STEERS GRAZING ENDOPHYTE-FREE TALL FESCUE - SEASONAL-CHANGES IN NUTRIENT QUALITY, FORAGE INTAKE, DIGESTA KINETICS, RUMINAL FERMENTATION, AND SERUM HORMONES AND METABOLITES

Six ruminally cannulated Holstein steers (average BW 514 kg) grazed a 33-ha, unirrigated, endophyte-free, tall fescue (Festuca arundinacea S chreb.) pasture from April 10 through December 7, 1989. Samples were c ollected in May, June, September, and November 1989. Total masticate N was relatively constant (P > .10) throughout the year. Masticate in v itro OM disappearance was less (P < .05) in September (48.4%) and Nove mber (50%) than in May (60.6%) and June (56%). Ruminal NH3N concentrat ions (milligrams/deciliter) were greater (P < .05) during May (20.5) a nd June (17.8) than during September (9.4) and November (5.9). Organic matter intake (grams/kilogram of BW) and particulate passage rate (pe rcentage/hour) were least (P < .05) in November (15.3; 2.6) and not di fferent (P > .10) during May (23.7; 3.1), June (20.7; 3.1), and Septem ber (21.0; 3.0). Extent and rate of NDF digestion and ruminal total VF A did not differ (P > . 1 0) across sampling dates. Serum glucose conc entrations were not affected (P > .10) by sampling date, but serum ure a N was greater (P < .05) during May and November than during June and September. Nonesterified fatty acid concentrations increased (P < .05 ) with advancing plant maturity. Serum insulin concentrations were gre ater (P < .05) during May than during other sampling periods; however, growth hormone concentrations were not altered (P > .10) by advancing plant maturity. Unirrigated fescue pasture maintained a high nutrient level throughout the grazing season, and masticate samples did not di splay the decrease in nutrient content often noted with other types of pasture forage.