Using supplemental condensed tannin to mitigate tall fescue toxicosis in non-pregnant, non-lactating ewes consuming tall fescue silage

Abstract

Tall fescue [Schedonorus arundinaceus (Shreb.)], the primary grazing forage in the mid-south, and has a symbiotic relationship with an endophytic fungus (Neotyphodium coenophialum) that produces ergot alkaloids that cause fescue toxicosis in grazing livestock. Some evidence indicates that condensed tannins (CT) can bind to ergot alkaloids and render them ineffective, thereby preventing symptoms of fescue toxicosis. Non-pregnant, non-lactating ewes [n = 20; 57 ± 1.3 kg initial body weight (BW)] were housed in individual pens (1 × 1.5 m) with metal grate flooring. Ewes were offered ad libitum access to either novel endophyte (NE) or toxic endophyte-infected tall fescue silage with no CT (E0), or CT at 10 (E10) or 30 (E30) g/kg of silage dry matter (DM). The CT used was Quebracho tannin (Schinopsis quebracho-colorado). All ewes received 4 g/kg BW liquid molasses, and this served as the carrier for the CT treatments. The study consisted of 2, 21-d periods with a 30-d washout between periods. A 14-d adaption was followed by 7-d of total fecal and urine collection in each period. Blood samples for prolactin analysis were taken on the last day of each period. Data were analyzed using individual ewe within period as the experimental unit, treatment was a fixed effect, and period and pen were random effects. Prolactin was lesser (P < 0.01) in endophyte infected silage treatments. Intake (DMI; g/kg BW) and neutral detergent fiber (aNDF) intake (g/kg BW) were greater (P = 0.05) in NE compared to other treatments. Dry matter digestibility (DMD; g/kg DMI) and aNDF digestibility (g/kg NDF) were greater (P = 0.01) in NE compared to other treatments and organic matter (OM) digestibility [(OMD, g/kg OM intake (OMI)] did not differ between NE and E10, but NE was greater (P = 0.01) than E0 and E30. Digestible DMI and OMI (g/kg BW) were greater (P = 0.01) from NE compared to other treatments. Apparent N absorbed (g/kg N intake) was greater (P = 0.03) in NE, E0, and E10 compared with E30. Fecal N (g/kg N intake) was greater in E30 compared to E0 and E10, but not different from NE. Nitrogen retained (g/kg N intake and N absorbed) did not differ (P ≥ 0.31) among treatments. Condensed tannin supplementation at 30 g/kg DM had negative impacts on DM and OM digestibility and did not prevent decreases in prolactin associated with tall fescue toxicosis.