• Nitrogen and Energy Budgets of Free-Roaming Cattle

      Senft, R. L.; Stillwell, M. A.; Rittenhouse, L. R. (Society for Range Management, 1987-09-01)
      Energy and nitrogen (N) budgets of free-roaming yearling heifers were quantified. Energy and N retention were estimated from liveweight gains. Intake and excretion of N and energy were measured directly. Dry matter intake per unit metabolic body weight (MBW = Bwkg.75) varied seasonally, peaking in late growing season. Fecal dry matter output, which was related to dry matter intake, also peaked late in the growing season. Urine volume, however, peaked early in the growing season. Urinary N excretion per MBW was correlated with dietary N concentration (r = .79). Fecal N excretion per MBW was relatively constant while fecal N concentration varied. Partitioning of N losses between feces and urine varied seasonally, with 54% excreted in urine during the growing season (April through October) and 45% in urine during the dormant season (November through March). On a year-round basis, 8% of ingested N was incorporated into body tissue. Fecal energy excretion trend followed that of gross energy intake. Digestible energy intake per MBW was relatively high throughout the growing season and steadily declined after onset of the dormant season. Urinary energy output was closely related to urinary N output and peaked early in the growing season. Metabolizable energy (ME) followed dynamics similar to those of digestible energy. Net energy for liveweight gain accounted for about 8% of gross energy intake on a year-round basis. ME and crude protein intake were above maintenance requirements during the growing season, but were inadequate during the dormant season. ME intake apparently limited growth early in the growing season; protein intake was limiting late in the growing season.
    • Nitrogen Concentration in Blood and Rumen Liquor of Cattle Fed Low Protein Diets

      Hinnant, R. T.; Kothmann, M. M. (Society for Range Management, 1987-09-01)
      Crude protein determination of a grazing animal's diet is difficult and expensive. Traditional methods include forage sampling (usually not representative of the diet selection process) and the use of fistulated animals for direct diet collections. Indirect methods were tested to provide a rapid estimate of diet protein at less cost. Concentration of blood serum urea N (BUN) and the concentration of total nitrogen (N), protein N, microbial protein N, and non-protein N (NPN) in rumen liquor were determined in 4 cows and 4 steers fed diets at maintenance (7.1%) and 3 sub-maintenance levels of crude protein (CP) (4.3, 5.2, and 6.2%). Cottonseed hulls constituted the basal diet, with cottonseed cubes added to vary the CP content and molasses added to provide isocaloric diets. However, diet CP affected the in vivo digestibility of the diets and hence their caloric values. Concentrations of BUN did not differ (P<.05) with changes in dietary CP. The concentration of total N, protein N, microbial protein N, and nonprotein N (NPN) in the rumen liquor (P<.05) increased as diet CP increased. The percentage of NPN in the total N was reduced when diet CP was below 5.2%, but it did not differ significantly when diet CP was between 5.2 and 7.1%. The ratio of microbial nitrogen to total protein nitrogen was not affected by level of dietary crude protein. Total N was a sensitive indicator of the CP content of the diet and was the easiest and quickest method tested.
    • Rainfall Interception by Midgrass, Shortgrass, and Live Oak Mottes

      Thurow, T. L.; Blackburn, W. H.; Warren, S. D.; Taylor, C. A. (Society for Range Management, 1987-09-01)
      Interception, as a function of simulated rainfall intensity and duration, was determined for a midgrass [sideoats grama (Bouteloua curtipendula (Michx.) Torr.)] and a shortgrass [curleymesquite (Hilaria belangeri (Steud.) Nash)]. In addition, the redistribution of natural precipitation via plant interception was determined for live oak (Quercus virginiana Mill.) mottes. Interception storage capacity for sideoats grama and curleymesquite was 81 and 114% of dry weight, respectively. This difference was attributed to physical characteristics of the species and their respective growth forms. However, because sites dominated by sideoats grama had more standing biomass (3,640 kg ha-1) than sites dominated by curleymesquite (1,490 kg ha-1), it was estimated that a sideoats grama dominated site had an interception storage capacity of 1.8 mm compared to curleymesquite dominated site with an interception storage capacity of 1.0 mm. Based upon precipitation event size and distribution for the study site at the Texas Agricultural Experiment Station near Sonora, Texas, the estimated interception loss for curleymesquite dominated sites was 10.8% of annual precipitation, compared to 18.1% interception loss for sideoats grama dominated sites. Only 54% of the annual precipitation reached mineral soil beneath the oak mottes as throughfall or stemflow. The remainder of the precipitation was intercepted by the motte canopy or litter layer and evaporated. Due to the water concentrating effect of stemflow, soil near the base of trees received about 222% of annual precipitation. Soil at a distance greater than approximately 100 mm from a tree trunk received only 50.6% of annual rainfall. Individual tree canopy width, height and depth measurements were insignificant predictors of stemflow and throughfall. Interception, throughfall and stemflow, expressed as percent of storm precipitation, were well-defined curvilinear functions.
    • Ranch Values and the Federal Grazing Fee

      Lambert, D. K. (Society for Range Management, 1987-09-01)
      Past analysis of the impacts of higher federal grazing fees on ranch values have been purely speculative due to the absence of observations on sales of Western cattle ranches under a wide range of fee levels. An income approach to ranch value determination is described here in which numerous parameters affecting value can be varied. Solutions attained under different grazing fees are capitalized into the net present value of a potential ranch investment. Substantial decreases in ranch revenues and ranch values can occur with large fee increases in cases where public land forage comprises a large share of a ranch's annual forage supply.
    • Soil Seed Banks Associated with Individual Broom Snakeweed Plants

      Osman, A.; Pieper, R. D.; McDaniel, K. C. (Society for Range Management, 1987-09-01)
      The influence of individual broom snakeweed (Gutierrezia sarothrae [Pursh] Britt. & Rushby) plants on the distribution of buried viable seed and the distribution of plants in the field was studied in a desert grassland in southern New Mexico. Surface soil samples collected at 3 distances from a central broom snakeweed plant were watered in pots in a greenhouse and numbers of each species emerging were counted. Densities of each species were also determined in the field. Some species (Sporobolus flexuosus [Thurb.] Rybd., S. contractus Hitchc., Descurainia pinnata [Walt.] Britton, and Dithyrea wislizenii Engelm.) emerged in greatest numbers from soil collected in the zones closest and at the greatest distances from the broom snakeweed. Emergence of other species declined in relation to distance from the central snakeweed plant. In the field, grasses generally increased in relation to distance from the central broom snakeweed plant while the pattern for forbs was not consistent.
    • Steer and Vegetation Response to Short Duration and Continuous Grazing

      Pitts, J. S.; Bryant, F. C. (Society for Range Management, 1987-09-01)
      Comparisons were made over a 4-year period between 1-herd, 16-pasture short duration grazing (SDG) and continuous grazing (CG) on the Texas High Plains. Animal performance, vegetation response, and diet quality were evaluated. Stocking rate on SDG was equal to that on CG the first year (13.3 ha/AU), double that on CG in the second year, and 1.5 times that on CG the third and fourth years. Average daily gain (ADG) of steers was the same (0.33 kg/day) between SDG and CG the first year. When stocking was doubled on SDG the second year, steers on SDG gained 0.15 kg/day compared to 0.25 kg/day under CG. In the third and fourth years, with stocking under SDG at 1.5 times that on CG, gains were similar. Standing crop biomass on SDG fell below that on CG after 1 year of grazing. In the second year standing crop was greater (P<0.05) on SDG than on CG, but in years 3 and 4, standing crop on the SDG was less than on CG. Changes in species composition were the same on both CG and SDG. Steer diet composition and quality were evaluated during the growing season (May to October) of year 4. Steers on SDG consumed 15% more forbs (39% vs 24%) than steers on CG. No differences (P>0.05) between CG and SDG were observed for dietary crude protein or in vitro digestible organic matter. SDG did not improve animal performance, diet quality, or forage availability over CG when evaluated over 4 years.
    • The Effect of Agriculture on Ferruginous and Swainson's Hawks

      Schmutz, J. K. (Society for Range Management, 1987-09-01)
      Raptors are an important component of prairie ecosystems. I examined the effects of grassland conversion to agricultural fields on densities of nesting prairie hawks. Densities of Swainson's hawks were recorded for comparison. The 2 species of congeneric hawks responded differently to habitat loss despite considerable overlap in their use of resources. As cultivation on study plots increased, ferruginous hawks declined. Swainson's hawks were more abundant in areas of moderate cultivation than in grassland or in areas of extensive cultivation. Differences in the hawks' responses were attributed to differences in their ecology, primarily prey utilization. There was no evidence that soil quality affected hawk abundance.
    • Vegetation Trends within Rest-Rotation and Season-long Grazing Systems in the Missouri River Breaks, Montana

      Watts, C. R.; Eichhorn, L. C.; Mackie, R. J. (Society for Range Management, 1987-09-01)
      Trends in canopy-coverage of vegetation and bare ground were measured inside and outside exclosures on recent burns within three-pasture rest-rotation and season-long grazing systems over a 10-year period. Results suggested that rest-rotation grazing may maintain vegetation and soil cover somewhat comparable to ungrazed cattle exclosures on rough breaks-type range in north-central Montana. Season-long grazing may not maintain satisfactory vegetation and soil cover in the area.
    • Ytterbium-Labeled forage as a Marker for Estimation of Cattle Fecal Output

      Musimba, N. K. R.; Galyean, M. L.; Holechek, J. L.; Pieper, R. D. (Society for Range Management, 1987-09-01)
      This study evaluated the accuracy of a once daily dose of ytterbium (Yb)-labeled forage as a marker to estimate fecal output of cattle grazing at the National Range Research Station, Kiboko, Kenya. Ytterbium-labeled forage was administered daily to 15 zebu steers for 10 consecutive days for each of 3 trials. During the last 5 days of each trial, fecal grab samples were collected at 6-h intervals. During this same 5-day period, total fecal output was collected from 9 of the steers. Ytterbium estimates of fecal output were 114%, 104%, and 144% of actual fecal output for March, April, and July trials, respectively. Dry matter and organic matter intake estimates between Yb and total collection procedures differed (P<.05) in the July trial, but not the March and April trials. Compared with total fecal collection, Yb overestimated organic matter intake by 20, 2, and 40%, respectively for March, April and July trials. Based on our results, daily dosing of Yb-labeled forage will provide reasonable estimates of fecal output when relative estimates of intake between range management treatments are needed.