Elizabeth Cronin North Dakota State University
During the bull-sale season many producers are deciding which bulls are going to sire their next calf crop. Buying the right bulls for an individual operation involves a critical and time-consuming set of decisions, but the work doesn’t end when the bull is on the ranch. Ensuring bulls are in good physical condition and physically fit for the upcoming breeding season is key to reproductive success, according to North Dakota State University-Extension specialists.
Most bulls are developed by seedstock producers and development strategies vary by operation.
“While there are a lot of different rations used to develop bulls, some types of high-concentrate rations are typically used to determine the genetic potential for growth in herd mates,” said Janna Block, North Dakota State University-Extension livestock systems specialist. Out of the Hettinger Research Extension Center. “A common complaint of bull buyers is that bulls lose condition quickly when they get home. This is often the result of failing to adjust to bull rations frequently from a high-energy ration to a forage-based diet. “
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The consequences of poorly infected bulls can include increased stress, digestive disturbances, body condition losses, and impacts on sperm quality and quantity.
In beef cattle, the rumen is the primary fermentation chamber of the stomach. It contains billions of microorganisms that break down feed consumed by the host animal. Different species of microbes have different functions and preferred food sources. Some digest starch and sugars, while others digest fiber. The numbers and proportion of each species vary based on diet composition. Therefore, when a high-energy diet is provided to the animal, the rumen microbial population consists of the starch-digesting bacteria. When the diet is changed abruptly, microbial populations are out of balance with the feed source.
“It can take four to six weeks for the fiber-digesting bacteria to concentrate after removal from the ration,” said Block. “Stepping down bulls from a high plane of nutrition through gradual reductions in grain combined with increased amounts of forage is necessary to stabilize the rumen microbial population and prevent digestive issues and rapid weight loss.”
Zac Carlson, North Dakota State University-Extension beef specialist, recommends that bull buyers get detailed information about the previous ration and try to get started with similar feedstuffs.
Carlson said, “A diet consisting of 80 percent to 90 percent of the previous amount can concentrate on being offered first, and then reduced by 10 percent every few days until the final diet formulation is reached. If information about the previous diet is not available, high-quality grass is concentrated and can provide concentrations of four to six pounds. “
Total ration crude protein should be between 10 percent and 11 percent, with energy, or total digestible nutrients, levels at 60 percent to 70 percent. Producers should analyze feeds for nutrient content and develop a ration. Because the semen production of the process takes about 60 days, it is ideal if a transition to a forage-based ration is completed at least 90 days prior to the breeding season.
Consider body-condition scores
Block said, “Body condition scoring is another important component in developing an appropriate nutrition program for bulls. Bulls should have a BCS of 5.5 to 6.5, depending on the length of the breeding season, cow-to-bull ratio and other factors. “
In the body condition score range of 4 to 7, there is a difference of about eight percent of body weight between each score. A yearling bull weighing 1,200 pounds with a body condition score of 6 would weigh about 100 pounds less as a body condition score 5. If there were 70 days until the breeding season began and the bull needed to gain one condition score, he would need to. gain about 1.4 pounds each day.
When the bulls have a body condition score of 6, no ribs will be visible, the back will appear slightly rounded, and there will be some evidence of fat in the brisket and tail head. If the bulls are thin, with a body condition score of less than 5, they will need to be on a steady plane to achieve optimal performance. In that situation the additional focus may need to be considered; However, bulls will still need to be transitioned to a high-forage diet prior to turnout.
“Some bulls will have to buy in excess condition and may need to lose fat and add muscle prior to breeding, but it is important to remember that they should still gain weight,” said Block. “If bulls are in excessive body condition after sale, the goal is to reduce the condition slowly to avoid issues.”
“It’s important to monitor the nutritional status of growing bulls closely for the first several seasons,” said Carlson.
After their first breeding season, the bulls should manage to weigh 65 percent to 75 percent of their estimated mature weight by the time they turn two. Bulls may need to gain significant amounts of weight to lose weight during the first breeding season and allow for continued growth.
If a bull with a mature weight of 2,000 pounds weighs 1,200 pounds at turnout and loses 200 pounds during the breeding season, he will gain 400 pounds between the end of the breeding season and his second birthday.
“Pulling yearling bulls early or using them for only a limited time during the breeding season can help reduce total weight loss and provide additional time to regain lost weight,” said Carlson. “Mature bulls will also need to regain weight loss during the breeding season, but their nutrient requirements are lower than growing bulls.”
Block said, “Feeding bulls to optimize fertility is not solely dependent on protein and energy. Minerals and vitamins play an important role in spermatogenesis and can also affect semen quality. In particular, copper, zinc and phosphorus have a direct role in fertility, and forages are often marginal to deficient in these minerals. “
Mineral analysis of forages and other feeds will allow producers to select a mineral that works best with the feeding strategy. Producers should also supplement vitamin A when feeding harvested forages, whether through a mineral supplement or an injection. Vitamin A deficiency may affect spermatogenesis.
The cost of bulls and their potential genetic contributions to the cow herd indicates that they should be managed to optimize performance. Visit www.ndsu.edu for more information.
Elizabeth Cronin is an information specialist with North Dakota State University.
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