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Barley Distillers Grains as a Protein Supplement for Dairy Cows1
Barley Distillers Grains as a Protein Supplement for Dairy Cows I W. P. WEISS, = D. O. ERICKSON, G. M. ERICKSON, and G. R. FISHER
Department of Animal and Range Sciences North Dakota State University Fargo 58105 INTRODUCTION
ABSTRACT
Dried distillers grains produced from a mix of 65% barley and 35% corn were evaluated in digestion and lactation experiments. Dried barley distillers grains had 56% NDF, 29% CP, 3% amino acid N, 2.5% NDIN (55% of total N), and 1.8% ADIN (39% of total N). Wet barley distillers grains had 38% NDF, 27% CP, 2.7% amino acid N, .5% NDIN (12% of total N), and .8% ADIN (19% of total N). Digestibility of DM and N was similar among lactating dairy cows fed diets conraining approximately 25% corn silage DM, 15% alfalfa silage DM, 15% alfalfa hay DM, plus varying amounts of a cornbarley concentrate mix and supplemental CP from soybean meal, barley distillers grains, or from 1:1 mixture of soybean meal and barley distillers grains. Digestibility of ADIN, NDF, and ADF increased with increasing amounts of barley distillers grains in the diet. Similar diets were fed to 60 Holstein cows for 84 d in a lactation experiment. Source of supplemental protein did not affect milk production (22.5 kg/d), FCM (20.4 kg/d), milk fat percent (3.6%), or DM intake (19.0 kg/d). Milk protein percent was decreased by feeding barley distillers grains. It was concluded that barley distillers grains were an acceptable protein source for dairy cows and that ADIN and NDF might not be appropriate measures of the nutritional value of this product.
Extensive research has been conducted to determine the feeding value of distillers grains derived from corn (3, 9). Diets containing corn distillers dried grains (CDG) produced variable responses by dairy cows. In two experiments it was found that CDG was equal or superior to soybean meal (SBM) as a CP source for dairy cows (10, 16), but in a more recent paper, it was reported that cows fed diets with CDG produced less milk than did cows fed SBM (22). The CDG in the Florida study (22) had extremely high ADIN concentrations, and the authors suggested this was the reason for the poor cow performance. Barley is an important crop in the northern plains, and recently, distilleries have started using barley as the feedstock for alcohol production. Very few published data exist on the composition and feeding value of barley distillers grains (BDG). A Montana researcher (21) reported that performance was similar when beef heifers were fed isonitrogenous diets containing either SBM or 5% BDG, but no reports on the use of BDG in dairy cattle diets were found. The CP content of BDG is similar to that of CDG, but NDF and ADF contents of BDG are markedly higher than in CDG (14, 15). The use of NDF to predict intake and aid in diet formulation has been proposed (11). If the negative relationship between dietary concentration of NDF and feed intake is valid for different sources of NDF, then the high concentration of NDF in BDG could limit feed intake and subsequent cow productivity. An additional concern regarding BDG is its relatively high concentration of ADIN. Acid detergent insoluble N is valuable for estimating Received June 20, 1988. Accepted September 23, 1988. the apparent digestibility of N in forages (20), ~Journal Article 1690 of the North Dakota Agricultural but questions have arisen recently regarding the Experiment Station. ZPresent address: Department of Dairy Science, Ohio use of ADIN to estimate N availability of Agricultural Research and DevelopmentCenter, The Ohio grains and protein sources (4, 5). Information is State University, Wooster 44691. lacking on the use of both NDF and ADIN to 1989 J Dairy Sci 72:980-987
980
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BARLEY DISTILLERS GRAINS FOR DAIRY COWS
TABLE 1. Ingredient and nutrient composition of diets consumed in the lactation trial. ~ Item2
SBM
BDG
SBM + BDG
Ingredients Corn silage Alfalfa silage Alfalfa hay Rolled barley Cracked corn Soybean meal Barley distillers grains Minerals/vitamins
31.1 18.8 14.9 14.2 14.2 6.0 0 .8
32.0 19.3 15.2 10.0 10.0 0 12.9 .6
30.6 18.5 14.7 13.3 13.3 4.5 4.5 .6
Nutrients CP ADIN~ NDF
15.1 .17 (7.0) 37.0
15.3 .39 (15.9) 42.3
15.5 .24 (9.7) 38.4
1Soybean meal (SBM), barley distillers's grains (BDG), or a 1:1 mix (SBM + BDG) provided the supplemental crude protein. 2All values are percentages of dry matter. 3Numbers in parentheses are expressed as percent of total N.
evaluate BDG. It is essential that chemical procedures used to evaluate different feeds be validated; otherwise, nutritive value of feeds can be grossly overestimated or underestimated, greatly influencing profitability of dairy producers. The objectives of these experiments were: 1) to examine the effect of drying wet BDG on its chemical composition; 2) to determine the feeding value of BDG for dairy cows; and 3) to determine if NDF and ADIN are valid for evaluation of this feed. MATERIALS AND METHODS
The barley distillers grains were produced from a mix of about 65% barley and 35% corn and included the soluble fraction. 3 Ethanol can be produced with 100% barley, but the high fiber content of barley causes flow problems at the distillery. Samples of wet distillers grains were obtained from the same source but later. Lactation Trial
Sixty Holstein cows (26 primaparous and 34 multiparous) in midlactation (average of 100 d
3Wet and dry barley distillers grains were donated by Dawn Enterprises, Walhalla, ND.
in milk) were fed one of three different protein supplements: soybean meal (SBM), BDG, or 50% SBM plus 50% BDG (SBM + BDG). Cows were housed in a freestall barn with 10 cows per pen and two pens per treatment. Forages (2.9:1.8:1 corn silage:alfalfa silage:alfalfa hay, DM basis) were blended and group fed to each pen of cows. Grain and protein supplements were individually fed via a dual dispensing computer controlled feeder (Boumatic 2030 feeding system, Madison, WI). Total concentrate (grain plus protein supplement) was fed at the rate of 1 kg concentrate (as fed basis) per 3 kg FCM. The amount of concentrate fed was updated biweekly based on the cows production the previous 2 wk. Diets were isonitrogenous but differed in concentration of NDF and ADIN (Table 1). The experiment lasted 84 d with feed intake and milk production measured daily. Feed and milk samples were taken biweekly for analysis. Cows were weighed monthly. Digestion Trial
Twelve cows were fed diets similar to the diets used in the lactation trial (Table 2). Due to an error in the chemical analysis of the forage, the diets in the digestion trial contained approximately 55% forage whereas the diets used in the lactation trial contained about 65% forage (DM basis). Cows were adapted to the Journal of Dairy Science Vol. 72, No. 4, 1989
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WEISS ET AL.
TABLE 2. Ingredient and nutrient composition of diets consumed in the digestion trial.1 Item2
Ingredients Corn silage Alfalfa silage Alfalfa hay Rolled barley Cracked corn Soybean meal Barley distillers grain Minerals/vitamins Nutrients CP ADIN3 NDF
SBM
BDG
SBM + BDG
26.1 15.5 14.0 18.0 18.0 7.8 0 .6
26.1 15.5 14.0 12.7 12.8 0 18.3 .6
26.1 15.5 1,t.0 16.7 16.7 5.3 5.1 .6
14.9 .10 (4.2) 35,3
14.9 .29 (12.2) 43.0
14.8 ,16 (6.8) 37,7
ISoybean meal (SBM), barley distillers's grains (BDG), or a 1:1 mix (SBM + BDG) provided the supplemental crude protein. 2All values are percentages of dry matter. 3Numbers in parentheses are expressed as percent of total N.
diets for at least 14 d prior to the start of a 5-d total collection digestion trial. Feed, orts, feces, urine, and milk were sampled daily and cornposited. All samples were frozen until analyzed.
Chemical Analyses Chemical analyses of feeds, feces, and orts were conducted either on the air dry sample or on a lyophilized sample. Total N (2), ADIN, N D F , ADF, and acid detergent lignin (18) were determined. Samples were dried in a 100°C oven for D M determination. Amylase was added to the detergent solution for grains and protein supplements, but no sulfite was used in any N D F extraction (18). Wet and dried B D G were analyzed for amino acids (26), following hydrolysis in 6 N He1. Milk fat, protein, and S N F were determined using infrared spectrophotometry.
Statistical Analysis Dam for the lactation trial were grouped into 2-wk periods so that adaptation to the diet could be examined. The experiment was analyzed statistically as a 3 x 6 nested factorial experiment (three diets and six time periods) with 19 or 20 cows nested within each diet (1). The model was: Journal of Dairy Science Vol. 72, No. 4, 1989
Yijk = ~t + D i + C(i)j + Pk + DPnc + CP(i)jk when: Yijk = dependent variable; g= overall mean (1 df); D i = effect of i th diet (2 df); C(i)j = effect of jth cow fed i ~ diet, error term for diet (56 dO; Pk = effect of k t~ period (5 dr); DPit = effect o f interaction between ith diet and k th period (10 dr); and CP(i)j k = effect of jth cow fed i th diet during k th period, error term for period and period x diets (280 dr). For total D M intake, forage intake, and total feed efficiency, pen was the experimental unit. The only main effect used in statistical analysis o f the digestion data was protein supplement with cow serving as the error term. One cow died during the lactation trial, and data from one cow on the digestion trial were not usable because of large amounts of urine in the feces. Least squares analysis o f variance was used because o f unequal cell size (8). When a statistically significant treatment effect was found, Duncan's multiple range test was used to separate means. Regression analyses with amount of S B M in the diet as the independent variable
BARLEY DISTILLERS GRAINS FOR DAIRY COWS
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TABLE 3. Chemical composition of soybean meal (SBM), corn distillers grains (CDG), and wet (WBDG) and dry (DBDG) barley distillers grams. Item1
SBM
WBDG
DBDG
CDG2
DM, % CP NDIN~ ADIN3 AAN3'4 NDF ADF Lignin5 Ca P
89.4 46.1 .5 (6.9) .5 (6.9) 6.2 (83.8) 14.7 9.2 .7 .3 .7
35.5 26.9 .5 (11.6) .8 (18.6) 2.7 (62.7) 38.0 22.9 5.5 ND6 ND6
87.5 28.7 2.5 (55.2) 1.8 (39.2) 3.0 (66.7) 56.3 29.2 9.3 .2 .8
94 28 1.6 (39.0) .6 (13.4) 2.3 (51.3) 44 18 1 .1 .7
XAll values expressed as percentage of dry matter. 2Source: (14, 24).
3Values in parentheses are expressed as percent of total N. 4AAN = Amino acid N. SAcid detergent-sulfuric acid method (18). 6ND = Not determined.
was used when a significant treatment effect was found. RESULTS AND DISCUSSION Composition of Barley Distillers Grains
Large differences in chemical composition among dried BDG, wet BDG, CDG, and SBM were found (Table 3). Comparing CDG with BDG, the largest difference occurs in fiber components and ADIN. Differences in fiber components reflect the higher fiber content of barley grain as compared to that of corn (20 vs. 10% NDF), but alterations in composition caused by processing could also be involved. Concentrations of NDF and NDIN were substantially higher in dry BDG than in wet BDG. Heating (drying) presumably reduced solubility of N in neutral detergent, thereby increasing concentration of NDIN. If this N was primarily in the form of protein N, this would account for almost all of the difference in NDF content between wet BDG and dry BDG. Dry BDG had two percentage units more NDIN than did wet BDG. This is equivalent to 12.5 percentage units of CP (2 x 6.25). Dry BDG had 18.3 percentage units more N D F than did wet BDG; therefore, changes in protein solubility could account for 70% of the change in NDF concen-
tration. Similar results were found for A D F and ADIN. This suggests that the composition of both the N D F and A D F fractions in wet BDG is different than of dry BDG. Dry BDG had high values for ADIN as compared to wet BDG and typical CDG. Concentrations of A D I N increase when feeds are heated (23), and in forages, amount of ADIN is correlated to the amount of heat (degree days) the forage received (20). Closer examination of the N fraction reveals that heating affects concentrates differently than forages. In ryegrass and alfalfa, heat increased ADIN but decreased the recovery of amino acid N (27, 28). Barley distillers grains (Table 3) exposed to heat (dry vs. wet) had higher ADIN concentrations but similar amino acid N values and amino acid composition (Table 4). Furthermore, in heated forages, amino acids made up about 20 to 40% of ADIN (27, 28), but in BDG, amino acid N comprised about 70% of ADIN. This value is similar to that for brewer's grains (12). This means that when forages are exposed to moderate temperatures (ca. 60°C) for long periods (weeks) amino acids are destroyed, whereas when BDG was exposed to relatively high temperatures (200°C) for short periods (minutes) amino acids were not destroyed, but simply rendered insoluble in acid detergent. The exception to this was lysine, Journal of Dairy Science Vol. 72, No. 4, 1989
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WEISS ET AL.
TABLE 4. Amino acid composition of wet and dried barley grains. Amino acid
Dry
Aspartic acid Glutamic acid Serine Glycine Alanine Tryosine Threonine Arginine Histidine Methionine Valine Phenylalanine Isoleucine Leucine Lysine Total
1.41 5.16 1.18 .95 1.30 .84 .99 1.81 .33 .29 1.10 1.15 .82 2.10 .39 19.82
Wet (% of DM) 1,07 3.95 1.02 .81 1.12 .79 .80 1.82 .22 .25 .93 1.01 .72 1.88 .61 17.00
which decreased from ,6% of DM in wet BDG to about .4% in dry BDG. Relative concentration of most of the other amino acids were similar for wet and dried BDG (Table 4). This loss was similar to that found in forages (27, 28). Lysine is especially sensitive to Maillard reactions because of its epsilon amino group. Previous research has suggested that ADIN is not a valid estimator of N availability in protein supplements (4, 5). The difference in N distribution between heated forages and BDG could explain why ADIN does not reflect N availability accurately. Lactation Trial
Most production measures were similar (P> .10) among treatments (Table 5). No treatment by time interactions were found (P>.20); therefore, adaptation to the diets was similar. Barley distillers grains appeared to be less palatable than SBM, resulting in a tendency for cows fed BDG not to consume their daily allotment of the supplement. Total concentrate intake was slightly lower for cows fed BDG than for cows fed the other two diets, causing BDG fed cows to consume more forage (P<.06), The concentration of N D F in the diet increased with increased BDG in the diet; however, no effect on total DM intake was found. The only other effect (P<.09) of protein source was milk protein percent. There was a positive linear relaJournal of Dairy Science Vol. 72, No. 4, 1989
Dry 6.93 22.94 7.35 8.28 9.55 3.03 5.44 6.80 1.39 1.27 6.15 4.56 4.09 10.48 1.75 100.00
Wet (mol/100 mol) 6.15 20.55 7.43 8.26 9.62 3.34 5.14 8.00 1.09 1.28 6.08 4.68 4.20 10.98 3.20 100.00
tionship between amount of SBM fed and milk protein percent (milk protein % = 3.26 + .03 (%SBM); r 2 = .81). Palmquist and Conrad (16) found the same response when cows were fed CDG or SBM. Those authors suggested that depression in milk protein percent of cows fed CDG was due to an amino acid imbalance, particularly low serum lysine. The diets of cows receiving BDG would have had the lowest concentrations of lysine in the diet, but we have no information on blood amino acids or the amount of digestible lysine reaching the small intestine. Our data, however, do lend support to their (16) hypothesis. The overall lack o f response to BDG, except for milk protein, indicates that when fed in isonitrogenous diets adequate in CP, BDG is essentially equivalent to SBM for mid to late lactation cows. The average intake of CP by cows in this experiment was 2.8 kg/d, and the cows' average calculated CP requirements (13) were about 2.5 kg/d. This means that the effect of protein source on cow performance could have been masked by excessive intake of total CP. Digestion data, however, support the concept of equal utilization of the CP sources. Digestion Trial
Dry matter digestibilities of all diets did not differ (P>.50) among treatments (Table 6). Dry matter digestion coefficients for all treatments
BARLEY DISTILLERS GRAINS FOR DAIRY COWS
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TABLE 5. Performance of cows fed soybean meal (SBM), barley distillers grains (BDG), or a 1:1 mix (SBM + BDG) as sources of supplemental crude protein. Item
SBM
BDG
SBM + BDG
SE
P
n1 Milk, kg/d FCM, kg/d Milk fat, % Milk protein, %~ Milk SNF, % Concentrate intake, kg/d Concentrate/FCM Forage intake, kg/d DM Intake, % BW2 DMI/FCM
20 21.8 20.0 3.7 3.5 9.0 6.4 .31 12.3b 3.19 .92
19 22.2 19.7 3.6 3.3 8.9 6.0 .30 13.1Y 3.17 .94
20 23.7 21.5 3.6 3.4 9.0 6.8 .31 12.6b 3.26 .90
1.0 .8 .09 .06 .09 .4 .01 .1 .05 .02
.35 .25 .52 .09 .62 .40 .65 .06 .38 .48
'~bMeans within a row differ by mated P value. ~Linear effect (P<.05) of percent SBM in diet. ~n = Two pens/treatment for forage and total DM intake. 2 % DM = Percent of body weight.
were 10 to 15% lower than expected for diets with 45% concentrate (6), but low DM digestion coefficients could be due, in part, to the low quality corn silage and hay used in this experiment. Digestibility of ADF and lignin tended to increase with increasing amounts of BDG in the diet, but there were no statistical differences among diets. Digestibility of N D F increased as concentration of BDG in the diet increased (P<.ll). Diets containing CDG also had higher NDF digestibility as compared to urea based diets (7). No statistically significant (/'>.15) linear relationships between digestibility of fiber components and BDG intake were found. Digestibility of N D F from BDG was calculated by difference assuming the presence or absence of SBM had no effect on overall N D F digestion. Digestibility of N D F from BDG ranged from 70 to 80%, which is in agreement with in situ data on CDG (25). The digestibility of BDG N D F was about 50% greater than NDF digestibility of the basal diet. The relatively rapid rate of degradation for N D F from distillers grains (25), plus its relatively high digestibility could explain why DM intake was not different among diets even though N D F content ranged from 35 to 42%. For this reason, better characterization of the N D F fraction of different feeds is needed before total concentration o f dietary N D F can be used as the sole dietary constituent to predict DM intake.
Intake of N was constant between treatments (465 + 32 g/d) and was above the animals' calculated protein requirements. This should have no effect on the interpretation of the digestion data. True digestibility of N is essentially independent of N intake when DM intake is constant (19). Differences in true digestibility of N among diets are reflected by differences in the apparent digestibility of N when N intakes are similar (17). Nitrogen digestibility showed no trend with increasing dietary BDG; however, N digestibility was lower (P<.I 1) for cows fed the diet containing both SBM and BDG as compared to cows fed diets containing either SBM or BDG. This was unexpected because of the high ADIN concentration in the diet with BDG (Table 2). Digestion of ADIN increased (P<.01) as the amount of BDG in the diet increased. This suggests that the composition o f ADIN in BDG is different from the basal diet and that this difference in composition affects digestibility. The poor relationship between A D I N content and N digestibility has been reported previously (4). Additionally, Britton et al. (4) found that digestibility of ADIN in diets with CDG was higher than was A D I N digestibility in the urea-based basal diet. In heatdamaged forages, increased concentrations of ADIN and decreased concentrations of amino acid N were responsible for the depressed N digestion (28). The BDG had high concentrations of ADIN, but amino acid N was not Journal of Dairy Science Vol. 72, No. 4, 1989
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WEISS ET AL.
TABLE 6. Nutrient digestibility by cows fed soybean meal (SBM), barley distillers grains (BDG), or a 1:1 mix (SBM + BDG) as sources of supplemental crude protein. Item
SBM
n
4
DM Intake, kg/d DM Digestibility, % NDF Digestibility, % ADF Digestibility, % Lignin 2 digestibility, % N Digestibility, % ADIN Digestibility, % ADSN 1 Digestibility, % N Balance, g/d
19.4 62.5 43.7 40.6 7.9 58.6 -ll.P 62.0 ~ 61
BDG
SBM + BDG
3
SE
P<
1.0 1.3 1.8 2.4 3.7 1.0 6.1 1.2 24.6
.90 .57 .11 .39 .48 .12 .01 .05 .93
4
19.5 60.9 50.7 45.1 9.4 57.6 46.9 ~ 58.5 be 74
19.8 60.7 46.9 44.4 8.7 55.4 25.7 b 56.6 c 62
'.b.¢Means within a row with unlike superscripts differ by stated P value. IADSN = Acid detergent soluble N. 2Determined by acid detergent-sulfuric acid method (18).
reduced (Table 3). This could explain why ADIN was not correlated to N digestibility. Digestibility of acid detergent soluble N (ADSN) was lower (P<.01) for the SBM + BDG diet than the diets containing a single protein supplement. Digestibility of ADSN was always higher than was digestibility of ADIN, but differences decreased as percent BDG in the diet increased. The differences among treatments for ADIN digestibility were much greater than for the digestibility of ADSN, suggesting that the composition of ADIN varies more among feeds than does the composition of ADSN. More extensive studies on the composition of the N fraction of feeds are needed to obtain a better predictor of N availability than ADIN for concentrate feeds. CONCLUSIONS
Dried distillers grains derived from a mix of 65% barley and 35% corn is an acceptable protein supplement for dairy cows. The high NDF content of this feed does not restrict intake as compared to soybean meal-based diets. This feedstuff had relatively high concentrations of ADIN, but this did not affect N digestion or N balance appreciably. These data support other research that has shown that ADIN is not a valid indicator of N availability in concentrates. ACKNOWLEDGMENTS
This research was supported in part by grants from the North Dakota Dairy Promotion Journal of Dairy Science Vol. 72, No. 4, 1989
Commission and the North Dakota Livestock Endowment Foundation. The assistance of Brent Peterson and Mike Aho in conducting this experiment is gratefully acknowledged.
REFERENCES 1 Anderson, V. L., and R. A. McLean. 1974. Design of experiments. Marcel Dekkar, Inc., New York, NY. 2 Association of Official Analytical Chemists. 1980. Official methods of analysis. 13th ed. Assoc. Offic. Anal. Chem. Washington, DC. 3 Aines, G., T. J. Klopfenstein, and R. A. Stock. 1987. distillers grains. Publ. MPS1, Univ. Nebraska Agric. Res. Div., Lincoln. 4 Britton, R. A., T. J. Klopfenstein, R. Cleale, F. Goedeken, and ~/. Wilkerson. 1986. Methods of estimating heat damage in protein sources. Proc. Dist. Feed Conf. 41:67. 5 Cleale IV, R. M., T. J. Klopfenstein, R. A. Britton, L. D. Sattedee, and S. R. Lowry. 1987. Induced non-enzymatic browning of soybean meal. 1II. Digestibility and efficiency of protein utilization by ruminants of soybean meal treated with xylose or glucose. J. Anita. Sci. 65:1327. 6 Colucci, P. E., L. E. Chase, and P. J. Van Soest. 1982. Feed intake, apparent diet digestibility and rate of particulate passage in dairy cattle. J. Dairy Sci. 65:1445. 7 Firkins, J. L., L. L. Berger, G. C. Fahey, Jr., and N. R. Merchen. 1984. Ruminal nitrogen degradability and escape of wet and dry distillers grains and wet and dry corn gluten feed. J. Dairy Sci. 67:1936. 8 Harvey, W. R. 1977. User's guide for LSML76: mixed model least squares and maximum likelihood computer program. Ohio State Univ., Columbus. 9 Klopfenstein, T. J. 1985. Distillers by-products backed by forty years of research. Proc. Dist. Feed Conf. 40: 9. 10 Loosli, J. K., R. G. Warner, and H. F. Hintz. 1961. Value
BARLEY DISTILLERS GRAINS FOR DAIRY COWS
of corn distillers grains, soybean oil meal, heated soybeans, and soybean oil meal plus starch for milk production. J. Dairy Sci. 44:1910. 11 Mertens, D. R. 1985. Factors influencing feed intake in lactating cows: from theory to application using neutral detergent fiber. Page 1 in Proc. Georgia Nutr. Conf. 12 Muscato, T. V., C. J. Sniffen, U. Krishnamoorthy, and P. J. Van Soest. 1983. Amino acid content of noncell and cell wall fractions in feedstuffs. J. Dairy Sci. 66:2198. 13 National Research Council. 1978. Nutrient requirements of dairy cattle. 5th ed. Natl. Acad. Press, Washington, DC. 14 National Research Council. 1982. U.S.-Canadian Tables of Feed Composition. 3rd rev. Natl. Acad. Press, Washington, 1212. 15 Newman, C. W., J. W. Pepper, and P. W. cGras. 1982. Utilization of barley distillers grains in swine rations. Page 24 in Montana St. Univ., Anita. Range Res. Highlights No. 201. 16 Palmquist, D. L., and H. R. Conrad. 1982. Utilization of distillers dried grains plus solubles by dairy cows in early lactation. J. Dairy Sci. 65:1729. 17 Preston, R. U 1972. Protein requirements for growing and lactating ruminants. Page 22 in Proc. Nottingham Nutr. Conf. for feed manufacturers. H. Swan and D. Lewis, ed. Butterworths, London. 18 Robertson, J. B., and P. J. Van Soest. 1981. The detergent system of analyses and its application to human foods. Page 123 in The analysis of dietary fiber in food. W. P. James and O. Theander, ed. Marcel Dekkar, Inc., NY. 19 Stallcup, O. T., G. V. Davis, and L. Shields. 1975.
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Influence of dry matter and nitrogen intake on fecal nitrogen losses in cattle. J. Dairy Sci. 58:1301. 20 Thomas, J. W., Y . Yu, T. Middleton, and C., Stallings. 1982. Page 81 in Protein requirements for cattle: Symposium. F. N. Owens, ed. Oklahoma State Univ. MP-109, Stillwater. 21 Thomas, O. O. 1982. Distillers dried grains for cattle fattening rations. Page 106 in Montana State Univ. Anita. Range Res. Highlights No. 201, Bozeman. 22 Van Horn, H. H., O. Blanco, B. Harris, Jr., and D. K. Beede. 1985. Interaction of protein percent with caloric density and protein source for lactating cows. J. Dairy Sci. 68:1682. 23 Van Soest, P. J. 1965. Use of detergents in analysis of fibrous feeds. III. Study of effects of heating and drying on yields of fiber and Iignin in forages. J. Assoc. Offic. Anal. Chem. 48:785. 24 Van Soest, P. J., and C. J. Sniffen. 1984. Nitrogen fractions in NDF and ADF. Proc. Dist. Feed Conf. 39:73. 25 Varga, G. A., and W. H. Hoover. 1983. Rate and extent of neutral detergent fiber degradation of feedstuffs in situ. J. Dairy Sci. 66:2109. 26 Weiss, W. P., W. L. Shockey, and H. R. Conrad. 1985. Determination of amino acids in forages by FIPLC. J. Dairy Sci. 68(Suppl. 1):127. (Ahstr.) 27 Weiss, W. P., H. R. Conrad, and W. L. Shockey. 1986. Amino acid profiles of heat-damaged grasses. J. Dai~ Sci. 69:1824. 28 Weiss, W. P., H. R. Conrad, and W. L. Shockey. 1986. Digestibility of nitrogen in heat-damaged alfalfa J. Dairy Sci. 69:2658.
Journal of Dairy Science Vol. 72, No. 4, 1989
Department of Animal and Range Sciences North Dakota State University Fargo 58105 INTRODUCTION
ABSTRACT
Dried distillers grains produced from a mix of 65% barley and 35% corn were evaluated in digestion and lactation experiments. Dried barley distillers grains had 56% NDF, 29% CP, 3% amino acid N, 2.5% NDIN (55% of total N), and 1.8% ADIN (39% of total N). Wet barley distillers grains had 38% NDF, 27% CP, 2.7% amino acid N, .5% NDIN (12% of total N), and .8% ADIN (19% of total N). Digestibility of DM and N was similar among lactating dairy cows fed diets conraining approximately 25% corn silage DM, 15% alfalfa silage DM, 15% alfalfa hay DM, plus varying amounts of a cornbarley concentrate mix and supplemental CP from soybean meal, barley distillers grains, or from 1:1 mixture of soybean meal and barley distillers grains. Digestibility of ADIN, NDF, and ADF increased with increasing amounts of barley distillers grains in the diet. Similar diets were fed to 60 Holstein cows for 84 d in a lactation experiment. Source of supplemental protein did not affect milk production (22.5 kg/d), FCM (20.4 kg/d), milk fat percent (3.6%), or DM intake (19.0 kg/d). Milk protein percent was decreased by feeding barley distillers grains. It was concluded that barley distillers grains were an acceptable protein source for dairy cows and that ADIN and NDF might not be appropriate measures of the nutritional value of this product.
Extensive research has been conducted to determine the feeding value of distillers grains derived from corn (3, 9). Diets containing corn distillers dried grains (CDG) produced variable responses by dairy cows. In two experiments it was found that CDG was equal or superior to soybean meal (SBM) as a CP source for dairy cows (10, 16), but in a more recent paper, it was reported that cows fed diets with CDG produced less milk than did cows fed SBM (22). The CDG in the Florida study (22) had extremely high ADIN concentrations, and the authors suggested this was the reason for the poor cow performance. Barley is an important crop in the northern plains, and recently, distilleries have started using barley as the feedstock for alcohol production. Very few published data exist on the composition and feeding value of barley distillers grains (BDG). A Montana researcher (21) reported that performance was similar when beef heifers were fed isonitrogenous diets containing either SBM or 5% BDG, but no reports on the use of BDG in dairy cattle diets were found. The CP content of BDG is similar to that of CDG, but NDF and ADF contents of BDG are markedly higher than in CDG (14, 15). The use of NDF to predict intake and aid in diet formulation has been proposed (11). If the negative relationship between dietary concentration of NDF and feed intake is valid for different sources of NDF, then the high concentration of NDF in BDG could limit feed intake and subsequent cow productivity. An additional concern regarding BDG is its relatively high concentration of ADIN. Acid detergent insoluble N is valuable for estimating Received June 20, 1988. Accepted September 23, 1988. the apparent digestibility of N in forages (20), ~Journal Article 1690 of the North Dakota Agricultural but questions have arisen recently regarding the Experiment Station. ZPresent address: Department of Dairy Science, Ohio use of ADIN to estimate N availability of Agricultural Research and DevelopmentCenter, The Ohio grains and protein sources (4, 5). Information is State University, Wooster 44691. lacking on the use of both NDF and ADIN to 1989 J Dairy Sci 72:980-987
980
981
BARLEY DISTILLERS GRAINS FOR DAIRY COWS
TABLE 1. Ingredient and nutrient composition of diets consumed in the lactation trial. ~ Item2
SBM
BDG
SBM + BDG
Ingredients Corn silage Alfalfa silage Alfalfa hay Rolled barley Cracked corn Soybean meal Barley distillers grains Minerals/vitamins
31.1 18.8 14.9 14.2 14.2 6.0 0 .8
32.0 19.3 15.2 10.0 10.0 0 12.9 .6
30.6 18.5 14.7 13.3 13.3 4.5 4.5 .6
Nutrients CP ADIN~ NDF
15.1 .17 (7.0) 37.0
15.3 .39 (15.9) 42.3
15.5 .24 (9.7) 38.4
1Soybean meal (SBM), barley distillers's grains (BDG), or a 1:1 mix (SBM + BDG) provided the supplemental crude protein. 2All values are percentages of dry matter. 3Numbers in parentheses are expressed as percent of total N.
evaluate BDG. It is essential that chemical procedures used to evaluate different feeds be validated; otherwise, nutritive value of feeds can be grossly overestimated or underestimated, greatly influencing profitability of dairy producers. The objectives of these experiments were: 1) to examine the effect of drying wet BDG on its chemical composition; 2) to determine the feeding value of BDG for dairy cows; and 3) to determine if NDF and ADIN are valid for evaluation of this feed. MATERIALS AND METHODS
The barley distillers grains were produced from a mix of about 65% barley and 35% corn and included the soluble fraction. 3 Ethanol can be produced with 100% barley, but the high fiber content of barley causes flow problems at the distillery. Samples of wet distillers grains were obtained from the same source but later. Lactation Trial
Sixty Holstein cows (26 primaparous and 34 multiparous) in midlactation (average of 100 d
3Wet and dry barley distillers grains were donated by Dawn Enterprises, Walhalla, ND.
in milk) were fed one of three different protein supplements: soybean meal (SBM), BDG, or 50% SBM plus 50% BDG (SBM + BDG). Cows were housed in a freestall barn with 10 cows per pen and two pens per treatment. Forages (2.9:1.8:1 corn silage:alfalfa silage:alfalfa hay, DM basis) were blended and group fed to each pen of cows. Grain and protein supplements were individually fed via a dual dispensing computer controlled feeder (Boumatic 2030 feeding system, Madison, WI). Total concentrate (grain plus protein supplement) was fed at the rate of 1 kg concentrate (as fed basis) per 3 kg FCM. The amount of concentrate fed was updated biweekly based on the cows production the previous 2 wk. Diets were isonitrogenous but differed in concentration of NDF and ADIN (Table 1). The experiment lasted 84 d with feed intake and milk production measured daily. Feed and milk samples were taken biweekly for analysis. Cows were weighed monthly. Digestion Trial
Twelve cows were fed diets similar to the diets used in the lactation trial (Table 2). Due to an error in the chemical analysis of the forage, the diets in the digestion trial contained approximately 55% forage whereas the diets used in the lactation trial contained about 65% forage (DM basis). Cows were adapted to the Journal of Dairy Science Vol. 72, No. 4, 1989
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WEISS ET AL.
TABLE 2. Ingredient and nutrient composition of diets consumed in the digestion trial.1 Item2
Ingredients Corn silage Alfalfa silage Alfalfa hay Rolled barley Cracked corn Soybean meal Barley distillers grain Minerals/vitamins Nutrients CP ADIN3 NDF
SBM
BDG
SBM + BDG
26.1 15.5 14.0 18.0 18.0 7.8 0 .6
26.1 15.5 14.0 12.7 12.8 0 18.3 .6
26.1 15.5 1,t.0 16.7 16.7 5.3 5.1 .6
14.9 .10 (4.2) 35,3
14.9 .29 (12.2) 43.0
14.8 ,16 (6.8) 37,7
ISoybean meal (SBM), barley distillers's grains (BDG), or a 1:1 mix (SBM + BDG) provided the supplemental crude protein. 2All values are percentages of dry matter. 3Numbers in parentheses are expressed as percent of total N.
diets for at least 14 d prior to the start of a 5-d total collection digestion trial. Feed, orts, feces, urine, and milk were sampled daily and cornposited. All samples were frozen until analyzed.
Chemical Analyses Chemical analyses of feeds, feces, and orts were conducted either on the air dry sample or on a lyophilized sample. Total N (2), ADIN, N D F , ADF, and acid detergent lignin (18) were determined. Samples were dried in a 100°C oven for D M determination. Amylase was added to the detergent solution for grains and protein supplements, but no sulfite was used in any N D F extraction (18). Wet and dried B D G were analyzed for amino acids (26), following hydrolysis in 6 N He1. Milk fat, protein, and S N F were determined using infrared spectrophotometry.
Statistical Analysis Dam for the lactation trial were grouped into 2-wk periods so that adaptation to the diet could be examined. The experiment was analyzed statistically as a 3 x 6 nested factorial experiment (three diets and six time periods) with 19 or 20 cows nested within each diet (1). The model was: Journal of Dairy Science Vol. 72, No. 4, 1989
Yijk = ~t + D i + C(i)j + Pk + DPnc + CP(i)jk when: Yijk = dependent variable; g= overall mean (1 df); D i = effect of i th diet (2 df); C(i)j = effect of jth cow fed i ~ diet, error term for diet (56 dO; Pk = effect of k t~ period (5 dr); DPit = effect o f interaction between ith diet and k th period (10 dr); and CP(i)j k = effect of jth cow fed i th diet during k th period, error term for period and period x diets (280 dr). For total D M intake, forage intake, and total feed efficiency, pen was the experimental unit. The only main effect used in statistical analysis o f the digestion data was protein supplement with cow serving as the error term. One cow died during the lactation trial, and data from one cow on the digestion trial were not usable because of large amounts of urine in the feces. Least squares analysis o f variance was used because o f unequal cell size (8). When a statistically significant treatment effect was found, Duncan's multiple range test was used to separate means. Regression analyses with amount of S B M in the diet as the independent variable
BARLEY DISTILLERS GRAINS FOR DAIRY COWS
983
TABLE 3. Chemical composition of soybean meal (SBM), corn distillers grains (CDG), and wet (WBDG) and dry (DBDG) barley distillers grams. Item1
SBM
WBDG
DBDG
CDG2
DM, % CP NDIN~ ADIN3 AAN3'4 NDF ADF Lignin5 Ca P
89.4 46.1 .5 (6.9) .5 (6.9) 6.2 (83.8) 14.7 9.2 .7 .3 .7
35.5 26.9 .5 (11.6) .8 (18.6) 2.7 (62.7) 38.0 22.9 5.5 ND6 ND6
87.5 28.7 2.5 (55.2) 1.8 (39.2) 3.0 (66.7) 56.3 29.2 9.3 .2 .8
94 28 1.6 (39.0) .6 (13.4) 2.3 (51.3) 44 18 1 .1 .7
XAll values expressed as percentage of dry matter. 2Source: (14, 24).
3Values in parentheses are expressed as percent of total N. 4AAN = Amino acid N. SAcid detergent-sulfuric acid method (18). 6ND = Not determined.
was used when a significant treatment effect was found. RESULTS AND DISCUSSION Composition of Barley Distillers Grains
Large differences in chemical composition among dried BDG, wet BDG, CDG, and SBM were found (Table 3). Comparing CDG with BDG, the largest difference occurs in fiber components and ADIN. Differences in fiber components reflect the higher fiber content of barley grain as compared to that of corn (20 vs. 10% NDF), but alterations in composition caused by processing could also be involved. Concentrations of NDF and NDIN were substantially higher in dry BDG than in wet BDG. Heating (drying) presumably reduced solubility of N in neutral detergent, thereby increasing concentration of NDIN. If this N was primarily in the form of protein N, this would account for almost all of the difference in NDF content between wet BDG and dry BDG. Dry BDG had two percentage units more NDIN than did wet BDG. This is equivalent to 12.5 percentage units of CP (2 x 6.25). Dry BDG had 18.3 percentage units more N D F than did wet BDG; therefore, changes in protein solubility could account for 70% of the change in NDF concen-
tration. Similar results were found for A D F and ADIN. This suggests that the composition of both the N D F and A D F fractions in wet BDG is different than of dry BDG. Dry BDG had high values for ADIN as compared to wet BDG and typical CDG. Concentrations of A D I N increase when feeds are heated (23), and in forages, amount of ADIN is correlated to the amount of heat (degree days) the forage received (20). Closer examination of the N fraction reveals that heating affects concentrates differently than forages. In ryegrass and alfalfa, heat increased ADIN but decreased the recovery of amino acid N (27, 28). Barley distillers grains (Table 3) exposed to heat (dry vs. wet) had higher ADIN concentrations but similar amino acid N values and amino acid composition (Table 4). Furthermore, in heated forages, amino acids made up about 20 to 40% of ADIN (27, 28), but in BDG, amino acid N comprised about 70% of ADIN. This value is similar to that for brewer's grains (12). This means that when forages are exposed to moderate temperatures (ca. 60°C) for long periods (weeks) amino acids are destroyed, whereas when BDG was exposed to relatively high temperatures (200°C) for short periods (minutes) amino acids were not destroyed, but simply rendered insoluble in acid detergent. The exception to this was lysine, Journal of Dairy Science Vol. 72, No. 4, 1989
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WEISS ET AL.
TABLE 4. Amino acid composition of wet and dried barley grains. Amino acid
Dry
Aspartic acid Glutamic acid Serine Glycine Alanine Tryosine Threonine Arginine Histidine Methionine Valine Phenylalanine Isoleucine Leucine Lysine Total
1.41 5.16 1.18 .95 1.30 .84 .99 1.81 .33 .29 1.10 1.15 .82 2.10 .39 19.82
Wet (% of DM) 1,07 3.95 1.02 .81 1.12 .79 .80 1.82 .22 .25 .93 1.01 .72 1.88 .61 17.00
which decreased from ,6% of DM in wet BDG to about .4% in dry BDG. Relative concentration of most of the other amino acids were similar for wet and dried BDG (Table 4). This loss was similar to that found in forages (27, 28). Lysine is especially sensitive to Maillard reactions because of its epsilon amino group. Previous research has suggested that ADIN is not a valid estimator of N availability in protein supplements (4, 5). The difference in N distribution between heated forages and BDG could explain why ADIN does not reflect N availability accurately. Lactation Trial
Most production measures were similar (P> .10) among treatments (Table 5). No treatment by time interactions were found (P>.20); therefore, adaptation to the diets was similar. Barley distillers grains appeared to be less palatable than SBM, resulting in a tendency for cows fed BDG not to consume their daily allotment of the supplement. Total concentrate intake was slightly lower for cows fed BDG than for cows fed the other two diets, causing BDG fed cows to consume more forage (P<.06), The concentration of N D F in the diet increased with increased BDG in the diet; however, no effect on total DM intake was found. The only other effect (P<.09) of protein source was milk protein percent. There was a positive linear relaJournal of Dairy Science Vol. 72, No. 4, 1989
Dry 6.93 22.94 7.35 8.28 9.55 3.03 5.44 6.80 1.39 1.27 6.15 4.56 4.09 10.48 1.75 100.00
Wet (mol/100 mol) 6.15 20.55 7.43 8.26 9.62 3.34 5.14 8.00 1.09 1.28 6.08 4.68 4.20 10.98 3.20 100.00
tionship between amount of SBM fed and milk protein percent (milk protein % = 3.26 + .03 (%SBM); r 2 = .81). Palmquist and Conrad (16) found the same response when cows were fed CDG or SBM. Those authors suggested that depression in milk protein percent of cows fed CDG was due to an amino acid imbalance, particularly low serum lysine. The diets of cows receiving BDG would have had the lowest concentrations of lysine in the diet, but we have no information on blood amino acids or the amount of digestible lysine reaching the small intestine. Our data, however, do lend support to their (16) hypothesis. The overall lack o f response to BDG, except for milk protein, indicates that when fed in isonitrogenous diets adequate in CP, BDG is essentially equivalent to SBM for mid to late lactation cows. The average intake of CP by cows in this experiment was 2.8 kg/d, and the cows' average calculated CP requirements (13) were about 2.5 kg/d. This means that the effect of protein source on cow performance could have been masked by excessive intake of total CP. Digestion data, however, support the concept of equal utilization of the CP sources. Digestion Trial
Dry matter digestibilities of all diets did not differ (P>.50) among treatments (Table 6). Dry matter digestion coefficients for all treatments
BARLEY DISTILLERS GRAINS FOR DAIRY COWS
985
TABLE 5. Performance of cows fed soybean meal (SBM), barley distillers grains (BDG), or a 1:1 mix (SBM + BDG) as sources of supplemental crude protein. Item
SBM
BDG
SBM + BDG
SE
P
n1 Milk, kg/d FCM, kg/d Milk fat, % Milk protein, %~ Milk SNF, % Concentrate intake, kg/d Concentrate/FCM Forage intake, kg/d DM Intake, % BW2 DMI/FCM
20 21.8 20.0 3.7 3.5 9.0 6.4 .31 12.3b 3.19 .92
19 22.2 19.7 3.6 3.3 8.9 6.0 .30 13.1Y 3.17 .94
20 23.7 21.5 3.6 3.4 9.0 6.8 .31 12.6b 3.26 .90
1.0 .8 .09 .06 .09 .4 .01 .1 .05 .02
.35 .25 .52 .09 .62 .40 .65 .06 .38 .48
'~bMeans within a row differ by mated P value. ~Linear effect (P<.05) of percent SBM in diet. ~n = Two pens/treatment for forage and total DM intake. 2 % DM = Percent of body weight.
were 10 to 15% lower than expected for diets with 45% concentrate (6), but low DM digestion coefficients could be due, in part, to the low quality corn silage and hay used in this experiment. Digestibility of ADF and lignin tended to increase with increasing amounts of BDG in the diet, but there were no statistical differences among diets. Digestibility of N D F increased as concentration of BDG in the diet increased (P<.ll). Diets containing CDG also had higher NDF digestibility as compared to urea based diets (7). No statistically significant (/'>.15) linear relationships between digestibility of fiber components and BDG intake were found. Digestibility of N D F from BDG was calculated by difference assuming the presence or absence of SBM had no effect on overall N D F digestion. Digestibility of N D F from BDG ranged from 70 to 80%, which is in agreement with in situ data on CDG (25). The digestibility of BDG N D F was about 50% greater than NDF digestibility of the basal diet. The relatively rapid rate of degradation for N D F from distillers grains (25), plus its relatively high digestibility could explain why DM intake was not different among diets even though N D F content ranged from 35 to 42%. For this reason, better characterization of the N D F fraction of different feeds is needed before total concentration o f dietary N D F can be used as the sole dietary constituent to predict DM intake.
Intake of N was constant between treatments (465 + 32 g/d) and was above the animals' calculated protein requirements. This should have no effect on the interpretation of the digestion data. True digestibility of N is essentially independent of N intake when DM intake is constant (19). Differences in true digestibility of N among diets are reflected by differences in the apparent digestibility of N when N intakes are similar (17). Nitrogen digestibility showed no trend with increasing dietary BDG; however, N digestibility was lower (P<.I 1) for cows fed the diet containing both SBM and BDG as compared to cows fed diets containing either SBM or BDG. This was unexpected because of the high ADIN concentration in the diet with BDG (Table 2). Digestion of ADIN increased (P<.01) as the amount of BDG in the diet increased. This suggests that the composition o f ADIN in BDG is different from the basal diet and that this difference in composition affects digestibility. The poor relationship between A D I N content and N digestibility has been reported previously (4). Additionally, Britton et al. (4) found that digestibility of ADIN in diets with CDG was higher than was A D I N digestibility in the urea-based basal diet. In heatdamaged forages, increased concentrations of ADIN and decreased concentrations of amino acid N were responsible for the depressed N digestion (28). The BDG had high concentrations of ADIN, but amino acid N was not Journal of Dairy Science Vol. 72, No. 4, 1989
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WEISS ET AL.
TABLE 6. Nutrient digestibility by cows fed soybean meal (SBM), barley distillers grains (BDG), or a 1:1 mix (SBM + BDG) as sources of supplemental crude protein. Item
SBM
n
4
DM Intake, kg/d DM Digestibility, % NDF Digestibility, % ADF Digestibility, % Lignin 2 digestibility, % N Digestibility, % ADIN Digestibility, % ADSN 1 Digestibility, % N Balance, g/d
19.4 62.5 43.7 40.6 7.9 58.6 -ll.P 62.0 ~ 61
BDG
SBM + BDG
3
SE
P<
1.0 1.3 1.8 2.4 3.7 1.0 6.1 1.2 24.6
.90 .57 .11 .39 .48 .12 .01 .05 .93
4
19.5 60.9 50.7 45.1 9.4 57.6 46.9 ~ 58.5 be 74
19.8 60.7 46.9 44.4 8.7 55.4 25.7 b 56.6 c 62
'.b.¢Means within a row with unlike superscripts differ by stated P value. IADSN = Acid detergent soluble N. 2Determined by acid detergent-sulfuric acid method (18).
reduced (Table 3). This could explain why ADIN was not correlated to N digestibility. Digestibility of acid detergent soluble N (ADSN) was lower (P<.01) for the SBM + BDG diet than the diets containing a single protein supplement. Digestibility of ADSN was always higher than was digestibility of ADIN, but differences decreased as percent BDG in the diet increased. The differences among treatments for ADIN digestibility were much greater than for the digestibility of ADSN, suggesting that the composition of ADIN varies more among feeds than does the composition of ADSN. More extensive studies on the composition of the N fraction of feeds are needed to obtain a better predictor of N availability than ADIN for concentrate feeds. CONCLUSIONS
Dried distillers grains derived from a mix of 65% barley and 35% corn is an acceptable protein supplement for dairy cows. The high NDF content of this feed does not restrict intake as compared to soybean meal-based diets. This feedstuff had relatively high concentrations of ADIN, but this did not affect N digestion or N balance appreciably. These data support other research that has shown that ADIN is not a valid indicator of N availability in concentrates. ACKNOWLEDGMENTS
This research was supported in part by grants from the North Dakota Dairy Promotion Journal of Dairy Science Vol. 72, No. 4, 1989
Commission and the North Dakota Livestock Endowment Foundation. The assistance of Brent Peterson and Mike Aho in conducting this experiment is gratefully acknowledged.
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BARLEY DISTILLERS GRAINS FOR DAIRY COWS
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Influence of dry matter and nitrogen intake on fecal nitrogen losses in cattle. J. Dairy Sci. 58:1301. 20 Thomas, J. W., Y . Yu, T. Middleton, and C., Stallings. 1982. Page 81 in Protein requirements for cattle: Symposium. F. N. Owens, ed. Oklahoma State Univ. MP-109, Stillwater. 21 Thomas, O. O. 1982. Distillers dried grains for cattle fattening rations. Page 106 in Montana State Univ. Anita. Range Res. Highlights No. 201, Bozeman. 22 Van Horn, H. H., O. Blanco, B. Harris, Jr., and D. K. Beede. 1985. Interaction of protein percent with caloric density and protein source for lactating cows. J. Dairy Sci. 68:1682. 23 Van Soest, P. J. 1965. Use of detergents in analysis of fibrous feeds. III. Study of effects of heating and drying on yields of fiber and Iignin in forages. J. Assoc. Offic. Anal. Chem. 48:785. 24 Van Soest, P. J., and C. J. Sniffen. 1984. Nitrogen fractions in NDF and ADF. Proc. Dist. Feed Conf. 39:73. 25 Varga, G. A., and W. H. Hoover. 1983. Rate and extent of neutral detergent fiber degradation of feedstuffs in situ. J. Dairy Sci. 66:2109. 26 Weiss, W. P., W. L. Shockey, and H. R. Conrad. 1985. Determination of amino acids in forages by FIPLC. J. Dairy Sci. 68(Suppl. 1):127. (Ahstr.) 27 Weiss, W. P., H. R. Conrad, and W. L. Shockey. 1986. Amino acid profiles of heat-damaged grasses. J. Dai~ Sci. 69:1824. 28 Weiss, W. P., H. R. Conrad, and W. L. Shockey. 1986. Digestibility of nitrogen in heat-damaged alfalfa J. Dairy Sci. 69:2658.
Journal of Dairy Science Vol. 72, No. 4, 1989