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The objectives of the present study were to determine if the molecular weight of condensed tannins (CT) from warm-season perennial legumes affects the biological activity of CT relative to suppression of methane (CH4) production by ruminants, and to identify potential North American native forage plants to use for mitigation of enteric CH4 emission. Eight North American native warm-season perennial legumes were evaluated: Leucaena retusa Benth. (littleleaf leadtree), Desmanthus illinoensis (Michx.) MacMill. Ex B.L. Rob. & Fernald (Illinois bundleflower), Lespedeza stuevei Nutt. (tall lespedeza), Mimosa strigillosa Torr. & A. Gray (powderpuff), Neptunia lutea (Leavenworth) Benth. (yellow puff), two ecotypes of Acacia angustissima var. hirta (Nutt.) B.L. Rob (prairie acacia), and Desmodium paniculatum (L.) DC. var. paniculatum (panicledleaf ticktrefoil). Two introduced legumes were also included: Arachis glabrata Benth. (rhizoma peanut) and Lespedeza cuneata (Dum. Cours.) G. Don (sericea lespedeza). Forages were fermented with cattle rumen fluid for 48 h anaerobically using an in vitro gas production technique. D. paniculatum, L. stuevei, and M. strigillosa were high in CT, ranging from 11.7 to 12.5%. D. illinoensis, L. cuneata, N. lutea, and two ecotypes of A. angustissima var. hirta had less CT (P

The beneficial effects of forages containing condensed tannins (CTs) on ruminants are well documented, but the chemical features of CT that yield benefits have not been defined. Some evaluations of limited numbers of highly purified compounds have resulted in positive correlations between CT molecular weight (MW) and biological activity, while others have failed to show a correlation. The objectives of this study were to determine if MW of CT could predict biological activity relative to protein precipitability. MW of condensed tannin, protein-precipitable phenolics (PPP), and the amount of protein bound (PB) were determined for nine species of warm-season perennial legumes. There was no correlation between PPP or PB and MW (R2 0.11 and R2 0.02, respectively). However, CT concentration did correlate with PPP and PB (R2 0.81 and R2 0.69, respectively). It was concluded that CT MW does not explain the variation in protein precipitation by CT from the forage legumes surveyed.

Preface 2 Members of the committee 3 Acknowledgements 3 An International Terminology for Grazing Lands and Grazing Animals 1. Grazing land terms 4 2. Vegetation: descriptive terms 6 3. Forage growth and harvest 8 4. Forage nutritive value and intake 9 5. Management of grazing lands 12 6. Land–forage–animal relationships 15 7. Stocking methods 16 References 18 Appendix I. References and additional information for selected terms 21

The effect of molecular weight of condensed tannins (CT) from a variety of warm-season perennial legumes commonly consumed by sheep and goats on anthelmintic activity has not been previously explored. The objectives of this study were to determine if molecular weight of CT from warm-season perennial legumes could predict the biological activity of CT relative to anthelmintic activity against ivermectin resistant L3 stage Haemonchus contortus (HC) using a larval migration inhibition (LMI) assay. A second objective was to determine if CT from warm-season perennial legumes possess anthelmintic properties against L3 stage (HC). Lespedeza stuevei had the greatest concentration of total condensed tannin (TCT; 11.7%), whereas, with the exception of Arachis glabrata, a CT-free negative control, Leucaena retusa had the least TCT (3.3%). Weight-average molecular weight of CT ranged from 552 Da for L. stuevei to 1483 Da for Lespedeza cuneata. The treatments demonstrating the greatest percent LMI were L. retusa, L. stuevei and Acacia angustissima var. hirta (65.4%, 63.1% and 42.2%, respectively). The ivermectin treatment had the smallest percent LMI (12.5%) against ivermectin resistant L3 HC. There was a weak correlation (R(2)=0.34; P=0.05) between CT MW and percent LMI, suggesting that molecular weight of CT is a weak contributing factor to CT biological activity as it relates to LMI of L3 stage HC. L. stuevei, L. retusa and A. angustissima var. hirta STP5 warrant further evaluation of anthelmintic properties in vivo.

To remain current, departments and programs offering curricula in natural resource science aim to ensure that students develop the knowledge and skills identified as being crucial by experts in the field. Texas A&M University’s Ecosystem Science and Management (ESSM) Department recently completed a large-scale curricular update assisted by academic developers at the Center for Teaching Excellence (CTE) within the university. Using the comprehensive Program (Re)Design (PRD) model created by the CTE academic developers, the ESSM Department began by forming a PRD team identified from the department’s faculty. This article details the process that the ESSM department utilized during their curriculum update, and provides a general overview of the PRD model. Examples of lessons learned (issues, solutions, and so forth) are also examined.

This paper presents a mechanistic model which simulates diet selection and animal intake. It incorporates quantitative representations for preference, palatability and availability as they affect diet selection and intake by herbivores. Preference is defined by an index calculated from forage crude protein and digestibility and a user-assigned avoidance parameter. Palatability is related to potential restrictions to forage intake by anti-quality components. Dietary restrictions arising from low forage availability are simulated using a Michaelis-Menten-type function. Inputs of forage quality and availability are obtained from a forage dynamics model, and output from the diet model goes to an animal production model. Sensitivity analyses were conducted to determine the diet selection and intake responses to variations in selected model inputs and functions. Diet selection and nutrient intake were highly responsive to changes in forage growth ratesm stock density, forage availability, and the forage quality functions in the desirability index. The model provides a working hypothesis for evaluating biological cause and effect mechanisms of diet selection and intake by grazing ruminants. Additionally, the level of resolution of the combined forage-diet-animal models is appropriate to provide a basis for developing management recommendations.

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).

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.

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.

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).

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.

A study was conducted to evaluate standing crop of forage and cattle diets for a ‘I-pasture high-intensity low-frequency (HILF) grazing system, and a ‘I-pasture short-duration grazing (SDG) system on the same area. A epasture, 3-herd (Merrill) deferred rotation grazing system was sampled as a standard for comparison. Standing crop of forage was highest for the HILF grazing system compared to the SDG and Merrill grazing systems. The Merrill system with brush control (Pasture 10) had a greater standing crop than the Merrill system without brush control (Pasture 16) or the SDG system. Standing crop in Pasture 16 was comparable to the SDG system. Cattle diets from the HILF system varied significantly between collections at the beginning and end of each grazing period. A significantly higher percentage of forbs were consumed at the beginning of each grazing period (Period A) compared to the end (Period B). Cattle selected the greatest amounts of pricklypear at the end of each collection period during fall and spring, but not during the winter. Greater amounts of pricklypear were selected when mature grasses and oak and juniper browse were the primary alternatives. Crude protein (CP) levels of diets from the HILF system decreased with shifts in forage selection from Texas wintergrass and forbs (Period A) to pricklypear and dry grass (Period B). Diets from the SDG system were characterized by higher percentages of grass and less forbs and pricklypear compared to the HILF grazing system. Also, there were no major shifts in forage selection between collection period A and B for the SDG system. This resulted in a non-significant difference in CP values for diets collected in period A compared to period B. However, a significant decline was recorded for digestibility of diets between the two collection periods. CP and digestibility were higher for diets from the SDG system compared to the HILF grazing system. Botanical composition and diet quality were comparable for the SDG and Merrill grazing systems. Competition between different kinds of animals may be reduced by changing management from a HILF to a SDG system. This would be important where combinations of animals such as cattle, sheep, goats, and deer utilize a common range. Based on diet quality, livestock production from a SDG system should be equivalent to a Merrill system. Most rangelands on the Edwards Plateau have been grazed yearlong and too intensively for almost 100 years, resulting in a significant decline of their productivity. By using proper kinds of animals, stocking rate, and system of grazing, Merrill (1959) found that declining productivity of these rangelands could be reversed. Acocks (1966) described non-selective grazing as an effective scheme for range improvement but indicated that it might reduce nutrient intake. At the time of the research authors were research scientist, professor, professor in charge, and research assistant, Texas Agricultural Experiment Station. This report is Technical Article No. 15258 from the Texas Agricultural Experiment Station. C.T. Taylor’s and LB. Merrill’s present address is P.O. Box 918, Sonora, Texas; M.M. Kothmann’s is Dept. of Range Science, Texas AM and D. Elledge’s is 110 N. Elm, Perryton, Texas. Manuscript received July 11, 1979. 428 During the past two decades, new grazing schemes have evolved utilizing several pastures and fewer herds of livestock (Booysen and Tainton 1978). They described two types of intensive rotational grazing systems. High utilization grazing is comparable to high-intensity low-frequency (HILF) grazing used in Texas and highperformance grazing is comparable to short duration grazing (SDG). Howell’s (1978) experience with the systems led to a shortening of the grazing and rest periods with subsequent improvement in animal performance. Savory (1979) reported new concepts in ranch fencing designs to facilitate frequent movement of animals under short duration grazing systems. Corbett (1978) found that steers on a HILF grazing system needed supplements during the latter part of the grazing periods throughout the year. HILF grazing systems using grazing periods longer than 2 weeks have resulted in reduced animal performance (Robbins 1975; Kothmann et al. 1975). The cause of reduced animal performance must be identified to improve the design of intensive rotational grazing systems. The objectives of this study were to determine the standing crop of forage in seven pastures grazed first under a HILF system and then under SDG and in two pastures grazed under a 4-pasture, 3-herd (Merrill) deferred rotation system. The botanical and nutrient compositions of diets selected by cattle under these grazing systems were also determined. Methods and Materials Botanical and nutritive compositions of cattle diets were determined on the Texas AM =YBXIXi xi Y4XlXi x2 (I-Y2) X3( 1 -Y3) X4( 1 -Y4) The relative weight per plant fragment of each forage class based on grass as equal to one Xi = 1, Xi = 3.15, Xi = 2.62, and Xl = 19.24. Once relative weight had been determined for all forage classes, the following formula was used to correct the species composition from percent fragments to percent by weight(Y). Computations of actual percent by weight are made by the appropriate adjustment of the numerator (XX’) over the common denominator.

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.

Results of a 1961-1974 grazing system study on the Texas Experimental Ranch in the Rolling Plains were used to evaluate annual net income stability characteristics for a cow-calf opera- tion. A linear programming risk analysis model was utilized to select optimal combinations of grazing systems which minimized annual negative net income fluctuations. Greatest annual net incomes, expressed in 1979 dollars, were obtained from heavier stocked, continuously grazed systems which received winter feed. For the 1961-1974 period, annual net income stability was not increased by selecting combination of grazing systems. However, when only the last 5 years were included in the analysis, the stability of annual net income was improved by selecting a combination of grazing systems. Supplemental winter feeding did not have a signif- icant effect on annual net incomes. However, under heavier stock- ing rates the standard deviation of annual net income was approximately doubled when cows did not receive supplemental winter feed. Annual income and income variability was determined to have increased during the last 5 years of the study, relative to the total study period. It is hypothesized that a portion of this increased variability at the heavier rates of stocking is the result of changes in the composition of vegetation. The general increase in variability across all systems indicates that ranch operators may need to consider alternatives for risk management as well as man- agement for profits. Ranch operators have long strived to become more efficient in the management of their ranch resources. This effort has been made in order to increase economic returns and reduce economic risks associated with ranching. Risks in the ranching industry are as a result of the nature of livestock market, weather, diseases, prices paid for inputs, the use of credit, and government regulation. In the Rolling Plains of Texas, and in the Great Plains in general, the need to reduce adverse economic impacts of fluctuating forage supplies has resulted in considerable research efforts by public institutions and agencies. A major goal of range research is to identify alternatives to more efficient harvest forage from range- land and to increase forage quantity and quality for use by domes- tic livestock. The major purpose of this study was to evaluate net returns and the annual stability of these net returns from five grazing management systems in the Rolling Plains of Texas from 1961 to 1974 (Fig. 1). In developing a ranch management plan, it is assumed that net income levels and net income stability (risk) associated with var- ious production strategies for increasing net income are of concern to ranch operators (Markowitz 1959). Agricultural firm managers

Biomass estimates were made with regression techniques using crown volume and weight relationships. The log-log function yielded the highest coefficient of determination for Vasey shin oak, plateau oak, Texas persimmon, and honey mesquite. A quadratic function was best for woollybucket bumelia, littleleaf sumac, agarito, and pricklyash. Sugar hackberry showed equally high coefficients with either the linear or quadratic. Coefficients of determination for catclaw acacia, elbowbush, and skunkbush sumac generally were low regardless of the type of regression equation used. When sampled at various periods over the year, predictive accuracy declined for Vasey shin oak and plateau oak through fall and winter but rose again in spring and early summer. For both species, the log-log function was best from late summer to winter but during spring and early summer the quadratic function was best. Browse biomass commonly is recognized as one of the most difficult of all vegetation components to measure (Blair 1958). Even so, the information has been valuable to foresters for measuring potential flammability (Brown 1976) and to range scientists for estimating utilization by herbivores (Dalrymple et al. 1965; Ferguson and Marsden 1977), forage available to herbivores (Bryant 1977), productivity of herbivores (Leigh et al. 1970), or the response to brush control (Bentley et al. 1970; Scifres et al. 1974). Thus, numerous methods have been developed for inventory of browse or shrub yield. Some of these different methods have been reported by Hamiss and Murray (1976). Recently, techniques used for predicting browse yield have included linear regressions of crown volume on the weight of plants to predict yield. Crown volume requires at least two measurements of the plant in addition to weight, and is well suited because a combination of measurements is usually better than any single measurement (Cook 1960). Also, volume generally yields a better relationship to weight than surface area to weight (Lyon 1968). These volume-weight relationships have usually included only one species (Lyon 1968; Scifres et al. 1974; Rittenhouse and Sneva 1977). Only Bentley et al. (1970) has dealt with more than one shrub species. Previous studies have not examined the same species at different sampling dates within a 1-year period to determine the impact of defoliation on the precision of the predictive equations. Lyon (1968) has, however, found that the precision of regression equations varied with range site for the single species being studied. The authors are assistant professor, Range and Wildlife Management, Texas Tech University; and associate professor, Department of Range Science, Texas A&M University. At the time of this research, Bryant was research assistant, Range Science, Texas A&M University. Financial support from the Texas Agr. Exp. Sta. at Sonora is gratefully acknowledged. This article is TA 14210 from the Texas Agricultural Experiment Station. Manuscript received April 28, 1978. The objective of this research was to evaluate the use of various regression functions for the prediction of biomass from crown volume for several browse species and for selected species at different sampling dates. Methods and Materials Crown volume and weight relationships were used on several browse species to estimate the availability of edible browse to herbivores. Two of the species were evaluated at different sampling dates over a 1-year period. An 8-ha study site was selected at the Texas Agricultural Experiment Station, Sonora, Texas (Fig. 1). The site had been rootplowed 7 years prior. All available browse was in a young age class and less than 2.2 m tall. Since 1970, the browse had received light used by cattle, sheep, Angora goats, and white-tailed deer (Odocoileus virginianus L.). In August, 1975, the density for each species was estimated using either point-center-quarter (Cottam and Curtis 1956) or the correctedpoint-distance technique (Laycock and Batcheler 1975), depending on the degree of aggregation. Two transects, 322 m long, were used and points were established every 30.5 m. The distance to the nearest individual of each species was measured and its height and diameter at the widest point were recorded. Height and diameter measurements were converted to conical volume using the formula

Cow-calf performance from 1960 through 1978 was contrasted between three grazing treatments at the Texas Experimental Ranch. Grazing treatments were yearlong continuous stocked at annual rates averaging 5.1 and 7.6 ha/ cow and a 4-pasture, 3-herd deferred rotation system stocked at an annual rate averaging 7.2 ha/cow. Averaged across three weighing periods, cows in the deferred rotation treatment averaged 447 kg while weight of cows in the heavily and moderately stocked continuous treatmentsaveraged 427 and 438 kg, respectively. Calf weaning weights averaged 204,212, and 217 kg for the heavy continuous, moderate continuous, and Merrill rotation treatments, respectively. Production/cow averaged 182,189, and 202 kg while production/ha averaged 35.9, 25.2, and 27.8 kg, respectively, for the heavy continuous, moderate continuous, and deferred rotation treatments. Cows fed winter supplement were significantly heavier in early spring and summer than nonsupplemented cows with no sign&ant differences in weights by late summer. Supplemented cows weaned calves averaging 214 kg as compared to 208 kg for calves weaned from nonsupplemented cows. Winter supplementation significantly increased production in the heavily stocked treatment but not in either of the moderately stocked treatments. Numerous statistically significant interactions accompanied the significant main effects, and the biological significance of each was examined. The Texas Experimental Ranch was created in 19S9 to provide researchers with the necessary facilities to evaluate the longterm responses of both livestock and vegetation to various grazing systems and rates of stocking. Kothmann et al. (1970, 1971) concluded from a thorough analysis of the cow-calf performance data collected at the ranch from 1961 through 1968 that no economic advantages were apparent from either yearlong continuous grazing at a light rate of stocking (I 1.5 ha/ AU) or from a 2-pasture, l-herd deferred rotation system (Joubert 1958) stocked at a moderate rate (8.4 ha/ AU) when contrasted to continuous grazing and a 4-pasture, 3-herd deferred rotation system (Merrill 1954) stocked at a moderate rate (8.0 ha/AU). In addition, it was concluded that feeding cottonseed meal (41% CP) as a winter supplement at a rate exceeding 0.68 kg/day was not economically justifiable in any of the grazing treatments. Thus, in 1969 only three grazing treatments that had been initiated in 1960 were continued. These treatments were yearlong continuous grazing at moderate and heavy rates of stocking and the 4-pasture, 3-herd deferred rotation system.

Travel is an important endergonic physiological function. Blaxter (1967) suggested that cattle expend about 15% more energy out-ofdoors than indoors. The maintenance energy requirement of grazing animals may be 25 to 50% greater than for animals in confinement, with the cost of travel contributing substantially to this increase (Osuji 1974). Animal travel may be influenced by location of water and minerals, weather, topography, forage availability and quality, and innate characteristics of the animal. As forage availability decreases, cattle spend more time grazing (Lofgreen et al. 1957; Arnold 1960). Also, Bos indicus cattle apparently travel more than do cattle of Bos taurus breeding (Herbel and Nelson 1966). Early travel data were obtained by following an animal and counting the number of steps of known length, taken by an observer (Cory 1927). Several researchers have obtained travel data by observing animals and mapping their movements (Dwyer 1961; Durham 1975; Malechek and Smith 1976). However, animal travel data obtained by observation may be more subjective than that obtained with mechanical techniques. Cresswell (1957) described the rangemeter as a satisfactory tool to monitor sheep travel. Powell (1968) reported on the use of a pedometer to monitor sheep travel. He evaluated the Suprex Pedometer' and concluded the disadvantages outweighed the advantages for measuring distances walked by sheep. Kiddy (1976) teported dairy cows' activity measured with pedometers during estrus was approximately four times that of animals in anestrus. The objective of this research was to evaluate one type of digital pedometere for monitoring travel of beef cattle on brushy rangeland.

Expressing the effects of grazing animals on herbage requires explicitly defined variables describing herbage growth and herbage disappearance, as well as variables describing net changes in herbage. This paper presents a mathematical framework on variables describing herbage growth, disappearance, and accumulation, which can be used to model herbage dynamics, and to develop and present field research. Describing herbage dynamics with or without livestock grazing requires measurement of both herbage growth and disappearance. Sequential measurements of standing crop define net changes in standing crop but do not indicate the changes that occurred in growth and disappearance. Often this distinction is essential in understanding and comparing effects of grazing management on herbage dynamics. We often hear that grazing systems (Society for Range Management 1974) such as short-duration grazing will maintain or increase growth rate of herbage, but less is said about effects on herbage disappearance. Similarly, in sampling during grazing studies, we usually emphasize standing crop measurements, while growth and disappearance measurements are often ignored. In general, while growth and disappearance have been frequently described and modeled in plant sciences, there is a need to mathematically formalize basic variables for application in grazing research. Quantification of dry-weight changes per unit area in standing crop, herbage growth, and herbage disappearance requires clearly defined variables developed from principles of systems analysis. Relationships among these variables should be clear and mathematical description of each variable explicit. This paper (1) defines concepts of herbage growth, herbage disappearance, and herbage accumulation; (2) offers a mathematically defined terminology for describing components of standing crop dynamics, and examines its relationship to previous papers on herbage terminology; and (3) discusses the importance of measuring herbage growth and disappearance in evaluating herbage dynamics in field grazing