Angora mutton goats (Capra hircus) were fed diets of either live oak [Quercus virginiana (Small) Sarg. var. fusiformis], alfalfa hay (Medicago sativa L.), Coastal bermudagrass hay (Cynodon dactylon (L.)Pers.) or female ashe juniper (Juniperus ashei Buchholz) plus Coastal bermudagrass hay during the spring and fall of 1991 in a digestion/metabolism study. Nitrogen concentration of Coastal bermudagrass hay was nearly equal to that of alfalfa hay; nitrogen concentration of ashe juniper and live oak were much lower than those of the hays, and were higher in fall than spring. Dry matter intake and dietary nitrogen were highest for alfalfa hay, intermediate for Coastal bermudagrass hay, and lower for ashe juniper and live oak. Goats retained more nitrogen when consuming alfalfa and Coastal bermudagrass hays than juniper or live oak during fall, but differences were smaller (P > 0.10) during spring. Nitrogen balance was negative for goats consuming live oak in the spring. Nitrogen balance was positive for live oak in the fall and positive for ashe juniper for the spring and fall. Animals fed hay diets had higher levels of urine output than those fed juniper or live oak. Dry matter digestibility of juniper and live oak diets was less in fall than in spring. During fall, dry matter intakes of juniper and live oak were significantly lower than those of alfalfa and Coastal bermudagrass hays. We conclude that both ashe juniper and live oak foliage can provide nutrients for goats but only as portions of diets.

Expert judgment, standardized in a meaningful format, can be used to identify research/survey needs and to characterize areas of (dis)agreement in species responses, associated traits, and factors affecting responses. Feasible methods are needed to facilitate the evaluation of expertise in a complex domain characterized by moderate to low learnability.Specific objectives for this study were 1) to evaluate agreement among experts on range plant species behavior and 2) to develop an agreement-based classification method for plant species responses. Declarative information at landscape scale was elicited from 7 role-suggested experts on expected responses to cattle grazing (none, moderate, or heavy) and fire (absent, applied in late summer or fall, or applied in late winter or spring) of 198 plant species from the Edwards Plateau (Texas). Trends were requested to be assessed in a 3-level ordinal scale (decrease, unaffected, increase). Kappa statistics (pair-wise and multi-rater versions) and log-linear models were used to evaluate agreement. A procedure based upon cumulative probability distributions of possible rating combinations was developed to classify plant species while accounting for agreement, A total of 4,584 opinions (cattle grazing: 2,959; fire: 1,625) was elicited and analyzed. Low to moderate agreement was observed. Average pair-wise kappa statistics ranged from 0.07 to 0.39; multiple-rater kappa coefficients ranged from -0.17 to 0.53. Log-linear analyses were consistent with those estimations: agreement beyond chance or baseline association between ratings (P < 0.05) was observed in 62 out of 114 possible pair-wise cases. Non-homogeneous marginal distribution of opinion were an important source of disagreement. Experts performed beyond chance expectations in all scenarios but agreement was better land pattern of agreement more consistent) when scenarios were most familiar to the experts (e.g., heavy grazing and winter/spring burning). Almost 80% of species was classified beyond chance (P < 0.15) in grazing scenarios in contrast to only 40 to 60% in fire scenarios. This resulted from less agreement among experts but also from apparent lack of knowledge. The procedure developed to classify plant species provides an objective criterion for evaluating agreement in an ordinal scale. Graphical representations facilitate understanding of relationships between the number of expert sources and their ability to distinguish among classes for a pre-defined confidence level.

Generalized linear mixed models were used to obtain best linear unbiased predictions (BLUP's) of herbivore preferences for range plant species from expert knowledge contained in range site descriptions produced by the USDA Soil Conservation Service (currently Natural Resources Conservation Service). A total of 4,558 assessments of preference for cattle, deer, goats, and sheep on 167 plant species were available from 55 range site descriptions for the Edwards Plateau (Texas). Consistency of predicted preferences was evaluated through intraclass correlation estimated by restricted maximum likelihood. Predictions in observed (3-level ordinal) and legit scales were very similar; rank correlations between predictions in different scales ranged from 0.994 (P < 0.0001) for cattle to 0.998 (P < 0.0001) for sheep. Estimated intraclass correlations were also high (0.74 to 0.84 in observed scale and 0.82 to 0.92 in legit scale) suggesting consistent rankings of plant species across range sites. Metric multidimensional scaling and principal components analysis showed distinct patterns among the 4 herbivores. Grasses and browse were the most informative forage classes for discriminating preferences among herbivores, Deer and cattle exhibited the least similar diet preferences. Sheep and goats were intermediate; with sheep closer to cattle and goats most similar to deer. The pair deer-goat showed the most similar pattern of preferences. BLUP's of plant species preferences showed good agreement with published research on both individual plant species and forage classes. Optimal properties of mixed model procedures can be exploited to predict animal preferences at the range site scale from standardized expert opinion. These estimated preferences may be useful for modeling grazing effects at spatial scales compatible with management decisions.

State and transition (ST) descriptions of rangeland vegetation dynamics provide information on current perceptions of explicit causes of change in dominant vegetation. Structural attributes of ST applications allow an evaluation of the complexity of the ST model and comparisons with the organization of the traditional succession-retrogression model of secondary succession. An analysis of 29 applications of the ST model revealed consistent trends. The number of transitions connecting states showed a less-than-expected increase with the size of the application. This is probably associated with limitations to interpret complex relationships and a need to produce relatively simple applications. Larger applications exhibited a shift towards stable states with pivotal positions within structures less connected (i.e., with fewer transitions) than expected by chance for a given number of states. Thus, some stable states assume hey intermediary roles as the number of states considered increases. It is debatable whether this is a property of larger systems or an effect of modeling bias. The analysis of causes of vegetation change confirmed current perceptions about the importance of man-related sources of disturbance. Grazing, fire, and control of woody plant species are visualized as the most relevant man-related agents of change. Some ST applications retain autogenic behaviors embedded in transitions in spite of the event-driven nature of the approach. However, the ST model removes autogenic processes from their central role as general causes for vegetation change. This approach is theoretically very limited because no general properties or attributes of the components (e.g., plant species assemblages, individual species) or processes (e.g., growth, reproduction, mineralization) of the system are used in any comprehensive way to generate predictive rules of wider than local relevance. Alternative approaches are suggested that would allow ecological generalizations and comparisons across systems.

This 10-year study was designed to evaluate vegetation response to increasing stocking rates under rotational stocking (3 days graze, 51 days rest) and long-term rest. The 4 stocking rate treatments ranged from the recommended rate for moderate continuous grazing to 2.7 times the recommended rate. Common curly-mesquite [Hilaria belangeri (Steud.) Nash] increased (P = 0.05) in all grazed treatments and decreased in the livestock exclosure. Sideoats grama [Bouteloua curtipendula (Michx.) Torr.] along with other midgrasses decreased (P = 0.07) in all grazed treatments and increased in the livestock exclosure. Because the midgrasses were palatable species and not abundant, they were defoliated too intensively and too frequently. Rotational stocking was not able to sustain initial species composition at any of the stocking rates tested.

Angora and Spanish goats (Capra bircus) were exposed to ashe (Juniperus ashei Buchholz) female, ashe male, redberry (Juniperus pinchotti Sudw.) female and redberry male branches in cafeteria style feeding trials. Preferences were consistent across seasons (except winter). Spanish goats generally consumed more juniper than Angoras. Both breeds preferred ashe over redberry juniper and female over male plants. Concentrations of volatile oils varied significantly between species of juniper and among seasons, but not between sexes. Concentrations of total oils were greater in the spring and summer than in the fall and winter. Concentrations of sabinine+beta-pinene were greater in redberry than ashe for all seasons. Concentrations of myrcene were significantly greater for redberry during the spring and summer. Significant correlation of oil concentration with grams of juniper consumed indicated that specific oils were influencing preference for juniper. Correlations were similar for Angora and Spanish goats, indicating no differences between goat breeds in sensitivity to oils.

Rangeland is defined as land on which the indigenous vegetation (climax or natural potential) is predominantly grasses, grass-like plants, forbs, or shrubs and is managed as a natural ecosystem. If plants are introduced, they are managed as indigenous species. Rangelands include natural grasslands, savannas, shrublands, many deserts, tundras, alpine communities, marshes, and meadows (Forage and Grazing Terminology Committee 1991).

Two 2-year trials were conducted to evaluate and compare frontal, continuous, and 2-paddock rotation grazing systems on 'Plains' Old World bluestem (Bothriochloa ischaemum (L.) Keng.). Frontal grazing allows livestock a continuous opportunity to graze fresh forage via a livestock-pushed, sliding fence which allocates and controls grazing within a pasture. Trial 1 treatments included frontal grazing at a very high stocking density of 13.3 head ha-1 and continuous grazing at 4 stocking densities described as low, moderate, high, and very high. The mechanical design and components of our frontal grazing system were quite adequate in terms of the system's operation and interaction with the livestock herd. Significant (P 0.05); however, they were less than those under rotation grazing (P 0.05).

Beef cattle producers need management guidelines to select grazing system, stocking rate, and supplementation practices. A case study was conducted in Southern Great Plains to monitor cow (Bos taurus) and calf weights and percent calf crops for 5 yr. Grazing systems (continuous, 2-pasture 1-herd, 3-pasture 2-herd, and 4-pasture 3-herd deferred-rotation), stocking rates (heavy and moderate), and winter supplement (with and without) were compared in an incomplete factorial design. Winter supplementation was 135 lb/head of 41% crude protein cottonseed cubes. Grazing system, with or without supplement, had little effect on calf production. The primary source of variation in animal performance was among years. Stocking rate had the second greatest influence on calf production. Heavily stocked systems produced more pounds of calf per acre, but had greater annual fluctuations in production. Moderately stocked systems had greater and more stable production per cow. Supplementation increased weaned calf crop following heavy broomweed infestation, but had little effect in other years. Analysis of reproduction data, for Hereford cows used in this study, revealed a critical minimum body weight of 760 lb at initiation of the spring breeding season. In poor years, moderate stocking and winter supplement were required to maintain cow condition above the critical minimum body weight.

Short-duration grazing (SDG) has been purported to increase forage production and utilization compared to other grazing systems, and thus can sustain higher stocking rates. This study was designed to determine if standing crop could be maintained as stocking rates increased. Four stocking rate treatments ranging from the recommended rate for moderate continuous grazing to 2.5 times the recommended rate were applied in a simulated 8-pasture SDG system. There was little change in frequency and composition of short-grasses over the study, but mid-grass frequency and composition both declined. Standing crop of all major forage classes declined as stocking rates increased. However, the rate of decline was less than proportional to the increase in stocking rate during the growing season. By fall, standing crop was inversely proportional to stocking rate, leading us to conclude that standing crop could not be maintained at the higher stocking rates. Low standing crop in the fall indicated a potential shortage of forage at the high stocking rates during the winter.

Botanical and chemical compositions of Angora goat (Capra hircus) diets, determined with esophageally cannulated animals, were studied with and independent of a cattle-sheep-goat herd in a short-duration grazing (SDG) system. The study site consisted of 2 pastures in a 14-pasture, 1-herd SDG system. Each collection period in both pastures began when 44 animal units of livestock moved into either pasture 1 or 2. This methodology allowed a comparison of diet selection with and without grazing pressure. Goats selected more grass during the summer and fall than during the winter and spring. Browse was preferred over grass and forbs. Generally, higher crude protein values tended to be associated with large amounts of browse and forb selection. In vitro digestibility was highest in April and lowest in August. Crude protein was highest in April and lowest in November. Under this particular stocking rate (.19 animal unit years/ha) and weather conditions, we concluded that increased grazing pressure, caused by a 4-day graze period in a SDG system, had little effect on goat nutrition.

Proponents of rotational grazing claim that individual animal performance in a properly managed rotational grazing (RG) treatment will be equal to or greater than that in other, less intensively managed treatments even when rate of stocking in the RG treatment is much greater. The objective of this study was to examine the effect of a heavily stocked RG treatment, at 2 stock densities, on quality and botanical composition of cattle diets. The control treatment was a moderately stocked, continuously grazed pasture. Diets were collected from all treatments on 8 dates over a 22-month period using esophageally fistulated steers. Only minor differences occurred among treatments in dietary crude protein (CP), organic matter digestibility (OMD), and botanical composition. Diet quality and species composition of diets were closely correlated with quality and availability of live herbage, which varied more among trials than among treatments. Quality and composition of diets collected during the first and last day of grazing in the RG paddocks were not different. These data support the hypothesis that installing rotational grazing at a high stocking rate does not lower diet quality and would not be expected to be a factor affecting individual animal performance.

The Texas A&M Beef Cattle Simulation Model was used to simulate the effects of 79 sets of management alternatives on the growth, reproduction and lactation of beef cattle under conditions common to the Coastal Prairie region of Texas. The results of 16 simulations, a base plus 15 with apparent potential for increasing net return, were selected for economic evaluation. Management practices evaluated were calving season (winter, spring, fall or split season), winter supplementation (three levels) and age at first calving (2 or 3 yr of age). The highest levels of production were obtained by calving first at 2 yr of age and by calving during the fall. The larger amounts of supplementation resulted in higher production but did not always produce higher net returns. The three most profitable sets of alternative practices involved spring calving. The two most profitable alternatives employed calving at 2 yr of age. Calving during the winter, with heifers calving at 3 yr of age and supplementing at the lowest levels consistently resulted in the lowest reproduction, smallest amount of herd production and lowest net returns. For the producer with practical alternatives for utilizing resources, local cow-calf production was not a viable, current economic choice; all of the production alternatives examined gave negative net returns over total costs. Several measures of production and economic efficiency were examined. Of those considered, none was found to be a satisfactory indicator for ranking management alternatives by net returns.