From the Loomix® Doctor’s Office

–by Dr. Kelley Neuhold, Loomix Technical Service Specialist

As I sat down to write this article, I was reminded of a sign that hung above the door in the sale barn café. It said “Cows may come and cows may go, but the bull in this place is forever.” Unfortunately, actual bulls won’t last forever but their useful life can sure be reduced with improper management and nutrition. Many times bull management is overlooked because they only make up 2.5 to 5 percent of a herd; however, keep in mind they contribute to 50 percent of the reproduction equation. Fertility problems in bulls can have a major impact on a ranch’s bottom line by lengthening the calving season, reducing calving percentages, and the cost of feeding open cows. Fertility is influenced by both the animal’s genetics and environment. Environmental factors include nutrition, health and management. Once a bull is born nothing can be done to improve his genes, but nutrition and management can be used to increase his breeding longevity.

Feeding and caring for mature bulls, older than 3 years, in good body condition (BC) is much like feeding and caring for dry cows in the second trimester of pregnancy (Table 1). A good BC score for a bull is similar to that of a cow. Prior to and during breeding season bulls should have a BC between 5.5 and 6.5 (Walker et al. 2008). Extremely thin and extremely fat bulls can have semen quality and libido issues for different reasons. Bulls should always have plenty of fresh water, a warm dry place to lie down (bedding maybe needed during extreme cold weather), room to exercise and full access to low to medium quality forage (6 to7 percent CP). Young bulls, younger than 3 years, need more consideration than mature bulls. These bulls are still developing and are more likely to be timid. Young bulls have higher protein and energy requirements (Table 1) than mature bulls due to their growth requirement.

Vitamins and trace minerals (TM) play a very important role in male reproduction. Manganese deficiency is associated with reduced male libido. Zinc (Zn) and vitamin A deficiencies are related to a reduction in spermatogenesis (Bearden and Fuquay, 1992). NRC (2000) suggests vitamin and TM requirements are similar for bulls and cows (Vitamin A = 1,275; Zn = 30 ppm). Arthington et al. (1995) used yearling bulls to evaluate Zn concentration and source on fertility. The three treatments were 1) 40 ppm from Zn sulfate, 2) 40 ppm 1/3 organic Zn 2/3 Zn sulfate, 3) 60 ppm Zn sulfate. They found across all fertility measurement evaluated bull on treatment number two had the most favorable results followed by treatment number three than treatment number one, suggesting that 30 ppm Zn suggested by the NRC maybe too low for yearling bulls. Rowe et al. (2011) used mature bulls to evaluate TM source (organic vs. inorganic) on semen quality and found bulls who were fed organic TM had improved semen quality (Table 2) over bulls fed the same concentration of inorganic TM. These experiments suggest providing bulls a portion of their TM from organic source may improve semen quality, which may improve conception rate in the herd.

Management of bulls should not be overlooked, it can mean the difference between being profitable and not. Keep in mind it takes about 60 days to produce mature sperm; therefore, it will take at least 60 days before management

changes will be realized. This emphasized the importance of evaluating BC and rations 90 days prior to breeding to give time for any change to take effect. The best advice I can give is to preform breeding soundness exams each year on your bulls. This is very cheap insurance, especially for producers who have single bull pastures.

¹Based on NRC 2000. ²NRC suggest zinc

level at 30 ppm, however research presented would suggest a minimum

of 40 ppm.

¹Adopted from Rowe et al. 2011. ²Organic trace minerals were provided

from Zinpro Availa4.

Sources’

Arthington, J., K. Johnson, L. Corah, C. Williams, and D. Hill. 1995. The effect of dietary zinc level and source on yearling

bull growth and fertility. J. Anim. Sci. Abstract.

Bearden, H. J., and J. W. Fuquay. 1992. Nutritional management. In: Applied Animal Reproduction. Prentice Hall, Englewood Cliffs, NJ, pp. 283-292.

NRC. 2000. Nutrient Requirements of Beef Cattle. Seventh Revised Edition. National Academy Press. Washington, DC.

Rowe, M. P., J. G. Powell, E. B. Kegley, T. D. Lester,

C. L. Williams, R. J. Page, and R. W. Rorie. 2011. Influence of organic versus inorganic trace mineral supplementation on bull semen quality. Univ. of Arkansas Systems Div. of Ag., Dept. of Anim. Sci., Fayetteville, Ark. AAES Research Series 597.

Walker, J., G. Perry, and

K. Olson. 2008. Bull Nutrition. SDSU Extension Extra Anim. and Range Sci. ExEx2065.

Dr. Kelley Neuhold can be reached at Kelley.Neuhold@allianceliquidfeeds.com.