Dormant grasses are usually deficient in nutrients needed to meet cattle requirements. Research results indicate that grazing activities are sensitive to some environmental variables and vegetative (sward) characteristics; however, minimal information is available on the influence of supplementation regimens on cattle grazing activities. Supplementation studies reviewed had forage N levels that ranged from .9 to 1.2% and forage intakes that ranged from 12.3 to 31.0 g of OM/kg of BW. Protein supplementation affected (P < .05) time spent grazing: unsupplemented (NS) cattle grazed approximately 1.5 h/d more than did supplemented (S) cattle. Type of supplemental protein and time of daily feeding did not affect (P > .10) this response. Different types and timing of starch-based supplements produced variable results; however, increasing the level of supplemental starch decreased (P < .05) daily grazing time. Protein supplementation increased (P < .05) harvesting efficiency (HE; grams of forage intake.kilogram of BW-1.minute spent grazing-1); however, high-starch supplements either did not alter (P > .10) or decreased (P < .05) HE compared with NS. Progressive defoliation can influence grazing behavior in both sheep and cattle grazing actively growing forage; however, evaluation of vegetative characteristics of dormant forage and the corresponding effect on grazing behavior are not known. The effects of various grazing management strategies on cattle behavior are inconclusive and deserve additional attention. Methods and (or) management practices that modify behaviors to control feed intake, improve efficiency, or reduce stress could be major contributions to the livestock industry.

Two experiments were conducted with beef steers (Exp. 1, average BW of 580 kg; Exp. 2, average BW of 247 kg) to evaluate the use of no supplements (CON) or daily supplementation with (OM basis) .34% of BW of cracked corn (CORN), .34% of BW of wheat bran (WBBW), or .48% of BW of wheat bran (WBISO; calculated to be isocaloric to CORN) on digestive responses (Exp. 1) and live weight gain (Exp. 2). In Exp. 1, type of supplement did not affect (P > .10) the dietary fiber or N constituents, but in vitro OM disappearance of the forage differed (P < .10) with supplementation and type of supplement fed. Supplemented steers consumed less (P < .05) forage and total OM. Particulate passage, fluid passage, and ruminal pH were not affected (P > .10) by supplementation. Ruminal NH3 N concentration showed (P < .05) a treatment x sampling time interaction and, in general, WBBW and WBISO steers had greater ruminal NH3 N than CORN and CON steers. Total VFA concentrations and molar proportions of propionate were lower (P < .10) in CON steers than in supplemented steers; no differences were noted (P > .10) among supplemented steers. Molar proportions of acetate were lower (P = .01) in supplemented steers than in CON steers and were greater (P = .03) in WBBW steers than in WBISO steers. Butyrate molar proportions were lower (P < .05) in CON steers than in supplemented steers and differed (P < .10) with type and quantity of supplement supplied. In situ forage NDF disappearance at 6, 9, and 24 h after feeding and rate of disappearance were greater (P < .05) in CON steers than in supplemented steers. In Exp. 2, CON steers weighed less (P = .01) than supplemented steers, CORN steers weighed more (P = .08) than wheat bran-supplemented steers, and WBISO steers weighed more (P = .02) than WBBW steers; ADG for 90 d followed a similar response. Results suggest that supplementation of wheat bran rather than corn did not seem to stop the reduction in forage intake or OM digestion associated with corn supplementation.

Twenty fine-wool, ruminally cannulated lambs (average weight 45-9 kg) were used in a completely random design to evaluate the ability of three internal markers to predict dry matter digestibility and two external markers to estimate faecal output. Lambs were allotted randomly to one of four diets: 100% prairie hay (PH), 100% lucerne hay (LH), 50% prairie hay:50% sorghum grain (PS) and 50% lucerne hay: 50% sorghum grain (LS). The trial consisted of a 14-day adaptation period followed by a 7-day total faecal collection period. Feed and faecal samples were subjected to 96 h ruminal fluid and 48 h acid-pepsin digestions, followed by extraction with acid detergent (IVADF) or neutral detergent (IVNDF) solution. Dry matter digestibility (DMD) calculated from feed:faeces ratios of IVADF, IVNDF and acid detergent lignin (ADL) was compared with in vivo apparent digestibility. Ytterbium-labelled forage (YLF) and dysprosium-labelled faeces (DLF) were pulse-dosed via ruminal cannulae, and faecal Yb and Dy excretion curves were fitted to a one-compartment, agedependent model for estimation of faecal output, paniculate passage rate (PPR) and mean gastrointestinal retention time. In vivo DMD in lambs fed PH was greater (P < 005) than DMD calculated from IVNDF, IVADF and ADL. In lambs fed LH and LS, in vivo DMD did not differ (P > 005) from marker estimates. In vivo DMD for lambs fed PS did not differ from IVNDF or IVADF estimates but was greater than (P < 005) the ADL estimate. No differences (P > 005) were observed in recovery among the three internal markers for any of the diets. Faecal output for lambs fed PH did not differ {P > 005) from marker estimates but was overestimated by 15 to 20% by YLF and DLF. Faecal output for lambs fed LH was similar to the estimate from YLF, but less than (P < 0-05) the estimate with DLF. For lambs fed PS, faecal output did not differ from marker estimates, but YLF and DLF values were 16% lower and 17% higher, respectively. No significant differences were observed in actual and estimated faecal output for lambs fed the LS diet. Estimates of PPR with DLF were numerically greater than YLF estimates for all diets except LS. Correspondingly, mean gastrointestinal retention time was less (P < 005) for DLF compared with YLF for all diets except LS.

Four field trials were conducted from early August to late October, 1982, on blue gramn (Boureloue graci&s) rangeland in south-central New Mexico to examine relationships among grazing season, diet botanical and chemical composition, and rumen fermentation in beef steers (Bos ciuwus). Diets contained an average of 83% grasses and 17% forbs from early August through late September and 77% forbs in late October. Cell wall content of the diet decreased from the early growing season (74.9%) through the onset of dormancy (64.9%) while acid detergent ffber and lignin increased (41.9 to 52.9% and 5.2 to 12.7%, respectively) and crude protein content declined from 18.4 to 11.7%. Soluble and insoluble nitrogen (N) fractions of the diet reflected crude protein; from 13 to 36% of N was in unavailable forms. The extent of in vitro organic matter digestion declined from the early growing season (66.5%) through onset of dormancy (47.9%). Ruminal ammonia concentrations declined as season progressed: 6.0 mg/109ml was the lowest concentration observed. Declining diet quality was accompanied by an upward shift in digestr pH and altered proportions of volatile fatty acids (VFA) in rumen contents. Total VFA concentration was highest in late August (106.3 mmoles/liter). Ruminal measures generally reflected changes in dietary protein and digestibility but concentrations could also reflect changes in digesta flow rates. Finally, data suggest that crude protein may not be a good measure of protein supply to livestock grazing on ranges with diverse forage types. Several authors have discussed the influence of advancing season of growth and nutritive value of range plants and relative values of forage classes (Cook 1983, Pieper et al. 1978, Kothmann 1980). Such changes are usually discussed in relation to the daily requirements of animals grazing in the plant communities. However, few studies have related diet quality to ruminal environment in the grazer. The rumen is the primary site of forage degradation. Products of ruminal fermentation (ammonia, volatile fatty acids) and the pH of ruminal contents can influence fiber digestion (Mertens 1979), microbial protein synthesis (Satter and Slyter 1974) and, finally, energy and protein supplied to the grazing host. Therefore, knowledge of seasonal fermentation patterns in grazing range animals might suggest means of enhancing diet utilization and animal performance. The objectives of this study and another reported subsequently (McCollum and Galyean 1985) were to relate seasonal changes in diet composition with changes in rumen function and forage intake in beef steers (Bos taurus) grazing native blue grama (Bouteloua gracilis) rangeland during 4 periods of a growing season. Study Area Materials and Methods The Fort Stanton Experimental Ranch is in the foothills between the Sierra Blanca and Capitan Mountains in southern Lincoln County, New Mexico. Pieper et al. (1971) described the vegetation, topography, and climate of the Ft. Stanton Ranch. Briefly, annual precipitation averages 40 cm and m...

To compare the effects of time of daily protein supplementation on grazing behavior, forage intake, digesta kinetics, ruminal fermentation, and serum hormones and metabolites, 12 ruminally cannulated Holstein steers (449 and 378 kg average initial and final BW, respectively) were allotted to three groups. Treatments consisted of CON = no supplement, AM = cottonseed meal (.25% of BW) at 0600, and PM = cottonseed meal (.25% of BW) at 1200. Steers grazed a dormant (1.1% N) intermediate wheatgrass (Thinopyrum intermedium Host) pasture. Sampling trials occurred in December, January, and February. Supplementation altered (P = .01) time spent grazing; CON steers grazed approximately 1.5 h longer than supplemented steers. Supplemented steers lost less (P = .02) BW (-40 kg) than CON steers (-75 kg) did. Supplementation did not alter (P greater than .15) forage OM intake; however, total OM intake was greater (P = .01) for supplemented steers (22.3 g/kg of BW) than for CON (18.4 g/kg of BW) steers. Supplementation did not affect (P greater than .15) digesta kinetics. Extent of in situ NDF (96 h) and rate (%/h) of disappearance for supplemented steers was greater (P = .01) than for CON steers. Across all periods, ruminal NH3 N and total VFA concentrations were lower (P = .01) for CON steers than for supplemented steers. Serum insulin (ng/mL) concentration was lower (P = .03) and concentration of serum growth hormone (ng/mL) was higher (P = .02) for CON steers than for supplemented steers. Cottonseed meal supplementation enhanced utilization of intermediate wheatgrass; however, supplementation time had minimal effects on the variables measured.

The sagebrush-grass rrnge in southcentral Wyoming presently summer and winter grazing seasons of 198 I. supports large numbers of feral homes and domestic livestock. Diets of feral horses and cattle during summer and winter grazing Study Area were evaluated using fecal analydr under 2 stocking levels in small pastures. Horses and cattle consumed primarily grasses during the Study sites were located in the Red Desert, northeast of Rock summer and winter. However, shrubs and forbs were also impor-Springs, Wyo., in Sweetwater County(Fig. I). A semiarid climatic tant dietary components. Needleandthread, Sandberg bluegrass, thickspike wheatgrass, Indian ricegrass, gray horsebrush, and winterfat were the maJor foods of horses and cattle during the summer anti wfnter. Dietary overlap between horses and cattle during the summer averaged 72% and Increased to 84% during the winter. Horses and cattle selected foods in a simllrr order. Large increases in feral horse (Equus cubaflus) numbers have occurred in the western United States since passage of the Wild Free-Roaming Horse and Burro Act of 1971 (Artz 1977, Wolfe 1980). These increases have become a major concern to public land managers, livestock producers, and animal welfare groups. Cook (1975) reported a 20-30% annual increase in feral horse populations in the western United States yearly from 1973 through 1975. This increase in population has forced public land administration agencies to reduce domestic livestock grazing in localized areas to accommodate the grazing pressure feral horses have added on Fig. 1. Locations ofsummer and winrer sites in the Wyoming Red Lksert. western ranges (Artz 1977). In 1974 the feral horse population in pattern prevails over both areas. Yearly precipitation averages 21.5 Wyoming was estimated at 4,434 animals; however a recently cm with approximately 40% falling from April to June. Snowfall completed census estimates the population at 10,448 animals usually occurs from October to May (BLM 1978 a,b). (USDI-BLM and USDA-FS 1980). Three distinct vegetation types cover most of the summer study An important factor in determining proper animal stocking area. The sagebrush-grass type on sandy and loamy range sites is levels for a given range is the botanical composition of diets of characterized by a shrub layer of big sagebrush (Artemisia tridenmajor herbivores and the relationship of diets to available forages. tata subsp. tridentata, vaseyanu, Wyomingensis), Douglas rabbit-Animal Science, University of Wyoming, assistant professor, Division of Range greasewood (Sarcobatus vermiculatus), rubber rabbitbrush (Chrymanagement, an! associate profeso~, Division of Animal Science, University of sothamnus nauseosus), fourwing saltbush (Atriplex canescens), Wypming, Laranue 8207 I. Mr. Krysl IS currently a graduate assistant! Department of ;;&?I and Range Scwnces. Box 3-1. New Mexxo State Universl(y, Las Cruces spiny hopsage (Grayia spinosa), Sandberg bluegrass, Indian ricegrass, needleandthread, lambsquarter (Chenopodium alba), west-This study was ...

Twelve ruminally cannulated and six intact crossbred beef steers were used in a randomized complete block design to evaluate the effects of stocking density of a riparian pasture in the Sierra Nevada mountains on grazing behavior, dietary selection, forage intake, digesta kinetics, and growth rates of Carex nebraskensis and Juncus balticus. Nine .5-ha pastures were assigned to one of three treatments: ungrazed (CON) or grazed to leave either 1,500 kg/ha (LOW) or 1,000 kg/ha (MOD). Two collections were conducted during the summer of 1992 (following winter drought) and 1993 (following above-average winter precipitation). Standing crop biomass was greater (P < .05) in grazed pastures than in CON pastures at initiation of grazing in 1992 but not in 1993. After grazing in both 1992 and 1993, a treatment x intrapasture location interaction was noted (P < .05). Tiller growth rates in both 1992 and 1993 were affected (P < .05) by a treatment x growth period interaction. Stocking density did not alter (P > .10) botanical or chemical composition of the diet in 1992, and only minor differences were noted (P < .05) in 1993. Forage intake, passage rate measures, and total time spent loafing did not differ (P > .10) between LOW and MOD steers. Within the mid-meadow area in 1992, loafing time was greater (P< .05) for MOD steers than for LOW steers. In 1993, a treatment x trial interaction was noted for loafing time in all three areas. Total time spent grazing was greater (P < .05) for MOD steers than for LOW steers in 1992 and was affected (P < .05) by a treatment x trial interaction in 1993. In 1992 grazing time along the streamside was greater (P < .05) for LOW steers than for MOD steers, and significant treatment x trial interactions were noted for grazing time spent along the forest edge and mid-meadow areas. In 1993, only streamside grazing time was influenced by treatment being greater (P < .05) for MOD steers than for LOW steers. In general, our data suggest that management decisions to reduce stocking densities may force cattle to congregate along streambanks and to concentrate grazing and loafing activities in those areas.

Six beef steers (British x Brahman) cannulated at the rumen, duodenum and ileum (avg wt 334 kg) and three mature steers (British x British) cannulated at the esophagus were used in a replicated 3 x 3 latin square design and fed no supplement (C), .5 kg soybean meal (SBM) or .5 kg steam-flaked sorghum grain (SFS).head-1.d-1 (DM basis) while grazing blue grama rangeland. Periods of the latin square included a minimum of 14 d for adaptation and 11 d for esophageal masticate collection and digesta sampling. In September, October and November, respectively, forage collected by esophageally cannulated steers averaged 74.5, 88.8 and 71.0% grasses; 2.06, 1.53 and 1.77% N and 68.3, (P greater than .10) by treatment, but total N intake was greater (P less than .05) for SBM vs C and SFS treatments. No differences (P greater than .10) were detected among treatments in OM, NDF, ADF and N digestibilities in the rumen, small intestine or hindgut, but total tract OM digestibility was greater (P less than .10) for SBM and SFS than for C, and total tract N digestibility was greater (P less than .10) for SBM than for C or SFS. Duodenal ammonia N flow was greater (P less than .05) when SBM was fed that when SFS and C were fed, but microbial N and non-ammonia, non-microbial N flows and microbial efficiency were not altered by treatment. Likewise, ileal N flow was not affected (P greater than .10) by treatment. Particulate passage rate, gastrointestinal mean retention time, forage in vitro OM disappearance and in situ rate of forage NDF digestion also were not affected (P greater than .10) by treatments. Ruminal fluid volume was greater (P less than .05) for SFS vs SBM and C treatments, but no differences were noted in fluid dilution rate. Ruminal fluid ammonia concentration was greater (P less than .05) when SBM was fed than when SFS and C were fed (13.5, 9.9 and 8.7 mg/dl, respectively), whereas pH and total VFA concentrations were not different (P greater than .10). Proportion of acetate in ruminal fluid was less (P less than .10) for SBM and SFS than for C. Small amounts of supplemental SBM and SFS had little effect on forage intake, ruminal fermentation and site of digestion but both increased total tract OM digestion in steers grazing blue grama rangeland.