Nutrient Removal Rates from Ruminoretic- ula of Cattle Grazing Kansas Flint Hills

A Hereford steer and heifer were used to compare rumen removal rates of forage nutrients from Kansas Flint Hills range over a 2-year period. Rumens were emptied after an overnight fast and the contents sampled, weighed, and returned to the mmen. The cattle were then fed a known amount of range forage and fasted for 12 hours, at which time the rumen evacuation procedure was repeated. Removal rate calculations were based on change in rumen contents during the It-hour fast. All nutrients studied passed the rumen more rapidly during spring and summer months than fall and winter months. Fibrous fractions were removed more rapidly than cell solubles and crude protein, which may indicate that optimum utilization of native Flint Hills range forage is not being achieved. Methods which increase microbial attack of plant cell wall contents may significantly improve livestock production on native rangeland. Nutrient removal rate is the rate at which nutrients are removed from the ruminoreticulum due to digestion, absorption, and passage of undigested residues to the omasum (Yadava and Bartley 1964). Alfalfa diets have shown more rapid removal of soluble than fibrous fractions (Kick and Gerlaugh 1935, Silver et al. 1935, Burroughs et al. 1946, Hale et al. 1947, Radisson 1955, Yadava and Bartley 1964). Krzywanek and Quitteck (1936) (pasture grass and clover); Hamilton et al. (1955) (grass mixture); Stallcup et al. (1956) (clover silage and grass hay); and Jacques (1981) (native range forage) show slower removal of soluble than fibrous fractions. ObJecttves of the present study were to determine rumen removal rates of nutrient fractions as range forage quality changed and to compare removal rates among those fractions. Study Area and Methods The study area was 5 km northwest of Manhattan, Kans. Vegetation was largely Andropogon gerardi (big bluestem), Sorghastrum nutans (indiangrass), and Andropogon scoparius (little bluestem). Experimental animals were a ruminally fistulated Hereford steer and heifer 2 to 3 years of age grazing Flint Hills range from May, 1979, to August, 198 1. Winter supplementation, when necessary, ceased 10 to 14 days prior to the sample date. Samples were taken biweekly from May through October and monthly from November through April. Cattle were penned and fasted overnight with water prior to the sample day. The following morning total contents of the rumen were removed as described by Yadava and Bartley (1964). Digesta was placed in a large tub, mixed thoroughly by hand for 3 to 5 minutes, quickly sampled with a 600-ml, 12-cm diameter container and weighed. Digesta was then returned to the rumen. This method was employed because its successful use at Kansas Authors are assistant professor and research agronomist, USDA-AR& Crop Production Research Unit, University of Missouri, Colombia 6521 I; professor of range management and research associate, Department of Agronomy Throckmorton Hall, Kansas State Univeristy, Manhattan 66506. This article is contribution No. 83-89-J. Dept. of Agronomy. Manuscript accepted May I, 1984. 70 State University and other institutions and its acceptance in a variety of scientific journals supports its validity for measuring the parameters of interest (Reid 1965). Forage offered to the cattle was cut with a sickle-bar mower either on the sample morning or the evening before. When cut the evening before, it was refrigerated overnight. Cattle were offered a known amount of forage for I hour or until they ceased eating. Refused forage was collected, weighed, sampled for water loss and subtracted from the total amount offered. After feeding, the cattle were fasted with access to water for 12 hours. Then their rumens were emptied, and the contents mixed, weighed, and sampled. Rumen and “forage-fed”samples were weighed, dried in a forcedair oven at 38”C, and weighed again to determine dry matter (DM). They were ground through a Wiley mill (l-mm screen) and cell solubles (CS), cell walls (CW), cellulose(C), and hemicellulose (HC) were determined (Goering and Van Soest 1970). Microkjeldahl nitrogen (N) was measured calorimetrically and crude protein (CP) estimated by N X 6.25. We used a randomized complete block type of design with animals as replications. Data were analyzed by analysis of variance with time as treatments. Means were separated using Duncan’s new multiple range test (K.05, Duncan, 1955). Results and Discussion Forage Fed Characteristics Greater CP and CS percentages and lower CW, C, and DM percentages were observed during periods of traditionally high forage quality. Crude protein and CS decreased and CW and C increased with maturity. Hemicellulose content varied little with maturity. Our forage quality observations support quality aspects of harvest recommendations for Flint Hills native hay (Launchbaugh and Owensby 1978) which state the best quantity-quality relationship came from mid-July harvesting. Soluble Fraction Removal among Dates Removal of soluble fractions (CS, CP) was more rapid (K.05) during periods of high forage quality than low quality periods. Cell soluble removal rates (Fig. 1) represent that phenomenon. Slowest removal rates often occurred during the latter portion of the dormant period. That may have been due to advanced weathering of standing forage and absence of cool-season selection in harvested forage fed to cattle. Fibrous Fraction Removal among Dates Removal rates of CW showed the same trend of more rapid removal (x.05) during higher quality periods than low quality periods (Fig. 2). Figures (not shown) for DM, C and HC are similar to that for CW. Increases in forage fibrous fractions (Allinson 1971, Wilkins 1972) and decreases in soluble fractions (Terry and Tiley 1964, Akin et al. 1977) are linked to decreases in digestibility (Connor et al. 1963, Allison 197 1, Duble et al. 197 1). Since greater digestibility results in increased intake and rate of passage (Blaxter et al. 1956, 1961) and reduced rumen retention time (Balch and Campling JOURNAL OF RANGE MANAGEMENT 38(l), January 1985