Research examining female productivity in tropical beef breeds was now being carried out on cattle in the south, a University of New England researcher has told the Warrnambool Te Mania forum.
The university’s Animal Genetics and Breeding Unit’s Matt Wolcott told forum participants the work was part of the Tasman Beef Cow Profitability Program.
“We are in a unique situation of understanding the genetics of female productivity in tropical breeds, a lot better than we do for temperate genotypes,” Dr Wolcott said.
“As a result of this research, and the adoption of new descriptors of female reproductive performance arising from it, we are seeing the genetic trend for days to calving moving in a favourable direction for the Brahman breed.”
“A lot of this new project aims to exploit what we have learned in northern genotypes, to drive productivity and genetic progress for these female traits in the south.”
Therewas not the problem with weaning rates in temperate breeds, which could be observed in some tropical genotypes.
But it was important to describe female reproduction as accurately as possible, in genetic evaluations, as selection pressure was applied to improve other aspects of productivity, such as growth and marbling.
He told the forum genetic evaluation in Angus female reproduction was currently “a little bit tenuous.”
“The key trait we currently have to describe female reproduction is days to calving, a measure of the days from mating to calving (DTC),” he said.
“DTC records include a lot of noise.
“They include significant environmental factors and have a lot of components we can’t define in a genetic evaluation, which contributes to the relatively low heritability, of less than 10 per cent, we observe for DTC in Angus.”
But Dr Wolcott said DTC was not the only thing, providing information about reproduction in the genetic evaluations for temperate breeds.
“We have also got information coming from the bull side, in the form of scrotal circumference measurements, which can also provide some information about female reproductive performance.
“Scrotal circumference measures are most useful when collected as groups reach puberty,” he said.
“When that’s done it’s a moderately heritable trait, at about 40 per cent, and has a low, but favourable genetic relationship with days to calving.”
He said that based on research results from northern Australia, a promising alternative to DTC was ovarian scanning, using ultrasound to identify oestrus.
“The problem is that it is an extremely labor intensive process,” he said.
It involved scanning heifers, from weaning, every four to six weeks, “until we identify oestrus.”
The northern research had shown Brahmans were reaching puberty at an average of 750 days of age.
That meant that, for animals which were to be mated as two year olds, a significant proportion would fail to be pubertal at their maiden mating.
The southern trial aims to collect ovarian scanning data on 5000 Angus and Hereford females, over two and a half, to three years.
Females will be scanned for age of puberty, which was discovered to be highly heritable, in the 1000 Brahman females tested in the north.
“The industry, up there has really taken it on board, with individual breeders getting females in and scanning them, every month, to describe that trait,” he said.
“Scanning for ovarian function is giving us accurate information about age at puberty, and the resulting trait is significantly more heritable than DTC.
“This presents the opportunity to achieve rates of genetic progress for female reproduction which would have been difficult in an evaluation where days to calving was the only direct measure of female reproductive performance.
He said the study would also look at cow size and body composition, “how they are able to maintain themselves, through pregnancy and lactation.”
“Phenotypically we are seeing a very clear relationship of cows which are more successful reproductively, having on average lower weight, fat and body condition.
“At the genetic level, however, these relationships are consistently low.
“Fatter cows, genetically, are not performing better reproductively - in fact for every class of female reproductive performance, the entire spectrum of body composition genetics are represented.”
A key result from this research was that body condition in lactating females and reproduction could be improved simultaneously by selection if both traits were measured and included in the genetic evaluation.
He said it was important for breeders to have a good description of reproductive performance in their genetic evaluation as they pushed for rapid improvement in growth, marbling and other economically important traits.
“If you are not measuring it, you just don’t know, until you have a problem, and having a problem with reproduction, is one that costs you, in a big way.”
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