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Comparison of eastern gamagrass grain and cottonseed meal as supplements for sheep fed mature eastern gamagrass hay
Animal Feed Science and Technology 76 (1998) 95±102
Comparison of eastern gamagrass grain and cottonseed meal as supplements for sheep fed mature eastern gamagrass hay Derek W. Baileya,*, Phillip L. Simsb a
Northern Agricultural Research Center, Star Route 36 Box 43, Montana State University, Havre MT 59501, USA b Southern Plains Range Research Station, USDA-ARS, 2000 18th Street, Woodward OK 73801, USA Received 7 October 1997; accepted 18 June 1998
Abstract Eastern gamagrass (Tripsacum dactyloides (L.) L.) is a highly palatable warm season grass that has the potential to become a perennial grain crop with a high protein content (29% crude protein). Twelve wether lambs were used to evaluate eastern gamagrass grain and cottonseed meal as protein supplements for mature eastern gamagrass hay in a conventional digestion and nitrogen balance trial. Voluntary intake of organic matter (OM), neutral detergent fiber (NDF) digestibility, and nitrogen balance were determined for hay alone (CONTROL), hay plus eastern gamagrass grain (GGG), and hay plus cottonseed meal (CSM) treatments. Organic matter intake of supplemented lambs (25.7 g/kg BW) was higher (p<0.001) than lambs fed only hay (20.6 g/kg BW). There was no difference (p0.22) in OM intake between GGG and CSM supplement treatments. Total tract digestibility of OM differed (p<0.001) among the GGG (61.8%), CSM (58.6%), and CONTROL (54.9%) treatments. However, differences in digestibility may be the result of addition of highly digestible protein and carbohydrate supplements, rather than an increase in digestibility of the hay. Digestibility of NDF was greater (p0.01) for supplemented lambs (58.4%) than unsupplemented lambs (57.4%) and differed (p0.04) between the CSM (59.1%) and GGG (57.7%) treatments. Addition of the supplements improved (p<0.001) the digestible (DE) and metabolizable energy (ME) of the total diet. The diet with GGG had more (p<0.001) favorable DE and ME values than the CSM supplemented ration. Nitrogen balance was more favorable (p<0.001) for supplemented (5.7 g N/day) than for unsupplemented lambs (1.7 g N/day). Lambs supplemented with GGG (6.3 g N/day) retained more (p0.01) nitrogen than lambs supplemented with CSM (5.0 g N/ day) even though nitrogen intake was similar (p0.98). The difference in the nitrogen retention between the supplement treatments was the result of higher (p0.01) urinary nitrogen excretion * Corresponding author. Tel.: +1-406-265-6115; fax: +1-406-265-8288; e-mail: [email protected] 0377-8401/98/$ ± see front matter # 1998 Elsevier Science B.V. All rights reserved PII: S 0 3 7 7 - 8 4 0 1 ( 9 8 ) 0 0 2 0 0 - 4
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from the CSM as compared to the GGG treatment, while fecal nitrogen excretion was similar (p0.63) for both supplement treatments. Eastern gamagrass grain was comparable to CSM as a protein supplement for moderate to low quality hay. # 1998 Elsevier Science B.V. Keywords: Protein; Supplement; Tripsacum dactyloides; Digestibility; Nitrogen balance
1. Introduction Eastern gamagrass is a highly productive and palatable perennial bunchgrass. Although eastern gamagrass is related to corn (Zea mays L), its seed production is low, normally below 100 kg haÿ1 (Dewald and Sims, 1990). However, Dewald and Dayton, 1985a, b described a gynomonoecious form of eastern gamagrass (Tripsacum dactyloides (L.)L forma prolificum Dayton et Dewald). This variant increases the seed production potential by 20±25 fold, and may allow the development of a perennial grain crop (Dewald and Sims, 1990). Annual species, such as corn, require more tillage than eastern gamagrass to produce grain, and annual production costs and the potential for soil erosion are correspondingly greater. Eastern gamagrass grain also has an excellent nutritional value comparable to corn with a high level of protein (27%) and a good amino acid balance (Bates et al., 1981; Bargman et al., 1989). Eastern gamagrass grain has potential as a protein and energy supplement for ruminants because of its relatively high protein and energy content. The grain from eastern gamagrass variants with higher seed production could also increase the productivity of livestock grazing the mature forage by providing additional protein. The objective of this study was to evaluate eastern gamagrass grain as a protein supplement for mature grass hay by comparing it to a commonly used supplement, cottonseed meal, in a conventional digestion and nitrogen balance trial. 2. Materials and methods A conventional digestion trial with 14 days adjustment and an 8 days total fecal and urine collection periods was conducted in a controlled environment facility. Twelve finewool crossbreed (DorsetRambouillet) yearling wether lambs were stratified by body weight into four blocks of similar body weight. The average weight of the lambs was 42.8 kg. Lambs were kept and fed in individual pens for the first 10 days of the adjustment period and confined to individual metabolism crates during the last 4 days of the adjustment period and during the collection period. Treatments consisting of eastern gamagrass hay alone (CONTROL), eastern gamagrass hay plus eastern gamagrass grain pellets (GGG), and eastern gamagrass hay plus cottonseed meal (CSM) were randomly assigned to animals within each block. The 282 g of GGG and 169 g of CSM supplements fed each day were designed to provide 76 g of supplemental crude protein per lamb per day and meet the level of crude protein recommended by NRC (1985) for 40 kg lambs gaining 100 g per day. Mature eastern gamagrass hay and supplements were offered daily at 0800 hours. Hay was offered again at 1630 hours.
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Table 1 Chemical composition of supplements and eastern gamagrass hay expressed on dry-matter basis Item
Dry matter, (%)
Ash, (%)
Crude protein (%)
Ether extract (%)
Gross energy (MJ/kg)
NDFa (%)
NSCb (%)
IVDMDc (%)
Hay±eastern gamagrass Grain±eastern gamagrass Cottonseed meal
92.6 90.3 91.3
6.9 2.2 6.6
7.4 29.8 47.2
1.53 9.62 2.88
18.7 21.9 20.1
74.7 13.1 23.5
9.5 45.3 19.8
53.0 87.2 77.7
a
Neutral detergent fiber. Nonstructural carbohydrates calculated as: 100ÿ(crude proteinNDFAshether extract). c In vitro dry matter digestibility. b
The eastern gamagrass hay was mature when it was harvested in July 1995. The hay was chopped to 2±4 cm lengths before feeding. The eastern gamagrass grain was dehulled by pneumatic impact. Pellets were formed at 74±798C by conventional methods. Chemical composition of the hay and supplements is shown in Table 1. From days 15 to 22 of the trial, voluntary intake was determined by recording the amounts of hay and supplements offered and refused. Hay was fed at levels high enough to ensure greater than 10% orts. Forage intake was calculated by assuming that all supplement was consumed. During the collection period, visual observations supported that almost all supplement was consumed with only small inseparable amounts of supplement in the orts. Samples of the hay and supplement were collected daily, partially dried at 50±558C for 48 h and later composited across days for analysis. Total collections of feces, orts, and urine were obtained daily. Urine aliquots (>10%) from each lamb on each day were composited and later was frozen until analysis. Subsamples of feces and orts (>10%) were partially dried at 50±558C for 48 h and composited across days for each lamb. 40 ml of 9.2 N sulfuric acid was added daily to the urine collection vessel to acidify the urine. Chemical analyses were performed on the hay, supplements, orts, and fecal samples that had been ground to pass a 1 mm screen. Dry matter (DM), OM, ether extract and total N were determined by standard procedures (AOAC, 1984). Gross energy of the hay, supplements, orts, feces and urine were determined using a Parr adiabatic oxygen bomb calorimeter (Parr Instrument, model 1241). Neutral detergent fiber (NDF) content of hay, supplements, orts, and feces were determined using the procedure of Goering and van Soest (1970). Intake of DM, OM, N, and NDF was adjusted for content in orts. Digestion coefficients for DM, OM, NDF were calculated as described by Schneider and Flatt (1975). Mixtures of supplements and hay in the approximate proportions fed in the in vivo digestion trial were analyzed in an in vitro digestion study. In addition, supplements and hay were individually analyzed in vitro. The Tilley and Terry two-stage method (Tilley and Terry, 1963) as modified by White et al. (1981) was used to determine in vitro dry matter disappearance (IVDMD). The in vivo trial was analyzed as a randomized complete block design using the GLM procedures of SAS (1985). The model included blocks and treatments. When the treatment F-test was significant (p<0.05), treatment means were compared using the
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following single degree of freedom orthogonal contrasts: (1) supplement vs. no supplement; and, (2) GGG vs. CSM. 3. Results and discussion Eastern gamagrass grain contained higher levels of ether extract than CSM or the eastern gamagrass hay. Ether extract from GGG supplement was more than three times and nonstructural carbohydrates were more than two times higher than CSM or hay (Table 1). Burkhart et al. (1994) found that eastern gamagrass seed contained low levels of saturated fatty acids and high levels of linoleic and oleic acid. Crude protein concentration of the GGG supplement in this study (29.8) was slightly higher than the 27% values reported by Bates et al. (1981) and Bargman et al. (1989). The higher level of lipids probably accounted for the higher energy content of GGG (Table 1). The quality of the eastern gamagrass hay was moderate to low (Table 1). Crude protein concentration of the hay was 7.4% and IVDMD was 53.0%. 3.1. Voluntary intake Total intake of supplemented lambs was higher (p<0.001) than unsupplemented lambs (Table 2). Lambs supplemented with GGG or CSM did not differ (p0.22) in total intake. However, intake of forage (supplements excluded) was similar (p0.39) among all treatments. Krysl et al. (1987) found supplementing ewes with cottonseed meal increased the intake of prairie hay. In contrast, Caton et al. (1988) reported that supplementing Table 2 Effect of GGG and CSM supplements on intake, digestibility, digestible energy and metabolic energy of eastern gamagrass hay Item
OM intakea (g/kg) BW Forage OM intakeb (g/kg) BW DM digestibility (%) OM digestibility (%) NDF digestibility (%) Gross energy intake (MJ/day) Fecal energy (MJ/day) Urine energy (MJ/day) Digestible energy (MJ/kg) DM Metabolizable energy (MJ/kg) DMd a
Supplements
p-values of contrasts
No supplement
GGG
CSM
SEM
Supplement vs. no supplement
GGG vs. CSM
20.6 20.6 53.9 54.9 57.4 17.7 8.4 0.7 9.8 9.1
26.2 20.3 60.6 61.8 57.7 23.4 9.3 0.9 11.7 11.0
25.1 21.7 57.4 58.6 59.1 21.8 9.5 1.0 10.7 9.8
0.58 0.60 0.42 0.37 0.35 0.77 0.38 0.04 0.08 0.08
0.001 NSc 0.001 0.001 0.008 0.013 NSc 0.012 0.001 0.001
0.219 NSc 0.001 0.001 0.039 0.176 NSc 0.044 0.001 0.001a
OM intake includes both hay and supplement because orts may have contained inseparable amounts of both diet ingredients. b Forage OM intake considers only hay and assumes that orts contained no supplement even though lambs may not have consumed small amounts of supplement that were inseparable from the hay. c NS ± Not significant. The F-test was not significant (p>0.05), and a contrast was not conducted. d Metabolizable energy (ME) values presented in this table have not been adjusted for methane losses and are not `true ME values'.
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cottonseed meal did not affect intake of low quality forage by wether lambs. Paterson et al. (1996) suggested that forage intake should be enhanced by protein supplementation when the crude protein content of the forage is less than 7%. In this study, crude protein of the eastern gamagrass hay (7.4%) was only slightly above this threshold. This may explain why we saw no effect of supplementation on forage intake. Supplements did not replace hay in this study, so the total intake of supplemented lambs was higher than lambs fed only hay. 3.2. Digestibility In vivo DM, OM, and NDF digestibilities of supplemented lambs were greater (p<0.01) than unsupplemented lambs (Table 2). DM and OM digestibilities of lambs supplemented with GGG were greater (p<0.001) than lambs supplemented with CSM, but NDF digestibility was greater (p0.04) for the CSM treatment. The higher level of lipids in the GGG supplement did not adversely affect digestibility of the total ration, but it may have affected NDF digestibility. However, Miner and Petersen (1989) found that feeding a protein supplement containing fat did not affect NDF fermentation rate. The GGG supplement contained higher levels of nonstructural carbohydrates (Table 1) which may have reduced NDF digestibility (Bowman and Sanson, 1996). The higher DM and OM total tract digestibility values from supplemented lambs appear to result from the higher digestibility levels of the supplements. The predicted digestibilities from forage and supplement DM intakes and the associated IVDMD values are roughly equal to the in vivo total tract digestibility values (Table 3). Caton et al. (1988) also suggested that the higher total tract digestibility values observed for protein supplemented lambs are the result of adding a highly digestible protein supplement to the diet, and not the result of higher digestibility of the hay. The IVDMD of simulated diets based on observed hay and supplement intakes were within 2% of the in vivo values (Table 3). Table 3 Predicted digestibility values for the GGG and CSM supplemented treatments using the IVDMD values for the eastern gamagrass hay (CONTROL) and supplements Item
CONTROL GGG CSM
DM Intake Forage, (kg/day)
Supplement, (kg/day)
0.941 0.949 0.992
0.00 0.255 0.154
Supplement IVDMD (%)
Predicted digestibilitya (%)
IVDMD of a simulated dietb (%)
In vivo digestibilityc (%)
± 87.2 77.7
53.0 60.2 56.3
53.0 60.2 56.5
53.9 60.6 57.4
a The IVDMD values for eastern gamagrass hay (53.0%) and the supplements were used to calculate the predicted digestibility of the total ration using the following equation:
Predicted digestibility b c
Forage DM intake 53:0=100 Supplement DM intake IVDMD=100 Forge DM intake Supplement DM intake
IVDMD of mixtures of hay and supplement in proportion to in vivo DM intakes. Observed total tract DM digestibility (Table 2).
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Table 4 Effect of GGG and CSM supplements on the nitrogen balance of lambs fed eastern gamagrass hay Item
N intake, (g/day) Fecal N, (g/day) Urinary N, (g/day) N retention, (g/day) N retention, (% of N intake)
Supplements
p-values of contrasts
CONTROL ± no supplement
GGG
CSM
SEM
Supplement vs. no supplement
GGG vs. CSM
12.3 5.5 5.1 1.7 13.5
24.5 8.3 9.9 6.3 25.9
24.5 8.1 11.4 5.0 20.5
0.52 0.36 0.30 0.25 1.57
0.001 0.004 0.001 0.001 0.003
0.98 0.63 0.01 0.01 0.05
Supplemented lambs consumed more (p0.01) energy each day and excreted more (p0.01) energy in their urine than lambs fed only hay (Table 2). However, fecal energy was similar (p0.84) among all treatments. References of metabolizable energy (ME) in this study only reflect adjustments for energy in the feces and urine and are not true ME values, because they have not been adjusted for methane losses. The digestible (DE) and ME of the diets of supplemented lambs was greater (p<0.001) than for unsupplemented lambs. Lambs fed GGG excreted less energy in their urine than lambs fed CSM. The GGG supplemented diet had higher (p<0.001) DE and ME values than the CSM diet, which can be at least partially explained by the greater lipid and gross energy content of the GGG supplement (Table 1). The DE and ME values of the eastern gamagrass hay were comparable to published values for corn stover silage (NRC, 1985), and higher than many forages harvested at less mature stages. 3.3. Nitrogen balance Supplemented lambs consumed, excreted, and retained more nitrogen (p<0.005) than unsupplemented lambs (Table 4). Nitrogen intake of lambs in the GGG and CSM supplement treatments were similar (p0.98). Fecal excretion of nitrogen was also similar (p0.63) for the GGG and CSM treatments. Lambs receiving GGG excreted less (p0.01) nitrogen in their urine and retained more (p0.05) nitrogen than lambs supplemented with CSM. Comparison among treatments was similar if nitrogen retention was expressed as g N/day or as a percentage of total nitrogen intake (Table 4). Similar improvements in nitrogen balance of lambs receiving protein supplements have been reported (Caton et al., 1988; Nunez-Hernandez et al., 1991). The higher level of nitrogen retention for the GGG supplement suggests that it was more fully utilized than CSM. Increased nitrogen uptake by rumen microbes is the most likely explanation for the higher nitrogen retention levels in the GGG diet. The higher total tract OM digestibility of the GGG treatment was probably associated with a higher ruminal OM digestibility which may have increased rumen microbial synthesis. In addition, rumen microbial activity may have been enhanced by the higher level of nonstructural carbohydrates in the GGG diet (Table 1). However, other factors may have contributed to the greater nitrogen retention in the GGG diet. The higher ME intake from the GGG diet may have allowed more nitrogen to be sequestered in tissue. The GGG
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supplement may have higher levels of ruminally undegradable protein or a more favorable amino acid composition (Egan and Moir, 1965) than CSM, which could account for higher level of nitrogen retention associated with the GGG supplement. Further studies are needed to examine protein degradability of eastern gamagrass grain in the rumen and the amino acid composition of ruminally undegradable protein. 4. Conclusions Supplementing eastern gamagrass grain or cottonseed meal to lambs consuming a mature eastern gamagrass hay increased total intake but did not affect intake of hay. Supplementation also increased the digestibility of the total ration, but it did not appear to improve the digestibility of the hay. Supplementing with eastern gamagrass grain resulted in a more favorable nitrogen status of lambs than occurred with the cottonseed meal supplement. Eastern gamagrass grain was comparable to cottonseed meal as a protein supplement for moderate to low quality forage. Acknowledgements The authors thank Bill Cooper for his assistance in data collection and Jerry McLaughlin for laboratory analyses. At the time of the research, Bailey was with USDAARS in Woodward, OK. Montana Agricultural Experiment Station Journal Series J5121. References AOAC, 1984. Official Methods of Analysis, 14th ed. Association of Official Analytical Chemists. Bargman, T.J., Hanners, G.D., Becker, R., Saunders, R.M., Rupnow, J.H., 1989. Compositional and nutritional evolution of eastern gamagrass (Tripsacum dactyloides (L)L.) a perennial relative of maize (Zea mays L). Lebensm. Wiss Technol. Food Sci. Technol. 22, 208±212. Bates, L.S., Bender, M., Jackson, W., 1981. Eastern gamagrass. Seed structure and protein quality. Cereal Chem. 58, 138±140. Bowman, J.G.P., Sanson, D.W., 1996. Starch- or fiber-based energy supplements for grazing ruminants. In: Judkins, M.B., McCollum, F.T. III (Eds.), Proc. 3rd Grazing Livestock Nutrition Conf. Proc. West. Sec. Am. Soc. Anim. Sci. 47 (Suppl. 1), 118±135. Burkhart, S., Kindiger, B., Wright, A., 1994. Fatty acid composition of oil from the caryopsis of Tripsacum dactyloides. Maydica 39, 1±4. Caton, J.S., Hoefler, W.C., Galyean, M.L., Funk, M.A., 1988. Influence of cottonseed meal supplementation and cecal antibiotic infusion in lambs fed low-quality forage I. Intake, digestibility, nitrogen balance and ruminal and cecal digesta kinetics. J. Anim. Sci. 66, 2245±2252. Dewald, C.L., Dayton, R.S., 1985a. Registration of gynomonoecious germplasm (GSF-I and GSF-II) of eastern gamagrass. Crop Sci. 25, 715. Dewald, C.L., Dayton, R.S., 1985b. A prolific sex form variant of eastern gamagrass. Phytologia 57, 156. Dewald, C.L., Sims, P.L., 1990. Breeding Tripsacum for increased grain production. Eastern Gamagrass Conf. Proc. The Kerr Center for Sustainable Agriculture, Poteau, OK, 27 pp. Egan, A.R., Moir, R.J., 1965. Nutritional status and intake regulation in sheep I. Effects of duodenally infused single doses of casein, urea and propionate upon voluntary intake of a low-protein roughage by sheep. Aust. J. Agric. Res. 16, 437.
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Goering, H.K., van Soest, P.J., 1970. Forage fiber analyes (apparatus, reagents, procedures and some applications), USDA-ARS Handbook No. 379. Krysl, L.J., Branine, M.E., Galyean, M.L., Estell, R.E., Hoefler, W.C., 1987. Influence of cottonseed meal supplementation on voluntary intake, ruminal and cecal fermentation, digesta kinetics and serum insulin and growth hormone in mature ewes fed prairie hay. J. Anim. Sci. 64, 1178±1188. Miner, J.L., Petersen, M.K., 1989. The effects of ruminal escape protein or fat on ruminal characteristics of pregnant winter-grazing beef cows. J. Anim. Sci. 67, 2782±2791. NRC, 1985. Nutrient requirements of sheep, 6th revised ed. National Academy Press, Washington, DC, 99 pp. Nunez-Hernandez, G., Wallace, J.D., Holechek, J.L., Galyean, M.L., King, D.W., Kattnig, R.M., 1991. Mountain mahogany and cottonseed meal as supplements for grass hay. J. Range Manage. 44, 497±500. Paterson, J., Cochran, R., Klopfenstein, T., 1996. Degradable and undegradable protein responses of cattle consuming forage-based diets. In: Judkins, M.B., McCollum, F.T. III (Eds.), Proc. 3rd Grazing Livestock Nutrition Conf. Proc. West. Sec. Am. Soc. Anim. Sci. 47 (Suppl. 1), 94±103. SAS, 1985. SAS User's Guide: Statistics. Version 5, SAS Inst. Inc., Cary, NC. Schneider, B.H., Flatt, W.P., 1975. The evaluation of feeds through digestibility experiments, University of Georgia Press, Athens, pp. 143±151. Tilley, J.M.A., Terry, R.A., 1963. A two-stage technique for the in vitro digestion of forage crops. J. Br. Grassl. Soc. 18, 104±111. White, L.M., Hartman, G.P., Bergman, J.W., 1981. In vitro digestibility, crude protein, and phosphorus content of straw of winter wheat, spring wheat, barley, and oat cultivars in eastern Montana. Agron. J. 73, 117±121.
Comparison of eastern gamagrass grain and cottonseed meal as supplements for sheep fed mature eastern gamagrass hay Derek W. Baileya,*, Phillip L. Simsb a
Northern Agricultural Research Center, Star Route 36 Box 43, Montana State University, Havre MT 59501, USA b Southern Plains Range Research Station, USDA-ARS, 2000 18th Street, Woodward OK 73801, USA Received 7 October 1997; accepted 18 June 1998
Abstract Eastern gamagrass (Tripsacum dactyloides (L.) L.) is a highly palatable warm season grass that has the potential to become a perennial grain crop with a high protein content (29% crude protein). Twelve wether lambs were used to evaluate eastern gamagrass grain and cottonseed meal as protein supplements for mature eastern gamagrass hay in a conventional digestion and nitrogen balance trial. Voluntary intake of organic matter (OM), neutral detergent fiber (NDF) digestibility, and nitrogen balance were determined for hay alone (CONTROL), hay plus eastern gamagrass grain (GGG), and hay plus cottonseed meal (CSM) treatments. Organic matter intake of supplemented lambs (25.7 g/kg BW) was higher (p<0.001) than lambs fed only hay (20.6 g/kg BW). There was no difference (p0.22) in OM intake between GGG and CSM supplement treatments. Total tract digestibility of OM differed (p<0.001) among the GGG (61.8%), CSM (58.6%), and CONTROL (54.9%) treatments. However, differences in digestibility may be the result of addition of highly digestible protein and carbohydrate supplements, rather than an increase in digestibility of the hay. Digestibility of NDF was greater (p0.01) for supplemented lambs (58.4%) than unsupplemented lambs (57.4%) and differed (p0.04) between the CSM (59.1%) and GGG (57.7%) treatments. Addition of the supplements improved (p<0.001) the digestible (DE) and metabolizable energy (ME) of the total diet. The diet with GGG had more (p<0.001) favorable DE and ME values than the CSM supplemented ration. Nitrogen balance was more favorable (p<0.001) for supplemented (5.7 g N/day) than for unsupplemented lambs (1.7 g N/day). Lambs supplemented with GGG (6.3 g N/day) retained more (p0.01) nitrogen than lambs supplemented with CSM (5.0 g N/ day) even though nitrogen intake was similar (p0.98). The difference in the nitrogen retention between the supplement treatments was the result of higher (p0.01) urinary nitrogen excretion * Corresponding author. Tel.: +1-406-265-6115; fax: +1-406-265-8288; e-mail: [email protected] 0377-8401/98/$ ± see front matter # 1998 Elsevier Science B.V. All rights reserved PII: S 0 3 7 7 - 8 4 0 1 ( 9 8 ) 0 0 2 0 0 - 4
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from the CSM as compared to the GGG treatment, while fecal nitrogen excretion was similar (p0.63) for both supplement treatments. Eastern gamagrass grain was comparable to CSM as a protein supplement for moderate to low quality hay. # 1998 Elsevier Science B.V. Keywords: Protein; Supplement; Tripsacum dactyloides; Digestibility; Nitrogen balance
1. Introduction Eastern gamagrass is a highly productive and palatable perennial bunchgrass. Although eastern gamagrass is related to corn (Zea mays L), its seed production is low, normally below 100 kg haÿ1 (Dewald and Sims, 1990). However, Dewald and Dayton, 1985a, b described a gynomonoecious form of eastern gamagrass (Tripsacum dactyloides (L.)L forma prolificum Dayton et Dewald). This variant increases the seed production potential by 20±25 fold, and may allow the development of a perennial grain crop (Dewald and Sims, 1990). Annual species, such as corn, require more tillage than eastern gamagrass to produce grain, and annual production costs and the potential for soil erosion are correspondingly greater. Eastern gamagrass grain also has an excellent nutritional value comparable to corn with a high level of protein (27%) and a good amino acid balance (Bates et al., 1981; Bargman et al., 1989). Eastern gamagrass grain has potential as a protein and energy supplement for ruminants because of its relatively high protein and energy content. The grain from eastern gamagrass variants with higher seed production could also increase the productivity of livestock grazing the mature forage by providing additional protein. The objective of this study was to evaluate eastern gamagrass grain as a protein supplement for mature grass hay by comparing it to a commonly used supplement, cottonseed meal, in a conventional digestion and nitrogen balance trial. 2. Materials and methods A conventional digestion trial with 14 days adjustment and an 8 days total fecal and urine collection periods was conducted in a controlled environment facility. Twelve finewool crossbreed (DorsetRambouillet) yearling wether lambs were stratified by body weight into four blocks of similar body weight. The average weight of the lambs was 42.8 kg. Lambs were kept and fed in individual pens for the first 10 days of the adjustment period and confined to individual metabolism crates during the last 4 days of the adjustment period and during the collection period. Treatments consisting of eastern gamagrass hay alone (CONTROL), eastern gamagrass hay plus eastern gamagrass grain pellets (GGG), and eastern gamagrass hay plus cottonseed meal (CSM) were randomly assigned to animals within each block. The 282 g of GGG and 169 g of CSM supplements fed each day were designed to provide 76 g of supplemental crude protein per lamb per day and meet the level of crude protein recommended by NRC (1985) for 40 kg lambs gaining 100 g per day. Mature eastern gamagrass hay and supplements were offered daily at 0800 hours. Hay was offered again at 1630 hours.
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Table 1 Chemical composition of supplements and eastern gamagrass hay expressed on dry-matter basis Item
Dry matter, (%)
Ash, (%)
Crude protein (%)
Ether extract (%)
Gross energy (MJ/kg)
NDFa (%)
NSCb (%)
IVDMDc (%)
Hay±eastern gamagrass Grain±eastern gamagrass Cottonseed meal
92.6 90.3 91.3
6.9 2.2 6.6
7.4 29.8 47.2
1.53 9.62 2.88
18.7 21.9 20.1
74.7 13.1 23.5
9.5 45.3 19.8
53.0 87.2 77.7
a
Neutral detergent fiber. Nonstructural carbohydrates calculated as: 100ÿ(crude proteinNDFAshether extract). c In vitro dry matter digestibility. b
The eastern gamagrass hay was mature when it was harvested in July 1995. The hay was chopped to 2±4 cm lengths before feeding. The eastern gamagrass grain was dehulled by pneumatic impact. Pellets were formed at 74±798C by conventional methods. Chemical composition of the hay and supplements is shown in Table 1. From days 15 to 22 of the trial, voluntary intake was determined by recording the amounts of hay and supplements offered and refused. Hay was fed at levels high enough to ensure greater than 10% orts. Forage intake was calculated by assuming that all supplement was consumed. During the collection period, visual observations supported that almost all supplement was consumed with only small inseparable amounts of supplement in the orts. Samples of the hay and supplement were collected daily, partially dried at 50±558C for 48 h and later composited across days for analysis. Total collections of feces, orts, and urine were obtained daily. Urine aliquots (>10%) from each lamb on each day were composited and later was frozen until analysis. Subsamples of feces and orts (>10%) were partially dried at 50±558C for 48 h and composited across days for each lamb. 40 ml of 9.2 N sulfuric acid was added daily to the urine collection vessel to acidify the urine. Chemical analyses were performed on the hay, supplements, orts, and fecal samples that had been ground to pass a 1 mm screen. Dry matter (DM), OM, ether extract and total N were determined by standard procedures (AOAC, 1984). Gross energy of the hay, supplements, orts, feces and urine were determined using a Parr adiabatic oxygen bomb calorimeter (Parr Instrument, model 1241). Neutral detergent fiber (NDF) content of hay, supplements, orts, and feces were determined using the procedure of Goering and van Soest (1970). Intake of DM, OM, N, and NDF was adjusted for content in orts. Digestion coefficients for DM, OM, NDF were calculated as described by Schneider and Flatt (1975). Mixtures of supplements and hay in the approximate proportions fed in the in vivo digestion trial were analyzed in an in vitro digestion study. In addition, supplements and hay were individually analyzed in vitro. The Tilley and Terry two-stage method (Tilley and Terry, 1963) as modified by White et al. (1981) was used to determine in vitro dry matter disappearance (IVDMD). The in vivo trial was analyzed as a randomized complete block design using the GLM procedures of SAS (1985). The model included blocks and treatments. When the treatment F-test was significant (p<0.05), treatment means were compared using the
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following single degree of freedom orthogonal contrasts: (1) supplement vs. no supplement; and, (2) GGG vs. CSM. 3. Results and discussion Eastern gamagrass grain contained higher levels of ether extract than CSM or the eastern gamagrass hay. Ether extract from GGG supplement was more than three times and nonstructural carbohydrates were more than two times higher than CSM or hay (Table 1). Burkhart et al. (1994) found that eastern gamagrass seed contained low levels of saturated fatty acids and high levels of linoleic and oleic acid. Crude protein concentration of the GGG supplement in this study (29.8) was slightly higher than the 27% values reported by Bates et al. (1981) and Bargman et al. (1989). The higher level of lipids probably accounted for the higher energy content of GGG (Table 1). The quality of the eastern gamagrass hay was moderate to low (Table 1). Crude protein concentration of the hay was 7.4% and IVDMD was 53.0%. 3.1. Voluntary intake Total intake of supplemented lambs was higher (p<0.001) than unsupplemented lambs (Table 2). Lambs supplemented with GGG or CSM did not differ (p0.22) in total intake. However, intake of forage (supplements excluded) was similar (p0.39) among all treatments. Krysl et al. (1987) found supplementing ewes with cottonseed meal increased the intake of prairie hay. In contrast, Caton et al. (1988) reported that supplementing Table 2 Effect of GGG and CSM supplements on intake, digestibility, digestible energy and metabolic energy of eastern gamagrass hay Item
OM intakea (g/kg) BW Forage OM intakeb (g/kg) BW DM digestibility (%) OM digestibility (%) NDF digestibility (%) Gross energy intake (MJ/day) Fecal energy (MJ/day) Urine energy (MJ/day) Digestible energy (MJ/kg) DM Metabolizable energy (MJ/kg) DMd a
Supplements
p-values of contrasts
No supplement
GGG
CSM
SEM
Supplement vs. no supplement
GGG vs. CSM
20.6 20.6 53.9 54.9 57.4 17.7 8.4 0.7 9.8 9.1
26.2 20.3 60.6 61.8 57.7 23.4 9.3 0.9 11.7 11.0
25.1 21.7 57.4 58.6 59.1 21.8 9.5 1.0 10.7 9.8
0.58 0.60 0.42 0.37 0.35 0.77 0.38 0.04 0.08 0.08
0.001 NSc 0.001 0.001 0.008 0.013 NSc 0.012 0.001 0.001
0.219 NSc 0.001 0.001 0.039 0.176 NSc 0.044 0.001 0.001a
OM intake includes both hay and supplement because orts may have contained inseparable amounts of both diet ingredients. b Forage OM intake considers only hay and assumes that orts contained no supplement even though lambs may not have consumed small amounts of supplement that were inseparable from the hay. c NS ± Not significant. The F-test was not significant (p>0.05), and a contrast was not conducted. d Metabolizable energy (ME) values presented in this table have not been adjusted for methane losses and are not `true ME values'.
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cottonseed meal did not affect intake of low quality forage by wether lambs. Paterson et al. (1996) suggested that forage intake should be enhanced by protein supplementation when the crude protein content of the forage is less than 7%. In this study, crude protein of the eastern gamagrass hay (7.4%) was only slightly above this threshold. This may explain why we saw no effect of supplementation on forage intake. Supplements did not replace hay in this study, so the total intake of supplemented lambs was higher than lambs fed only hay. 3.2. Digestibility In vivo DM, OM, and NDF digestibilities of supplemented lambs were greater (p<0.01) than unsupplemented lambs (Table 2). DM and OM digestibilities of lambs supplemented with GGG were greater (p<0.001) than lambs supplemented with CSM, but NDF digestibility was greater (p0.04) for the CSM treatment. The higher level of lipids in the GGG supplement did not adversely affect digestibility of the total ration, but it may have affected NDF digestibility. However, Miner and Petersen (1989) found that feeding a protein supplement containing fat did not affect NDF fermentation rate. The GGG supplement contained higher levels of nonstructural carbohydrates (Table 1) which may have reduced NDF digestibility (Bowman and Sanson, 1996). The higher DM and OM total tract digestibility values from supplemented lambs appear to result from the higher digestibility levels of the supplements. The predicted digestibilities from forage and supplement DM intakes and the associated IVDMD values are roughly equal to the in vivo total tract digestibility values (Table 3). Caton et al. (1988) also suggested that the higher total tract digestibility values observed for protein supplemented lambs are the result of adding a highly digestible protein supplement to the diet, and not the result of higher digestibility of the hay. The IVDMD of simulated diets based on observed hay and supplement intakes were within 2% of the in vivo values (Table 3). Table 3 Predicted digestibility values for the GGG and CSM supplemented treatments using the IVDMD values for the eastern gamagrass hay (CONTROL) and supplements Item
CONTROL GGG CSM
DM Intake Forage, (kg/day)
Supplement, (kg/day)
0.941 0.949 0.992
0.00 0.255 0.154
Supplement IVDMD (%)
Predicted digestibilitya (%)
IVDMD of a simulated dietb (%)
In vivo digestibilityc (%)
± 87.2 77.7
53.0 60.2 56.3
53.0 60.2 56.5
53.9 60.6 57.4
a The IVDMD values for eastern gamagrass hay (53.0%) and the supplements were used to calculate the predicted digestibility of the total ration using the following equation:
Predicted digestibility b c
Forage DM intake 53:0=100 Supplement DM intake IVDMD=100 Forge DM intake Supplement DM intake
IVDMD of mixtures of hay and supplement in proportion to in vivo DM intakes. Observed total tract DM digestibility (Table 2).
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Table 4 Effect of GGG and CSM supplements on the nitrogen balance of lambs fed eastern gamagrass hay Item
N intake, (g/day) Fecal N, (g/day) Urinary N, (g/day) N retention, (g/day) N retention, (% of N intake)
Supplements
p-values of contrasts
CONTROL ± no supplement
GGG
CSM
SEM
Supplement vs. no supplement
GGG vs. CSM
12.3 5.5 5.1 1.7 13.5
24.5 8.3 9.9 6.3 25.9
24.5 8.1 11.4 5.0 20.5
0.52 0.36 0.30 0.25 1.57
0.001 0.004 0.001 0.001 0.003
0.98 0.63 0.01 0.01 0.05
Supplemented lambs consumed more (p0.01) energy each day and excreted more (p0.01) energy in their urine than lambs fed only hay (Table 2). However, fecal energy was similar (p0.84) among all treatments. References of metabolizable energy (ME) in this study only reflect adjustments for energy in the feces and urine and are not true ME values, because they have not been adjusted for methane losses. The digestible (DE) and ME of the diets of supplemented lambs was greater (p<0.001) than for unsupplemented lambs. Lambs fed GGG excreted less energy in their urine than lambs fed CSM. The GGG supplemented diet had higher (p<0.001) DE and ME values than the CSM diet, which can be at least partially explained by the greater lipid and gross energy content of the GGG supplement (Table 1). The DE and ME values of the eastern gamagrass hay were comparable to published values for corn stover silage (NRC, 1985), and higher than many forages harvested at less mature stages. 3.3. Nitrogen balance Supplemented lambs consumed, excreted, and retained more nitrogen (p<0.005) than unsupplemented lambs (Table 4). Nitrogen intake of lambs in the GGG and CSM supplement treatments were similar (p0.98). Fecal excretion of nitrogen was also similar (p0.63) for the GGG and CSM treatments. Lambs receiving GGG excreted less (p0.01) nitrogen in their urine and retained more (p0.05) nitrogen than lambs supplemented with CSM. Comparison among treatments was similar if nitrogen retention was expressed as g N/day or as a percentage of total nitrogen intake (Table 4). Similar improvements in nitrogen balance of lambs receiving protein supplements have been reported (Caton et al., 1988; Nunez-Hernandez et al., 1991). The higher level of nitrogen retention for the GGG supplement suggests that it was more fully utilized than CSM. Increased nitrogen uptake by rumen microbes is the most likely explanation for the higher nitrogen retention levels in the GGG diet. The higher total tract OM digestibility of the GGG treatment was probably associated with a higher ruminal OM digestibility which may have increased rumen microbial synthesis. In addition, rumen microbial activity may have been enhanced by the higher level of nonstructural carbohydrates in the GGG diet (Table 1). However, other factors may have contributed to the greater nitrogen retention in the GGG diet. The higher ME intake from the GGG diet may have allowed more nitrogen to be sequestered in tissue. The GGG
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supplement may have higher levels of ruminally undegradable protein or a more favorable amino acid composition (Egan and Moir, 1965) than CSM, which could account for higher level of nitrogen retention associated with the GGG supplement. Further studies are needed to examine protein degradability of eastern gamagrass grain in the rumen and the amino acid composition of ruminally undegradable protein. 4. Conclusions Supplementing eastern gamagrass grain or cottonseed meal to lambs consuming a mature eastern gamagrass hay increased total intake but did not affect intake of hay. Supplementation also increased the digestibility of the total ration, but it did not appear to improve the digestibility of the hay. Supplementing with eastern gamagrass grain resulted in a more favorable nitrogen status of lambs than occurred with the cottonseed meal supplement. Eastern gamagrass grain was comparable to cottonseed meal as a protein supplement for moderate to low quality forage. Acknowledgements The authors thank Bill Cooper for his assistance in data collection and Jerry McLaughlin for laboratory analyses. At the time of the research, Bailey was with USDAARS in Woodward, OK. Montana Agricultural Experiment Station Journal Series J5121. References AOAC, 1984. Official Methods of Analysis, 14th ed. Association of Official Analytical Chemists. Bargman, T.J., Hanners, G.D., Becker, R., Saunders, R.M., Rupnow, J.H., 1989. Compositional and nutritional evolution of eastern gamagrass (Tripsacum dactyloides (L)L.) a perennial relative of maize (Zea mays L). Lebensm. Wiss Technol. Food Sci. Technol. 22, 208±212. Bates, L.S., Bender, M., Jackson, W., 1981. Eastern gamagrass. Seed structure and protein quality. Cereal Chem. 58, 138±140. Bowman, J.G.P., Sanson, D.W., 1996. Starch- or fiber-based energy supplements for grazing ruminants. In: Judkins, M.B., McCollum, F.T. III (Eds.), Proc. 3rd Grazing Livestock Nutrition Conf. Proc. West. Sec. Am. Soc. Anim. Sci. 47 (Suppl. 1), 118±135. Burkhart, S., Kindiger, B., Wright, A., 1994. Fatty acid composition of oil from the caryopsis of Tripsacum dactyloides. Maydica 39, 1±4. Caton, J.S., Hoefler, W.C., Galyean, M.L., Funk, M.A., 1988. Influence of cottonseed meal supplementation and cecal antibiotic infusion in lambs fed low-quality forage I. Intake, digestibility, nitrogen balance and ruminal and cecal digesta kinetics. J. Anim. Sci. 66, 2245±2252. Dewald, C.L., Dayton, R.S., 1985a. Registration of gynomonoecious germplasm (GSF-I and GSF-II) of eastern gamagrass. Crop Sci. 25, 715. Dewald, C.L., Dayton, R.S., 1985b. A prolific sex form variant of eastern gamagrass. Phytologia 57, 156. Dewald, C.L., Sims, P.L., 1990. Breeding Tripsacum for increased grain production. Eastern Gamagrass Conf. Proc. The Kerr Center for Sustainable Agriculture, Poteau, OK, 27 pp. Egan, A.R., Moir, R.J., 1965. Nutritional status and intake regulation in sheep I. Effects of duodenally infused single doses of casein, urea and propionate upon voluntary intake of a low-protein roughage by sheep. Aust. J. Agric. Res. 16, 437.
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Goering, H.K., van Soest, P.J., 1970. Forage fiber analyes (apparatus, reagents, procedures and some applications), USDA-ARS Handbook No. 379. Krysl, L.J., Branine, M.E., Galyean, M.L., Estell, R.E., Hoefler, W.C., 1987. Influence of cottonseed meal supplementation on voluntary intake, ruminal and cecal fermentation, digesta kinetics and serum insulin and growth hormone in mature ewes fed prairie hay. J. Anim. Sci. 64, 1178±1188. Miner, J.L., Petersen, M.K., 1989. The effects of ruminal escape protein or fat on ruminal characteristics of pregnant winter-grazing beef cows. J. Anim. Sci. 67, 2782±2791. NRC, 1985. Nutrient requirements of sheep, 6th revised ed. National Academy Press, Washington, DC, 99 pp. Nunez-Hernandez, G., Wallace, J.D., Holechek, J.L., Galyean, M.L., King, D.W., Kattnig, R.M., 1991. Mountain mahogany and cottonseed meal as supplements for grass hay. J. Range Manage. 44, 497±500. Paterson, J., Cochran, R., Klopfenstein, T., 1996. Degradable and undegradable protein responses of cattle consuming forage-based diets. In: Judkins, M.B., McCollum, F.T. III (Eds.), Proc. 3rd Grazing Livestock Nutrition Conf. Proc. West. Sec. Am. Soc. Anim. Sci. 47 (Suppl. 1), 94±103. SAS, 1985. SAS User's Guide: Statistics. Version 5, SAS Inst. Inc., Cary, NC. Schneider, B.H., Flatt, W.P., 1975. The evaluation of feeds through digestibility experiments, University of Georgia Press, Athens, pp. 143±151. Tilley, J.M.A., Terry, R.A., 1963. A two-stage technique for the in vitro digestion of forage crops. J. Br. Grassl. Soc. 18, 104±111. White, L.M., Hartman, G.P., Bergman, J.W., 1981. In vitro digestibility, crude protein, and phosphorus content of straw of winter wheat, spring wheat, barley, and oat cultivars in eastern Montana. Agron. J. 73, 117±121.