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      A minimum scrotal circumference for bulls should be established as a selection goal. Avoid bulls failing to meet the minimum standard. Scrotal circumference is easily measured and is an excellent indicator trait since a significant, positive correlation exists between scrotal circumference and both volume of semen and percentage normal sperm cells. Furthermore, research has also found a strong genetic relationship between scrotal circumference in bulls and the fertility of their daughters as measured by earliness of puberty. Bulls measured at one year of age should have a scrotal circumference of at least 30 centimeters.

     Sex drive or libido is also a vital part of bull fertility, although it has little association with other fertility traits such as semen quality or scrotal circumference. Libido testing of yearling bulls in research stations has revealed sizable differences in libido test scores of bulls that were later verified by significant differences in actual conception rate.

     While libido testing is still in the experimental stage, it may soon be a useful part of some seedstock breeders' bull evaluation programs. It would be particularly advisable to expose bulls to a few cycling females prior to turning them in with the cow herd. Close observation at this time will permit identification of shy breeders, fighters, bulls that form a bond with one particular cow while ignoring others in heat, and bulls that have poor mounting orientation. Such bulls sire fewer calves and are economic liabilities to cow?calf producers.

Putting It All Together
Bull selection depends on the type of cows to be bred and the objectives of the producer. The best bull for one herd will not necessarily be a good choice for another herd. Following are three examples of how the herd situation can affect bull selection:

     Producer 1 has a small herd of crossbred cows. He works in town during the day and has a limited amount of time to spend with the cattle. He has at best average pastures with limited facilities and needs to use the same bull on both heifers and mature cows. For Producer 1, calving-ease would be of major importance, so low birth weight EPDs would be necessary. This producer may have to accept somewhat lower weaning and yearling weight EPDs to find a low birth weight bull. With his pasture situation, average milk to moderately low milk production would be acceptable. Producer 1 would want to avoid extremes in frame. With limited facilities, disposition would also be a major consideration.

     Producer 2 has an average size herd of medium-frame, crossbred cattle that works well under his management situa-tion. He has good pastures and needs a bull to breed to mature cows in a rotational cross-breeding program. Producer 2 would balance moderate birth weight EPDs against higher weaning and yearling EPDs. He would be willing to accept somewhat higher birth weights than Producer 1 in order to get higher weaning and yearling EPDs. With good pastures, moderately high milk EPDs may be desirable. Since his cows are working well in their environment, a bull of similar frame and muscle would be chosen.

     Producer 3 has a large herd of medium?frame cattle and plans to breed some of his mature cows to a terminal sire. All of these calves will be placed in the feedlot. Producer 3 will want to maximize weaning and yearling weight EPDs. He will have a higher tolerance for birth weight than either Producer 1 or 2, but he will still avoid bulls with extremely high birth weight EPDs. Since all heifers are going into the feedlot, milk EPDs are not a factor. A larger framed bull may be desirable to produce a specific carcass weight. A heavy muscled bull would also be desirable.

     In the above examples, these producers with three different herds and objectives would choose three different bulls. Setting goals and evaluating the cow herd are important first steps in bull selection.

     That's the latest from one of the "Bull Is Foundation For Profitable Herd" authorities. Once you're familiar with these ideas, you'll be ready to move to the next level.

Bull Talk 


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