The hardest time in the life of a young bull is when he’s turned out with cows for his first breeding season, after being well-fed all winter. Most bulls are confined in a pen after weaning and are fed high-concentrate feeds, pushed for fast growth. Some have gone through a bull test to measure rate of gain and feed efficiency.

Thiago Martins, a veterinarian and state extension beef reproduction specialist at the University of Missouri, says it’s common for purchased bulls to be overly conditioned because they’ve been provided nutrition to express their performance potential. They shouldn’t be turned out with cows with a sudden change in nutrition.

Looks can be deceiving

While fat may look good on a bull, it is not good for a bull.

“Bulls should not be fat, but should be still growing and gaining weight, since you can expect them to lose 1 to 2 points of body condition during breeding season,” Martins says. “They should start the season with a condition score of 6 to 6.5 to have a little buffer.”

You don’t want them any fatter than that, or they will have fat in the scrotum that acts as insulation, making it harder for proper temperature regulation and optimum sperm production and storage, he explains. The end result: The bull will be less fertile.

“Too much fat impairs production of testosterone and interferes with spermatogenesis. There will be more abnormalities in his sperm,” says Martins. It takes time to lose that fat, and gradually “let down” a bull if he is overly fat when you buy him.

Only 45% of extremely overconditioned bulls pass their breeding soundness exam, compared to 81% of bulls with just adequate body condition.

Pedro Fontes, assistant professor of beef cattle reproductive physiology at the University of Georgia, is doing studies with overly conditioned bulls, evaluating records from breeding soundness exams (sometimes referred to as a BSE). Only 45% of extremely overconditioned bulls pass their breeding soundness exam, compared to 81% of bulls with just adequate body condition.

“If they have a body condition score higher than 6.5, the producer should continue to provide a feed similar to what was given before the bull was purchased, then gradually decrease that concentrate portion of the diet,” says Martins.

Similar ingredients

“You can’t always provide feed exactly the same, but could provide something similar,” he adds. “The amount should be decreased by 10% each week until the desired level is achieved. Bulky feeds such as forages should replace the grain, as the bull is transitioned to forage.” This gives the rumen microbes time to adjust.

Phillip Lancaster, a clinical assistant professor with the Beef Cattle Institute at Kansas State University, says it may be expensive for a producer to continue to feed grain to a bull that’s been on test and on a diet that was 70% grain and corn silage.

“The cow-calf producer may not have those same feed ingredients,” he says, “but [they] still need to try to match the new bulls’ previous diet fairly closely and then work them gradually off that.”

A person might be able to get some cracked corn, which could be mixed with soybean pellets or something that could be acquired locally, he says.

“Work with your local nutrition person and figure out what feed ingredients might be available to be able to keep a relatively high-energy diet for that bull and then drop it down,” advises Lancaster.

Nutrients to grow

Yearling bulls are still growing.

“They should continue to gain 1.5 to 2 pounds per day even after you’ve cut down the original ration,” says Martins. “They need to lose fat, but not muscle.”

If you are feeding hay, it should be at least 7% — ideally 8%-10% — crude protein (CP) on a dry-matter (DM) basis, says Martins, explaining bulls need adequate protein to grow.

Not much research has been conducted on taking cattle off a high-grain, high-energy diet and putting them on grass, Lancaster observes.

“In a feedlot we worry about the opposite — going from grass to grain,” he says. “There’s been more research on that kind of transition.”

Even though there is a lack of research on stepping down the nutrition, producers should try to match the “feed test” diet at least in the beginning of the transition, for about a week, then step down from that, a little at a time.

“Just think about how we transition calves onto feed in the feedlot, and do it in reverse,” says Lancaster.

“After about three or four weeks, depending on when you are going to turn him out with cows, keep feeding him a little grain,” Lancaster advises. Transition him to pasture gradually. Don’t suddenly take all the grain away.

It also helps to feed hay during the period before the bull goes on pasture. He can handle dry hay better than lush green pasture.

“I’m not concerned about what kind it is — whether [it’s] alfalfa or grass. That’s not as big a deal as turning the bull out on lush pasture. Hay slows things down in the gut and stimulates rumination better than green grass, so the animal is chewing the cud more. This is better than switching directly to lush grass that doesn’t contain much fiber,” says Lancaster. Bulls need to lose fat if they were fed heavily during a feed test, but a sudden change may cause dramatic weight loss.

“You can continue to feed grain at about 1% of his body weight to keep him growing, but if he is overconditioned you might want to drop that down to 0.5% of his body weight. You want him to lose condition, but not muscle mass,” says Lancaster.

“If you have a 1,300-pound bull coming off test, 0.5% to 0.75% of his body weight in grain would give him enough energy to maintain muscle mass and keep him growing, but he will start to convert some of that fat to muscle and be in better shape to handle a higher activity level when you turn him out with cows.”

Feeding too much starch after weaning can lead to growth defects, not only in hoof structure (laminitis), but also skeletal growth, with developmental orthopedic disease. Young bulls pushed for fast growth with a lot of grain can develop osteochondritis dissecans (OCD) lesions — pockets of weaker bone/cartilage that may later lead to breakdown in those joints. They are more susceptible to injuries later because of those defects.

Give him time

“Generally you should not buy a bull only 30 days or less before your breeding season,” says Martins. “I recommend buying bulls at least 90 days ahead so you’ll have time to adjust nutrition. Once they are with the cows, you can’t do much. They are on the same nutritional plane as the cows and will also be very active.”

It takes 60 days to produce sperm, Martins observes. “If you stress a bull in that time period, it may have an adverse effect on sperm by the time he goes out with cows. If you purchase him 90 days ahead of the breeding season, you can gradually decrease the amount of concentrate in his diet, and he’ll have time to adjust and have good sperm.”

A bull you buy will have had a breeding soundness exam, but Martins encourages producers to conduct another before the bull breeds cows. Things can change, especially if it’s been a while since the first one.

“This is important to check, especially if you were adjusting the nutrition,” he says. You spend a lot of money for a bull and don’t want to find out later that he wasn’t as fertile as you thought.

Exercise

To have a bull in shape for breeding, make sure he gets some exercise. This is as important as proper nutrition.

“It helps if he’s in a pen large enough that you can put the mineral and supplements on the opposite side as the water, so he has to walk back and forth between them,” says Martins.

“If there are several young bulls in the pen, they will exercise themselves just sparring around, but you also have to be careful about putting together a group of new bulls that don’t know each other,” Lancaster warns. “You don’t want them to get hurt.”