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 net energy and metabolizable protein requirements for maintenance, pregnancy, and growth from d 160 of gestation to calving. Post-calving, all females were limit-fed chopped tall-fescue hay supplemented to meet lactational nutrient requirements in Calan gates to constrain calves’ diets to milk only until d 147. Four-hour milk yields were measured 5 times; calf size was determined every 21 d. Data were analyzed with treatment, calving date, and calf sex (when P < 0.25) as fixed effects; day and day x treatment were included for milk yield. From calving to d 147, CON cows had greater (P ≤ 0.003) BW, BCS, and backfat, but NR cows gained more (P ≤ 0.004) BW, BCS, and backfat. Milk weight and volume was 15% less (main effect; P < 0.04) for NR cows. Calf size did not differ at birth (P ≥ 0.27). From d 42 to 147, calves born to NR dams had lower (P ≤ 0.02) BW. Heart, abdominal, and flank girths were less (P ≤ 0.07) for NR calves through d 147. Calf ribeye area tended to be less (P ≤ 0.11) in NR calves at d 42, 84, and 126. Nutrient restricted calves had less shoulder to rump length (d 63 to 147; P ≤ 0.08), shoulder height (d 63 to 126; P ≤ 0.02), cannon length (d 42 to 105 and 147; P ≤ 0.09), and cannon circumference (d 63 and 105 to 147; P ≤ 0.06). These data indicate that even when dams are fed to meet lactational requirements, milk yield and calf growth are reduced by late gestational nutrient restriction.
Determination of energy and protein requirements for crossbred Holstein × Gyr preweaned dairy calves
