Genetic Parameter Estimation for Foot Structure in American Angus Cattle

To enable breeders to select for correct foot and leg structure to increase productive life of beef cattle, the American Angus Association is developing genetic selection tools for these important traits. The Association accepts categorical 1 to 9 scores, with 5 being ideal, from its members for two traits, foot angle and claw set. Objectives were to explore alternative genetic evaluation approaches for these traits and estimate genetic parameters using 5,722 records collected on Angus bulls and heifers ranging from 320 to 460 days of age. Frequency of observations in the 1-9 categories, respectively, were 0, 1, 6, 197, 3845, 1468, 166, 34 and 5 for foot angle and 0, 0, 5, 263, 3251, 1883, 270, 45 and 5 for claw set. All traits were analyzed using a linear animal model with ASREML 3.0. In addition to a model fitting all phenotypes (1-9), each of the traits was also analyzed as two independent traits depending on the score to investigate if foot angle 1-5 (steep) were different from 5-9 (weak) and claw set 1-5 (spread) was different from 5-9 (scissor) with 5 being ideal for each trait. A two-trait model for foot angle and claw set (1-9) was used to investigate the genetic correlation. All models included contemporary group (customer, scoring date, sex and diet type) and weaning creep type as fixed effects, age at measurement as a covariate, animal and error as random effects. Heritability estimates were 0.34, 0.21, 0.16, 0.25, 0.22 and 0.37, respectively, for foot angle, claw set, spread, scissors, steep and weak, with a low genetic correlation between claw set and foot angle (0.22) determined with the bivariate model. The moderate heritability estimates for these foot score traits indicate that genetic evaluations are warranted. The traits of scissor and weak (5-9) appear to have a slightly higher heritability than the respective overall (1-9) traits, but it is not clear if splitting the traits is warranted for genetic evaluation. These genetic parameters will play an important role in the American Angus Associations development of genetic evaluations for foot structure.