Vets Voice by Dr. Dave Barz: Do you know what your bulls are doing?
May 29, 2015
May has been a great month for precipitation in our area. It seems we get an inch of rain every weekend and now and then a few showers during the week. I think the grass will really grow once the temperatures warm up. It seems many clients believe summer begins with Memorial Day. This means breeding season will begin soon, if you haven't started already.
Most of you have performed a breeding soundness exams on your bulls. This exam means the day of the collection the bull was producing adequate volumes of live normally formed sperm. It is an examination of probable fertility and not of the bull's libido. If your bull has little or no desire to breed females, very few cows will be settled. This may be a major problem in young inexperienced bulls, but can also be a problem in older bulls.
Careful observation is needed during the breeding season. If you have a small pasture, like many in our area, you may have turned in only one bull. The inexperienced bull may 'fall in love' with a single cow or heifer while several other females are cycling. Many yearling bulls spend more time chasing than breeding. Older bulls which are overweight may also become lazy. A Canadian study showed thinner bulls sired more calves than fat ones in multiple bull pastures. There are several reasons for the phenomenon. Heavy bulls are not as athletically fit as thin bulls. They are out of shape and more likely to hurt themselves. Fat also inhibits the bull's ability to regulate body temperature. If there is fat in the wall of the scrotum, the bull is less fertile because the fat insulates the testicles. This keeps the temperatures too high for optimum sperm production. The bull also regulates testicular temperature by raising and lowering the testicles. Fat deposits in the spermatic cord limit the ability of the bull to regulate temperatures.
In multi-bull pastures, one bull is usually the dominant bull. That bull may breed a very high percentage of cows in the pasture. Many producers put several yearling bulls with two or three mature bulls. The next spring at calving, the owners see very few, if any, calves from the yearling bulls. You must remove the dominant bull if he becomes ill or injured. Even if he is lame and cannot breed, he will not allow other bulls to mount the cows in heat.
There are many scenarios which may render the bull infertile during breeding. The most common problem is lameness, but any fever will lower fertility because sperm production is interrupted. We suggest at least thirty days rest before returning to the herd. Penile and prepucial injuries interfere with the mechanical ability of the bull to deposit semen. These injuries usually indicate the end of the season for the bull and a re-check early next spring to assure no permanent damage.
Breeding season is very important to economic success of your herd. Even if bulls are meticulously prepared, problems can occur. Careful and timely observation will help you identify and eliminate problems before they can become catastrophic. Consult your veterinarian, extension specialist or nutritionalist to prepare a plan for your herd. Careful planning and observation will ensure the best results for your breeding season and thereby assuring maximum profitability of your herd.