THE real challenge for northern Australia's cattle producers looking to boost the genetics to improve their whole herd profitability is just where to source better bulls every year that carry the much-needed female reproductive traits.
Addressing this month's Beef Australia International Genetics Conference, Dr David Johnston told the gathering of Australia-wide and international delegates that the 10 year Beef CRC research effort was well on the way to identifying new female reproductive traits that can be measured by seed stock producers.
Dr Johnston, a principal scientist with the Animal Genetics and Breeding Unit of the University of New England, said the comprehensive study of 2200 Brahman and tropical breed composite females representing the progeny of 50 sires had recorded the full reproductive history of these cows across six breeding seasons.
"We used ovarian ultrasound scanning for the first time as a means of determining when the heifers ovulated which provided an accurate measure of the age of puberty," Dr Johnston said.
"The research also reviewed the lactation anoestrous interval where it revealed that 50 per cent of first calf Brahman females did not resume the breeding cycle until the calf was weaned. That lactation anoestrous is less evident in the tropical breed composites."
Dr Johnston said that from 356,000 individual female recordings to measure age of heifer puberty and cow reproductive performance, researchers can now say these are heritable traits which were under considerable genetic control.
Both these genetic traits carried significant variation so by including age of puberty and lactation anoestrous into the selection criteria, cattle producers could achieve higher lifetime female reproduction within their herds. In general, early puberty genetics (particularly in Brahmans) translates to high pregnancy rates while short lactation anoestrous genetics delivers high lifetime reproduction.
Dr Johnston said that to improve northern Australia's cattle industry weaning rates which were currently below 50 per cent, cattle producers must to make better use of superior genetics – not just cull non-breeders.
"To improve lifetime reproduction, seed stock producers will have to incorporate these female measures into well-balanced EBVs (Estimated Breeding Values) to select the better bulls," he said.
The research showed that the industry can improve northern Australia's weaning rates through selection.
In a review of the genetics of male reproductive traits in tropical beef cattle, cattle geneticist Dr Brian Burns, a Rockhampton-based senior research fellow, said that prior to the CRC fertility research for tropical cattle in northern Australia, there was little information available with the exception of scrotal size measurement.
From 2004 to 2010, a CRC project has measured 109 traits involving 3500 Brahman and tropical breed composite progeny representing 136 sires. Recordings from birth to 24 months included each animal's weight, scrotal size, blood hormones and soundness evaluation.
Dr Burns said it was now possible to identify a number of new male traits that were heritable. It was the variation within these hertitable traits that could pave the way for future genetic gains.
"The bull selection effort needs to be placed on scrotal circumference in combination with the analysis of the percentage of normal sperm," Dr Burns said.
"We know we can select for semen quality traits without detriment to productive traits.
"The way forward is for seed stock producers to combine the traditional EBV bull selection criteria with the newly identified traits to ultimately improve the fertility of their daughters," Dr Burns said.