Vet´s Perspective

News
May 31, 2013
by WLJ

Finding the right sire

Regular evaluation of breeding stock should be a no-brainer to producers of small-, medium-, and largesized operations. Besides routinely examining heifers and cows in order to determine a ‘bred’ or ‘open’ status—bulls of any age should also be evaluated for libido, physical attributes and semen quality. It has been estimated in previous studies that in the world of ‘beef economics,’ that fertility is 10 times as important as carcass quality and five times as important as the rate of gain. Typically, in a group of five bulls, at least one will be considered subfertile and lacking optimal ability to serve cows, or maintaining a poor quality of semen production.

Veterinarians typically will conduct breeding soundness examinations by following a protocol created by the Society of Theriogenology, a group of veterinary reproduction specialists. A challenge among many breeders is the short window breeding season in which animals must achieve a high pregnancy rate for efficient production. Although cow fertility is also of utmost importance, the much smaller ratio of bulls to cows demonstrates the importance of a sound breeding bull to fit the bill. Delays in conception rates are the most critical economic factor related to subfertility in the beef industry. It has been estimated that every 21-day cow ‘open’ period holds a loss of approximately 50 pounds of weaning weight in the next years’ production measurements.

Often times, a more productive bull in a multiplebull herd can make up, and thus ‘mask,’ the inefficiency of his counterpart. When it comes to the economics of feeding and managing the lesser animal, however, push comes to shove rather quickly.

Healthy bulls require the following attributes in order to be designated as a satisfactory breeding animal: adequate libido or desire to perform, physical condition soundness, and good semen quality. Libido evaluations are often conducted with the bull in its natural pasture environment; this allows visualization of behavior and interactions between both bulls and cows in estrus (heat cycles).

The serving capacity or libido examination is of particular importance in younger animals that have little to no breeding experience with cows and heifers.

Yearling bulls often require exposure to estrus females for some period of time in order to develop their breeding instincts. Older animals may lack desire to perform due to prior skeletal or penile injuries.

The breeding examination is conducted with the bull securely placed in stocks that allow exposure for the veterinarian to access the rectum and penile areas. A general assessment of the animal’s musculoskeletal system is made while the bull is moved towards the chutes—at this time, the veterinarian can observe the gait of the bull and detect lameness issues that may prohibit proper mounting of cows in estrus. During the mounting act of breeding, the full weight of a bull is placed on the hind limbs and feet, therefore good conformation or bone structure of each animal is critical to preventing a short-lived efficiently breeding bull in the herd.

General health of the bull is also assessed while animals are within the chutes.

Bulls should be free from signs of respiratory illness, such as cough, nasal discharge, and decreased body condition due to lack of proper nutrition. The eyes should be examined for signs of ulcers, inflammation, or blindness, that may cause pain and lack of ability to breed cows due to poor eyesight.

Next, your veterinarian will examine and measure the size of each bull’s scrotum. The scrotal shape should be a uniform oval and regular (no straight or wedge-like surfaces), with a small ‘waist’ of tissue above the testes themselves. This neck-like region contains the countercurrent artery and vein bundles that allow heating and cooling within the testes. One should not palpate a significant amount of fat or any herniated tissue within the neck region as this may prohibit adequate temperature regulation within the testes. The testicles should move freely within the scrotum, and not demonstrate any firm or masslike textures.

Abnormal palpation may be a sign of abscesses, tumors or trauma to the gonads. Testes that are ‘soft’ or lack average firm texture of herd mate bulls can signify degeneration of the testicle.

A measuring tape is placed around the largest portion of the testicle and compared with reference values stated by the Society of Theriogenology. These values indicate a higher centimeter value with an increased ability to produce daily sperm quotas and improved sperm quality.

A rectal palpation is done in order to assess the urethra and accessory sex glands of the bull. Abnormal enlargements, episodes of pain demonstrated during palpation, or changes in normal organ texture can indicate clinical signs of illness or inflammation.

Next, semen will be collected for examination under a microscope. Most often, this collection is made by a technique termed electroejaculation. A large probe is inserted into the bull’s rectum and a set voltage conducts stimulation to the hindquarter muscles and ultimately the glands that allow protrusion and ejaculation of a semen sample that is collected with a cone and promptly taken into the lab for analysis.

Semen quality is evaluated via a combination of factors. Motility of sperm is assessed and ranked from “very good,” meaning rapid swirling motion to “poor,” being little to no cell motion within the sample.

Morphology or cellular shape allows evaluation of sperm for abnormalities that may hinder their ability to produce offspring when united with the female egg. The current recommended guidelines call for each sample to have at least 70 percent normal sperm morphology.

Bulls may be classified as satisfactory, decision deferred, or unsatisfactory for breeding, based upon final examination. A deferred rank allows a bull that has not met every guideline to have an opportunity for retesting at a set date. Overall, breeding soundness examinations allow a producer to have a better idea what he or she is dealing with in any herd and should be taken seriously as an added measure for economic success. — Dr. Genevieve Grammer

[Dr. Genevieve Grammer is a mixed-species veterinarian practicing in eastern Colorado. Please direct correspondence to drgigi19@gmail.com.]


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