Economic selection index coefficients for terminal traits in Beefmaster cattle

Abstract Text:

In the design of an economic selection index, the relative importance of traits in the breeding goal is reflected by their economic weighting in the index. The objective of this study was to develop an economic selection index for Beefmaster cattle for a terminal production system where bulls will be mated to mature cows with all resulting progeny harvested. Selection criteria were chosen from expected progeny differences (EPD) currently reported by Beefmaster Breeders United (BBU), and included yearling weight (YW), ultrasound ribeye area (UREA), ultrasound rib fat (UFAT), and ultrasound intramuscular fat percentage (UIMF). Goal traits, which directly influence profitability in a terminal system, included hot carcass weight (HCW), marbling score (MS), ribeye area (REA), 12^th-rib fat (FAT), and feed intake (FI). Phenotypic and genetic parameter values among the selection criteria and goal traits were obtained from literature. National averages of feed prices, veterinary costs, and carcass premiums/discounts from 2010 to 2014 were used to establish income and expenses associated with a terminal system. Economic values were determined from a simulation of 100,000 animals using SAS 9.4. Values were obtained by approximating the partial derivatives of the profit function by perturbing traits one at a time, by one unit, while holding the other traits constant at their respective means. In the simulation, the means (SD) for HCW, MS, REA, FAT and FI were based on literature values, and were 320 (38.8) kg, 5.4 (0.9) marbling score units, 76.5 (9.3) cm², 1.2 (0.32) cm, and 8.59 (1.09) kg, respectively. Relative economic values for HCW, MS, REA, FAT and FI were found to be 91.29, 17.01, 8.38, -7.07, and -29.66, respectively. By using phenotypic (co)variances among the selection criteria in the derivation, index coefficients may be applied to phenotypic measures. Index coefficients for phenotypic measures of YW, UREA, UFAT and UIMF were 0.74, 0.08, -31.04, and 13.32, respectively. By using genetic (co)variances among the selection criteria in the derivation, index coefficients may be applied directly to EPD. Index coefficients for EPD of YW, UREA, UFAT and UIMF were 1.72, 0.81, -36.60, and 12.37, respectively. The application of this index would aide Beefmaster breeders in their sire selection decisions, facilitating genetic improvement for a terminal breeding objective.

Keywords: beef cattle, economic weight, selection index