Performance of Beef Heifers Grazing Stockpiled Endophyte-infected, Endophyte-free or Non-toxic Endophyte-infected Tall Fescue

Abstract

A two-year grazing study was conducted from December to February of 2002-2003 and 2003-2004. The objective of this study was to evaluate animal performance and agronomic persistence of non-toxic endophyte-infected (EN) fescue in comparison to endophyte-infected (E+) and endophyte-free (E-) tall fescue in a stockpiling system. Forty-eight (year one) and 60 (year two) Angus-cross heifers were grazed on one of three treatments for 70 days in year one and 86 days in year two. Plots were established in the fall of 1999 and averaged 1.01 ha. All plots were clipped in August and fertilized in September with 94.9 kg/ha (year one) and 84.2 kg/ha (year two) nitrogen from 30% liquid urea/ammonium nitrate. From August forward the forage was allowed to accumulate until the initiation of the study in December. Each day heifers were given a fresh allotment of forage through use of a stripgrazing management system. Digestibility of the forage did not differ by treatment (P = 0.51) but was higher in year one than in year two (IVTDMD 80% year one, 65% year two; P < 0.01). Crude protein tended to be greater in year one (10.9%) than in year two (9.74%; P = 0.08). Average daily gain (ADG) did not differ by treatment (P > 0.21) and was higher on pasture during year two than year one (0.48 kg/d vs. 0.40 kg/d, respectively; P = 0.03; SE &#177; 0.053). Final body condition scores (BCS) were higher in year one (5.25 E+, 5.26 E-, 5.14 EN) than in year two (5.06 E+, 4.98 E-, 4.96 EN; P = 0.01; SE &#177; 0.049). Serum urea nitrogen (SUN) did not differ by treatment (P = 0.77) but there was a significant year effect (P < 0.01) with SUN levels being higher in year two than in year one, and there was also a significant year by treatment interaction (P = 0.02). The percentage of heifers that experienced an estrous cycle at least once over the course of the study did not differ by treatment (P = 0.61) or year (P = 0.25). Endophyte-free fescue did not perform as well under heavy grazing conditions as did endophyte-infected or non-toxic endophyte-infected fescue over the course of the two-year study. The area grazed was greater both years for E- fescue (0.870 ha year one, 0.656 ha year two) than for E+ fescue (0.678 ha year one, 0.555 ha year two) or EN fescue (0.708 ha year one, 0.582 ha year two; P = 0.01; SE &#177; 0.0473). The percentage of non-fescue species in the sward was greater for E- plots (18.9% year one, 25.0% year two) than for E+ (12.2% year one, 13.1% year two) or EN plots (12.5% year one, 15.9% year two; P = 0.02; SE &#177; 2.03) during both years. Total pre-graze forage mass was lower both years for E- plots (P = 0.05). Animal grazing days, gain per hectare and carrying capacity were all greater in year two than in year one (P < 0.01) but did not differ due to treatment. The percentage of fescue that was green was greater in year one (66.5%) than in year two (51.8%), but there was no significant difference due to treatment (P = 0.91). These results indicate that E+ fescue may not affect ADG, BCS and progesterone concentrations when stockpiled and stripgrazed in the piedmont of North Carolina over the winter. Non-toxic endophyte-infected fescue seems to support animal performance to a level equal that of E- fescue and have agronomic properties similar to E+ fescue.