351
Effects of feeding stockpiled tall fescue versus tall fescue hay to late gestation beef cows on circulating plasma amino acid concentrations in neonatal calves
We hypothesized that cows grazing stockpiled tall fescue (STF) during late gestation have increased nutrient intake compared with cows fed summer-baled hay, which would result in improved fetal development and subsequent calf performance. Forty-eight multiparous, spring-calving crossbred beef cows (683 + 16 [SE] kg, BW) were allocated by BW, BCS, age, and expected calving date to either strip-graze endophyte-infected STF (59.7% NDF, 12.3% CP; DM basis) in 4.05 ha pastures (n = 4) or consume ad libitum endophyte-infected tall fescue hay (HAY; 64.9% NDF, 6.2% CP; DM basis) in uncovered drylots (n = 4) beginning on d 188 ± 2 of gestation. Cows remained on their respective treatments until calving, but STF cows were moved to drylots at 7.0 ± 1.0 d pre-calving and fed ryelage (58.6% NDF, 12.3% CP; DM basis). At 52 ± 0.6 h postnatally, jugular blood samples were obtained from calves for plasma determination of circulating AA. Data were analyzed with treatment as a fixed effect and pasture or drylot as the experimental unit; calf date of birth and sex were included in the model when P < 0.25. Total AA and total essential AA concentrations (µmol/L) tended (P ≤ 0.11) to be greater for calves born to STF cows than calves born to HAY cows. Total branched-chain AA were greater (P ≤ 0.05) for calves born to STF cows compared with HAY as a concentration, percent of total AA, or percent of total essential AA. Plasma concentration of Val, Asn, Glu, and Pro were greater (P ≤ 0.04) and Ile, Leu, Asp, and Cit tended (P ≤ 0.10) to be greater for STF calves versus HAY; there were no differences (P ≥ 0.17) in all other essential AA concentrations. When expressed as a percent of total AA, Val, Asn, and Glu were greater (P ≤ 0.05) for STF calves than HAY. Plasma Val was greater (P = 0.03) for STF calves when expressed as percent of total essential AA. Conversely, calves born to HAY cows had greater (P ≤ 0.02) Thr when expressed as a percent of total AA or total essential AA. In conclusion, calves born to STF cows had greater total, essential, and branched-chain AA concentrations which may indicate increased nutrient supply to fetal and neonatal calves born to cows grazing STF.
Keywords: amino acids, developmental programming, pregnancy