Steer growth and feed efficiency on pasture are favourably associated with genetic variation in sire net feed intake

Abstract

In 1995 and 1997, growth, feed intake and feed efficiency were measured from spring to summer on Angus and Hereford weaner steer progeny of sires with known estimated breeding values for net feed intake (EBV_NFI). Each year, the steers were grown on 3 different pasture systems and pasture intakes were measured twice using the alkane technique. Final data analysed consisted of 77 and 50 records for steers from Years 1 and 2, respectively. They were the progeny of 42 sires (23 Hereford; 19 Angus), 3 sires having progeny in both years. Significant (P<0.05) regression coefficients for steer performance traits against sire EBVNFI indicated that genetic variation in NFI was associated with phenotypic variation in steer performance on pasture. Initial and final liveweight of the steers, and feed intake, were not associated with variation in sire EBV_NFI (P>0.05). However, daily gain by the steers tended (P<0.1) toward a favourable negative association with sire EBV_NFI (-0.16 ± 0.10 (s.e.) kg/day per kg EBV_NFI). Net feed intake and feed conversion ratio (FCR) had positive associations with sire EBV_NFI (NFI, 2.2 ± 1.2 kg/day per kg EBV_NFI; FCR, 4.2 ± 2.0 kg/kg per kg EBV_NFI; P<0.05). The results show that 1 kg/day lower EBV_NFI of a sire produced steer progeny that grew 19% faster, with no increase in feed eaten, had a 26% lower NFI, and a 41% better FCR.