It can be easy to forget bulls and focus on cows when weather hits, but management strategies during the winter months can impact a bull’s performance in the upcoming breeding season. Managing herd bulls properly to prevent frostbite of the testes and properly manage body condition score before the next breeding season is imperative.
“Owning bulls during the idle months is not all sunshine and rainbows,” says Beth Reynolds, Iowa State University Extension and Outreach program specialist. “Broken fence, beat up hay rings, injuries from fighting …. And all that comes with bored boys — I mean bulls — in the winter.”
She says in a recent Iowa Beef Center Growing Beef Newsletter article that bull management must be kept to high standards in order to get a good return on investment, because quality bulls are not cheap.
“Winter management puts a large emphasis on periods of cold stress and temperature fluctuation,” Reynolds explains. “The negative impacts of poor winter management are broad, but two general categories are nutritional and breeding soundness.”
She stresses these three keys to managing bulls during the winter.
1. Provide windbreaks.
Reynolds says managing the breeding soundness impacts of cold weather on herd sires requires being proactive and using tools to mitigate frigid temperatures.
“Windbreaks are very impactful in mitigating cold stress effects,” she explains.
Temporary windbreaks using portable windbreak panels, hay bales or even stock trailers can be effective if placed with prevailing winds in mind.
According to South Dakota State University, there are several considerations for designing windbreaks, and the requirements for sizing will largely depend on the number of animals that will be usng the structure for shelter.
“A common rule of thumb is to allocate 25 sq. ft. of protection per cow, or 1' of fence length per cow,” explains SDSU guidelines. “The protected zone of a windbreak will extend out to the leeward side by 8 to 15 heights of the structure with a reduction of wind speed of approximately 50%. Previous research has identified an ideal ratio of length to height of 10:1, so for example a 10’ windbreak should be a minimum of 100’ long for maximal protection. Structures should be placed at least 75' upwind of any roads, alleys or buildings to reduce the impact of high winds and drifting snow.”
2. Provide bedding.
Dry areas to lay are important to consider when wintering bulls. These areas can be achieved by providing bedding or areas within a pasture that provide adequate cover from wind and snow.
“Bedding is especially important to create a barrier, keep the scrotum off the frozen ground to prevent frostbite and help alleviate the increased nutritional needs,” Reynolds says.
A feedlot trial from SDSU found providing 4 lb. of bedding per head per day reduced energy maintenance requirements by 20% to 40% compared to unbedded counterparts on cement. While less research has been done on breeding stock to quantify changes, Reynolds says one would expect providing bedding would also reduce maintenance requirements for bulls and cows during cold-stress periods.
Wet and cold conditions increase the risk of frostbite. Frostbite presents as a scab, discoloration and/or sloughing of the bull’s scrotum. These tissue damages limit or prevent the ability for a bull to regulate testis temperature. This is caused by the inhibition of the raising and lowering of the testes that occurs naturally. Come breeding season, this can result in a decrease in fertility.
“Arguably, the most discussed negative impact of not managing cold stress in bulls is frostbite on the scrotum,” Reynolds explains. “Mild frostbite will set back normal sperm production for 45 to 60 days, and severe frostbite may cause permanent damage.”
Additionally, in periods of cold stress, a cortisol spike can be expected. Cortisol can transfer from the bloodstream to semen, and in vitro trials have observed negative effects on sperm quality.
3. Provide adequate and strategic nutrition.
Reynolds explains managing the nutritional impacts of cold weather on herd sires will look very similar to nutritional adjustments needed for the gestating cow herd. The genera rule of thumb for cold stress still applies: for every degree the temperature is below the lower critical temperature, energy needs increase by 1%. The lower critical temperature for a dry winter hair coat on cattle in good (5-6) body condition is around 20°F.
Cold stress for brief or extended periods increases energy requirements while protein, mineral and vitamin needs remain consistent. If adequate forage is available, bulls will increase their dry matter intake during periods of cold stress. Depending on hay quality, this could perpetuate the problem of needing more energy in the diet. In cold stress scenarios, supplemental grains high in energy can be extremely effective for bulls on high-forage diets.
Use the offseason to bring bulls back into good condition after the breeding season and allow plenty of time and space for them to recover from any immune system strains or physical injuries.
Underfed bulls are more prone to disease, poor libido and lower quantity and quality sperm.
“Micronutrients and the mineral program in particular should not be overlooked if you expect a healthy, active bull to pass a BSE and perform well in the following breeding season,” Reynolds says. “For example, zinc and selenium are essential for testicular function in addition to their importance for an effective immune response.”
Other Stress Reduction Strategies
Reynolds encourages trying to reduce bull stress in general by ensuring commingled bulls have adequate room to reduce fighting. This goes beyond providing space for bulls to “get away” and roam. It includes providing enough space at the feed bunk or hay ring, as well as a larger area for bedding down to reduce fighting when active, eating and resting.
Cold weather and frozen ground can also strain bulls’ hooves, making them prone to toe abscesses, foot rot and other infections.
“To promote hoof health, be diligent in maintaining pens in the warm spells when uneven ground and manure can be addressed,” she says.
Even if all available cold stress prevention strategies are used, follow up with your veterinarian to schedule breeding soundness exams. A close-up examination is needed to catch some physical injuries and sperm abnormalities, even after the best off-season management.
“When scheduling, remember that sperm production takes about 60 days. Although some bulls may go from a failed to a passing BSE if rechecked, a plan B likely requires purchasing another bull, and bull sale season is underway,” Reynolds says.
Producers in the Midwest should also be cautious if the primary fall and early winter feed source is pasture containing a significant portion of mature, unimproved fescue.
“Endotoxins found in Kentucky 31 fescue cause vasoconstriction, or reduced blood flow to the extremities,” she says. “This will ultimately perpetuate any negative effects of cold stress at warmer temperatures than would be expected on other feed sources.”
Lastly, don’t forget water. Be sure bulls always have sufficient access to clean, fresh water.
“The moral of the story,” Reynolds stresses, “don’t forget about herd sires in the winter months or in the spring when calving season is in full swing.”
Your Next Reads:
Wanted: Bulls Ready to Work
Why Bull Rest Matters: Time to Prepare for the Next Breeding Season
