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Rasby: Yearling bulls need special attention during and after breeding season

by Wyoming Livestock Roundup

Most ranchers have a goal of getting their cows bred, and preferably early in the breeding season, according to University of Nebraska Beef Extension Specialist Rick Rasby. 

To have a successful breeding season, Rasby encourages producers to pay attention to their bull to female ratio. 

“The bull to female ratio is dependent upon several factors like the age of the bull, terrain and pasture size,” he explained during a recent webinar. “A good rule of thumb is the age of the bull in months is equal to the number of females he can be expected to service, up until he is mature. At that point, we figure one bull to 25 to 35 cows.” 

Before and after

During the beginning of the breeding season, Rasby recommends checking the pastures two to three times a week to make sure the bulls don’t become injured and are doing their job. Once a producer is sure things are going well, he could check the pastures less frequently. 

“In single-sire pastures, you may want to consider rotating bulls in case one bull goes bad, and you don’t catch it,” he explained. “In multi-sire pastures, the other bulls cover up the mistakes or injuries of a bull, and there is less chance of the females being open at the end of the breeding season.

I would also write down the ear tag numbers of the cows that you see the bull servicing,” he continued. “See that they aren’t cycling again 21 days later.”

Rasby said yearling bulls should be left in the cowherd no longer than 60 days during the breeding season. 

“Every day beyond that affects their condition and can have long-term affects on their growth,” he said. 

After the breeding season is complete, Rasby urges producers to check the bulls for physical problems, primarily in their feet and legs. The bulls may also need some nutritional attention to get them back into shape before winter. 

“Mature bulls should do well when they are back on pasture,” Rasby said. “They have lots of room to exercise, just make sure to provide them with some vitamin and mineral supplement.”

Yearling considerations

Yearling bulls need to be kept separate from mature bulls, because they may need some extra attention. 

“Yearlings need to be fed or grazed on some good quality forage or pasture,” Rasby said. “It is possible for a younger bull to lose 100 to 300 pounds during the breeding season.”

Rasby continued, “If you have a vegetative pasture for them, they could gain 1.5 to 1.75 pounds a day. They will also need to be supplemented with vitamins and minerals.”

If a producer is considering supplementing the bulls on dormant grass, a feeding program should be designed so that the bull reaches 75 percent of its mature weight at 24 months of age. 

“Be cognizant that young bulls have to gain the weight back that was lost during the breeding season, plus gain towards their mature weight,” he explained.

Rasby said if a 1,200 pound yearling bull loses 200 pounds during the breeding season, and needs to reach 1,800 pounds by 18 months of age, it will need to gain two to 2.2 pounds a day. 

“If you are trying to get him ready for the spring and summer breeding season, I would recommend starting early so less grain is needed,” Rasby explained.

Mineral is important for young, growing bulls to help them develop bone, Rasby said. 

“If you use distillers grains, make sure you don’t add any more phosphorus to the ration. In fact, you may want to add some calcium to keep the ratio in balance,” he cautioned. 

Bulls can develop urinary calculi problems if the calcium to phosphorus ratio isn’t balanced.

Recommended rations

A 1,200 pound bull will consume about 2.2 to 2.5 percent of its body weight a day on a dry matter basis, which is about 26 to 30 pounds of feed. 

University of Nebraska Beef Extension Specialist Rick Rasby said an ideal ration for bulls would include: 0.59 to 0.65 mega-calories (MCal) per pound net energy for maintenance (NEm); 0.39 to 0.41 mega-calories per pound for net energy gain (NEg); nine to 11 percent crude protein; 56 to 64 percent total digestible nutrients; 0.33 percent calcium; and 0.20 percent phosphorous.

Gayle Smith is a correspondent for the Wyoming Livestock Roundup. Send comments on this article to

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