Biology of bovine sperm and breeding soundness (Proceedings)

Abstract

Approximately 20 years ago, studies centered on the ability of bull sperm to fertilize eggs in vitro. Higher fertility semen donors produced sperm that were more readily 'capacitated' in lab media. Therefore, the hunt was on to identify differences in seminal components from high and low fertility bulls that altered the ability of sperm to capacitate. A protein produced in the seminal vesicles, prostate, and Cowper's glands named fertility-associated antigen (FAA) binds to sperm during ejaculation. An antibody-based test was developed which utilizes a lateral-flow cassette and can be conducted in 20 minutes as part of a breeding soundness qualification. Bulls with detectable FAA are 16-19% more fertile than herdmates lacking measurable FAA, even though physical characteristics are identical between those two groups of bulls. Field trials indicate that 25% of bulls will be identified as FAA-negative and should be removed as prospective breeders.

Why Predict Fertility?

In beef cattle, we are measuring many traits to develop selection indices that can be used to breed better animals that are more profitable. As a trait, fertility is 5 to 10 times more important to overall profitability in a beef production enterprise than any other trait we can measure (Trenkle and Wilham, 1977). In 2005, the net value of an additional calf can be estimated conservatively to be $100. With 38 million beef cows in the U.S. herd, a 1% increase in calves born would translate into a $38 million profit to the industry. At $150 per calf, $57 million would be earned by the industry for every 1% increase in our calf crop. Therefore, if we can identify high from low fertility potential in bulls with an objective test, we can make a substantial impact on the "bottom line" for beef producers, seed stock as well as commercial cow-calf operators.

Table 1. Society for Theriogenology minimum recommendations for evaluation of scrotal circumference and semen analysis.1

Breeding Soundness Evaluation (BSE)

With "mad cow" disease caused by bovine spongiform encephalopathy (BSE), the time has come to find another term to describe breeding soundness in bulls. Therefore, for purposes of this discussion, a former BSE will now be called a breeding soundness qualification (BSQ).

What does a BSQ do? The American Society for Theriogenology has developed guidelines that are meant to be used to identify a bull as a "potential satisfactory breeder" (Chenoweth et al., 1992; Hopkins and Spitzer, 1997). Besides a general physical examination, a BSQ also includes measuring scrotal circumference and evaluating a semen sample. Minimum thresholds have been established for breed-type and age that establish whether or not a bull passes a BSQ. In general, for non-Brahman cattle, at 14 months of age, the following criteria should be satisfied:

In general, 25% of bulls tested will not pass a BSQ for various reasons. A bull may be re-tested at a later date to see if he can pass at that point in his life. Older bulls that fail are probably not worth keeping in hopes that things will get better, especially if younger cohorts are satisfactorily passing their BSQ's.

Table 2. Fertility of range beef bulls at King Ranch in relation to sperm morphology.

Unfortunately, a BSQ cannot distinguish a high from low fertility bull. Once two bulls qualify on the basis of a satisfactory BSQ, the real question to be answered is which one will produce more calves when bred to a population of heifers/cows? Therefore, the detective hunt has been on to find specific components in semen that might serve as a marker(s) for fertility potential. Papers which follow provide details of protein components found in semen which hold utility as diagnostic markers and semen additives.

Table. 3. Frequency distribution of bulls changed when a 34 cm threshold was established for minimal scrotal circumference.

What Technology Is Beyond A BSQ?

In 2003, Dr. Bob Foote wrote an excellent review article summarizing the situation of being able to sort bulls on the basis of their actual fertility (Foote, 2003). He concluded that the cattle industry needs a specific component that can be accurately measured to identify fertility. Ideally, such a component would be found in semen and could be tested as a sequel to a BSQ. The good news for early 2005 is that several such components have been identified. One of those, coined "Fertility-Associated Antigen" (FAA), can be assayed in minutes using a lateral-flow cassette, utilizing technology similar to a home pregnancy test as detailed in the April, 2004 cover article of IVD Technology (McCauley et al., 2004).

References

Chenoweth, P., J.C. Spitzer, and F.M. Hopkins. A new bull breeding soundness evaluation form. Proc. Ann. Mt. Soc. Theriogenology. 1992; San Antonio, TX.

Foote, R.H. Fertility estimation: a review of past experience and future prospects. Anim. Reprod. Sci. 2003; 75:119-139.

Hopkins, F.M. and J.C. Spitzer. The new Society for Theriogenology breeding soundness evaluation system. Vet. Clin. North Am. Food Anim. Pract. 1997; 13:283-293.

Killian, G.J., D.A. Chapman and L.A. Rogowski. Fertility-associated proteins in Holstein bull seminal plasma. Biol. Reprod. 1993; 49:1202-1207.

McCauley, T.C., G.R. Dawson, J.N. Oyarzo, J. McVicker, S.H.F. Marks and R.L. Ax. Developing and validating a lateral-flow cassette for fertility diagnostics in bulls. In Vitro Diagnostic Technology 2004; 10:35-40.

Spitzer, J.C. Bull breeding soundness evaluation: current status. In: Topics in bull fertility. Chenoweth, P.J. (Ed.). International Veterinary Information Service, Ithaca, N.Y. 2000; (www.ivis.org).

Trenkle, A. and R.L. Wilham. Beef production efficiency. Science 1977; 198:1009.