Performance of growing cattle grazing stockpiled Jesup tall fescue with varying endophyte status1

摘要

The objective of this study was to evaluate the performance of growing cattle when in- tensively grazing stockpiled endophyte-infected (E+), endophyte-free (E-), and nontoxic endophyte-infected (EN) tall fescue during the winter. The experiment was conducted over 5 consecutive winters. In each year, plots (1 ha each, 4 per treatment) were harvested for hay in August, fertilized in September, and forage was allowed to accumulate until grazing was initiated in early December. Each year, 48 Angus-cross tester cattle (4 per plot) were given a daily allotment of forage, under strip-grazing (frontal grazing) management, with a target residual height of 5 cm. Steers were used the first year, arid heifers were used iii subsequent years. The grazing periods for determination of pasture ADG were 86 d (yr 1), 70 d (yr 2), 86 d (yr 3), 72 d (yr 4), and 56 d (yr 5). Pasture ADG of cattle did not differ among treatments (P = 0.13) and were 0.51, 0.59, and 0.56 kg/d (SEM 0.03) for E+, E-, and EN, respectivcly. Serum prolactin concentrations of heifers grazing E+ were less (P 0.20) except in yr 4. During yr 4, serum prolaci in of heifers grazing E- was greater (P = 0.05) than that of heifers grazing EN. Serum urea- N concentrations (SUN) tended to differ among treatments (P = 0.10) and there was a treatment x year interaction (P = 0.05). During yr 1 through 3, SUN did not differ (P > 0.15) among treatments. However, as the stands aged, E- had a greater invasion of other plant species, which increased the CP content of the sward, thus causing heifers grazing E- during yr 5 to have greater (P 0.20) among treatments. The use of stockpiled E+ as a source of low-cost winter feed is a viable option for producers, whereas grazing of EN may be more beneficial during the spring and fall, when more severe negative effects of ergot alkaloids have been observed. [PUBLICATION ABSTRACT]