5 December 2010

3 minute read

Selection for improved feed efficiency will not have any unfavourable repercussions for carcass traits. And, if anything, selection for improved feed efficiency – lower feed conversion ratio (FCR) and lower residual feed intake (RFI) – will result in larger, leaner carcases with better conformation.

Some good news for beef producers from Teagasc’s John Crowley, who led a study to quantify the genetic relationship between feed efficiency (FE) and three carcase traits, carcase fat (CF), carcase conformation (CC) and carcase weight (CW), in Irish beef cattle.

“Feed is the largest variable cost on farms and there is much interest in selecting for improved feed efficiency. But prior to recommending selection on any trait, the expected response to selection on other economically important traits needs to be quantified,” he explained to delegates at this year’s British Society of Animal Science’s annual conference, held at Queen’s University, Belfast.

Data for this analysis originated from two separate sources. The first data set consisted of feed intake (FI) and bodyweight (BW) records collected at the Irish bull performance test station. Different measures of FE were subsequently calculated.

The second dataset consisted of information on CC, CF and CW on 2,566,969 animals slaughtered in 30 abattoirs in Ireland during 2005, 2006, 2007 and 2008. In the present study, the EUROP classification grades were transformed to a 15-point linear scale with a carcass fat score of 1 implying low fat coverage and a carcase conformation score of 1 implying poor conformation.

Only males slaughtered between 300 and 1,200 days of age and females slaughtered between 300 and 875 days of age were retained. And only animals with Aberdeen Angus (AA), Belgian Blue (BB), Charolais (CH), Friesian (FR), Hereford (HE), Holstein (HO), Limousin (LM) and Simmental (SI) breed fractions were retained leaving 822,763 records. Also animals where less than 75 per cent of their breed fraction was known were discarded. And carcass weights of less than 150 kg and greater than 550 kg were also omitted.

“And we found absolute genetic correlations between the performance test measures, excluding FE traits, and the three carcase traits ranged from 0.004 to 0.33,” said Mr Crowley.

Although standard errors were large, ranging from 0.10 to 0.16, they were considerably smaller than other studies with similar objectives. And most of the genetic correlations with performance traits estimated in this study were not more than two standard errors from zero with the exception of the correlation between CF and BW, so selection for increased BW is expected to have a negative effect on CF.

“With regard to the feed efficiency traits, CC and CW were both negatively correlated with FCR and this suggests that selection for improved, or lower, FCR will improve both CC and CW,” explained Mr Crowley.

“Furthermore, CF and RFI were correlated indicating that selection for improved, or lower, RFI will yield leaner carcases.”

He also stressed that the standard errors of the genetic correlations were large similar to previous studies, attributable mainly to the relatively small datasets for the FE variables.

“Therefore, there may be merit in pooling data from international sources to increase the dataset size and potentially generate more precise estimates of genetic parameters,” he added.