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.