Cow-Calf Commentary for Iowa Cattleman Magazine
By Randie Culbertson, Cow-Calf Extension Specialist
April 2026
Spring training for your bulls
As the weather warms, snow melts, and green grass begins to grow, calves are hitting the ground and it’s time to get your bulls ready for breeding season. Bulls play a critical role in herd productivity, and preparing them well before turnout is crucial, especially for yearling bulls. Start planning a few months out to set your bulls up for a successful breeding season.
Adaptation Period: Allow for an adaptation period for bulls, especially when introducing new bulls onto the farm. Bulls coming off a sale or long transport are already under stress, and a new environment can result in reduced feed intake. Dietary changes going from an environment where 100% of feed is offered to a grazing environment can also create challenges. Without time to acclimate, the risk of excessive weight loss, injury, or illness increases, all of which can lead to reduced conception rates. Giving a bull adequate time to settle into his new surroundings before turnout will help ensure he is healthy and ready to work. All new bulls entering the herd should be quarantined for a minimum of 30 days, ideally 60 days, to allow any illnesses to present themselves and shedding of pathogens to cease.
Introducing new bulls into an established group can also be challenging. Bulls establish hierarchies, and adding a new bull, whether young or mature, can lead to fighting. If space allows, run bulls alongside each other with a strong fence line between them before turning them out together. If pen space is limited, skip the small pen introduction and turn them out directly in a large pasture where bulls have room to escape confrontations and maintain distance from one another. Some producers have used apple cider vinegar to reduce fighting when introducing new bulls, but this is anecdotal with no research to support (or disprove) its use.
Breeding Soundness Exams (BSE): A bull’s job is to get cows pregnant. If he is infertile or physically unable to accomplish this, conception rates will suffer. This is especially true for dominant bulls, as an infertile dominant bull can push other bulls away from cows, compounding the problem in multi-sire pastures. Breeding soundness exams are our best tools for ensuring a bull’s breeding ability and health heading into the breeding season. Common causes for BSE failures include structural unsoundness, physical reproductive problems, sexual immaturity, faulty scrotal thermoregulation, and sexual rest. Keep in mind that it takes 60 days for a bull to complete spermatogenesis, the process by which cells develop into viable semen, so in some cases your vet may recommend retesting a bull that initially failed. It is generally recommended to have BSEs conducted 30 to 60 days prior to turnout.
Body Condition Score (BCS) and Nutrition: Before turning bulls out for breeding, make sure they are at an ideal BCS of 5 to 6 on a 1 to 9 scale. At a BCS of 6, a bull’s ribs and spine would not be visible, with noticeable flesh in the flank area, visible hooks and pins, and some fat deposits in the brisket area and tailhead. Bulls will typically lose 1 to 2 BCS during the breeding season, so going in at the right condition is critical.
Bulls should have access to high quality forage, feedstuffs, and mineral supplementation to achieve the target BCS of 5 to 6 to provide adequate energy reserves prior to heading out to breeding pastures. Good quality hay and supplemental feed should be offered as needed to meet their nutritional requirements.
Be cautious of over-conditioning your bulls. A BCS of 7 or higher can negatively impact fertility, libido, and scrotal thermoregulation due to excess fat deposition, which reduces sperm production. Research from University of Georgia has shown that over-conditioned bulls had a greater percentage of sperm defects and reducer sperm motility compared to bulls at the target BCS of 5 to 6. If you notice your bulls put on too much weight during the off-season, consider cutting back on corn or other concentrates, shifting to a higher roughage diet, and getting your bulls some exercise before turnout.
As breeding season approaches, don’t ignore your bulls. Start looking at them now and assess what changes may need to occur before turn out. And call your vet today to schedule a BSE.
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