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
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.