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Effects of pre-feedlot growth rate on carcass composition and meat tenderness
vii, 120 leaves : illustrations ; 28 cm.
The effects of pasture growth rate and breed and sex treatments (F₁ Angus x Brahman steers; Simmental-sired calves from F₁ Angus x Brahman or Hereford x Brahman dams) were examined on carcass composition and tenderness. Calves were randomly assigned within breed type and sex to low (3.7 hd/ha), medium (5.1 hd/ha) or high (6.8 hd/ha) stocking rate (SR) pastures. Calves were fed a high-grain diet in a commercial feedlot to an approximate carcass weight of 361 kg. Carcass characteristics were measured 36 h postmortem. Soft tissue from 9-10-11 rib sections was analyzed for fat, protein and moisture content. Longissimus muscle sections were aged for 14 and 35 d and 2.54 cm steaks were removed for Warner-Bratzler (WB) shear force measurement, percent soluble collagen and sensory analysis. Pasture average daily gain (ADG) was affected (P =.0001) by SR (1.14, .77 & .38±.03 kg/d for low, medium & high SR, respectively), and Angus x Brahman steers had higher ADG (P < .001) than Simmental-sired steers and heifers (.86, .77 & .68±.03 kg/d, respectively). Carcass weight was used as a covariate to analyze carcass data. Backfat thickness was (P = .05) lower in low-and medium-SR calves than in high-SR calves (.93, .86, l .03±.06 cm). Quality grades were (P < .001) lower for medium-SR calves compared to high-SR calves (623.74, 653.7±06). Low-SR calves had (P < .001) lower percent soluble collagen (6.34 vs 8.48 and 8.47±.4 %) than did medium or high-SR calves, respectively. Calpastatin activity was affected (P = .0001) by SR (1.69, 2.19, 3.04±.16 activity/g) for low, medium and high SR, respectively. Warner-Bratzler shear force values after 14 and 35 days of aging were not affected by SR. Simmental-sired steers had (P < .001) less backfat (.75 vs 1.08 and .99±.06 cm), and less (P < .001) rib fat (24.23 vs 29.2 and 28.72±.7 %). Angus x Brahman steers compared to Simmental-sired steers and heifers had higher (P < .001) quality grades (665.33 vs 622.12 and 643.14±06 cm). Reducing growth rates by increasing SR did not affect meat tenderness but influenced calpastatin and collagen solubility.
Issued also on microfiche from Lange Micrographics.
Includes bibliographical references (leaves 62-76).