Residual feed intake as selection tool in South African Bonsmara cattle

Abstract

The largest expense in the beef industry is feed costs and decreasing feed intake without decreasing growth performance and avoiding an increase in mature weight, will decrease cost and thereby increase profits. Feed efficiency is therefore an important trait in the beef cattle industry. The Bonsmara breed was used as it is currently the breed with the highest participation in Phase C testing and has feed intake records. The most widely used measure of feed efficiency is feed conversion ratio (FCR), which is highly correlated with growth (ADG= -0.66 ± 0.04) and mature size (length = 0.58 ± 0.06; height= 0.41 ±0.06) and may increase the maintenance cost of the herd. Residual feed intake (RFI) is a linear trait and is the difference between actual feed intake and predicted feed intake required for the observed rate of gain and body weight. It has favourable genetic correlations with mature size (length = 0.01 ± 0.07; height = -0.05 ± 0.07) and feed intake (0.79 ± 0.03). The purpose of this study was to determine RFI’s association with traits of economic importance the effect on ranking of bulls when selecting for RFI instead of FCR or Kleiber ratio (KR). Data from centralised growth tests were analysed and found a h2 estimate for RFI of 0.27 ± 0.02, and genetic correlations of 0.65 ± 0.04 with FCR, 0.12 ± with KR, -0.08 ± 0.04 with scrotal circumference (SC), -0.01 ± 0.09 with weaning weight (WW) and 0.02 ± 0.07 with metabolic mid-weight (MMW). Spearman correlations were calculated and showed a difference in ranking of EBV’s for RFI and FCR (0.60), RFI and KR (0.18), and FCR and KR (-0.54). In this study, small contemporary groups posed a problem in the reliability of RFI. The genetic variation of RFI justifies its inclusion in a selection programme for the Bonsmara breed in South Africa, however, small contemporary groups, the possibly more favourable results that may be obtained through a selection index, and some concerns over the lack of association with growth rate requires further investigation before applying RFI selection in the industry.