71 Effects of Late Gestational Nutrient Restriction on Calf pre-Weaning Growth, Backgrounding and Feedlot Performance, and Carcass Composition

Abstract

Abstract Fall-calving Hereford-SimAngus heifers [single-sired; BW: 451 ± 28 (SD) kg; BCS: 5.4 ± 0.7] bred to a single sire were individually fed 100% (control; CON; n = 12) or 70% (nutrient restricted; NR; n = 13) of NASEM metabolizable energy and metabolizable protein requirements for maintenance, pregnancy, and growth from day 160 of gestation to calving. Post-calving, all females were fed chopped tall-fescue hay supplemented to meet lactational nutrient requirements in Calan gates to constrain diets of calves to milk only until day 147, then pen-fed in drylots until weaning at day 242 ± 3 (SD). Post-weaning, calves were fed a tall fescue hay-based backgrounding diet in the same large drylots for 53 ± 12 d, then moved to partially covered pens with GrowSafe feeding systems in 2 groups and fed a corn-based feedlot diet (formulated to be 18.3% CP, 1.21 Mcal NEg/kg, DM basis; 89% DM) for 255 ± 3 d (similar days on feed rather than carcass endpoint). Cattle were harvested in a commercial plant, and camera carcass grading was performed. Data were analyzed with maternal treatment, calving date, and calf sex (when P < 0.25) as fixed effects; feedlot group was included for feedlot and carcass measures. We previously reported that birth weight was not affected (P = 0.72), but NR decreased (P < 0.04) milk production by 15%. Calves born to NR dams had reduced ADG from birth to day 147 (P = 0.02), day 147 to weaning (P = 0.08), and birth to weaning (P = 0.003), resulting in NR calves having 13% lighter (P = 0.004) weaning weight. Backgrounding ADG was not affected (P = 0.80) by maternal treatment; thus, feedlot entry BW was 11% less (P = 0.009) in NR calves. On day 28, 56, 84, and 112 on feed, NR calves weighed less (P ≤ 0.09) than control. Final BW was not affected (P = 0.91) by maternal treatment. Feedlot ADG was greater for NR calves from day 168 to slaughter (P = 0.02) and the overall feeding period (P = 0.03), but not before day 168 on feed (P ≥ 0.22). Calves born to NR dams had less (P = 0.02) dressing percentage, but improved (P = 0.02) yield grade and backfat thickness. Hot carcass weight, ribeye area, marbling score, and KPH were not affected (P ≥ 0.26) by maternal treatment. Percent prime, yield grade ≤ 2, and yield grade ≥ 4 were not affected (P ≥ 0.29) by maternal treatment. Overall, late gestational nutrient restriction decreased growth pre-weaning but increased late finishing growth, without affecting backgrounding or early feedlot growth. These cattle had leaner carcasses after similar days on feed, suggesting that late gestational nutrient restriction altered growth patterns or body composition.