Effects of backgrounding and finishing growth rates on P8 fat and intramuscular fat in Bos taurus steers.

摘要

The present study investigates the effects of backgrounding and finishing growth rates of Bos taurus steers grown out on three post-weaning growth pathways, across 4 years (1995-1998) on fat deposition. Scanned P8 fat at backgrounding exit (SP8_exit), scanned P8 fat before slaughter (SP8_sla) and carcass intramuscular fat (IMF, %) were evaluated. Four equations to predict SP8_sla and four equations to predict carcass IMF across years were developed. Three post-weaning growth pathways (GPs) generated by different nutritional treatments across years were used in the study. Growth pathways were created by backgrounding steers on pasture with no supplementation (GP1), pasture plus supplementary feeding formulated pellets (GP2) or pasture with access to a forage crop (GP3). The steers were then finished in a feedlot or on pasture to slaughter weights of 520 kg (Korean market specification) or 600 kg (Japanese market specification). Cubic smoothing splines were fitted to the liveweight of all animals from the start of backgrounding until slaughter. Backgrounding growth rates were interpolated off the GP curves and the mean average daily gain (ADG, kg/day) at Day 100 (D100, Days 100-91 before relocation to the finishing phase), and Day 150 (D150, Days 150-141 before relocation to the finishing phase) were calculated. Significant (P<0.01) differences between SP8_exit and backgrounding ADG (BADG) were detected in all years except GP2 v. GP3 in 1997. GP1 steers had the lowest BADG across all years, ranging from 0.39 to 0.88 kg/day. At backgrounding exit, the mean SP8exit for the different GPs was ranked, with GP1 < GP3 for all years, with significant (P<0.01) differences among GP1, GP2 and GP3 in all years except 1996. At the end of finishing, the mean carcass IMF over all years and finish (pasture and feedlot) (P<0.05) was 4.71% for GP1 v. 5.09% for GP3 for Korean market steers and the mean SP8_sla (P<0.01) was 14.59 mm for GP1 v. 16.04 mm for GP3 and the mean carcass IMF (P<0.01) was 5.54% for GP1 v. 6.27% for GP3 for Japanese market steers. The residual correlation of the multivariate response variables, namely, D100, D150 and BADG v. SP8_exit (n=1054), SP8_sla (n=1049) and carcass IMF (n=1002), indicated that the highest correlations, all significant (P<0.01), were 0.33, 0.20 and 0.12 for BADG v. SP8_exit, SP8_sla and carcass IMF, respectively. The residual variances (mm2) of the four SP8_sla equations were 6.14, 7.44, 8.72 and 10.73 for 1995, 1996, 1997 and 1998, respectively, and the residual variances (%2) for the four carcass IMF equations were 2.51, 2.26, 1.75 and 0.84, for 1995, 1996, 1997 and 1998, respectively.Digital Object Identifier http://dx.doi.org/10.1071/AN11184