Technical information - Reproduction

Do fertile bulls breed more fertile progeny?

from Beef CRC Bulletin WINTER 2007


New Beef CRC research is investigating whether fertility traits in bulls, such as scrotal size, semen quality and various hormones and proteins are linked to fertility traits in both their male and female progeny.

Dubbed the Beef CRC “Male Indicators Project”, data are currently being collected from nearly three and a half thousand bulls donated by Beef CRC collaborators from industry (Northern Pastoral Group of Companies and individual seedstock breeders from Central Queensland) and CSIRO to determine the links between the fertility of males and females.

The goal of the project is to discover better predictors of female fertility in bulls, in much the same way as dairy bulls are selected to improve the milking ability of their daughters.

If predictor traits can be identified in bulls early in life, then selection for female fertility will become easier for beef producers, not only because of the earlier selection and greater selection pressure in bulls, but also because of the greater influence that bulls have on future herds relative to individual breeding cows.

Beef CRC Project leader Dr Dick Holroyd of the Queensland Department of Primary Industries and Fisheries, said that given there is a common origin for both male and female hormones suggests there may be some correlation in fertility across the sexes.

Past research has already found bulls with a larger scrotal size produced daughters that reached puberty earlier. But the Beef CRC wants to take this research one step further and assess a range of fertility indicators.

The Male Indicators project will utilise comprehensive data from another Beef CRC Project called the “Lifetime Reproductive Performance” project, which is providing an exhaustive database of growth, reproductive and adaptive trait records that have been gathered on their dams.

Part of the challenge,Dr Holroyd said, is that there is still a degree of uncertainty in what makes some bulls produce more calves than others when mated in either single or multiple-sire groups.

“At best we can account for about 60 per cent of the factors relating to calf output in bulls in multiplesire herds; at worst 30 per cent,” Dr Holroyd said.

“And whether those factors are directly related to reproductive Beef CRC Researchers carrying out routine evaluation of bulls on Brigalow Research Station, Queensland performance of their female relatives is not known.”

lf predictor traits can be identified in bulls early in life, then selection for female fertility will become easier for beef producers...

So while Beef CRC researchers will be doing traditional assessments of bull fertility such as scrotal size, condition of penis and sheath and collecting semen to assess density, motility and percentage of normal sperm, their research brief also extends to the analysis of various biochemical markers found in blood, seminal fluid and semen and the relationships of all of these factors to improvement of female reproductive performance, which is the primary trait of interest to this project.

Not only will bulls be subjected to a breeding soundness examination at 12, 18 and 24 months of age, but Dr Holroyd said blood will also be collected from all bull calves prior to puberty.

“Blood samples will be used to assess whether hormones existing in these young animals give some indication of future reproductive performance - a step toward giving breeders a tool to assess bull performance well before the bull enters the breeding herd,” Dr Holroyd said.

Research to date has involved the collection of seminal fluid, semen and blood for the measurement of various biomarkers including luteinizing hormone (LH) and inhibin in pre-pubertal bulls and various proteins in seminal fluid and semen.

“These proteins may play an important role in fertilisation and early embryo development, independent of sperm morphology,” said Dr Holroyd.

“When we can determine all these genetic correlations, we have the possibility of a test or an index that will not only determine whether bulls are more likely to be being mechanically and reproductively sound, but also are able to sire male and female progeny that are more fertile,” said Dr Holroyd.

Dr Holroyd expects the Beef CRC Male Indicators project to offer important flowon benefits for industry.

“We may never again have the opportunity to examine the same number of bulls with their detailed reproductive histories,” he said. “So our attitude has been to ‘store and explore’ where blood, seminal fluid and semen from bulls at 12, 18 and 24 months of age has been frozen with the view of determining levels of various hormones and proteins in future.”

This research forms part of the Beef CRC Female Reproductive Performance Research Program which aims to deliver a $46.5 million value-add to the Australian beef industry per annum from 2012 via the development of a comprehensive genetic improvement package incorporating genomic and other animal breeding technologies for the genetic improvement of female reproductive performance in breeding cattle.