COMPREHENSIVE research on an Angus herd throughout the course of more than a decade has demonstrated producers need not be shy about seeking high muscling attributes in British-breed cows out of concerns it may hinder maternal productivity.
Despite perceptions held for years high muscling may compromise productivity in breeding cows, the research conducted by the NSW Department of Primary Industries (DPI) has demonstrated cattle with high muscling did not suffer productivity losses but were rather at an advantage given better saleyard returns for cattle with a higher muscle score.
NSW DPI livestock research officer at the Beef Industry Centre in Armidale Dr Linda Cafe, who headed up the past few years of the study, said the research was carried out on two DPI research stations - at Glen Innes and Grafton - using a predominantly Angus herd.
The herd started out with Hereford/Angus cross cows, which were bred back to Angus bulls for several generations.
Cows and bulls were selected for the low or high muscle lines based on visual assessment of live muscle score.
About 300 breeders were used for the research project, Dr Cafe said, although with dry conditions this year that had to be cut back to about 250.
The main aim behind this study, she said, was to see what advantages or disadvantages occurred with selection for increased muscling in the cow herd.
"Producers knew they wanted higher muscling in their progeny, but didn't want it in their cows given the perception it could affect maternal productivity," Dr Cafe said.
"The data we analysed was taken from 1998 through to 2012."
The study included low muscled cattle (with an average muscle score of D-) as well as high muscled cattle (with an average muscle score of C+).
The cattle were run under average grazing conditions for 10 years, from 1998 through to 2009, while from 2010 to 2012 the herd was tested under poor nutrition.
She said the study demonstrated - under the normal nutritional conditions - the higher muscled cows produced the same weight in their weaners each year as the lower muscled cows, which by extension demonstrated their fertility and milking comparable.
The higher muscled cows also produced higher muscling in their progeny, which offered producers a clear advantage in returns.
She said there was typically a premium of 20 cents a kilogram for each full muscle score increase.
"You can get the same turnoff weight with a higher muscle score."
And further, under poor lower nutritional conditions, while cow and weaner weights were lower, the low and high muscled cows still performed similarly to each other, demonstrating the high muscled cows, again, had similar maternal productivity but also the advantage of higher muscling, and therefore, higher returns.
The specific research data demonstrated under fair-to-good nutrition, there were minimal differences between the low- and high-muscled lines in the herd in terms of days to calving (low 310 days, high 308 days), calf birth weight (low 35.6kg, high 35.5kg) and calf wean weight (low 245kg, high 249kg).
And under low nutrition, while performance was reduced as expected, the results were still similar between the low-muscle and high-muscle lines, including days to calving (low 310 days, high 313 days), calf birth weight (low 32.7kg, high 33.4kg), and calf wean weight (low 175kg, high 171kg).
"The herd was pushed hard enough both lines reduced their calf-wean weight, but there was no difference in how the lines performed."
Results were also similar - on both good and lower nutrition - for live calving rate, weaning rate and the weights of calves weaned per cow joined per year.
These measures of maternal productivity showed little difference in performance between low and high-muscled cattle, Dr Cafe said.
And at the core are the price benefits producers receive for higher muscled cattle.
She said producers could take away practical implications from this study.
"They can certainly use high-muscled bulls over their cows and retain the well-muscled heifers without any detriment to their productivity, and therefore produce progeny with higher muscling and higher returns," she said.
As part of this study, the performance of the steer progeny of this herd was measured.
All steers in the herd, born in 2008 and 2009, were measured for their dressing percentage and retail meat yield.
"If you have more muscle in your animals, they have a higher dressing percentage, and they yield well" she said.
The study measured 230 steers which spent 100 days on grain at the Tullimba research feedlot, Kingstown, before being killed.
"In the carcases there wasn't any difference in fat between the low- and the high-muscled cattle, but the highs had increased retail beef yield," Dr Cafe said.
"Feed efficiency also improved with increased muscling."
"This study is the proof in the pudding that high muscling doesn't have a detrimental effect on the productivity of the cows, and there are also benefits to their progeny."
In her report on the study, Dr Cafe said the results demonstrated "the increase in muscling achieved by selection for visual muscle score in British-breed cows and bulls increased meat yield via increased muscle to bone rations of their progeny".
She said in the process of sourcing high muscled Angus bulls to use over the herd, she had seen changing perceptions among producers regarding high muscling and maternal productivity, with more recognising it didn't have a detrimental impact, as supported by this study.
"I think the study is very applicable to the industry, which is trying to be more efficient and better meet market specifications - and using cattle with higher muscling is a good way to achieve those things," Dr Cafe said.
Dr Cafe said being able to combine high muscling without a reduction in maternal performance was "a win-win".
An element of the project is continuing through to August, measuring the performance of the herd now they have returned to normal nutritional levels.
She said the cows ended their period of low nutrition at the weaning of the calves in 2013, with the study tracking the recovery of the cows through to weaning this year; the results are set to be supplied to Meat and Livestock Australia at the end of August.
The group is currently working on proposals for further research using the Angus herd to study both phenotypic and genetic questions around muscling.