Cow-Calf Commentary for Iowa Cattleman Magazine

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By Beth Reynolds, Extension Beef Specialist

May 2022

Getting new bulls ready
It’s no secret that Iowa has some great seedstock operations. However, even bulls purchased from the most experienced breeders need your personal evaluation upon delivery and before getting turned out into the breeding pasture.

Evaluate the bull’s nutritional status and body condition. Ask the seedstock operator about the previous diet. The bulk of developing bulls are fed winter feeds in a drylot scenario prior to being delivered, and are expected to be effective breeders on pasture in a few short months. Gradually transition bulls onto a grazed forage diet. Any nutritional changes occurring too abruptly can lead to acidosis, which can be a root cause of longevity problems with the foot and respiratory health. Additionally, acidosis can directly impact sperm quality. In fact, previous research found that even a subacute acidosis event reduced the percent normal sperm for 88 days.

When evaluating body condition, keep in mind that a successful bull must perform as an athlete. It is not uncommon for bulls to be overly conditioned for sale day, and at delivery. We really would like to see bulls at a BCS of 5 - 5.5, so some bulls need to be "let down" or "hardened up" gradually to prevent them from falling apart quickly when breeding season starts. Excess body condition will hinder their ability to physical demands, as well as lead to excess scrotal fat. To much scrotal fat insulates the testes, and reduces fertility. Some ISU data demonstrated this by showing backfat to be negatively correlated with sperm motility and sperm morphology during breeding soundness exams. On the other hand, a bull that’s to thin will struggle to produce viable sperm, or have the energy to get the job done.

Preparing bulls for the increase in physical activity required to both breed cows and consume enough calories during the breeding season is also important. House bulls in larger areas leading up to breeding season. Ideally, bulls will already be grazing a spring pasture diet prior to turnout with females.

Another important step to set new bulls up for success is to introduce them to the other bulls that will work in the same pasture early. Comingling these bulls will allow them to establish dominance prior to turnout, so that they get to work rather than get hurt at the beginning of the breeding season. When comingling, allow enough space for bulls to separate and recover to prevent injury.

Finally, a successful herd sire is a healthy herd sire. Work with your veterinarian to determine if and what vaccinations, de-wormers, and other health products are advised. If the bull did not have a breeding soundness exam (BSE) before purchase, get one done. Even if your bull did go through a BSE, consider a second one within 30 days of the start of the breeding season.


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