Abstract:
A study was conducted to determine effects of year and season on diet quality
of beef cattle grazing northern Great Basin rangelands from 1990 to 1993. Forage
quality was high early in the growing season, then declined as seasons progressed
(P<.05). Plant chemical composition was higher early in the growing season in 1992
and 1993 (P<.05). Later in the season, quality was higher in 1990 and 1991 (P<.05).
Changes in precipitation amount and distribution and variations in temperature between
years were determined to be the primary factors affecting yearly changes in diet quality.
Research addressing the potential of winter grazing as a grazing management
plan in the northern Great Basin was conducted during the winters of 1991-92 and
1992-93. Feeding 2 kg/d of alfalfa hay or pellets on a daily or alternate day (4 kg) basis
did not affect cow or calf performance, intake, digestibility or grazing behavior
(P>.10). Intake, digestibility, diet quality and time spent grazing estimates decreased in
period 2 (mid-January) versus period 1 (early December). Cow performance was
lower the first 28 days of the study (P<.05), improved by day 56, then declined again at
day 70 (P<.05).
Animal response to winter environmental conditions were estimated during the
winter of 1992-93. Moving from a grazing to a hay-feeding situation increased forage
intake, digestibility and digesta kinetics (P<.05), while reducing grazing behavior
(P<.05). Cow body weight increased and body condition decreased as the study
progressed (P<.05). Animals responded positively to slight environmental stresses initially when environmental conditions remained relatively mild. As environmental conditions worsened, animals reduced intake and grazing behavior in response to increased stress (P<.05). Attempts to estimate daily intake by grazing animals appeared to be successful.
Effects of early spring grazing of rangeland utilized in a winter grazing program were determined in 1992 and 1993. Cow-calf pairs grazed the selected pasture in mid to late March. In November, estimates of total forage production and plant chemical composition were obtained from grazed and ungrazed sites. Spring grazing reduced total forage production (P<.05); estimates of diet quality collected from esophageal steers were similar between treatments (P>.10). Estimates of forage production were higher and diet quality lower in 1993 (P<.05).
