Postweaning substitution of grazed forage with a high-energy concentrate has variable long-term effects on subcutaneous fat and marbling in Bos taurus genotypes1

Abstract

ABSTRACT:The objective of this study was to quantify the effects and interactions of stage of growth and genotype on commercial carcass traits and intramuscular fat (IMF) content in 5 muscles of Bos taurus steers (n = 165) and to test the hypothesis that substituting pasture with a high-energy concentrate during the immediate postweaning period increases IMF. Cattle of 3 genotypes (Angus, Hereford, and Wagyu × Angus; n = 55/genotype) were selected at weaning from commercial herds, targeting genotypic differences in marbling and subcutaneous fatness. Following weaning, steers were fed for 168 d within 2 different improved, temperate pasture-based nutritional systems: a forage-only system (FS) and forage with high-energy supplemented system (SS), with 2 replicates per system. The supplement was fed at a level of 1% of average BW adjusted every 2 wk to provide an estimated 50% of energy requirements for 168 d from weaning. Pasture on offer in both systems was managed to match the BW of the FS and SS steers during the postweaning treatment period to avoid confounding due to differences in growth rate during this period. Steers were then regrouped into 2 replicates and backgrounded on improved, temperate pasture for 158 d and then grain fed within 1 group for 105 d (short fed) or 259 d (long fed). Groups were slaughtered at commencement (d 0) and end of postweaning nutritional treatments (d 168), end of backgrounding (d 326), and after short (d 431) or long feedlotting (d 585). Serial slaughter stage had an effect on all traits assessed (P < 0.01). The FS steers had more rib fat (P < 0.01) and higher Meat Standards Australia marbling score (P < 0.05) and a tendency (P < 0.10) to have greater eye muscle area than the SS steers throughout the study. Genotypic differences were evident (P < 0.05) for all traits assessed except HCW, dressing percentage, rib fat depth, ossification score, ultimate pH, and IMF in the semitendinosus muscle. The results for marbling and IMF do not support the use of a high-energy feed as a substitute for an equivalent amount of energy from pasture during the immediate postweaning period to enhance development of marbling.

Gene expression identifies metabolic and functional differences between intramuscular and subcutaneous adipocytes in cattle

“…The basic experimental details relating to this animal trial have been previously reported [12]. In brief we studied 15 individual 259 day grain fed Angus, Hereford and Wagyu x Angus steers (n = 5 per breed) slaughtered at~26 months of age as part of the larger experiment detailed by [12]. Management was standardised for all individuals during growth on pasture from weaning through long-feedlotting.…”

“…Management was standardised for all individuals during growth on pasture from weaning through long-feedlotting. For the transcriptome analysis of the fat depots we focussed on animals' pasture-fed only during the immediate post-weaning period, rather than animals that received supplement during the immediate post-weaning period [12].…”

“…In terms of differential metabolism between depots, previous biochemical evidence points to IMF having relatively slow rates of lipogenesis in both cattle [9] and pigs [10] and under certain nutritional circumstances a substrate preference for glucose carbon over acetate when compared to SC [6,11]. Post-weaning diets tailored to these specific metabolic properties of IMF, such as strategic feeding with high energy concentrate, have had mixed success [12] for reasons not certain but which probably include net energy available for tissue deposition. A recent review emphasises castration, digestion and absorption of feed, glucose availability and vitamin A, D and C levels as important factors in marbling development [13].…”

“…Here, we analyse data from 5 bovine fat depots (IMF, SC, intermuscular, kidney and omental), with a particular focus on the IMF versus SC depot comparison. These functional genomic data are one component of a much larger animal experiment exploring cattle genotype by nutritional effects on fat depot biology [12]. Tissue samples for the present study were taken from 26 month-old steers of 3 genotypes, Angus, Hereford and Wagyu x Angus following high energy nutrition in a feedlot for 259 days.…”

Gene expression identifies metabolic and functional differences between intramuscular and subcutaneous adipocytes in cattle

“…Of particular interest was an indication of very elevated activity of the cholesterol 25 hydroxylase enzyme in the IMF depot. A suite of oxysterol metabolites were quantitated in plasma using mass spectrometry and appear to be promising circulating biomarkers for whole carcass IMF content.MethodsBeef CRCIII marbling and fat distribution experimentThe basic experimental details relating to this animal trial have been previously reported[12]. In brief we studied 15 individual 259 day grain fed Angus, Hereford and Wagyu x Angus steers (n = 5 per breed) slaughtered at ~26 months of age as part of the larger experiment detailed by[12].…”