By Rachel Endecott, Ph.D.
Managing bulls for a target body score of 6 at turnout allows for general body-condition loss during the breeding season.
Ensure young bull success as herd sires after the sale.
You’ve gone through the sale catalog, pored over videos of the offering, walked through the pens on sale day, and now you’re the successful bidder on a new bull or bulls for your operation. The work shouldn’t end there. What can you do to ensure your new purchases provide return on your investment?
When conditioning bulls for breeding season, a 30 to 90 day adjustment period for new purchases is ideal. Yearling bulls should continue to gain 1.5 to 2 pounds per day, which can usually be achieved by a diet of 11 – 12% crude protein and 70% total digestible nutrients. Remember that bulls consume 10 – 15% more than a comparable weight steer. Consult your veterinarian regarding appropriate health programs for new and established bulls. Bulls of any age generally lose 100 – 300 pounds during the breeding season, so it’s recommended to manage bulls for a target body condition score of 6 by turnout.
What about after the breeding season? Mature bulls may be able to get by on an all-forage diet, but young bulls should be managed to achieve around 75% of their mature body weight by the time they are two-years-old. For example, let’s say you bought a 1,250 pound yearling bull that lost 200 pounds during the breeding season and now weighs 1,050 pounds. If you expect him to weigh 2,000 pounds at maturity, he needs to gain 450 pounds to weigh 1,500 pounds (0.75 x 2000) by the time he turns two. Bulls benefit from year-round vitamin and mineral supplementation just as the cow herd does. Trace minerals like copper, zinc, manganese, and selenium, along with vitamins A and E, are important antioxidants that can prevent sperm damage from stress.
Normal sperm formation only occurs at four to five degrees below body temperature, the regulation of which depends on coordination of three structures: the tunica dartos muscle in the walls of the scrotum, which relaxes when hot and contracts when cold; the external cremaster muscle within the spermatic cord, which lengthens or shortens to lower or raise the testicles depending on temperature; and the pampiniform plexus, which is a coil of veins that provide an effective counter-current temperature exchange by cooling arterial blood entering the testicle and transferring its heat to the venous blood leaving the testicle. Any damage or impairment to any of these three structures could result in infertility. Overfeeding bulls can result in fat layers around the scrotum, which can interfere with temperature regulation. For those in cold climates, protection from inclement weather is critical because of the very real concern of frostbite of the scrotum. While mild frostbite generally has a good recovery, severe frostbite can lead to scarring that can hinder a bull’s ability to raise and lower the testicles.
While most bulls work for a short time each year, bull management is not a “set it and forget it” process. You’ve invested in those herd bulls for the future of your cow herd and sustainability of your operation. Proper bull management puts a little insurance policy on that investment.
For more information, here are some helpful links: