There's nothing glamorous or new age about auditing the fertility of bulls, but it's still one of the simplest and cheapest ways cow/calf producers can hedge their bets on bull investment.
After all, Glenn Coulter of the Lethbridge Research Center for Agriculture Canada at Lethbridge, Alberta, points out, “In an unselected population (of bulls), we say 20-40% of them are deficient reproductively. They aren't sterile, but they will have fewer calves than you want them to.”
That means you may get calves on the ground, but you may not get as many sired by the bulls you invested more heavily in.
“An individual has to look at their objectives, where they want to go, how they want to get there and how much risk they can comfortably live with to accomplish their goals,” Coulter says. “Getting cows pregnant is one thing; making significant genetic improvement is another thing.”
As an example, assume a bull whose genetic merit you are relying on ends up being 20% less fertile (defined here as number of conceptions/cow exposed) than a sire of equal merit that you could have used on a particular group of cows. Now figure an 85% calf crop/cow exposed — 25 cows/bull.
The difference between knowing and not knowing adds up to about 12 calves across three breeding seasons. Besides passing genetic merit forward, that kind of lost opportunity adds significantly to the cost of each pregnancy.
Examine Breeding Soundness
With that in mind, Coulter recommends annual scrotal measurements and breeding soundness examinations (BSE) as the first step in hedging the fertility bet each year.
First, Coulter says, “Taking a scrotal measurement is the easiest and cheapest thing you can do.”
He emphasizes scrotal measurements should be more than a selection tool. Routine measurements a couple of times each year can help detect new fertility challenges; for instance, if the measurement declines 2-3 cm. over time, he says, that may indicate a problem.
“The next step is semen testing,” says Coulter. “I believe it's useful, and I recommend producers do it each year. It's useful in yearling bulls because you can make sure you have a basis for selection before buying. It's useful in older bulls to make sure they're producing semen as well as they were last year.”
Likewise, Vincent Traffas, DVM, of Traffas Vet Service in Smith Center, KS, explains, “Routinely, bulls should be assessed for soundness in legs, eyes and the reproductive tract.”
Evaluate Physical Ability, Libido
In addition to a BSE before each breeding season, Traffas recommends an evaluation of the libido and physical ability of bulls to service cows during the first week of the breeding season.
Traffas points out that even producers who routinely conduct a BSE on their bulls often do so just before turning them out.
“During breeding season, penile injuries and accessory gland problems are very common. If one waits until the start of the next breeding season, these things may escape detection and never be realized,” he explains. Besides, Traffas adds, “If there is a problem with a bull, he can be readied for salvage, and plans can be made to replace him sooner.”
As well, Traffas advises, “During the off-season, bulls still need to be monitored for health. Vaccination status should be maintained and hoof and leg soundness heeded. Vibrio and Lepto immunizations are routinely recommended, and others may be necessary depending on your area and the recommendations of your consulting veterinarian.”
In Traffas' practice area of Nebraska and Kansas, he says approximately 3% of bulls are affected by Trichiomoniasis. With that in mind, he emphasizes, “From a biosecurity standpoint, I'm really against leasing bulls.”
Short of conducting a BSE on every bull prior to each breeding season, Traffas says, “If there is any unaccountable deviation from normal pregnancy rates, bulls should be fertility tested. The closer to an event that factors can be evaluated, which determine the outcome of an event, the easier it is to discover what the problem was.”
Stress Impacts Fertility
Moreover, Traffas and other bull fertility experts point out injuries and stressors that can impact fertility — including nutritional and health stress — continue to impact fertility long after the aggravation is removed. Part of that has to do with the spermatogenic cycle. Basically, it takes about 56 days from the time a sperm cell starts to develop in the testes to the time it leaves the epididymides and is available for ejaculation. So, stresses today can impact semen quality soon after the event and for as long as eight weeks later.
All told, the cost of knowing the fertility potential of bulls before each breeding season is a bargain compared to wishful thinking.