Bulls not equally prolific in the pasture

Producers expect breeding duties among their cows to be shared when they use multiple bulls in a pasture.

However, DNA parentage data collected over three years at the Western Beef Development Centre near Lanigan, Sask., showed that some bulls are far more prolific than others. Some bulls sired as few as three calves while others did more than their share.

“There was a lot more variation in what bulls were actually doing and how many calves were sired by a bull,” said Stacey Domolewski, whose master’s degree involved testing bull prolificacy.

She is the science and extension co-ordinator for the Beef Cattle Research Council.

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“We were surprised by how uneven it was,” she said in a Nov. 16 webinar organized by the council.

The recommendation is one bull per 25 cows, but results from the first year showed that one bull produced just one calf while the highest was 53 calves. The average was 21 calves per bull.

The researchers created a bull prolificacy index to account for pregnancy rate, bull-to-cow ratio and the number of bulls in the pasture.

Bulls that do not pull their weight do not pay their own way.

Making parentage information available allows producers to track the calves’ successes or failures back to the sire.

For example, one might be responsible for calving difficulties and could be removed to prevent dystocia. It has been found that of all the calves that die at or around calving, more than half had a difficult birth. Calving difficulty may be the fault of either the bull or management.

Producers looking for specific traits such as improved weaning weights could trace that quality back to a specific bull.

Parentage testing could also prevent inbreeding and be another way to remove non-prolific sires.

“He still costs the same room and board, so it may be a way to get rid of those freeloader bulls,” said Domolewski.

Bulls can depreciate like any other asset. The cost of a bull includes purchase price, feed, bedding, veterinarian bills and minerals.

A bull that sires only one calf does not cover the cost of its upkeep. The WBDC offers a herd sire calculator to figure out the costs on an operation and whether an individual bull pays its way.

Producers also want improved weaning weights because they are paid on a per pound basis.

The assumption that some bulls may sire fewer calves but pass on desirable traits such as improved weights may not be enough.

This research found that the most prolific also had the highest calving percentage and more calves survived to weaning.

The study also looked at the age of bulls that are turned out.

They found mature bulls tended to sire the most calves, but there was still considerable variation among the yearlings, two year olds and mature sires. The mature bulls tended to sire the most, but there were still variations in their success.

“Because a bull is older does not necessarily mean he is going to sire more calves, and there may be a lot of other factors at play here,” she said.

The first year of the study found a group in which the yearlings sired the most, but usually the mature bulls were producing more. In the second year of the study yearling bulls were often the least prolific while the two years olds produced the most calves.

While the mature bulls seemed to sire more calves, further research is needed to see if yearlings develop and become more prolific as they age. The researchers also want to know if a bull that was highly prolific in one season repeats that performance the following year.

All the bulls in the study had to pass a breeding soundness test that assessed scrotal circumference and sperm scores.

Researchers also looked at the production cycle.

Sixty percent of the herd should be calving within the first 21 days for a more consistent set of calves, and cows should then rebreed as soon as possible to produce a calf every year. Researchers wanted to know if certain bulls were responsible for producing the most calves in the early part of the season, but this needs more work.

They also need to look at cattle management, dominance of certain bulls and libido.

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