Joe D. Wallace

Forage intake by grazing livestock: a review.

Highlight: A wealth of experimental data has been accumulated on quantitative intake of pen-fed livestock; such information has been widely employed to develop a keener nutritional knowledge of such animals. Data of this type are, however, distressingly lacking for grazing livestock. The procedures used for measuring intake by animals under grazing conditions have often been disappointing, and many have provided unreliable data. Forage intake measurements with grazing livestock are more commonly expressed as g DM or OM/Wk -75 or simply as a percent of body weight. Most estimates of inta gk e for cattle and sheep grazing ranges in Western United States fall within the range of 40 to 90 g DM/Wkg’” or from 1 to 2.8% of body weight. Intake usually decreases with advancing plant maturity.

Influence of native shrubs on nutritional status of goats: nitrogen retention.

In vivo digestibility trials were conducted to evaluate the influence of shrubs containing low and high levels of soluble phenolic/tannins on digestibility and nitrogen retention by Angora goats. Each of 6 shrubs and alfalfa hay (Medicago sativa L.) were fed to goats at 30% (dry matter basis) of the diet in a barley straw-prairie hay mixture. The mixture was regulated so that all diets contained about 8% crude protein. High soluble phenolic shrubs used included big sagebrush (A rtemisia tridentata Nutt. ssp. tridentata), gray oak (Quercus grisea Liebm.), true mountain mahogany (Cercocarpus montanus Raf.), and one-seed juniper (Juniperus monosperma [Engelm.] Sarg). Low-soluble phenolic species included common winterfat (Ceratoides lanata [Pursh.], J.T. Howell), fourwing saltbush (A triplex canescens [Pursh.], Nutt.), and alfalfa. Nitrogen digestibilities of winterfat, gray oak, mountain mahogany and one-seed juniper diets were less (P .05) compared with the alfalfa control. Retained nitrogen (g/d) differed (P<.05) only among alfalfa, juniper, and mountain mahogany diets. Goats fed juniper had greater (P<0.05) retained nitrogen than the alfalfa control. Shrubs high in soluble phenolics, with the exception of big sagebrush, had elevated fecal nitrogen losses, but reduced urinary nitrogen losses compared with the alfalfa control. Forage organic matter intake (% body weight) and nitrogen intake (g/d) were correlated more highly with nitrogen retention than dietary crude protein (%) or digestible protein (%). Present data indicate that protein found in palatable native shrubs is assimilated with similar efficiency to that in alfalfa hay if these shrubs are consumed at

Evaluation of fecal indices to predict cattle diet quality.

A study involving 6 feeds of widely varying chemical properties fed to 6 steers in a Latin square design was conducted to evaluate the potential of fecal chemical characteristics for predicting ruminant nutritional status. Forage intake, diet in vivo digestibility %, and diet nitrogen % were used as dependent variables and fecal nitrogen %, nucleic acid %, nonflber bound nitrogen %, ether extract %, neutral detergent fiber %, acid detergent fiber %, acid detergent lignin %, water soluble material %, and acid/pepsin disappearance % were used as independent variables in regression equations. Forage intake and diet in vivo digestibility could not be accurately predicted from any single variable or combination of independent variables. Fecal acid/pepsin disappearance was the independent variable most highly correlated with forage intake (r = .63) and diet in vivo digestibility (r = .33). Diet nitrogen % was highly correlated with fecal nitrogen % (r = .81) and fecal acid pepsin disappearance % (r = .83). Combined data from this and other studies give a generalized regression equation that shows potential for detecting nitrogen deficiencies in steer diets from fecal N % (organic matter basis) when steer diets contain low levels of soluble phenolics. When steer fecal nitrogen % drops below 1.7%, dietary nitrogen deficiencies should be

Cattle grazing blue grama rangeland. I. Seasonal diets and rumen fermentation.

Four field trials were conducted from early August to late October, 1982, on blue grama (Bouteloua gracilis) rangeland in south-central New Mexico to examine relationships among grazing season, diet botanical and chemical composition, and rumen fermentation in beef steers (Bos taurus). Diets contained an average of 83% grasses and 17% forbs from early August through late September and 77% forbs in late October. Cell wall content of the diet decreased from the early growing season (74.9%o) through the onset of dormancy (64.9%) while acid detergent fiber and lignin increased (41.9 to 52.9%o and 5.2 to 12.7%, respectively) and crude protein content declined from 18.4 to 11.7%. Soluble and insoluble nitrogen (N) fractions of the diet reflected crude protein; from 13 to 36% of N was in unavailable forms. The extent of in vitro organic matter digestion declined from the early growing season (66.5%) through onset of dormancy (47.9%0). Ruminal ammonia concentrations declined as season progressed: 6.0 mg/100ml was the lowest concentration observed. Declining diet quality was accompanied by an upward shift in digesta pH and altered proportions of volatile fatty acids (VFA) in rumen contents. Total VFA concentration was highest in late August (106.3 mmoles/liter). Ruminal measures generally reflected changes in dietary protein and digestibility but concentrations could also reflect changes in digesta flow rates. Finally, data suggest that crude protein may not be a good measure of protein supply to livestock grazing on ranges with diverse forage types. Several authors have discussed the influence of advancing season of growth and nutritive value of range plants and relative values of forage classes (Cook 1983, Pieper et al. 1978, Kothmann 1980). Such changes are usually discussed in relation to the daily requirements of animals grazing in the plant communities. However, few studies have related diet quality to ruminal environment in the grazer. The rumen is the primary site of forage degradation. Products of ruminal fermentation (ammonia, volatile fatty acids) and the pH of ruminal contents can influence fiber digestion (Mertens 1979), microbial protein synthesis (Satter and Slyter 1974), and, finally, energy and protein supplied to the grazing host. Therefore, knowledge of seasonal fermentation patterns in grazing range animals might suggest means of enhancing diet utilization and animal performance. The objectives of this study and another reported subsequently (McCollum and Galyean 1985) were to relate seasonal changes in diet composition with changes in rumen function and forage intake in beef steers (Bos taurus) grazing native blue grama (Bouteloua gracilis) rangeland during 4 periods of a growing season. Materials and Methods Study Area The Fort Stanton Experimental Ranch is in the foothills between the Sierra Blanca and Capitan Mountains in southern Lincoln County, New Mexico. Pieper et al. (1971) described the vegetation, topography, and climate of the Ft. Stanton Ranch. Briefly, annual precipitation averages 40 cm and mean annual At the time of this research, authors were graduate assistant, associate professor, graduate assistant, and professor, respectively, Department of Animal and Range Sciences, New Mexico State University, Las Cruces 88003. McCollum is currently assistant professor, Animal Science Department, Oklahoma State University, Stillwater 74078. This article is a contribution from New Mexico Agr. Exp. Sta. Journal Article No. 1087. The authors wish to acknowledge the assistance of Drs. A.L. Goetsch, R.E. Estell, and M.B. Judkins, E.E. Parker, and Harley Segotta. Manuscript accepted 19 April 1985. temperature is 11.10 C. Most vegetational growth usually occurs during June through September. The study pasture, an open grassland area, was situated at approximately 1,900 m elevation and received about 35 cm precipitation the year of the study (65% occurred between mid-July and the end of September). Vegetation of the study pasture was dominated by blue grama and cholla cactus (Opuntia imbricata) (Pieper et al. 1971). Field trials Four trials were conducted during 1982 (9 Aug.-17 Aug., EAug; 29 Aug.-Aug.-4 Sept., LAug; 23 Sept.-l Oct., LSept; 23 Oct.-31 Oct., LOct). Trials were conducted at these times to reflect phenological changes in the plant community. During each trial, 3 esophageal-cannulated dry, mature beef cows (Hereford X Angus) and 6 rumen-cannulated (10.2 cm ID cannulas) steers (Hereford X Angus; x weight = 303 kg) were allowed to freely graze the pasture. No other animals were grazed on the study pasture during adjustment and sampling periods. It was assumed that the diets of the cows and steers were similar. Cows were placed on pasture a minimum of 1 week before each trial, while steers were placed on pasture 2 weeks before the EAug trial and grazed continuously through the LOct sampling period. Diet samples were collected the first 2 days of each 8-day trial. The cows were penned each day at 1200 hour and samples were collected during 30-minute periods between 1700 and 1800 hours. The cows were hazed to the area being grazed by the steers during collection periods. Following the collections, an aliquot of each extrusa sample was frozen in a plastic bag and stored until analyzed. Rumen samples were collected on the third day of each trial. At 0800 hours, 250-ml sample of whole rumen contents was withdrawn after thorough hand-mixing of the rumen. Rumen pH was evaluated immediately with a combination electrode. Samples were strained through 4 layers of cheesecloth, and strained fluid was acidifed (1 ml 20% v/v H2S04 per 100 ml strained fluid) and stored frozen. After sampling, steers were allowed to return to normal grazing activities. The sampling process was then repeated at 1200, 1600, and 2000 hours. To facilitate rumen sampling, temporary pens were transported to and erected on an area immediately adjacent to the site being grazed by the steers at each sampling time. Laboratory Analyses Esophageal samples were dried at 50 0 C for 54 hours and ground through a 2-mm screen in a Wiley mill. Dry matter and ash contents were determined by standard procedures (AOAC 1980). Dietary fiber constituents (acid detergent fiber, ADF; acid detergent lignin, ADL; neutral detergent fiber or cell walls, NDF) were determined according to Goering and Van Soest (1970). Nitrogen (N) was determined by Kjeldahl procedures (AOAC 1980) and fractioned into soluble N (SN) and insoluble N (IN) by the sodium chloride method of Waldo and Goering (1979). Insoluble unavailable N (ADIN) was the N present in ADF residue. Crude protein (CP) was calculated as 6.25 X N. In vitro digestion analyses were conducted on samples composited across cows and sampling days. Rumen fluid inoculum was collected from 3 steers consuming a 50:50 mixture of alfalfa (Medicago sativa) and prairie hay. Extent of organic matter disappearance (IVOMD) was estimated using techniques of Tilley and Terry (1963). JOURNAL OF RANGE MANAGEMENT 38(6), November 1985 539 This content downloaded from 157.55.39.78 on Sat, 25 Jun 2016 07:06:53 UTC All use subject to http://about.jstor.org/terms Microhistological examination of dried and ground esophageal masticate samples followed procedures outlined by Sparks and Malechek (1968). Ten systematically located fields per slide and 5 slides per sample (individual cow samples) were examined at lOOX

Passage Rates, Rumen Fermentation, and Weight Change in Protein Supplemented Grazing Cattle

Protein supplementation is widely used to enhance the nutritional status of cattle on rangeland. The effects of protein supplementation on particulate and fluid passage rates, rumen fermentation, and weight gain were evaluated on cattle grazing dormant blue grama rangeland. Twelve rumen-cannulated steers were randomly allotted to 3 equal supplement groups (Utreatment): cottonseed cake (CSC), pelleted alfalfa (ALF), or no supplement (CON). Supplements were individually fed every other day at isonitrogenous levels (1.7 kg/hd CSC vs 3.6 kg/hd ALF). Particulate passage rate was measured during 2 collection periods. Concurrently, 102 yearling heifers were allotted to the same treatment groups for measurement of average daily gain. Cattle were fed these treatments from January through April 1983. In a second trial, 9 rumen-camudated steers were randomly allotted to the same treatment groups as trial 1. An intraruminal dose of CoEDTA was used to estimate fluid passage rates. Rumen ammonia, volatile fatty acids, and pH were also measured. In trial 1, average daily gain did not differ between ALF and CSC supplemented heifers; however, both ALF and CSC gained more than CON heifers. Passage rate estimates were not different among treatment groups. In trial 2, rumen fluid dilution rate, vohune, and oufflow rate were not different among treatments. Rumen ammonia-N was different at 11 h postsupplementation when the CSC steers had higher levels than steers in other treatment groups. Rumen pH was not influenced by supplementation. Molar proportions of acetate and propionate at 8 and 11 h after supplementation differed among treatment groups. Acetate was lowest in ALF, intermediate in CSC, and highest in CON supplemented steers. Propionate followed the reverse trend. Overall, protein supplementation improved livestock performance but the mechanism involved was not elicited. The current data suggest shifts in fermentation patterns and meeting dietary demands for gain are the factors involved in improving performance.

Forb and shrub influences on steer nitrogen retention.

Two experiments with steers were conducted to evaluate the influence of native forbs and shrubs on nitrogen utilization by cattle. Diets in Exp. 1 were blue grams (Bouteloua gracilis [H.B.K.])(BG), BG plus 23% alfalfa (Medicago sativa) hay (ALF), BG plus 42% forbs and BG plus 41% shrubs. Diets in Exp. 2 included barley (Hordeum vulgare L.) straw, and straw plus either 42% ALF, 63% forbs, or 62% shrubs. Forbs used in our study were scarlet globemallow (Sphaeralcea coccinea Nutt.) and leatherleaf croton (Croton pottsii Lam.). Shrubs included fourwing saltbush (Atriplex canescens [Pursh.]) and mountain mahogany (Cercocarpus montanus Raf.) Forb and shrub mixtures were 50:50 of each species. Blue grams and straw basal diets contained 7.6 and 3.5% CP, respectively. Diets containing ALF, forbs, and shrubs were isonitrogenous (10.5% CP) in both experiments. In Exp. 1, no differences (P>.10) were observed among treatments for N retention (g/d). In Exp. 2, N retention was least (P .05), and intermediate for the forb diet. Inclusion of forbs or shrubs with low-quality forage diets was, in most instances, comparable to inclusion of ALF. Our results indicate that maintaining palatable forbs and shrubs on rangelands should reduce the need to supply cattle with protein during periods when grasses are dormant.

Influence of two native shrubs on goat nitrogen status

In vivo digestibility trfnls were conducted in metrbolism stalls at New Mexico State University to evaluate the influence of leaves of true mountain mahogany (Cercocurpus montanus Raf.) and fourwing saltbush (A tr@w cunescens [Pursh.] Nutt.) on nitrogen retention and digestibility hy Angora goats. Each of the 2 shrubs were fed at 3% and 6% (air dry basis) of the diet along with prairie hay that was comprised mostly of blue grama (Bouteloua grucilis [H.B.K.] Lag. Ex. Griffhhs). High and low shrub diets contained about 12% and 8% crude protein, respectively. Nitrogen retention did not differ (IQO.05) among mountain mahogany and fourwing saltbush diets; however, goats fed the 60% shrub level had greater (P<O.OS)nitrogen retention than did those fed the 3% level. Mountain mahogany diets had a greater soluble phenolic/tannin content than fourwing saltbush diets, but this did not appear to influence nitrogen retention. Forage organic matter intakes averaged 2.% of body weight and did not differ (890.05) among the 4 treatments. Total fecal output of nitrogen (g/d) was highly correlated (1-2 = .71, n = 15) with nitrogen retention. Hence, total fecal nitrogen output may be useful as an indicator of grasing ruminant protein status. Digestible protein (70) and dietary crude protein concentrations were associated poorly with nitrogen retention in our study. Blood serum analysis showed no toxicosis problem for any of the 4 dietary treatments. We concluded that leaves from fourwing saltbush and true mountain mahogany have potential to he an effective source of protein for range livestock consuming low-quality grasses.

Evaluation of fecal indicators for assessing energy and nitrogen status of cattle and goats.

In vivo digestibility trials involving cattle (steers) and goats (wethers) fed shrub and nonshrub mixtures were conducted to evaluate the potential of fecal output, fecal nitrogen output, and fecal nitrogen percent for assessing diet intake, nitrogen balance, and digestibility. Two cattle digestion trials involving 8 feeds and 4 goat digestion trials involving 13 feeds were used to develop simple linear and multiple regression equations between fecal and diet characteristics. Crude protein percent (organic matter basis) of cattle diets ranged from 3.9 to 12.0%; that of goats ranged from 7.5 to 14.4%. Low-phenolic and high-phenolic shrubs were fed in separate diets to goats while cattle diets involved only low-phenolic shrubs. Fecal output of organic matter (percentage of body weight) was correlated (r2>0.80) with forage organic matter intake (percentage of body weight) for both cattle and goats when all feeds were included in the regression. Linear regression intercepts, but not slopes, differed (P<0.05) among cattle and goats. Multiple regression equations did not improve evaluation of forage intake over simple linear equations using fecal output. Fecal nitrogen output (g N/kg BW) was associated more closely with nitrogen balance (g N/kg BW) than other fecal indicators. Further, fecal N output was best associated with nitrogen balance for both cattle and goats (r2 = 0.64, 73, respectively) when used in multiple regression equations. Multiple regression equations showed potential for evaluating nitrogen intake (g N/kg BW) of both cattle and goats, (R2 = 0.91, 0.87, respectively). Although it is doubtful that our equations have broad applications, our approach might be useful if specific equations were developed for individual range types.

Evaluation of total fecal collection for measuring cattle forage intake.

Conventional digestibility trials with steers were conducted to evahutte relationships between actual forage intake and estimated forage intake using the total fecal collection procedure. Actual forage intake of 6 of the 9 forages fed was not accurately estimated by the widely used technique of dividing total fecal output by forage indigestibility estimated by in vitro procedures. This was because 4811 in vitro digestibility poorly estimated in vivo digestibility of 6 forages. Regression equations based on in vivo-in vitro digestibility relationships can reduce but not solve this problem because in vivo processes such as mastication and rumination are bypassed with in vitro techniques. The use of a 36-h microbial digestion period for nongrasses and a 72-96-h microbial digestion period for grasses shows potential to improve in vitro digestibility estimates of cattle in vivo digestibility. Another potential means of improving in vitro digestibility estimates is to select the highest digestibility value from forage or diet snmpies subjected to 36,4&, 60-, 72-, 84 and 96-h microbial digestion periods.

Performance and phosphorus status of range cows with and without phosphorus supplementation.

Performance and phosphorus (P) status were studied in 2 groups of range cows, one of which had free access to salt alone (control) and the other to a mineral mix (P-supplemented). The mineral mix contained 50% dicalcium phosphate, 45% salt, and 5% cottonseed meal. Performance traits (birth date, calving interval, weaning weight, suckling gain, and percent calf crop) were compared over 5 years (1979-83), one of which was considered a drought year (1980). Cows involved in the study received no supplemental protein or energy during the experiment. Lack of P supplementation had a detrimental effect on cow performance only when coupled with the effects of drought. This apparent combined effect delayed postpartum estrus in control cows during the 1980 drought, thus causing them to calve later (7 April vs. 11 February; P .05) between the 2 groups during any year of the study, although in both groups, this trait was considerably lower in 1981 than in other years because of the 1980 drought. These results suggest that rainfall or P supplementation before and during the breeding season may be critical in maintaining early calving dates and heavier weaning weights but, even with P supplementation, lower conception rates may occur under drought conditions. Phosphorus status of cows was estimated from fecal, saliva, and rib bone biopsy samples collected at 6 intervals from April 1981 to January 1982. Fecal P varied (P .10) between groups and was higher (P<.001) than during lactation, which indicates bone P levels can be replenished following lactation without P supplementation. Most phosphorus (P) nutrition research with grazing animals was conducted 30 to 50 years ago in the United States (Ross et al. 1948, Black et al. 1949, Knox et al. 1951) and in Africa (Theiler et al. 1928). These early studies reported aphosphorosis in cattle resulting from seasonal declines in plant P. Recent research in the United States and Australia has shown no difference in reproductive performance of beef females fed 65 or 100% of the National Research Councils (N RC 1980) requirement for P (Call et al. 1978, Little 1980), suggesting clinical aphosphorosis may not result from Authors are graduate assistant, professor, assistant professor, and research technician, Department of Animal and Range Science, New Mexico State University, Las Cruces 88003. This manuscript is Journal Article 1057, Agricultural Experiment Station, New Mexico State University, Las Cruces 88003. Manuscript accepted June 7, 1984. low P diets. Measuring the mineral status of confined animals is a formidable task which is further complicated with grazing animals. Underwood (1966) suggested that phosphorus status of grazing animals is best determined by blood inorganic P level. In contrast, Gartner et al. (1965), Little and McMeniman (1973), and Cohen (1973) reported that plasma P levels do not adequately reflect P status. As a result, Little (1972) proposed a rib bone biopsy technique to measure P status of sheep and cattle. In addition, Cohen (1973) proposed measurement of dietary P level from blood, bone, saliva, and fecal P. The purpose of this study was to evaluate bone, saliva, and fecal P trends, and reproductive performance of range cows with and without P supplementation. Experimental Procedure Data for this study were collected at New Mexico State Universitys Fort Stanton Experimental Ranch, Lincoln County, New Mexico, on a site typical of the blue grama foothill-mountain rangeland of the Southwest. Vegetation in the study area is dominated by blue grama (Bouteloua gracilis [H.B.K.] Lag.). Other grasses include sideoats grama (B. curtipendula [Michx.] Torr.), galleta (Hilariajamesii[Torr.] Benth.), sand dropseed (Sporobolus cryptandrus [Torr.] Gray), mat muhly (Muhlenbergia richardsonis [Trin.] Rydb.) and ring muhly (M. Torreyi [Kunth] Hitch.). Important forbs include carruth sagewort (Artemisia carruthii Wood), scarlet globemallow (Sphaeralcea coccinea [Pursh.] Rydb.) and Dakota verbena (Verbena bipinnetifida Nutt.). Open grassland vegetation exists on the mesas and canyon bottoms while slopes support sparse to dense stands of pinyon-juniper (Pinus edulis Engelm., Juniperus spp.) and wavyleaf oak (Quercus undulata Torr.) (Groce and Pieper 1967). Climate in the area is mild with warm summer days (mean maximum 28.90 C) and cool winters (mean minimum -6.7? C). The 94-year average precipitation is 348 mm with 228 mm (66%) occurring during the growing season of June through September (Parker et al. 1974). Precipitation during the growing season was 265 mm for 1979, 295 mm for 1980, 333 mm for 1981, and 370 mm for 1982. However, low precipitation during June and July of 1980 (June = 15 mm, July = 40.5 mm; 94-year average: June = 32.0 mm, July = 79 mm) created drought conditions. Above-average rainfall late in August (96 mm) and September (143 mm) was too late to stimulate forage growth during the breeding season. Materials and Methods In the spring of 1979, 78 Angus X Hereford cows were sorted by previous treatment and randomly allotted to 2 treatment groups (39 cows per group). One group (control) received only free choice salt, while the other group had free access to a salt:mineral mixture (50% dicalcium phosphate, 45% salt, and 5% cottonseed meal). Average monthly consumption of the salt and mineral mix is JOURNAL OF RANGE MANAGEMENT 38(2), March 1985 139 This content downloaded from 207.46.13.176 on Mon, 20 Jun 2016 06:00:30 UTC All use subject to http://about.jstor.org/terms Table 1. Average supplemental consumption of salt and phosphorus by range cows with free access to either salt only or a mineral mix for 1980,1981, and 1982.1 Treatment JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV NOV x