title: Performance of growing cattle grazing stockpiled Jesup tall fescue with varying endophyte status.
abstract: The objective of this study was to evaluate the performance of growing cattle when intensively 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, and heifers were used in 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, respectively. Serum prolactin concentrations of heifers grazing E+ were less (P < 0.05) than those grazing E- and EN during all years except yr 2. In yr 2, E+ and E- did not differ (P = 0.11). Serum prolactin of heifers grazing E- and EN did not differ (P > 0.20) except in yr 4. During yr 4, serum prolactin 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 < 0.01) SUN than heifers grazing E+ and EN, which did not differ (P = 0.89). Forage disappearance (DM basis) did not differ (P = 0.75) among treatments and was 4.7, 4.7, and 5.0 kg/animal daily (SEM 0.27) for E+, E-, and EN, respectively. Body weight gain per hectare was greater (P = 0.04) for E+ (257 kg) than for E- (220 kg) or EN (228 kg). In most years, animal grazing days on E+ were greater than those on E- or EN. However, in yr 5, animal grazing days did not differ (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.
authors.affiliation: Department of Animal Science, North Carolina State University, Raleigh 27695, USA. medrewno@ncsu.edu
authors.forename: M E
authors.initials: ME
authors.lastname: Drewnoski
authors.forename: E J
authors.initials: EJ
authors.lastname: Oliphant
authors.forename: B T
authors.initials: BT
authors.lastname: Marshall
authors.forename: M H
authors.initials: MH
authors.lastname: Poore
authors.forename: J T
authors.initials: JT
authors.lastname: Green
authors.forename: M E
authors.initials: ME
authors.lastname: Hockett
mesh_terms: D000821:Animal Feed / Q000032:analysis / Q000382:microbiology*; D000818:Animals; D001806:Blood Urea Nitrogen; D001824:Body Constitution / Q000502:physiology; D002417:Cattle / Q000254:growth & development / Q000502:physiology*; D004032:Diet / Q000662:veterinary*; D004435:Eating / Q000502:physiology; D005260:Female; D031751:Festuca / Q000382:microbiology*; D005516:Food Microbiology; D008297:Male; D055328:Neotyphodium / Q000502:physiology; D011388:Prolactin / Q000097:blood; D011897:Random Allocation; D012621:Seasons; D013696:Temperature; D013997:Time Factors; D015430:Weight Gain / Q000502:physiology
chemical_list: D011388:Prolactin