing of the animals involved in their sport.

Other practice interests involve the purebred and show cattle industries and servicing the needs of individual producers. He has been actively involved in the show steer industry in Texas, helping many children with their projects and even raising a few of his own. All three of his children grew up showing steers with many championships. Two of his children, Dr. Jenna Beyer and Dr. Kelly Warner, now practice veterinary medicine and the youngest, Jacob, is a third-year veterinary student at Texas A&M University College of Veterinary Medicine. Dr. Warner is a career-long member of AVMA, TVMA (served as longtime member and chair of the Beef Practice Committee), AVC, AABP, Production Animal Consulation, and the Society for Theriogenology, where he served a long tenure on the executive board culminating in becoming president of that organization in 2011-2012. Dr. Warner, along with his wife Terry, remain actively involved in the cattle industry at their ranch north of Elgin, producing show steers and high quality replacement females. He continues to support the beef cattle production community and is always available to colleagues for consultation.