High energy supplement post-weaning does not enhance marbling in beef cattle

Objectives of this study were to l) determine whether high energy supplement during the immediate post-weaning period enhances marbling; 2) determine whether nutrition and genotype interact to affect intramuscular (IM) and subcutaneous (SC) fat; 3) obtain data and samples for detailed study of fat depot development. Weaner steers (n=l65) within three genotypes were studied. Targeted genotypes were high IM and high SC fat (Angus, A), low IM and high SC fat (Hereford, H) and high IM and lower SC fat (Wagyu x Angus, WA). From weaning, steers were fed pasture, or pasture plus high energy pellets (12.3 MJME/kgDM, 110 g CP/kgDM) at 1% liveweight (LW) for 168 d. Pasture-fed (P) and supplemented (S) steers were then backgrounded until feedlot entry at 18 month of age. Steers were then short (100 d) or long (250 d) feedlot fed. LW did not differ due to nutritional treatment at any stage. Base-line steers (n=15) were slaughtered at weaning, and groups slaughtered at end of nutritional treatments (n=30), prior to feedlot entry (n=30), and after short (n=30) and long (n=60) feedlotting. Genotype, Kill (1 to 5) and Post-weaning nutritional effects and interactions on carcass traits were assessed (at P<0.05) by analyses of variance, with initial LW as a covariate due to Angus being heavier. Hereford steers had more SC fat at the P8 site and less marbling than the other genotypes. Carcass weight, SC fat depths and marbling increased with kill number. Post-weaning supplement depressed Rib fat depth compared with forage only feeding. No interactions were evident. We conclude that post-weaning supplement did not enhance marbling and had a somewhat suppressive effect on SC fat. The genotypes had predicted marbling characteristics, although SC fat did not differ overall between A and WA. The phenotypic data will be used in detailed studies of fat depot development.