Location: Meat Safety and Quality
2018 Annual Report
Objectives
Objective 1: Develop strategies to manage and improve variation in meat quality, composition, and healthfulness traits.
Sub-objective 1.A: Identification of genetic markers for myoglobin content of pork muscles to increase redness of pork products.
Sub-objective 1.B: Estimate effects of three maternal lines and two mating systems on lamb carcass merit.
Sub-objective 1.C: Genomic control of dark cutting and other beef quality traits.
Sub-objective 1.D: Genomic control of pork fat quality and fatty acid profile.
Sub-objective 1.E: Identify and validate novel single-nucleotide polymorphisms (SNP) for beef lean color stability.
Sub-objective 1.F: Determine the effect of VQG' pork loin grading camera tenderness class on optimal aging time of boneless pork loins.
Sub-objective 1.G: Impact of backgrounding strategies on beef carcass merit.
Sub-objective 1.H: To determine the effects of replacing tylosin phosphate (Tylan®) with an essential oil containing limonene in the diet of finishing beef cattle on carcass characteristics.
Objective 2: Characterize biological variation in meat quality, composition, and healthfulness traits.
Sub-objective 2.A: Determine the impact of sire line on the meat quality defect characterized by a band of very pale, almost white, muscle tissue on the superficial portion of ham muscles (halo).
Sub-objective 2.B: Characterize the effect of muscle metabolic efficiency, particularly in mitochondrial efficiency on beef tenderness and lean color stability attributes across varying pH classes in beef carcasses exhibiting normal lean color.
Sub-objective 2.C: Determine if there are metabolomic differences between tender and tough beef across postmortem aging times.
Sub-objective 2.D: Identification of differentially expressed proteins in beef longissimus steaks classified as tender with stable lean color during simulated retail display compared to steaks classified as tough with labile lean color during simulated retail display.
Sub-objective 2.E: Develop technologies for measuring and predicting important traits relating to meat product quality and consistency and the biological mechanisms that control these traits.
Approach
The overall goal of this project is to develop approaches to improve quality and healthfulness while reducing the variation in meat products. This will be accomplished by providing the red meat industries with the information and tools necessary to facilitate equitable valuation of carcasses and meat, improve the quality and consistency of meat, and optimize carcass and meat composition of beef, pork, and lamb. The two objectives of this project address needs in improving consistency of quality, composition, and healthfulness of red meat products by developing strategies and instrumentation to manage and improve these traits using basic and applied research approaches. Genetic and genomic strategies will be developed that may be combined with animal and meat management strategies to optimize quality and composition traits. Research will be conducted using proteomics and other biochemical tools to characterize variation in quality and composition as well as to evaluate and facilitate implementation of instrumentation for measuring or predicting value determining traits such as carcass grade traits, tenderness, lean color stability, and fat quality.
Progress Report
Objective 1. In order to evaluate various lamb production systems, lambs (n = 1,237) were produced by a multi-sire mating of three maternal lines (Katahdin, Polypay, and Easycare) in two mating systems: a purebred mating, system in which each maternal line was mated with rams of the same genetic line, and a terminal mating system, in which ewes were mated with Texel rams. Lambs (2,279) produced in the 2016 and 2017 lamb crops of a large sheep breeding project were harvested at a large-scale commercial packing plant that uses the VSS 2000 lamb carcass imaging system to evaluate each carcass as the hot carcasses move from the harvest floor to the chiller. The increased prolificacy of Easycare ewes relative to Polypay and Katahdin, in the low-input production system, offset the reduction in growthiness and leanness of Easycare as more pounds of carcass was produced per ewe exposed for breeding for Easycare than Polypay and Katahdin. Use of Texel rams in a terminal mating system improved growthiness, carcass leanness and carcass conformation of lambs from Easycare ewes; however, complementarity of sire breed for other growth and carcass traits should be investigated further.
Using genomics to study pork fat quality, a mutation was discovered that affects the level of desaturation of fatty acids in pork fat. On-going work is being conducted to determine if other polymorphisms in the gene discovered in this work are more strongly related to the level of desaturation. This work should allow the swine industry to select for decreased desaturation, which will result in higher quality bellies that yield more, high-quality bacon.
A large-scale project was conducted collaboratively with the University of Illinois and Kansas State University to determine the effect of increased carcass weights on pork quality. The heaviest group of carcasses weighed 36% more than industry average and represent the expected carcass weight after 35 years of genetic selection. Despite the increased carcass weight, there were little differences in pork quality, although, slice shear force, an objective measure of tenderness, was improved with increased carcass weight.
We continued ongoing work to study the effect of backgrounding steers on fall cover crop on beef carcass quality. Relative to steers backgrounded on oats, steers backgrounded on oats + rape produced carcasses were heavier and more highly-marbled.
The pork industry has identified that increasing color scores (more red) as an industry-wide goal. Most efforts in this area have addressed management of muscle pH. However, the amount of pigment present in muscle is an important driver of lean color, particularly redness. Moreover, increasing myoglobin (pigment) content in ham muscles may mitigate the Halo color defect. Thus, we conducted a genomic study for pork longissimus myoglobin content. These efforts included quantifying myoglobin content and pH in 600 pork loin samples and extracting DNA on those samples. The resulting analysis identified two quantitative trait loci for myoglobin content of pork longissimus muscle. The most highly associated QTL was located in the calcineurin gene which is associated with shifts in muscle fiber type.
Objective 2. Cured ham color is of great importance in meeting consumer expectations for ham products. Recently a condition has been identified by the meat industry where a band of very pale lean tissue is present on the outside portion of ham muscles. This pale tissue does not produce normal cured color when the muscles are processed into ham products. We began working with pork processors and ham processors to quantify and characterize the phenomenon. Current results indicate the condition occurs in the vast majority of pigs regardless of production system and management and the pale portion of the muscle is higher in muscle pH and much lower in myoglobin concentration. These differences coincide with a significant shift in muscle fiber type towards white (glycolytic) fibers. Ongoing efforts include collaboration with a large pork processor to evaluate differing genetic lines on the incidence and severity of the condition. Moreover, the genomic study to identify genetic markers associated with myoglobin content may provide a strategy to mitigate the defect. We continued ongoing efforts to improve instrument grading with the beef grading camera. Implementation of the GigE upgrade to the beef grading camera resulted in a shift in beef grade distributions. At the request of USDA-AMS and beef industry leaders, we participated in a large-scale study to determine how the GigE camera should be adjusted. After several rounds of data collection and adjustment calculations, the GigE grading cameras were in line with expected results.
Accomplishments
1. Identified genes associated with lean color stability in beef striploin steaks. Beef lean color is a primary determinant of consumer purchasing decisions. Cuts produced from the carcasses of some animals do not possess sufficient color life for commercial case-ready programs. USDA-ARS scientists at Clay Center, Nebraska evaluated lean color stability on steaks from a large population of cattle representing the 18 most prevalent breeds in the U.S. beef herd. An analysis of the genome of these cattle identified 417 genes associated with variation in lean color stability. These genes indicate the importance of energy metabolism, which suggest mechanisms requiring further investigation. Follow-up efforts include additional DNA sequencing to identify the specific gene alterations with the greatest effects on color as well as investigating protein and metabolite profiles to further understand the role of these genes in regulating lean color stability.
2. Identified a gene alteration that reduces dark-cutting lean beef. Dark cutting beef results in an annual loss of potential revenue for the U.S. beef industry in excess of $70 million. Dark cutting beef has long been understood to be caused by the animal having a negative energy balance before slaughter, which results in depletion of the animals muscle energy stores. However, it was not understood why a group of cattle could all be exposed to identical conditions resulting in some carcasses exhibiting the dark-cutting condition and others exhibiting “normal”, bright, cherry-red lean color. ARS scientists at Clay Center, Nebraska discovered a naturally-occurring genetic mutation in cattle that decreases the susceptibility of cattle to the dark-cutting condition. The mutation discovered in this work helps to account for much of the unexplained variation in susceptibility to dark cutting. The genetically-conserved sequence is highly-conserved across all mammals and increases susceptibility to the dark-cutting condition. Thus, the mutant, which appears to have originated in British breeds of cattle, confers the desired bright, cherry-red lean. The frequency of the favorable allele ranges from 0 to 0.7 in beef breeds and the frequency of the favorable allele is very low in Holstein steers, which are the primary source of dairy beef. Selection for the favorable allele in this gene should significantly reduce the costly occurrence of dark-cutting beef.
Review Publications
King, D.A., Shackelford, S.D., Schnell, T., Pierce, L., Wheeler, T.L. 2018. Characterizing the ham halo condition: A color defect in fresh pork biceps femoris muscle. Meat and Muscle Biology. 2(1):205-213. https://doi.org/10.22175/mmb2018.02.0001.
Cross, A.J., King, D.A., Shackelford, S.D., Wheeler, T.L., Nonneman, D.J., Keel, B.N., Rohrer, G.A. 2018. Genome-wide association of myoglobin concentrations in pork loins. Meat and Muscle Biology. 2(1):189-196. https://doi.org/10.22175/mmb2017.08.0042.
