Bulls in multi-sire breeding pastures sire a widely divergent number of calves, yet the cost of paternity testing calves through DNA still runs higher than the value of sorting the Romeos from the wallflowers. In fact, according to a recent University of California-Davis (UC-Davis) study, paternity-testing calves through DNA would have to cost less than $7 in order to break even with the value of identifying and culling low-prolificacy bulls.

“For cull rates up to 25% (one in four bulls tested) and paternity tests costing $10-$20/head (current test prices), the cost of testing is always greater than the dollars saved by culling low-prolificacy bulls,” says Alison Van Eenennaam, UC-Davis Extension animal genomics and biotechnology specialist.

About the study

Van Eenennaam shared study results at the most recent Applied Reproductive Strategies in Beef Cattle Meeting in Joplin, MO. The study was conducted for USDA and the National Institute of Food and Agriculture. It accounted for 2,400 cows bred/year to a potential of 74 bulls on three commercial ranches in Northern California across eight breeding seasons.

On average, bulls present for an entire breeding season sired 17.8 calves/season. The most profligate bulls sired as many as 54 calves in a season. Across the entire study, 2.3% of the bulls never sired a calf.

Bull ages in the study averaged 3.4 years and ranged from 0.7-9.0 years. The cow-to-bull ratio was approximately 25:1.

Keep in mind, the UC-Davis study considers only the value of paternity testing to sort out the least profligate bulls in multi-sire pastures. It wasn’t designed to account for the benefits of using multi-sire breeding pastures, such as higher fertility, tighter calving seasons and eliminating sire failure.

Nor did the study consider other benefits, like identifying sires causing calving problems, determining heifer replacements from the most maternal sires, collecting individual calf data for in-herd bull performance indices and genetic evaluation.

Other tendencies uncovered

Researchers uncovered other tendencies worth considering. For instance, according to the study, “…producers often purchase ‘heifer’ bulls with high calving ease EPDs to avoid dystocia. As these bulls mature and get too heavy to breed the heifers, they are often moved to breed the cows, despite the fact that cows have little calving difficulty and selection for bulls to breed cows would ideally put emphasis on a different suite of traits.

“A preferable approach may be to use semen from high calving ease AI bulls on heifers, and focus herd-bull selection on traits of importance to breeding cows. This would accelerate genetic progress. This would accelerate genetic progress in traits of importance to the cow herd by reducing the selection emphasis on calving ease which is of less importance when considering herd bulls to breed cows, and ensure the use of low-risk, well-proven calving ease bulls on heifers. ”

Other highlights and reminders gleaned through the UC-Davis study include:

  • Combining yearlings and older bulls in a breeding pasture often results in few progeny from the less-experienced bulls and increases the chance of bull injury.
  • There are few EPDs available for selection on reproduction.
  • Hybrid vigor (heterosis) resulting from crossbreeding continues to be an important approach to improve reproductive performance.