Often times, says James Henderson, things aren’t necessarily what they seem. Or perhaps more accurately, aren’t necessarily just the way you were told they were.
Never is that situation more true than when it comes to figuring out which bull  was in which pasture and whether or not he’s really doing his job.
Henderson is part of the Bradley 3 Ranch at Memphis, TX, which was one of the early adopters of measuring performance traits in cattle. While Bradley 3 Ranch is a seedstock operation, it’s managed much the same as a commercial operation. The cows are run in big pastures, some two sections or larger, and are expected to hustle a living for themselves and their calves with minimal inputs, breed back in a 60-day breeding season, and bring a baby from the brush to the branding every year.
Industry Resource Page: Bull Management Advice 
“One of the big problems with running cattle in two-section pastures and trying to run a 60-day breeding season, is it doesn’t work without running multiple sires in a pasture,” Henderson says. For commercial and seedstock producers  alike, that can present a challenging management situation because it can be helpful to know which bulls sired which calves.
So in 1997, Bradley 3 Ranch began using emerging DNA technology to determine parentage. In fact, Henderson says, they were the first seedstock Angus ranch in the U.S. to do so.
“We’ve learned a lot in that process. We learned that if we put 2-3 bulls in a pasture, we may have a bull that’s not siring many calves,” Henderson says. But that doesn’t necessarily mean he needs to go to town. “You put him with a different set of bulls and he might sire the most. It really depends on the dominance of those bulls in the pasture.”
A Closer Look: Factors That Affect The Breeding Ability Of Bulls 
Generally, you can determine the dominance structure within each set of bulls in a pasture by taking time to observe them during the breeding season. Most of the time, over a number of observations, you can get a feel for how each bull is performing. If one or more bulls seem to spend more time shaded up than working, you may be able to increase breeding performance by moving bulls to another pasture with a different set of sires.
But not always. “We have one bull that I swear is nocturnal,” Henderson says. “We never saw him with a cow, yet he bred three-quarters of the cows in that pasture.”
Beef Production Tips: Practical DNA Application 
In addition, through using DNA to determine parentage , they found that some bulls are what they call herders and others are free floaters. The herders will put their harem together “and, by golly, that’s their herd of cows and they’re going to breed those.”
That presents another reason why a bull might not necessarily breed as many cows as he should – injuries and lameness . When the free-floater wanders by looking for opportunities, the herder will protect his harem and one, or maybe both, of the combatants may become crippled.
In another instance, they discovered that a bull jumped seven fences and bred a bunch of cows he wasn’t supposed to. “So there are a lot of things that you find in that kind of environment that you didn’t expect to,” Henderson says.
For many years, the Bradley operation had a packing plant and sold beef to specialty stores. One day, Henderson remembers they were harvesting some heifers and quickly discovered that many of them were bred.
He called the owner to report the situation and the owner said it was impossible, as there weren’t any bulls in the pasture. “I told him he might want to get in the pickup and head south because something miraculous had happened,” Henderson says.
After a long pause, the rancher replied that he was told some bulls had gotten into the pasture, “but they just ran through.”
“So, sometimes things are not as they seem or as we’ve been told they are; DNA can tell that picture ,” he says.