Breeding success depends on the reproductive health of both the cow and the bull. But, because a bull is expected to service various numbers of cows, the potential fertility of the bull is much more important than determining the fertility of any individual cow, says Bryan Kutz, with the University of Arkansas ag extension.

What genetic and physical improvements need to be made? What sire breed would best complement my cow base? How many bulls are needed to correctly cover my cows? Do I need to use two different sire breeds? These are all very relevant questions that need to be answered as we approach the spring breeding season. Nonetheless, without a proper Breeding Soundness Exam (BSE), these decisions may not matter. The greatest bull with bad semen will not produce calves.

It is essential to evaluate bulls every year before breeding starts because the fertility of an individual animal can vary from year to year. The breeding soundness exam should be performed 30 to 60 days before the start of breeding season. It is important to allow sufficient time to replace questionable bulls. This will also allow enough time for stressed animals to recover and to be tested again before beginning the breeding season.

The physical examination includes evaluating body condition, feet and leg structure and the general health of the individual bull. The external evaluation of the reproductive tract includes evaluation of the testes, spermatic cords and epididymis. Scrotal circumference is an important measure since it is directly related to the total mass of sperm-producing tissue, sperm cell normality and the onset of puberty in the bull and his female offspring.

Circumference measurements should be taken at the widest point on the scrotum.

Depending on the breed type of the bull being tested, the minimum scrotal circumference can vary. Maximum testicular size usually occurs at 4 to 6 years of age. With advancing age, testicular tissue may lose some sperm-producing capacity. Therefore, scrotal circumference measurements are not as accurate after this time. The table below illustrates the minimum scrotal circumference (SC) that will allow a bull to pass a breeding soundness exam. However, bull buyers should not feel comfortable in accepting the minimum, but rather select bulls that are average or above average for the breed and the age of the bull. Therefore, the “Good” column of the following table is a better guideline for bull selection.

Recommended Scrotal Circumference

Age

Minimum SC (cm)

Good

< 15 months

30

> 34

15 -18 months

31

> 36

18 -21 months

32

> 37

21 -24 months

33

> 38

> 24 months

34

> 39

There is great variation in scrotal circumference between breeds of bulls. Measurement of many English and European bulls has shown that yearling bulls should have scrotal circumference of at least 30 cm and by 20 months of age have a scrotal circumference of at least 32 cm. Brahman breed bulls will have smaller testes at the younger ages, and they will reach maturity at an older age. The Brahman breed bulls will have adult scrotal circumferences similar to other beef breeds.

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