2002 Annual Report
Dickinson Research Extension Center
1089 State Avenue
Dickinson, ND 58601
of Grazing Management Treatments on Forage Intake, Diet Quality, Digestion Site,
and Protein Flow for Forage Selected by Grazing Animals, and on Seasonal Change
of Herbage Quality of Native Rangeland in Western North Dakota
L. Manske PhD1,
Joel S. Caton PhD2, and Holly Pitcher2
North Dakota State University
Research Extension Center
2Animal and Range Sciences Department
costs for the beef industry in western North Dakota are unnecessarily high because
the industry relies on traditional pasture management practices that inefficiently
capture the nutrients produced on a land base. These practices result in higher
costs for the nutrients ingested by the animals and in increased annual production
costs per animal. Development of efficient pasture management strategies requires
an understanding of herbage nutritional quality curves, the seasonal quality
of animal-selected diets, and the seasonal digestibility of and protein supply
from forage managed with different grazing treatments.
A two-year collaborative
graduate-student project will evaluate the influence grazing management treatments
applied during the growing season have on livestock forage intake, diet quality,
digestion site, and protein flow for forage selected by grazing animals with
ruminal and duodenal cannulas. Simultaneously, a second portion of the project
will evaluate seasonal changes in nutritional quality of the herbage as influenced
by grazing management treatments. Funding for portions of this project is provided
from a Range Research Initiative.
Crossbred beef steers will
be fitted with indwelling ruminal and duodenal cannulas according to approved
institutional animal care and use protocols. Steers will be randomly assigned
to the twice-over rotation grazing treatment and the 4.5-month seasonlong grazing
treatment. Samples will be taken from steer cannulas during collection periods
in June, July, August, September, and, if weather permits, October during the
2000 and 2001 grazing seasons.
Each collection period
will consist of 12 days. On days 1 and 2, steers will be ruminally evacuated
at dawn and allowed to graze for 30 to 60 minutes. During this grazing time,
total evacuated ruminal contents will be weighed and subsampled for determination
of total, dry matter, and fluid fill. After the allotted grazing time, steers
will be gathered, and diet masticate samples will be removed from the rumen.
Samples will be stored on ice until being transported to freezer compartments
for storage. On day 1, an additional sample from whole ruminal contents will
be collected and stored frozen. Later, bacterial cells will be isolated from
these samples and used to determine bacterial nitrogen to purine ratios. These
ratios will be evaluated to determine the levels of microbial protein synthesis.
This information will allow distinction between microbial and dietary origins
of the duodenal protein flow. The evacuated ruminal contents remaining after
all samples have been collected will be returned to the rumens of the respective
Masticate samples will
be transported frozen to the NDSU nutrition laboratory. All samples will be
lyophilized before being analyzed for nutrient composition. A subsample from
each masticate sample will be oven dried at 45C and used for the estimation
of in vitro digestibility (Tilley and Terry 1963).
Twice-daily ruminal dosing
of chromic oxide will begin after evacuation procedures are completed on the
morning of day 2 of each collection period and will continue through day 12.
Chromic oxide will be used as an indigestible flow marker in the masticated
ruminal contents. It will be dosed via the rumen cannula at 0700 and 1900 hours
daily for the duration of each collection period. Chromic oxide will be preweighed
into #8 gelatin capsules (8+/-0.005g) and stored in a cool, dry place until
dosed. Fecal grab samples will be taken at 0700, 1100, 1500, and 1900 hours
on days 7 to 11. These daily samples will be composited for the 5-day sampling
period for each steer during each collection period.
Duodenal sampling will
also begin on day 7 and will continue through day 11. Duodenal samples will
be collected at 0700, 1100, 1500, and 1900 hours daily. Approximately 250 ml
of duodenal contents will be collected from each steer at each sampling time.
Duodenal samples will be composited for all sampling times for each steer and
collection period. Duodenal samples will be stored frozen until analyses are
On day 12, ruminal fluid
will be collected from each steer via suction strainer at 0700 hours. The ruminal
fluid from each steer will be placed in 12 in vitro tubes and used as inoculum
for in vitro digestibility estimates. In vitro digestibility estimates will
be conducted for 3 dried and ground masticate samples, 3 alpha cellulose samples,
3 blank samples, and 2 standard samples. After 48 hours of incubation, the contents
of the in vitro tubes will be frozen to stop microbial fermentation and transported
to the NDSU nutrition laboratory for the second stage of the in vitro digestion
procedure. In vitro indigestibility and fecal output estimates will be used
to estimate forage intake. Chromium will be used as the flow marker and will
be used to estimate duodenal organic matter flow. Summarized data will provide
intake, chemical composition, site of digestion, degraded and undegraded intake
protein supply, and microbial efficiency of grazed forage diets as influenced
by season and grazing treatment.
Seasonal herbage nutritional
quality will be evaluated for replicated native rangeland management treatments:
twice-over rotation, 4.5-month seasonlong, 6.0-month seasonlong, and long-term
nongrazed treatments. Aboveground herbage samples will be collected by the standard
clipping method from 2 range sites of each pasture and separated into 4 categories:
cool-season grasses, warm-season grasses, sedges, and forbs. Sampling periods
will be early June, late June to early July, late July to early August, late
August to early September, and mid October to mid November. Five years of previously
collected samples and samples collected during the 2000 and 2001 grazing seasons
will be analyzed for nutritional quality. Samples will be analyzed for dry matter
ash, crude protein, and acid detergent fiber (ADF) by standard procedures (AOAC
1990). Soluble and insoluble N will be determined using the 0.15 M NaCl procedure
of Waldo and Goering (1970). Acid detergent insoluble N will be determined as
the N remaining in the ADF residue. Mineral analyses (Ca, P, Mg, Zn, Cu, Fe,
Mn, K, Na, S, Co, Mo) will be conducted by standard techniques including UV-Vis
and atomic absorption spectrophotometry. Summarized data will determine the
seasonal changes in nutritional quality of herbage as influenced by different
grazing management treatments.
Data collected for Experiment
A will be reported in a graduate student thesis scheduled for completion in
the spring of 2002.
Samples collected for Experiment
B are being analyzed for nutritional quality. Macromineral and micromineral
requirement curves for cow production periods are reported in "Mineral requirements
for beef cows grazing native rangelands", located in this section.
AOAC. 1990. Official
Methods of Analysis (15thEd.). Association of Official Analytical
Chemists. Arlington, VA.
and R.A. Terry. 1963. A two-stage technique for the in vitro digestibility
of forage crops. J. Br. Grassl. Soc. 18:104-111.
Waldo, D.R., and H.R. Goering. 1979. Insolubility of proteins in ruminant feeds by four methods. J. Anim. Sci. 49:1560-1568.
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