Selection Criteria for Efficient Beef Production

Abstract

Individual body weights, postweaning feed consumption records and 12th rib carcass backfat measurements were used to predict genetic (sire progeny) differences in efficiency of beef production. Data from years 1961 through 1967 included 222 Hereford heifers and 502 purebred and crossbred Hereford, Angus and Shorthorn steers at Fort Robinson, plus 147 bulls and 122 steers (Angus) at Lincoln, with a total of 99 degrees of freedom anong sire progenies within type of mating and years. Efficiency was defined as value of (essentially) boneless retail cuts, adjusted for marbling score, less feed and time variable costs, from 200 days of age (E₁) or from 182-kg live weight (E₂) to a 410-kg slaughter weight, or from 200 days to constant age at slaughter (E₃). Net efficiency (H) also included expected changes in cow-herd costs from associated increases in cow size and in birth weights (i.e., in calving difficulty and fertility). Accuracy of index (I) selection for E₁ was maximum (R = 0.45) when I included 200-day weaning weight (W), postweaning daily gain (G) and backfat (F₁); omitting backfat reduced accuracy to R = 0.40 but adding feed intake (N₁) did not help; substituting yearling weight (Y) for W and G reduced accuracy by 0.03. Maximum accuracy of selection for E₂ was lower (R = 0.31) than for E₁; most information (R = 0.29) came from F₁ plus G or feed intake (N₂), but N₂ added little to F₁ unless W or Y was substituted for G. Selection for age-constant E₃ was more accurate (R = 0.59) than for E₁ or E₂ and involved little change in carcass composition; yearling weight (Y₃) and backfat (F₃) gave maximum accuracy (R = 0.59); adding feed intake (N₃) did not help; Y₃ and N₃ were little better than Y₃ alone (R = 0.57 vs. 0.56). Accuracy suffered when weaning weight (W) was omitted (R = 0.44 with G alone to 0.47 with G, N₃ and F₃). When net effects on calf mortality, reproduction and cow size were included in definition of efficiency (H), expected improvement was increased 6 to 7% by adding selection for smaller birth weight (B) to that for heavier yearling weight (I_H = Y3 — 3.2 B₃) or for yearling weight and backfat (I_H = Y3 — 3.2B₃ — 2.9F₃). Adding selection against B reduced expected increases by 55% in birth weight and by 25% in mature cow size but by only 10% in yearling weight. Copyright © 1974. American Society of Animal Science . Copyright 1974 by American Society of Animal Science.