Animals that are fed well during a critical six week window before weaning will reach puberty faster and be more fertile
Young bulls need more attention and care than mature bulls, according to Dr. John Kastelic, a veterinarian and professor of cattle reproductive health at the University of Calgary.
“There’s a critical window of bull development from about six weeks of age up to weaning age. If bull calves are fed really well during that time, they reach puberty quicker, have larger testes and produce more sperm,” he said.
If their dam milks well, or if they are creep-fed, they do better than a young bull that’s underfed.
After weaning it’s mainly a matter of feeding young bulls to keep them growing, healthy and fit but not fat. Too much fat in the scrotum interferes with fertility because fat’s insulating effects inhibit heat loss and cooling.
Fat in the neck of the scrotum hinders the ability of a bull to raise and lower its testes for optimum temperature control.
Young bulls overfed for a sale or for the show ring are often too fat, Kastelic said. When they go out with cows for the first time they often don’t hold up and may lose weight.
“In grossly over-fitted young bulls, there can be permanent damage,” said Kastelic. “If you bought a young bull that’s too fat, don’t try to have him lose the extra weight too quickly; transition him gradually to a forage diet and let him slowly lose the extra fat as he continues to grow.”
Travis Olson of Ole Farms in Athabasca, Alta., said it’s a big adjustment for a young bull to go from massive nutrition through barley or corn to simple grazing, while also being asked to breed cows.
“When those bulls come back from the breeding pastures they’ve lost a lot of weight,” he said.
“Also at that age they are losing baby teeth and starting to get their adult teeth. The new incisors are coming in, along with the check teeth (molars), at about 24 to 30 months of age. This is a challenging stage for young bulls and it may be harder for them to eat normally,” said Olson.
Younger bulls also have higher demands for energy and protein.
“One of the biggest mistakes I see is that some people run their bulls with the cows for the winter if they don’t have a facility for keeping the bulls separate. The bulls keep losing weight. Having a place for the bulls, and an extra pen for the young ones, so they can be fed more than the mature bulls, can make a big difference.
“We have one pasture for older bulls (three years and older) and another for the yearlings and two-year-olds. Then the feeding becomes a simple matter of calories. Bulls are still growing up to the age of three, and need to be fed adequately.
“It’s no different from a first-calf heifer that lost weight during her first lactation. She’s raising a big calf, still growing, and we’re asking her to rebreed. This is a difficult time for her, and a bull of that age is the same in his needs for nutrition,” Olson said.
Bulls can lose weight if they came from operations where they were fed too much. “This is why 18 to 24-month-old bulls usually look like death warmed over after their first breeding season.”
However, young bulls in that situation will likely have efficient short-term compensatory weight gain.
“They can use feed with greater efficiency and restore much of that lost body condition,” Kastelic said, so they should be given that chance by penning them separately from the older bulls that might keep them away from feed.
“Make sure young bulls have adequate protein, as well as energy, since they are still growing. Older bulls generally need more of a maintenance diet, since you don’t want them getting too fat before the next breeding season,” said Kastelic.
“Young bulls should be in compatible groups, keeping an eye on dominance issues, making sure none get beaten up by a pen mate and become too timid to come to the feed. If a bull is low in the pecking order, he may need to be by himself or with one other bull he gets along with, with less competition,” he said.
Adequate feed-bunk space will help ensure every bull gets its share.
“You don’t want to feed excessive energy, but some will need higher levels to regain body weight. If they are footsore and lame, they also need extra care.”