Herbage allowances during mid to late gestation affect growth performance and physiological responses of beef cow–calf pairs, and offspring skeletal muscle development

Our objectives were to determine the effects of two herbage allowance levels during mid to late gestation on growth performance, physiological responses of cow-calf pairs, and offspring skeletal muscle development through weaning. Fifty-six pregnant Nellore cows 444 ± 42 kg initial shrunk body weight (SBW) and 3.66 ± 0.28 body condition score (BCS), each carrying a male fetus, grazed Urochloa brizantha cv. Marandu pastures under either low HA (LHA; 2.80 kg dry matter (DM)/kg BW) or high HA (HHA; 7.60 kg DM/kg BW) during the final 151 days of gestation (d 140 ± 15 of gestation). As intended, differences in HA (P < 0.01) were established by manipulating stocking rate (P < 0.01; 1.70 vs. 3.40 AU/ha for HHA and LHA, respectively). LHA cows had lower body weight (BW; P < 0.001), average daily gain (ADG; P < 0.001), BCS (P < 0.001), Longissimus muscle area (LMA; P = 0.002), and subcutaneous fat thickness (SFT; P = 0.02) than HHA cows during gestation. During lactation, LHA and HHA cows showed similar BW, LMA, and SFT (P ≥ 0.12); however, LHA cows had greater ADG (P < 0.001) and lower BCS (P < 0.001) than HHA cows. In late gestation, LHA cows exhibited higher plasma urea (P < 0.01) than HHA cows, but no differences were detected in milk yield or composition during lactation (P ≥ 0.20). HHA calves had greater BW at birth (P < 0.01), at 120 days of age (P < 0.01), and at weaning (P < 0.01) than LHA calves. HHA calves also had more muscle fibers at 30 (P < 0.01) and 240 (P < 0.01) days of age than LHA calves, whereas muscle-fiber cross-sectional area did not differ at either 30 or 240 days days of age (P ≥ 0.21). In conclusion, adequate herbage allowance during mid- to late gestation improves maternal performance and metabolic status, supporting fetal skeletal muscle development and enhancing offspring growth through weaning.