3 October 2011

5 minute read

Beef CRC researchers have meticulously tracked a thousand Brahman females and 1100 Tropical Composite females, derived from about 100 sires, across six joinings in as many years. The findings of this huge undertaking, the Northern Female Lifetime Reproduction project, will be delivered to the northern beef industry by June 2012.

Already, though, some game-changing knowledge has emerged. Wayne Upton, a breeding specialist who manages the extension side of the project, said an early finding is that the north’s low calving rates can be lifted by re-thinking genetic selection processes.

There are very good reasons for the north’s calving rates to be considerably lower than in the south, Mr Upton observes, not least survival. In the harsh conditions of the rangelands, the energy needed to conceive and maintain a cow and calf through to weaning may not always be available.

Brahman reproduction patterns

Brahman cattle excel in this environment because they can allocate energy towards survival and adaptation to environmental stressors more efficiently than their Bostaurus counterparts. A consequence is that often, Brahman cows will not conceive with a calf at foot—an evolutionary adaptation that gives more importance to the survival of the cow-calf unit than the annual production of a calf.

But what if it’s possible for a cow to produce a calf every year, and survive?

One of the clear messages of the Beef CRC project is that this is achievable. Across the four northern properties running the project’s cattle, almost all cows that conceived every year over the six joinings survived and were retained in the breeding herds.

Nutrition + genetics = better conception rates

Nutrition plays a big role, Mr Upton says, but the Beef CRC has demonstrated that an investment in better nutrition to lift conception rates should be matched by an investment in genetics to properly capitalise on the nutrition.

Female fertility—the number of calves a cow can produce in her lifetime—hinges on two genetic factors: the age at which a heifer will first conceive, and how soon after one calf she will be ready to conceive another.

Beef CRC researchers have found that across the sire groups used in the lifetime reproduction project, different Brahman sires will produce heifers that differ by up to 150 days in the age at which they reach puberty and are ready to conceive. The spread in age at puberty in the Tropical Composite heifers is about 100 days.

Identifying sire lines for improved fecundity

When researchers looked at the sire influence on how soon cows would begin cycling after their first calf, they found a 130 day difference between the best and worst Brahman sires. The heifers in the worst sire lines do not begin cycling again soon enough to produce a calf in a twelve month cycle. Half the Brahman cows in the project did not cycle while they had a calf at foot.

“There lies one of the north’s fertility problems,” Mr Upton says. “On the positive side though, there is also the 50 per cent of Brahman females who will cycle with a calf at foot—and there is a very big genetic component in that.”

“So if producers can identify sire lines whose female progeny will re-conceive while they have their first calf at foot without compromising their own survival or the survival of the calf at foot, they are going to change the profitability of their herd. These females have jumped two hurdles: they have been pubertal when they were put into the breeding herd for the first time, and they have reconceived in their second joining period. Heifers who are not pubertal when they enter the breeding herds conceive much later in the breeding season, and most only have a calf every two years. Those females capable of producing a calf every year, year after year within 12 months are extremely valuable animals.”

Value for seedstock producers

For this knowledge to influence northern herd profitability, it needs to be used by seedstock producers. The researchers are identifying fertile cows through ovarian scanning and other high-cost, labour intensive methods. But Mr Upton says seedstock producers have a much cheaper tool at their disposal.

“The BREEDPLAN EBV for ‘days to calving’ is highly correlated with these expensive measures. It’s not going to give the accuracy that can be achieved if heifers are scanned for these traits, but the days to calving EBV has enough accuracy to bring about significant change in northern herds.”

At the moment, few northern seedstock producers record ‘days to calving’ data. “This CRC research suggests that a culture change is needed. There’s a tool that’s ready to go, and it’s relatively simple. The breeder just has to record the day the bull goes into the paddock, the calving date and the disposal date of any cows that failed to conceive.”

Genetic traits for bulls

The seedstock industry can also take immediate advantage of research that has found the potency of bulls is associated with indicator traits like scrotal size and semen production. This can be readily measured through a bull breeding soundness evaluation (BBSE), which is performed by a vet and produces data that can be recorded in BREEDPLAN.

“If a commercial producer wants to take advantage of these genetic differences—and they can make a massive difference to a herd—then he needs to be putting pressure on his bull breeder to record days to calving and do a BBSE.”

Mr Upton says there are already herds that have used this technology, “and made massive strides”. A more detailed picture of female fertility will emerge by the end of the project, with cycling performance mapped against the physical characteristics of highly fertile cows.

Some cows make enormous sacrifices to rear a calf, Mr Upton says: in some cases, losses of up to 25-30 square centimetres of eye muscle have been recorded in lactating cows. The factors that push some lactating cows to the brink of survival but allow others to flourish are now emerging from the data.