|ROLFE, KELSEY - University Of Nebraska|
|NIELSEN, MERLYN - University Of Nebraska|
|FERRELL, CALVIN - Retired ARS Employee|
|JENKINS, THOMAS - Retired ARS Employee|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/18/2011
Publication Date: 11/1/2011
Citation: Rolfe, K.M., Snelling, W.M., Nielsen, M.K., Freetly, H.C., Ferrell, C.L., Jenkins, T.G. 2011. Genetic and phenotypic parameter estimates for feed intake and other traits in growing beef cattle, and opportunities for selection. Journal of Animal Science. 89:3452-3459.
Interpretive Summary: Feed intake is an important cost factor for beef production but it is also expensive to measure and use for selection. This research was undertaken to study the genetic and phenotypic relationships between measures of feed intake and cattle growth. In addition, a measure of temperament (flight speed) was evaluated as a predictor of feed intake variation. Individual feed intake and weight gain of steers representing two-, three- and four-breed crosses of seven beef breeds (Angus, Charolais, Gelbvieh, Hereford, Limousin, Red Angus, and Simmental) were measured during the finishing period prior to harvest. Relationships with feed efficiency expressed as residual feed intake (RFI, intake adjusted for weight and gain) were also evaluated. Feed intake, and thus feed costs, can be reduced through selection. Given that gain and feed intake are positively correlated, selection that places positive emphasis on growth in addition to negative emphasis on feed intake is most promising to yield economic results. An index composed of gain and RFI gave the best economic outcome. In growing steers of the age and weight range studies here, no advantage was found for explaining feed intake variation by adjusting for body fatness. Even though heritability was moderate for our measure of temperament (flight speed), it was not helpful as an indicator of feed intake. Finally, and perhaps surprisingly, neither breed differences nor heterosis was a large source for explaining variation in growth and feed intake in this data set.
Technical Abstract: Growth, feed intake, and temperament indicator data, collected over 5 yr on a total of 1,141 to 1,183 mixed-breed steers, were used to estimate genetic and phenotypic parameters. All steers had a portion of either Hereford or Angus or both plus varying percentages also of Simmental, Charolais, Limousin, Gelbvieh, Red Angus and MARC III composite. Because the steers were slaughtered on various dates each year and thus the animals varied in days on feed, weight and feed data were adjusted to a 140-d feeding period basis. Adjustment of measures of feed efficiency (gain:feed, G:F or residual feed intake, RFI, intake adjusted for metabolic body size and gain) for body fatness recorded at harvest had little effect on results of analyses. Average daily gain was less heritable (0.26) than mid-test body weight (MBW; 0.35). Measures of feed intake had greater estimates of heritability with 140-d dry matter intake (DMI) at 0.40 and RFI at 0.52; heritability estimate for G:F was 0.27. Flight speed (FS) was the only indicator of temperament studied; estimated heritability of FS was 0.34 and repeatability was 0.63. As expected, strong genetic (0.86) correlation was estimated between ADG and MBW; genetic correlations were less strong between DMI and ADG or MBW (0.56 and 0.71). Residual feed intake and DMI had a genetic correlation of 0.66. Indexes for phenotypic RFI and genotypically restricted RFI (no correlation with gain) were compared to simple economic indexes incorporating feed intake and growth to elucidate expected selection responses under different criteria. In general, few breed differences were detected across the various measurements. Heterosis contributed to greater DMI, RFI, and MBW, but it did not significantly affect ADG, G:F or FS. Balancing output (growth) with input costs (feed) is needed in practicing selection, and FS would not be recommended as an indicator trait for selection to change feed efficiency. An index including gain and RFI produced the best economic outcome.