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ASAS Centennial Paper: Utilization of pasture and forages by ruminants: A historical perspective¹

USDA-ARS and Crop Science and Animal Science Departments, North Carolina State University, Raleigh 27695

	Abstract

Top Abstract INTRODUCTION FORAGE-ANIMAL INTERFACE BEYOND THE INTERFACE LITERATURE CITED

 
Pastures, forages, and grasslands dominate the landscape across the United States and support a large ruminant population that supplies the nation with value-added animal products. A historical perspective is presented of the innovations as they occurred in the Journal of Animal Science over the past 100 yr in pasture and forage research. Consideration was given to both animal and pasture perspectives. Areas given consideration from the animal perspective were schemes for feedstuff analysis, experimental design and statistics, forage sample preservation, indirect methods of measuring intake and digestion, TDN and energy, nutritive value, harvested forage, and innovations in the grazing environment. Areas given consideration from the forage perspective were a framework for forage-animal interface research, determining pasture yield, choice of stocking method, grazing management, partitioning of forage DM, near-infrared reflectance spectroscopy technology, antiquality constituents, and forage sample preservation. Finally, the importance was discussed of applying research results from the forage-animal interface to general ruminant nutrition research beyond the interface that is focused on altered diets.

Key Words: centennial • forage • forage-animal interface • historical • ruminant

	INTRODUCTION

Top Abstract INTRODUCTION FORAGE-ANIMAL INTERFACE BEYOND THE INTERFACE LITERATURE CITED

 
The design, both the anatomy and the physiology, of herbivores, and specifically ruminants, implicates fibrous material as their natural diet (Van Soest, 1994). The ruminant has the ability to convert fibrous sources of feed not sought after or efficiently utilized by monogastrics into products such as meat, milk, and fiber that are relished by humans, thus giving them monetary value. These animal products provide the basis for the economic development of otherwise just another complex, but interesting, biological system. The need for ruminant products generally, but not exclusively, acquired through domesticated animal enterprises is predicated on the economic production of animal feeds. Because of their herbivority, the major source of feed for ruminants is pasture and forages, which are green plants that ecologically are a primary producer (i.e., that capture sunlight and carbon to produce biomass). This remains true whether the feed is roughage or concentrate. Efficient capture, utilization, and conversion of this feed source, through the animal, generates value-added marketable animal products.

The area in which pasture or forage and ruminants have commonality is frequently termed the forage-animal interface. Events and research contributions generated through the dynamics of this interface over the past 100 yr are addressed relative to their occurrence in the Journal of Animal Science. Innovations in these areas are presented in either written or tabular form, depending on the specific area and numbers, and the reader is encouraged to access the original documents for further details on their contributions. Shortcomings in technology transfer in ruminant nutrition research, beyond the forage-animal interface, are also noted.

	FORAGE-ANIMAL INTERFACE

Top Abstract INTRODUCTION FORAGE-ANIMAL INTERFACE BEYOND THE INTERFACE LITERATURE CITED

 
The Interface

Because of the close linkage between and dependency of the ruminant and associated industries on the green plant for energy and nutrients, the process lends itself to be viewed as having a plant sector (agronomic production) and an animal sector (ruminant production). This view was greatly assisted by both 1) the very early (pre-1900) emergent structure of agricultural research, especially in the land-grant system, and 2) the concept of end products of research. In the former case, the land-grant system greatly aided polarization by placing plant and animal scientists, and hence student education and training, into separate departments with rather rigid departmental requirements and boundaries, which functioned as potential barriers (Burns, 2006). In the latter case, plant scientists of annual (grain) crops generally have had as their end product of research improved grain yield per hectare and, in some cases, improved grain quality, whereas forage scientists have viewed improved forage yield per hectare as one of numerous research end products (i.e., persistence, leafiness, regrowth rate) that included improved nutritive value (NV) and quality. The latter takes on an animal component and has frequently not been well addressed. On the other hand, the end products of research for the ruminant scientist have generally been oriented toward biological efficiency of the animal products of interest and have been expressed on a per-animal basis per unit of time (e.g., ADG). Such an arrangement has resulted in a limited interest by the forage scientists to extend their end products of research into the animal domain and by the animal scientists to extend forage findings into their nutritional studies.

This emergent structure is depicted in Figure 1, in which the plant scientists achieve their goals (extreme left) and the animal scientists achieve their goals (extreme right), leaving the continuum (interface dynamics) nearly void, except for relatively few. Research conducted in areas to the extreme left and extreme right generally exhibit tweaking of the objectives (i.e., slight changes) and are not the topic of this paper. Of focus is the area in which forage and the ruminant have commonality and interact (Figure 2), frequently termed the plant-animal interface.

View larger version (34K): [in this window] [in a new window]   Figure 1. Depiction of the forage component (left) and the animal component (right) of the forage-animal interface (center), with forage viewed as feed entering the animal domain but as roughage in diet manipulation studies.

View larger version (31K): [in this window] [in a new window]   Figure 2. Research areas within the forage-animal interface showing animal responses from harvested forage, the addition of land-area responses when grazing, and the evaluation of forages by using ruminants.

Journal Formative Years (1908 to 1942). In the formative years of the Journal [initially named American Society of Animal Nutrition (1908 to 1911), renamed American Society of Animal Production in 1912 (1912 to 1940), and renamed the Journal of Animal Science in 1940, with the first volume published in 1942 (including 1941 and 1942)], the emerging ruminant industry was apparently already grain (concentrate) focused as a means of increasing individual animal productivity (Tomhave, 1916). This was made evident by H. R. Smith (1910), who wrote: "Many cattle feeders who have depended almost wholly upon corn in the past seem to find difficulty in adjusting themselves to present conditions and are inclined to stick to the old method of pouring in the grain with lavish hand, often to find when the cattle are marketed that the profits are on the wrong side of the ledger."

Smith (1910) further addressed the need for a reduction in grain feeding: "I have called attention to some of the results of our experiments, simply to show the possibilities of lighter grain feeding and its marked advantage under present conditions which prevail—namely, high priced corn, the need of more alfalfa and clover to enrich the soil, the abundance of cheap roughage, a large part of which annually goes to waste, and a market which discourages over-fat animals."

This philosophy, which amazingly addresses the present-day climate, apparently provided some impetus at that time for increased forages in animal production systems as some general issues in the forage-animal area began to be examined. For example, the first grazing trial (demonstration), which began in 1916 in North Dakota, was reported in the Journal by Trowbridge (1921). The Hohenheim system, widely practiced in Europe, was demonstrated in Massachusetts beginning in 1928 (Parsons, 1929). Good (1916) gave the first report on the carryover effect of feeding steers corn (Zea mays L.) silage in the winter on subsequent gain on pasture, with McCampbell (1923, 1924) clarifying that the effect was associated with backfat and not with silage per se. The use of grain as a supplement to pasture for fattening steers was demonstrated (1928 to 1930) and published by Bray (1931), and Sheets (1934) was the first to show that meat from grain-fed and pastured steers was similar.

Lush (1933) noted that before 1928 there were few actual plant composition data on early-growth pasture, and he was impressed by the elevated CP and reduced fiber in early-cut pasture samples. By 1935, interest in forages from the animal perspective had progressed to the point that Garrigus (1935) expressed the need for and developed the first procedure published in the Journal to estimate DMI of pasture. Following in 1937, Hinman (1937) suggested the use of animal BW gain as a measure of pasture yield, and Peters (1937) gave the first report in the Journal on the use of a summer annual [sudangrass (Sorghum bicolor (L.) Moench] for pasture (1935 to 1937).

This emerging interest by ruminant nutritionists in the status of nutrient composition and assessment of the NV of forages rested solely on the proximate analysis (after the Weende system proposed in the early 1800s) and consisted of chemical fractionation of the plant into CP, crude fiber (CF), nitrogen-free extracts, ether extract, and ash (Morrison, 1942).

Journal—Post-1942 (1942 to 2008). The first volume (1941 to 1942) of the Journal of Animal Science contained one report on forages and consisted of steers (Bos taurus L.) grazing winter wheat (Triticum aestivum L.) pasture, with emphasis on blood mineral concentrations (McMillen and Langham, 1942). This study (demonstration) was conducted by using 5 lots, with 5 to 7 steers per lot and without pasture replicates. A second paper concerning forages addressed the value of and changes in lignin and cellulose, with emphasis directed toward predicting the feeding value of forage plants (Patton and Gieseker, 1942). The next 3 reports were related more heavily to the animal but had implications for the plant. They consisted of concerns regarding the validity of the TDN system for evaluating feeds (Mitchell, 1942) and introduced the concepts of using direct methods to balance rations as opposed to trial and error (Schneider, 1942), the importance of statistics in animal studies, and the associated need for individual animal data (Crampton, 1942). Although the latter 2 authors used pig data, their interest was in extending the concepts into the area of ruminant nutrition.

In volume 2 (1943 and 1944), concern was given to the biology of the ruminant relative to forages with a method of estimating ME of feedstuffs (Forbes and Thacker, 1943), specifically, protein value (Mitchell, 1943), and a proposed scheme for feedstuff analysis (Crampton and Whiting, 1943). Subsequent articles addressed the biological response of ruminants concerning blood composition from steers grazing alfalfa (Medicago sativa L.) pasture (Cole et al., 1943), the quality of ‘Atlas’ sorgo [S. bicolor (L.) Moench] when fed to dairy cattle (Bechtel et al., 1943), and the value of sericea lespedeza [Lespedeza cuneata (Dum. Cours.) G. Don] for grazing (Henson et al., 1943). The nature of the forage-animal articles in the first 2 volumes of the Journal provided the basis and format for emerging topics through volume 86, 2008. Because of the random sequence in which specific studies in various areas of research appeared in the Journal of Animal Science and the incorporation of advances reported elsewhere, a tabular approach, when appropriate, was selected to simplify the historic presentation of progress. The intent was to note when a specific topic was first addressed in the Journal and not to be inclusive of further contributions unless they added an aspect of innovation.

The areas of interest, as they related to forage utilization, were 1) schemes for feedstuff analysis, 2) experimental design and statistics, 3) forage sample preservation, 4) indirect methods of estimating intake or digestion, 5) TDN and energy, 6) NV, 7) harvested forage, and 8) the grazing environment.

Schemes for Feedstuff Analysis. As noted above, Crampton and Whiting (1943) proposed an improved fractionation of plant constituents over the traditional components of the proximate analysis. This was followed by further improvement in the fractionation of greater and lesser digestible components (Sullivan, 1955), which included direct determination (as opposed to determination by difference) of the carbohydrate fraction (holocellulose) that was pulled from the traditional nitrogen-free-extract and CF fractions of the proximate analysis (Ely and Moore, 1955). In 1960, Crampton et al. (1960) proposed a system whereby consideration was given to both the level of feed intake (expressed as a value relative to a standard forage) and its digestibility, and termed it the Nutritive Value Index. Further, the digestibility estimate could be measured by in vitro fermentation data. In 1964, the detergent fiber system of analysis was introduced in the Journal by Van Soest (1964), and a new comprehensive system for feed analysis was described in 1967 (Van Soest, 1967). This system has received widespread acceptance and remains the mainstay in the area of forage NV estimates throughout the world.

Experimental Design and Statistics. Although the area of experimental design and statistics is not highlighted in most biological journals, historically, it is of interest to note that the first grazing experiment (replicated and data statistically analyzed) in the Journal of Animal Science was published in 1945 (Kincaid et al., 1945). Further, a study on forage evaluation presenting probability levels for the statistical test used appeared in 1946 (Ellis et al., 1946) and the SE of an estimate was first shown in 1950 (Forbes and Garrigus, 1950). The experimental design (stall-feeding trial) was first mentioned in 1951 (Jordan and Staples, 1951), and the discussion of data with a statistical inference appeared in 1963 (Carter et al., 1963). A mixed model was applied to analyze grazing response data in 1993 (Thompson et al., 1993). Historically, the statistical approaches for pasture-animal research were generally lacking until the late 1950s (Burns, 2006).

Forage Sample Preservation. The area of sample preservation in preparation for analyses first appeared in the Journal in 1954, when the digestibilities of paired fresh- and dried-pasture samples were compared (Miller et al., 1954), followed in the 1960s and into the 1970s by evaluations of the effect of freezing before feeding on subsequent animal response (Pigden et al., 1961). A comparison was made based on in vitro results when paired samples were analyzed fresh, freeze-dried, or oven-dried (Reid et al., 1964; Danley and Vetter, 1971). Differences were noted among methods, and the magnitude of the difference was forage dependent. The application of microwave technology to forage sample drying was imminent and was reported in 1986 in reference to masticate drying (Karn, 1986).

Indirect Methods of Measuring Intake or Digestion. In 1948 (volume 7), the first report of an indirect method applied to estimate DM digestion appeared, in which the lignin ratio technique was used (Table 1, item 1). This was followed by assessing fecal nitrogen for that purpose but was deemed too variable. The artificial rumen was introduced in 1950 to estimate cellulose digestion, and plant pigments (chromogen) were introduced in 1951 to estimate digestion coefficients for the various plant constituents. The effort continued into 1975 with the introduction of the rare-earth element dysprosium to evaluate its potential as an inert marker with application in determining forage digestion (Table 1, items 1 to 11) and into 1989 to determine passage rate with lutetium and mordanted chromium. More recently, in 2000 methods were reported regarding the use of gas production in an in vitro system inoculated with feces from the diet of interest, as well as the development of universal equations to predict the energy status based on specific forage constituents (Table 1, items 12 and 13).

Harvested Forage. The second volume (1943) of the Journal of Animal Science provided the first evaluation of a summer annual harvested and preserved as silage. Thereafter, through 1959, reports appeared describing a biological method to measure protein value, and pelleting was applied to rations. Further, voluntary intake was shown to be restricted by digestion rates of cellulose and hemicellulose, and that the cell wall was an entity that differed among forages. A model was developed describing passage rate, which allowed total mixing of the ingesta (Table 4, items 2 to 6). In the 1960s, it was shown that DM digestion and digestion of CP, CF, nitrogen-free extract, energy, and TDN estimated in either cattle or sheep (Ovis aries L.) were well correlated. Further, the concept of gut fill and the differences among forages were introduced, as was the influence of advancing maturity on animal DMI, digestion, and passage rate. In this period, an in-depth review was published on in vivo and in vitro methods of forage evaluation (Table 4, items 7 to 12).

Innovation in the Grazing Environment. The first grazing trial (demonstration) reported in the first issue of the newly reorganized societal publication, Journal of Animal Science (volume 1, 1942), addressed the blood minerals of cattle grazing winter wheat (McMillen and Langham, 1942). The first grazing experiment (with design and replication for hypothesis testing) was reported in 1945 (Table 5, item 11) by Kincaid et al. (1945). From 1942 through 1950, the topics addressed were bloat, the potential of lespedeza as a pasture forage, the introduction of the concept of determining pasture yield based on calculating TDN harvested by the animal (TDN for maintenance plus TDN for gain) and the TDN concentration in the pasture, and the similarity in digestion capacity between steers and wethers (Table 5, items 8 to 14). The period from 1950 to 1964 showed the emergence of the concept of selective grazing and the introduction and application of the esophageal fistula to characterize diets selected from both tame and native pastures. Further, the differential in NV between esophageal collection and hand plucking was established, and the potential of using the collected masticate to determine botanical composition relative to plant species consumed was documented (Table 5, items 15 to 27). The 1970s brought the concept of managing animals based on pasture characteristics and that BW gain per animal and per hectare were related. The 1970s ended with the relationship being established between summer syndrome and tall fescue (Table 5, items 28 to 32).

Efforts in the 1990s addressed the modeling of intake of grazing animals, that selective grazing could overcome plant differences in morphology, that stable carbon could be used in forage-animal experiments to examine the response of grazing animals, that mixed animal-species grazing was useful, and that the need existed to examine forage-animal systems when considering beef cattle production (Table 5, items 38 to 43). During the last 8 yr (2000 to 2007), interest has shifted some to examination of the economic optimum, as opposed to maximum daily performance, and to the examination of pasture management strategies, including methods to measure intake of animals on pasture to enhance cattle production, and has terminated with the application of NIRS technology to estimate the botanical composition of the diet of the animal (Table 5, items 44 to 52).

Forage Perspective

Historical innovations of forage origin, as they occurred in the Journal of Animal Science and as noted above, were in part an outcome of, or an extension of, forage-based programs that were underway in agronomic departments at land-grant universities (some jointly with USDA-ARS scientists) and at some USDA-ARS research locations. The forage evaluation component of these programs had applications directed toward, and sometimes involved, animal utilization trials (grazing or confinement experiments; Barnes et al., 1988). It is out of this environment, and the continued additive contributions of many scientists, that the following areas were defined and developed, ultimately to serve the ruminant sector.

Framework for Grazing Research. A comprehensive assessment of the pasture-animal system was published in the proceedings of a special symposium titled "Range Research Methods" held at Denver, CO, May 1962 (USDA Misc. Publ. No. 940). In the paper by Lucas (1962a), he provides a detailed framework depicting the initial status of a plant-animal system (factors affecting both forge production and herbage mass per hectare), factors altering the type and quantity of forage consumed by animals, factors altering forage yield and the production per animal and per hectare, and the pathways through which the initial status is altered during time periods throughout the grazing season. Key relationships examined were how the diet of animals was related to available forage and how production per animal was related to the forage consumed. Lucas (1962b) further provided a summary of factors that determine production per animal and followed up with a treatment of designs applicable to both grazing and confinement feeding involving supplementation.

Determining Pasture Yield. The concept of using an indirect method to determine pasture yield was initially proposed by Knott and Hodgson (1934) as early as 1934 in the Journal of Dairy Science. This approach, based on the back calculation of energy used from animal maintenance and BW gain, and expressed as TDN on an area (hectare) basis, was further considered by Kidder in 1946 and published in the Journal of Animal Science (Kidder, 1946). The concept was more fully developed in the 1950s for useful application by Lucas (1952) and Mott and Lucas (1952). They proposed and outlined 3 methods (designated I, II, and III) of computing animal responses on a unit-area basis, and the topic has been treated elsewhere (Burns, 2006). The concept of shifting from a TDN to an NE basis was proposed in 1962 by Lucas (1962a) and termed Effective Feed Units. This concept was further developed through the designation of conversion coefficients for maintenance and gain and was published in 1968 by Petersen and Lucas (1968). The latest contribution appeared in 1994, in which Petersen (1994) provided numeric examples of methods I, II, and III with associated statistical treatments. The Effective Feed Unit procedure has provided the forage agronomist with a technique to determine pasture yield when grazed and provides the animal nutritionist with an energy estimate from pasture that can be used in determining carrying capacity for a specific class of animals provided energy requirements are available.

Choice of Stocking Method. Because the grazing animal determines its own diet from within the boundary of the constraints imposed, the choice of stocking has major implications in both research and producer settings. In a research setting, it is important that specific pasture treatments be compared fairly, whether that entails the same relationship between herbage mass and the animal or, if each treatment is to maintain a specific herbage mass, based on the forage species being evaluated (Mott, 1960). The choice of fixed-continuous or variable stocking was mentioned by Lucas in 1952 and in 1962 in his publications on experimental designs (Lucas, 1952, 1962b) and was considered in detail by Wheeler et al. (1973). The latter document provides an in-depth assessment of the insight of both groups (fixed vs. variable stocking) into the other’s perspective.

Grazing Management. The term "management" conveys the concept of human intervention to accomplish a predetermined outcome. The innovations by R. E. Blaser and associates, such as top and bottom grazers (Bryant et al., 1961), first and last grazers (Blazer et al., 1969), first and last rotational grazers (Blaser et al., 1986), and creep or forward-creep grazers (Blaser et al., 1986), introduced the concept of flexible management in pasture utilization. The approach was to manipulate animal ADG and BW gain per hectare while controlling forage utilization (Blaser et al., 1981). The concept was summarized well in 1982 in his presentation of the Stobbs Memorial Lecture, Brisbane, Australia (Blaser, 1982).

Partitioning of Forage DM. Movement beyond proximate analysis, which was the major method of estimating the NV of forage throughout the 1950s, began with the concept of soluble and insoluble, but partially available, fractions in the plant (Van Soest, 1963a,b, 1969). The soluble fraction was available for enzyme activity in the digestive tract, whereas the insoluble fraction required microbial attachment and breakdown (Barnes, 1973). The fiber fractions that emerged as valuable in estimating NV were NDF, ADF, and lignin (Van Soest and Robertson, 1980), with standardized procedures recommended (Van Soest et al., 1991). Fractionation was further aided in the 1980s by the development of specific analytical equipment such as the Fibertec (Foss North America, Eden Prairie, MN) and in the 1990s by the Ankom fiber analyzer (Ankom Technology, Macedon, NY).

NIRS Technology. Ben-Gera and Norris (1968) were the first to apply NIRS technology to agricultural products. The general history, from the understanding of the technology through its use in analyses of food crops, processed foods, and nonfood products, has been reviewed (Workman and Shenk, 2004). The developmental history of NIRS for the estimation of forage NV has been addressed by Shenk and Westerhaus (1995) and, more recently, by Roberts et al. (2004). Further, the potential to make direct estimates of in vivo DM and DMI by using calibrated NIRS was assessed by Coleman et al. (1999).

The use of NIRS in forage evaluation has many attributes, including minimal sample preparation, small quantity of sample required, short time (minutes) required to predict a large number of variables describing NV (including antiquality constituents such as ergovaline and nitrate concentrations), recovery of the unaltered sample when in limited supply, and its degree of accuracy and precision when properly calibrated. Furthermore, IVDMD can be obtained from the same scan. The potential to estimate DMI and its digestibility directly from the near-infrared spectra would mean many magnitudes of reduction in the forage needed, as opposed to large-animal intake (Burns et al., 1995) and digestion (Cochran and Galyean, 1995) trials. This sets the stage for the use of DMI and DM digestibility as selection criteria in forage (legume and grass) breeding programs.

Antiquality Constituents. The antiquality constituents present in forages can have a major impact on animal responses. Antiquality factors can be either soluble or insoluble constituents having varying degrees of impact on subsequent animal daily responses. Three unique types of antiquality constituents elucidated to date are the endophyte-alkaloid relationship noted for tall fescue, the alkaloid-plant relationship noted for reed canarygrass, and the cell wall structural limitation, as noted for bermudagrass. In the former case, tall fescue pastures in Ohio in the early 1950s were noted as supporting poor animal performance (Pratt and Hayes, 1950), and severe toxicosis was recorded in 1973 in cattle grazing 1 of 3 tall fescue pastures in Georgia. The pastures causing toxicosis had a fungal endophyte reading for nearly 100% of the plants, whereas the readings from the other 3 pastures were much less (Bacon et al., 1977). Later, Hoveland et al. (1980) noted that endophyte infection levels of approximately 18% supported steer ADG that were 51% greater compared with infection levels of 80%. Further, steer ADG and BW gain per hectare, respectively, averaged 66 and 28% greater compared with steers on pasture that was 94% infected (Hoveland et al., 1983). Recently, 2 improved tall fescue cultivars that are endophyte free, named ‘Jesup’ (Bouton et al., 1997) and ‘HiMag’ (Sleper et al., 2002), have been released. A novel, but different, nontoxic endophyte was inserted into these cultivars, and they were renamed ‘MaxQ’ and ‘ArkPlus’, respectively, and have been shown to have potential in ruminant production systems (Bouton et al., 2002; West et al., 2003; Nihsen et al., 2004). Unfortunately, ‘ArkPlus’ has been withdrawn from the market because of patent restrictions.

In the second case, a negative relationship between alkaloid concentration and both palatability (Simons and Marten, 1971; Marten, 1973) and ADG (Marten and Jordan, 1974) was shown for grazed reed canarygrass. Both sheep and steers showed physiological upset when consuming tryptamine-carboline- vs. gramine-containing plants (Marten et al., 1976). A safe threshold level for indole alkaloid concentrations was determined (Marten et al., 1981) and a nontoxic germplasm was released in 1983 (Hovin and Marten, 1983).

In the third case, coastal bermudagrass (released in 1943) had greatly improved yield potential compared with other available warm-season grasses and is widely used across the South (Burton, 1954). Its cell wall (NDF) component, however, frequently exceeded 75% of the DM and was of moderate digestibility when immature. Selection for improved IVDMD resulted in the release of ‘Tifton 85’ (Burton et al., 1993), with similar or greater NDF concentrations than ‘Coastal’ but with a reduction in the ether-linked ferulic acid fraction (Mandebvu et al., 1999a), which improved cell wall degradability by rumen flora (Mandebvu et al., 1999b), resulting in greater calf ADG (Corriher et al., 2007).

Sample Preservation. This critical area, also addressed above in the Animal Perspective section, warrants additional comments. Proper preservation of the plant samples relative to how the resulting NV data are to be applied remains a concern. These concerns were evident as early as the 1950s (Miller et al., 1954), and the effect of differential drying was reviewed in 1981 (Burns, 1981). In general, the choice when relating the NV of forage samples from pasture (hand harvested or esophageal collected) to the response of the grazing animal is to quick-freeze (with liquid nitrogen), freeze-dry, and store it in a freezer until analyzed. This process stops respiration and avoids the alteration of chemical constituents. Oven drying, on the other hand, may actually accelerate respiration for a time (depending on the sample size and temperature setting) until the sample is sufficiently dehydrated to terminate respiration and may subsequently alter chemical composition during the drying process. Oven drying generally reduces the differences among plant samples, and the resulting NV may or may not be of value in relating to subsequent animal responses. As recently as 1987, the influence of drying method was observed to differ among cultivars and was associated with the TNC fraction (Fisher and Burns, 1987). In the case of hay, which has already been dehydrated (sun cured or artificially dried), the influence of subsequent oven drying on NV is nil.

	BEYOND THE INTERFACE

Top Abstract INTRODUCTION FORAGE-ANIMAL INTERFACE BEYOND THE INTERFACE LITERATURE CITED

 
Although not the focus of this paper, it is of interest to note the lack of consideration given to the fiber component in many ruminant nutrition studies with supplements and additives as the focus (Figure 3, right-hand section). In many trials, the fiber component is a forage (frequently termed "roughage") and is apparently assumed to provide only the fiber effect in maintaining a healthy rumen environment. Beginning in the early 1940s, research findings from forage-animal interface experiments have provided numerous insights into the nature of the forage plant (see above). These forage characteristics have relevance to subsequent animal responses when a forage is a component of various nutrition studies. Some of the more important findings are listed in a nonhierarchical order:

View larger version (37K): [in this window] [in a new window]   Figure 3. Technology transfer gap (TTG) depicted beyond the forage-animal interface, where ruminant nutrition research responses are focused on diet amendments and manipulations.

• Lignin and cellulose increase with season.
  
• The cell wall matrix, and hence digestibility, differs among grasses.
  
• The entity "cell wall" differs in composition among forages.
  
• The leaf-to-stem ratio of forages alters digestibility.
  
• Gut fill when using fiber fractions is forage specific.
  
• Energy yields of the nonfiber fraction of forages are not constant.
  
• Intake is limited by digestion rate of cellulose and hemicellulose.
  
• Chemical composition is more closely related to digestion than to intake.
  
• Ingestive mastication produces a diversity of particles and is forage-species specific.
  
• Nitrogen fertilization influences the NV and quality of hay.
  
• Forage cut in the evening has greater NV than forage cut in the morning.
  

The above findings clearly indicate that fiber source in a ration will nearly always be a variable in nutrition studies, and this represents a gap in information transfer from forage-animal interface studies to subsequent ruminant-nutrition studies (Figure 3). Variation in the forage (fiber) component will occur within and among experiments, requiring careful characterization of its NV and its contribution to digestion and, ultimately, utilization. As noted above, NDF (cell wall) is not the same NDF regardless of source, as is often assumed. The nature of NDF, for example, is specific to forage species and cultivars within species, and varies among plant parts within cultivars and among plant parts among cultivars. The nature of NDF and its constituent fiber fractions, and the soluble constituents of the cell within each of these classes are also altered by external factors. These include management (maturity at harvest, fertilizer application rates), climate (temperature and rainfall), and soil conditions (fertility, type).

Further evidence for an information-transfer gap is the terminology often found in the literature describing the forage source as fescue grass, prairie grass, or prairie hay, or simply roughage. These descriptions are not very useful. For example, the fescues are all grasses and there are several species. In addition, prairie grass or hay will be a mixture of several very different grass species as well as associated legumes and forbs. This mixture will vary greatly in botanical composition over short distances within a field and from harvest to harvest, and hence in NV. Failure to recognize such variation in the fiber (forage component) of the diet has justified the practice of using a composite sample from some randomly selected bales to represent a bulk forage lot. The assumption is that the fiber characteristics represented by the composite sample from a bulk lot will be the same when fed to all animals for the duration of the experiment. This assumption frequently is difficult to meet, and a better practice is to obtain a daily "as-fed" sample of the diet fed to each animal (Fisher et al., 2005).

Ignoring the animal response data emerging from the forage-animal interface experiments results in animal responses from supplement and additive experiments beyond the interface that are extremely limited in utility (i.e., to that experiment). This is not to say that the experiments are poorly conducted, but at issue is both the limited application (experiment specific) and the potential pitfalls encountered when trying to extrapolate animal response data from one experiment to another.

Conclusions

For the past 100 yr, the Journal, sponsored by the American Society of Animal Science, has been a conduit for the dissemination of forage management and utilization principles in a form to challenge the ruminant nutritionist with a keen interest in herbivory. Ideally, the Journal will move toward attracting manuscripts that make these principles sufficiently palatable to elicit interest and be a challenge to even the more traditional (supplement-based) ruminant nutritionists. In essence, forage evaluation in a ruminant setting has moved from the chemical-based proximate analysis, through biologically based fractionation of the DM by the detergent fiber system of analysis, and into the realm of predicting NV via NIRS, which is based on elemental bonding. This technology yet holds the potential to estimate DMI and its apparent digestibility directly from the spectra. Progress has also been achieved regarding schemes of feedstuff (including forage) analysis and experimental design and statistics, and in the areas of indirect methods of estimating intake and digestion, determination and use of TDN and associated energy, forage sample preservation, harvested forage, and the grazing environment. In the early years of the society (pre-1930), the need to decrease the dependence of animal production on concentrate diets and to increase the use of abundant forage resources was expressed. Interestingly, these words are being echoed today in the 21st century. The potential integration of forage principles into the animal domain was advanced by the society in 1989 (volume 67) by designating a section editor to the area Pasture and Forage Utilization within the Ruminant Nutrition section and by expanding it in 1995 (volume 73) to include rangeland. This created a new section, Rangeland, Pasture, and Forage Utilization (volume 74, number 2, 1996), which provides a home for the unique research generated across the forage-animal interface. In the past 100 yr, much of the ruminant nutrition research has taken place beyond the forage-animal interface, with concentrate and additive manipulations of the diet being a major focus. One has to question yet again whether the call for a greater dependence on forage and reduced use of concentrate in ruminant diets will still echo across the land some 100 yr from now.

	Footnotes

 
¹ Mention of a trade name, proprietary product, or specific equipment does not constitute a guarantee or warranty by either USDA-ARS or North Carolina ARS and does not imply approval to the exclusion of other products that may be suitable.

² Corresponding author: Joe.Burns{at}ars.usda.gov

Received for publication June 16, 2008. Accepted for publication July 24, 2008.

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