Abstract |
- Research was conducted on the Keating rangelands in north-eastern Oregon to determine the food habits of deer and cattle and
similarity of their diets, and to estimate deer and cattle months of
grazing on both a quantitative and nutritional basis. Data were
collected during the winters of 1978-1979, 1979-1980 and during the
spring and fall of 1979 and 1980. In the Crystal Palace, Tucker
Creek and Spring Creek study areas, field fecal collections were
made and the microhistological method was used in the laboratory to
determine the food habits of both deer and cattle. Similarity indices were calculated comparing food habits of both deer and cattle.
In delineated plant communities, available herbaceous forage was
estimated within 0.5m² circular plots employing a double sampling
technique, and available browse was estimated employing a multiple
linear regression technique. Subsamples of available forage were
analyzed for in vitro dry matter digestibility and crude protein.
An extensive literature review was conducted to determine nitrogen
(N) and metabolizable energy (ME) requirements of both deer and cattle. Cattle and deer months of grazing were calculated for each
plant community on a quantitative (i.e., forage biomass) and nutritional (i.e., metabolizable energy and nitrogen) basis employing the
resources available
following relationships: number supported = resources available/resources required. Management recommendations were made based on data collected in this
study.
Grass was the most dominant forage consumed by cattle, while
deer consumed both grass and browse. Forbs were not an important
dietary constituent for either cattle or deer. During the early
winter period of 1978-1979, browse and grass averaged 57.4 percent
and 1.6 percent of the deer diets, respectively. However, during
the late winter period of 1978-1979, browse and grass averaged 40.2
percent and 31.5 percent of the deer diets, respectively. During
the 1979-1980 winter, browse and grass averaged 35.4 percent and
51.9 percent of the deer diets, respectively. The predominant grass
and browse consumed by deer was Sandberg's bluegrass and big
sagebrush, respectively. During the spring period, crested
wheatgrass, cheatgrass and Sandberg's bluegrass averaged 21.8, 29.1
and 19.5 percent of cattle diets, respectively. During the fall
period,.cheatgrass and Sandberg's bluegrass averaged 30.4 and 24.9
percent of cattle diets, respectively. Diet similarity ranged
from 27.1 percent to 52.8 percent while the average spring overlap
for both years was 37 percent and the average fall overlap was 50
percent. Most of the dietary overlap occurred on Sandberg's
bluegrass.
The literature review revealed that on a forage biomass basis a cow-calf pair in spring required 14 kg/day, while a dry pregnant
cow in the fall required 10 kg/day. On an energy and nitrogen
basis, a nursing cow required 26.6 Meal/day of ME and 206 g of N,
while a dry pregnant cow required 10.0 Meal/day of ME and 94.5 g of
N. On a forage biomass basis, a wintering adult deer required
.9 kg of forage per day while a fawn required .6 kg per day.
Considering the length of the winter period, the energy obtained by
catabolism of fat, and the energy and nitrogen required in gesta
tion, I determined that during the early and late winter periods of
1978-1979 deer required 1.81 and 1.80 Meal/day of ME and during the
1979-1980 winter, they required 1.73 Meal/day of ME. The literature
also revealed that a wintering deer required 12.9 g of N per day.
Quantitative forage analysis showed that depending upon study
area and pasture on a kg/ha basis the predominant grasses available
to cattle were crested wheatgrass, Sandberg's bluegrass and
cheatgrass. Determination of available browse biomass was made
employing a multiple linear regression model for mountain big
sagebrush (log y = -6.37 + .9337 log H + 1.49 log W₂), and a simple
linear regression model for gray rabbitbrush (log y = -3.70 + 1.81
log W) and basin big sagebrush (log y = -3.84 + .9870 log A).
Depending upon study area and plant community, quantitative analysis
of the forage showed that big sagebrush and Sandberg's bluegrass
were the dominant species available to deer.
Early spring grazed pastures could carry more AUMS on a nutritional basis than on a quantitative basis. Pastures sampled in late
spring showed that total AUMS on a forage quantity basis exceeded those on a nutritional basis. During the fall on an old-growth
(i.e., previous year's growth) and fall growth basis, total AUMS
based on N generally exceeded those based on ME or forage quantity,
except in the crested wheatgrass-dominated pasture where more AUMS
were calculated on a quantity basis than on a nutritional basis. On
a fall-growth-only basis, more AUMS were calculated on a nutritional
basis than on a quantity basis. Generally, the least number of AUMS
could be carried on the medusahead communities while the most AUMS
could be carried on the crested wheatgrass seedings.
Deer months calculated for the two winters across the
three study areas showed more deer months per plant community were
calculated on a forage quantity basis than on an ME or N basis.
However, an exception to this trend occurred in the grassland com
munities where more deer months were calculated on an N basis than
on an ME or forage quantity basis. Generally, the most deer months
were calculated for the basin big sagebrush communities while the
least number of deer months were calculated on the medusahead communities.
|