Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: May 25, 1995
Publication Date: N/A
Technical Abstract: Proportions of animals in yield and quality grade classes, weights of carcasses in those classes, and the proportion of animals that are below minimum and above maximum weights characterize many beef carcass valuation schemes. A primary determinant of quality grade in fed cattle is marbling score. The distribution of marbling scores when converted to the usual numerical values is skewed (mode is less than mean) and kurtotic (more peaked than a normal distribution). The distribution of marbling scores was estimated from the first three cycles of the Germ Plasm Evaluation project. A third-order polynomial transformation of a normal distribution was fit by maximum likelihood. The coefficients of the polynomial varied according to genetic differences, days on feed, and yearly differences. After transformation to a normal distribution, multivariate normal theory was then used to predict proportions of carcasses in yield and quality grades and their weights. Predicted proportions of Choice + Prime carcasses were .23, .65, and .88 when average marbling scores were Slight, Small, and Modest, respectively. Predicted carcass weights of Choice + Prime carcasses exceeded the mean weight by 11, 5, and 2 kg for these same average marbling scores. A FORTRAN program was developed which allows the user to input the average carcass weight, marbling score, and yield grade for a group of cattle and the CV for marbling score and SD for yield grade. Output summarizes proportions and carcass weights by yield grade, quality grade, and their combinations. Values of different grade combinations and discounts for heavy and light weight carcasses can be input to determine average value. Although not user specified, it is easy to modify definitions of grades in the program.