Vet’s Voice by Dave Barz: Semen test bulls early

What a change! Most of you are working through the first cutting of hay. It looks good to me, but I have not heard any reports on tonnage or quality. Some producers in our area took a first cutting of alfalfa, burned it down with Roundup and planted soybeans. Hopefully the roughage price will decrease and help the cow-calf man. We pray the rains will continue and the pastures will continue to produce all summer.

This week we were busy with bull semen testing immediately before turnout. We recommend screening your bulls early to allow you to select another bull while they are still available from purebred producers in the area. It is best to retest yearling bulls close to turnout. If you purchased your bull several months ago, it would be a good idea to retest before turnout. We expect young bulls to mature as they get older, but sometimes they may develop testicular or seminal infections which decrease their fertility. These result in low semen counts, poor motility, and white blood cells. Many of these bulls were tested several months ago and were fine. The key question is where did the bull encounter the pathogen which causes the problem?

It is accepted that a bull should be recovering in 30 days after the initial insult. Some producers have problems every year after the purchased bulls when they take them home to acclimate them to their home pathogens. It is suspected the bulls are infected with common herd pathogens and became infertile for a short time. If you retest these bulls during this period of time, they will fail their fertility exam.

The first thing we must understand is reproductive efficiency varies from day to day. The semen exam is merely a snapshot in time and does not assure yearlong results. If the bull develops a problem with sperm formation (spermatogenesis) it will require at least thirty days for recovery. It is also important to watch bulls after turnout for injury and lameness. If the bull is unable to mechanically breed, he will not get cows bred. It is important to get as many females bred in the first cycle of the breeding season to assure uniform, heavy calves at weaning.

We must also understand that the bull may respond differently to stimulation. Many bulls will give no collection, but if retested shortly later they will be fine. You must also have confidence in the ability of your veterinarian or technician to stimulate the bull to release a sample. Semen collection is more an art than a science. Many bulls branded as infertile have been used and fertilize cows producing good reproductive rates.

Semen evaluation is an important tool in the reproductive management of you cow-calf herd. Remember it is a dynamic process which can change from day to day. Your careful observation will minimize problems and increase your fertility rates. This will greatly improve your herd profits.