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

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

The Kink Turn, a Key Architectural Element in RNA Structure

AbstractKink turns (k-turns) are widespread structural elements that introduce an axial bend into duplex RNA with an included angle of 50°. These mediate key tertiary interactions and bind specific proteins including members of the L7Ae family. The standard k-turn comprises a three-nucleotide bulge followed by G·A and A·G pairs. The RNA kinks by an association of the two minor grooves, stabilized by the formation of a number of key cross-strand hydrogen bonds mostly involving the adenine bases of the G·A and A·G pairs. The k-turns may be divided into two conformational classes, depending on the receptor for one of these hydrogen bonds. k-turns become folded by one of three different processes. Some, but not all, k-turns become folded in the presence of metal ions. Whether or not a given k-turn is folded under these conditions is determined by its sequence. We present a set of rules for the prediction of folding properties and the structure adopted on local sequence

Intramuscular fat levels in sheep muscle during growth

A 5 × 4 factorial experiment was designed in which lambs representing five genotypes were slaughtered at four ages (110, 236, 412 and 662 days of age). The genotypes represented were Poll Dorset growth × Border Leicester Merino, Poll Dorset growth × Merino, Poll Dorset muscling × Merino, Merino × Merino and Border Leicester × Merino. Both sexes (ewes and wethers) were represented for each genotype and slaughter age combination. In total, 595 animals were slaughtered and the carcass composition and intramuscular fat were measured. Carcass composition [fat, ash and protein (lean)] was determined by dual energy X-ray absorptiometry, with the intramuscular fat percentage determined using near-infrared spectroscopy following removal and weighing of the entire longissimus thoracis et lumborum (LL) muscle. Analysis revealed that the proportion of intramusular fat in the loin relative to total carcass fat decreases as animals mature, thus indicating that intramusular fat deposition occurs early in the maturation of sheep. Furthermore, as animals became heavier and older the accretion rate of intramuscular fat in the LL muscle slowed down. Both genotype (P < 0.05) and sex (P < 0.001) were found to impact on this pattern, with Border Leicester × Merino animals exhibiting the largest increase in intramuscular fat proportion in the LL muscle (4.92 and 5.50% at 22 months of age for ewes and wethers, respectively). The Poll Dorset growth × Border Leicester Merino animals were found to have the greatest absolute levels of intramuscular fat in the whole LL muscle (80.95 and 97.60 g at maturity for ewes and wethers, respectively). The amount of intramuscular fat significantly increased as the sheep became older and fatter; however, these differences were quantitatively small. As such, finishing prime lambs to high levels of total carcass fatness would have little effect on any eating quality benefits associated with increased intramuscular fat proportion

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