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Veterinarian discusses care differences between young and mature bulls

by Wyoming Livestock Roundup

Young bulls need more feed and care than mature bulls, according to Veterinarian and Professor of Cattle Reproductive Health at the University of Calgary John Kastelic.  

“There is a critical window of bull development from about six to eight weeks of age up to weaning age,” Kastelic explains. “If bull calves are fed really well during this time, they reach puberty quicker, have larger testes and produce a lot more sperm.”  

Feeding for optimum condition 

If bulls have a dam that milks well or if they are creep-fed, they do better than a young bull who has been underfed. 

“After this, it’s a matter of feeding the young bulls to keep them growing, healthy and fit, but not fat,” says Kastelic.  

Too much fat in the scrotum interferes with fertility due to the insulating effects of the fat which inhibits heat loss and proper cooling. Testes on over-conditioned bulls tend to be too warm for optimum sperm production and viability.  

Additionally, fat in the neck of the scrotum hinders the ability of a bull to raise and lower his testes properly for optimum temperature control. 

Young bulls overfed for a sale or for the show ring are often considered too fat for optimum reproduction, interfering with soundness and fertility. When those bulls go out with cows for the first time, they often fall apart and don’t hold up, or may lose an excessive amount of body condition.  

“In grossly over-fitted young bulls, there can be permanent damage so there is no justification for overfeeding bulls,” Kastelic notes. 

If producers purchase an over-conditioned young bull, it is recommended to allow him time to lose extra weight.  

Slowly changing the bull’s diet to a forage-based diet and letting him gradually lose the extra fat as he continues to grow is better for his health in the long run. 

Breeding season diet 

“After a bull completes their first breeding season – such as yearling bulls coming off breeding pastures – they may have lost substantial weight,” Kastelic explains. “Bulls also have an alarmingly high rate of injuries associated with breeding and need time to recover.”  

If fed well, however, young bulls who lost weight during their first breeding season will have efficient short-term compensatory weight gain.  

“These bulls will be able to use feed with greater efficiency and be able to restore much of the lost body condition,” he says. 

 It is important to give bulls this chance for gain by penning younger bulls separately from older, more aggressive bulls which may keep young bulls away from feed. 

“Producers should make sure young bulls have adequate protein in their diet, as well as energy, since they are still growing,” Kastelic recommends. “Older bulls generally need more of a maintenance diet, since we don’t want them getting too fat before the next breeding season.” 

Producers should consistently monitor body condition, keeping in mind any lost condition should be restored without putting too much cover on the bull.  

Post-breeding considerations 

“Young bulls should be in compatible groups and ranchers should keep an eye on dominance issues to make sure none of the bulls get beaten up by a pen-mate or become too timid to come to feed,” says Kastelic. “If a bull is low in the pecking order, he may need to be by himself or put with one other bull he gets along with for less competition.”  

It is important to have adequate feed bunk space, so every bull gets his share. If the younger bulls come off the breeding pasture in poor body condition, they need more attention and extra energy in the ration. 

“Producers don’t want to feed excessive energy and get bulls too fat, but some will need higher levels to regain body weight. If they are a bit footsore and lame, they may also need extra care,” he adds. 

Sometimes producers bring home their bulls after the breeding season and put them in the back pasture and ignore them.  

“Paying a little more attention to bulls, adjusting their feed if necessary and having more than one bull pen, so they can be separated as needed, can help avoid problems,” explains Kastelic. “We don’t want to have some bulls fail to thrive just because they are low in the pecking order, or have some of the older bulls becoming grossly overweight because they are dominant and keeping the others away from the feed.” 

Introducing sale bulls 

Travis Olson of Ole Farms Athabasca in Alberta, Canada, says it’s usually a big adjustment for young sale bulls to go from a massive amount of nutrition to grazing grass and still be asked to grow and  breed cows at the same time.  

“When those bulls come back in from the breeding pastures they’ve lost a lot of weight, and it is a difficult transition,” Olson says. 

He continues, “Also at this age, bulls are losing their baby teeth and starting to get their adult teeth. The new incisors are coming in, along with the premolar teeth around 24 to 30 months of age.”  

“This is a challenging stage for young bulls because the teeth are changing and it may be harder for them to eat normally,” he adds.  

“We have a pasture for our older bulls, including bulls above the age of three, and another place for the yearlings and two-year-olds,” Olson explains. “Then, the feeding becomes a simple matter of calories. Bulls are still growing to age three and need to be fed adequately.” 

“It’s no different from a first-calf heifer who lost a lot of weight during the first lactation period,” he notes. “The heifer is raising a big calf and still growing, and we’re asking her to rebreed. This is a difficult time for her, and a bull of this age is similar in his needs for nutrition.” 

Young bulls are still growing while being asked to reproduce. Many lose a considerable amount of weight during their first breeding season and require care to return to premium condition.  

Heather Smith Thomas is a corresponding writer for the Wyoming Livestock Roundup. Send comments on this article to 

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