The Effects of the F94L Myostatin Gene Mutation in Beef-X-Dairy Crossed Cattle on Muscle and Carcass Characteristics, Boxed Beef and Retail Yields, Steak Shape, and Palatability

Abstract

in the first study, producer live performance data and carcasses from steers (n=116) resulting from the mating of four Limousin/Angus sires heterozygous for the F94L myostatin mutation to Jersey/Holstein dams were utilized to evaluate the effects of one copy of the F94L allele on live performance, carcass traits and USDA grades, and boxed beef and retail yields. Slaughter data were collected at time of harvest and carcass data was collected 48 hours postmortem. One side of each carcass was fabricated into boxed beef and retail cuts by experienced lab personnel 5-8 days postmortem. One copy of the F94L allele did not affect gestation length, birth weight, percent unassisted births, feedlot average daily gain, live weight at harvest, hot carcass weight, or dressing percentage (P > 0.05). Fiber type analysis indicated that the increase in muscularity by the F94L allele in the semitendinosus and longissimus was likely due to hyperplasia as there was a 19% increase in the quantity of Type IIA and IIX fibers in the semitendinosus (P < 0.05) and no effect to the muscle fiber size (P > 0.05). Carcasses from steers with one F94L allele had larger ribeye areas (99.2 versus 92.3 sq.cm.), greater ribeye width: length ratios (0.498 versus 0.479), lower USDA yield grades (2.21 versus 2.66), and lower marbling scores (438 versus 480) (P < 0.05). Additionally, for boxed beef yields, one F94L allele (versus zero F94L alleles) increased (P < 0.05) 85/15 trimmings (+3.4 kg), top round (+1.50 kg), strip loin (+0.67 kg), eye round (+0.52 kg), tenderloin (+0.35), boneless foreshank (+0.33 kg), cap/wedge (+0.32 kg), and tri-tip (+0.22 kg) per animal. Overall, carcasses from steers with one F94L allele had greater boxed beef yield (+1.06%), boxed beef plus 85/15 trimmings yield (+1.65 %), and total retail cuts plus ground beef 85/15 yield (+1.78%) than carcasses from steers with zero F94L alleles (P < 0.05). One copy of the F94L allele utilized in beef ✕ dairy breeding system had no significant impact on live performance traits but resulted in lower marbling scores and increased muscularity as evidenced through larger, more symmetrical ribeyes, lower USDA yield grades, and higher carcass cutout yields (both boxed beef and retail yields).In the second study, carcasses from steers (n=57) resulting from the mating of two Limousin/Angus sires heterozygous for the F94L myostatin mutation to Jersey/Holstein dams were utilized to evaluate the effects of one copy of the F94L allele on striploin dimensionality, Warner-Bratzler shear force (WBS) and slice shear force (SSF), and sensory panel ratings. Following carcass fabrication, samples of longissimus (LD), psoas major (PM), gluteus medius (GM), semitendinosus (ST), serratus ventralis (SV), triceps brachii (TB), and biceps femoris (BF) muscles from carcasses were vacuum packaged, aged until 10 days postmortem, and frozen until processed into 2.54-cm-thick steaks for sensory and shear force analysis. Carcasses from steers (n=58) from two additional heterozygous F94L sires were identified at a commercial packing plant; strip loins were excised for sensory panel analysis and shear force measurements. Individual strip steaks were imaged at a fixed height on a gridded background and processed through image analysis software capable of measuring individual pixel size (Fiji Image J) for strip loin dimensionality. Frozen steaks allocated to both sensory and shear force analyses were thawed for 24 hours at 2°C to 0-4°C prior to cooking. Steaks were cooked at 204°C with 0% relative humidity until peak internal temperature of 69°C was reached then removed from the oven and rested until the internal temperature reached 71°C. Steak sensory attributes were identified and quantified by trained panelists using the lexicon developed by Adhikari et al. (2011). In strip steaks from carcasses with one F94L allele, longissimus muscle area was increased in steaks 4, 5, 7, 8, and 9 which resulted in less angular steaks from the center and posterior end of the strip loin (steaks 6-10) (P < 0.05). Of the seven muscles observed, there were no differences among the WBS or SSF regardless of carcasses F94L genotype (P > 0.05). LD and GM cooked steaks from carcasses with one copy of the F94L had no differences in sensory panel ratings compared to steaks from carcasses with no copies of the F94L allele (P > 0.05). ST cooked steaks from carcasses with one F94L rated lower in fat-like flavor compared to carcasses with no F94L allele (P = 0.0348). PM cooked steaks from carcasses with one F94L allele rated lower in juiciness, fat-like flavor, buttery flavor, and umami flavor compared to no copies of the F94L (P < 0.05). One copy of the F94L allele utilized in beef ✕ dairy cross steers decreased strip loin angularity and fat-like flavor attributes in the PM and ST while WBS and SSF measurements were not impacted. Use of F94L homozygous terminal beef sires would be an easily implemented strategy for dairy producers to improve steak portion size and shape in carcasses from non-replacement calves.