Effects of Late Gestational Forage System on Fetal Growth and Neonatal Calf Blood Chemistry

We have previously reported that grazing stockpiled tall fescue (STF) during late gestation increases cow circulating metabolites and fetal growth compared with feeding poor quality tall fescue hay. Our current objective was to investigate the effects of late gestational forage system on calf size at birth and perinatal nutrient supply, assessed through neonatal blood chemistry. Multiparous spring-calving cows (n = 56; 638 ± 21 [SE] kg initial BW; 5.3 ± 0.1 initial BCS; 5.9 ± 0.4 yr of age; February 16, 2016 average calving date) were allocated by BW, BCS, age, and expected calving date to either strip-graze endophyte-infected STF (n = 4 pastures; 12.5% CP, 59.5% NDF; DM basis) or consume ad libitum endophyte-infected tall fescue hay (n = 4 uncovered drylots; 7.5% CP, 65.3% NDF; DM basis) for the last 75.0 ± 1.7 d of gestation. Cows remained on their respective treatments, but STF cows were moved to drylots on 13.5 ± 1.6 d pre-calving and fed tall fescue haylage (12.6% CP, 61.7% NDF; DM basis) to allow for calf sample collection. Jugular blood samples were obtained from calves at 0 (pre-suckling but after standing), 6, 12, 24, 48, and 72 h postnatally for blood chemistry analysis. Data were analyzed with forage system as a fixed effect and pen as experimental unit. Blood chemistry data were analyzed using a mixed model containing effects of forage system, hour, and their interaction; hour was a repeated effect. Calf birth weight, shoulder-to-rump length, heart girth, and abdominal girth were not affected by forage system (P ≥ 0.23) in the current study. Calves born to cows grazing STF tended to have longer (P = 0.09) gestation length than hay (278.9 ± 0.9 vs. 276.2 ± 1.0 d). Calf serum urea nitrogen was affected by the forage system x hour interaction (P = 0.009). Serum urea nitrogen was greater (P < 0.008) in calves born to cows grazing STF at 0, 6, 12, and 24 h. Calves born to cows fed hay had greater (P = 0.04) serum Ca. Serum aspartate aminotransferase tended to be greater (P = 0.06) in calves born to cows grazing STF. No other blood chemistry measures were affected by forage system (P > 0.10). An effect of hour (P < 0.001) was observed for all serum measures except bicarbonate (P = 0.26). These data suggest that late gestational forage quality impacts gestation length and perinatal calf nitrogen supply.