61 Effects of fescue cultivar on performance of beef cow/calf pairs grazed on summer stockpiled tall fescue pastures

Abstract

This 2-year experiment evaluated productivity of wild-type endophyte-infected tall fescue (KY-31) and novel endophyte-infected tall fescue (MaxQ) summer stockpiled (SS) pastures and the performance of fall-calving beef cow/calf pairs grazed on each cultivar. Pregnant Simmental x Angus cows (128 total, 64 each year) were stratified by BW, BCS, and expected calving date, then allotted to 1 of 10 groups. Forage growth was stockpiled from April to initiation of strip-grazing on 31 August of 2017 and 2018. Cows grazed treatment pastures for 52 d from 23 ± 14 d prepartum to 29 ± 14 d postpartum, and calved on treatment pastures. Forage quadrats were clipped from the grazed and ungrazed portions of each pasture to determine weekly forage mass (FM). Total ergot alkaloid (TEA) concentrations were analyzed for all pastures at the beginning of the experiment and every subsequent 2 weeks for KY-31. Cow BW was recorded on 2 consecutive d and BCS determined at the start and end of the experiment. In year 2, ultrasound 12th rib fat thickness (BF) was measured at the beginning and end of the treatment period Milk production was estimated using the weigh-suckle-weigh technique at 29 ± 14 postpartum. In year 1, TEA concentrations for KY-31 pastures did not differ (P < 0.48) over time. Fescue cultivars were not different (P ≥ 0.15) in forage CP, TDN, and grazed or ungrazed FM. Cow BW, BCS, and BF at the beginning and end of grazing were not different (P ≥ 0.41) by treatment. Milk production was higher (P < 0.01) for KY-31 grazed cows. Calving date, calf BW, calf ADG were not different (P ≥ 0.65) by treatment. Neither AI nor overall conception rates differed (P ≥ 0.23) between cultivars. Performance of fall-calving cows pre-exposed to KY-31 was not improved when grazed on MaxQ in a SS system.