14 Mitigation Strategies for Heifer Development on ‘KY-31’ Tall Fescue

Abstract

Abstract Tall fescue (Schedonorus arundinaceus) is the predominant cool-season perennial forage in the Eastern U.S. However, a symbiotic endophyte reduces performance of animals grazing tall fescue. This results in losses of around $2 billion annually. Due to the vasoconstriction caused by the endophyte, a decrease in conception rates among cows and heifers consuming tall fescue has been observed. With rising input costs, it is necessary to explore alternative mitigation strategies these production losses. The objective of this study was to mitigate the toxic effects of ‘KY 31’ tall fescue by limit-grazing cool-season annuals as an alternative to feed supplementation. In January 2022, 48 heifers [14 months of age; 365.9 ± 11.89 kg body weight (BW)] were randomly assigned to tall fescue only, tall fescue with supplemental feed at 1% of BW, tall fescue with limit grazing of cool-season annuals for 24 h per week, and cool-season annuals only. Four animals grazed in each of three replicated paddocks per treatment. Cool-season annual pasture was a mixture of crimson clover (Trifolium incarnatum), annual ryegrass (Lolium multiflorum), and oat (Avena sativa). Body condition scores (BCS), hair coat scores (HCS), and BW were recorded every 30 d. Forage samples were taken for biomass, nutritive value, and ergovaline concentration every 30 d. On April 1, 2022, heifers were artificially inseminated (AI), and conception rates were determined 45 d after AI. Data were analyzed using the Glimmix procedure of SAS 9.4 (SAS Inst, Cary, NC) with α = 0.05. There were no differences among treatments in HCS at any weigh date (P > 0.05). The BCS for all treatments was less in February than January or March (5.6, 6.1, 6.1, respectively; P < 0.0001), but there were no differences among treatments at any sampling date (P > 0.05). Conception rates were not different among treatments (P > 0.10) but averaged 75, 67, 42, and 50% for the continuous-cool season, limit graze, supplemental feed, and tall fescue treatments, respectively. Crude protein (CP) concentrations for the control and limit grazing fescue treatments were greater than the limit grazing cool-season annual treatment, continuous grazing cool-season annual treatment, and the supplemental feed treatment (13.5, 10.7, 10.4, and 8.9%, respectively, (P < 0.012). Neutral detergent fiber (NDF) and acid detergent fiber (ADF) were different among the supplemental treatment when compared with the limit grazing fescue, limit grazing cool-season annual, control, and continuous cool-season annual (48.2 vs 64.7% NDF and 25.8 vs. 37.0% ADF; P < 0.0361). At this time, the results indicate that limit grazing cool-season annual forages may be an advantageous option to mitigate fescue toxicosis in replacement heifers grazing tall fescue pastures in the spring.