Ruminal Degradation of Dried Brewers Grains, Wet Brewers Grains, and Soybean Meal

Ruminal Degradation of Dried Brewers Grains, Wet Brewers Grains, and Soybean Meal L. E. A R M E N T A N O , 1,2 T. A . H E R R I N G T O N , I C. E. P O L A N , 1,3 A. J. M O E , 1 J. H. H E R B E I N , 1 and P. U M S T A D T 2

Department of Dairy Science College of Agriculture and Life Sciences

Virginia Agricultural Experiment Station Virginia Polytechnic Institute and State University Blacksburg 24061 and Department of Dairy Science College of Agriculture and Life Sciences University of Wisconsin Madison 53706 ABSTRACT

similar for diets containing brewers dried grains or soybean meal.

A series of trials was conducted to determine the ruminal degradation of nitrogenous compounds and dry matter of soybean meal, wet brewers grains, and dried brewers grains. In situ and in vitro estimates of degradation were positively correlated but yielded different absolute values for measures of ruminal degradation. Ruminal digestion of protein, predicted from in situ data, was 42, 73, and 83% for brewers dried grains, brewers wet grains, and soybean meal. Drying of wet grains at either 50 or 150°C increased resistance to ruminal digestion equally. Measurements of flow of dry matter and nitrogen of feed origin to the duodenum were made in vivo for diets containing either brewers dried grains or soybean meal. Negative apparent digestibility of nitrogen in the rumen for a 13% crude protein, brewers dried grains ration indicates the potential for using a nonprotein nitrogen supplement with this ration. Resistance to digestion of nitrogen from brewers dried grains occurred only in the rumen. Amino acid patterns delivered to the small intestine and digestion of duodenal contents were

INTRODUCTION

Received January 9, 1986. a Virginia Polytechnic Institute and State University.

2 University of Wisconsin. 3To whom reprint requests should be sent. 1986 J Dairy Sci 69:2124-2133

Rumen microbes degrade a portion of feed protein resulting in precursors for synthesis of microbial proteins. When diets high in rapidly degradable proteins are fed to dairy cattle, rate of degradation may exceed rate of microbial synthesis, resulting in inefficient use of feed nitrogen and excessive ammonia absorption from the rumen (17). Feeding proteins with resistance to rumen degradability increases the flow of protein to the duodenum, provided that microbial protein synthesis is not reduced. Increased protein flow at the duodenum results in increased production of milk (5). By feeding resistant proteins at the same protein concentrations as degradable proteins, greater milk production may be achieved (6). Alternatively, resistant proteins could be complemented with nonprotein nitrogen sources and fed at recommended protein concentration (4), resulting in maintained milk production at potentially reduced feed cost. A third possibility is that protein mixtures of optimal degradability could be fed at lower protein concentrations, again maintaining milk production at potentially reduced cost (6). In situ and in vitro measurements have been made on a number of protein sources resulting in the identification of several feeds that have resistance to rumen degradation (13). Fo'r a resistant protein to be useful in any of the three strategies noted, the protein evading ruminal degradation must be digestible and have an

2124

RUMINAL DEGRADATION OF PROTEIN SUPPLEMENTS

2125

TABLE 1. Composition of diets fed in trial 1.1 Protein supplement used in diet 2 BDG

BWG

SBM

Ingredients Alfalfa silage Ensiled shelled corn Corn silage BDG BWG SBM Mineral supplement

13.9 32.6 30.6 17.4 0 0 5.5

13.7 32.9 27.4 0 20.6 0 5.4

13.8 20.2 49.2 0 0 10.5 5.5

Analysis Dry matter 3 Crude protein Acid detergent fiber ADF N4

54.9 15.9 20.1 12.4

40.7 17.0 20.6 12.6

47.2 16.1 20.9 5.2

1Data are g/lO0 g ration dry matter if not indicated otherwise. BDG = Brewers dried grains, BWG = brewers wet grains, and SBM = soybean meal. 3 Grams per 100 g feed as fed. 4 Grams nitrogen in acid detergent fiber/100 g dietary nitrogen.

appropriate a m i n o acid pattern. Additionally, the protein s u p p l e m e n t must n o t reduce microbial yields w h e n included in the diet. These characteristics can be d e t e r m i n e d only by in vivo m e t h o d s . Brewers dried grains are an e x c e l l e n t protein source for lactating cows (14) and also contain protein resistant to r u m e n degradation (2). The purpose of our research was to d e t e r m i n e if brewers dried grains provide an increased flow o f " g o o d " quality protein to the duodenum of lactating cows as c o m p a r e d with an isonitrogenous soybean meal diet and if increasing protein c o n c e n t r a t i o n in a brewers dried grains ration increases the f l o w o f required a m i n o acids to the d u o d e n u m . We also c o m p a r e d in vitro, in situ, and in vivo m e t h o d s for determining ruminal protein degradation. R u m e n degradability of brewers wet grains and the effect o f drying on degradability also were determined.

4 Tetco, Inc., Elmsford, NY.

MATERIALS AND METHODS Trial 1

Three multiparous, lactating Holstein cows e q u i p p e d with r u m e n fistulas were assigned to a 3 × 3 Latin square with cow and period as blocking factors. F e r m e n t a t i v e degradation of dry m a t t e r (DM) and crude protein present in brewers wet grains, brewers dried grains, and soybean meal were d e t e r m i n e d using in situ and in vitro techniques. Each protein s u p p l e m e n t was tested while the cows received an experim e n t a l diet (Table 1) containing protein f r o m that supplement. Diets were identical to the m e d i u m protein diets described in detail (14). Diets were fed for at least 10 d prior to determining degradability. Bags for in situ m e a s u r e m e n t s were made by folding 26-cm square pieces of precision w o v e n pecap polyester with a pore size of 59 #.4 T w o seams were sewn with polyester thread and needle holes were sealed with a commercial seam sealer. Protein s u p p l e m e n t was weighed into a tared bag to provide a p p r o x i m a t e l y .3 g nitrogen. The top of each bag was tied with nylon cord, resulting in a p p r o x i m a t e l y 450 cm 2 of effective surface area and a m a x i m u m of Journal of Dairy Science Vol. 69, No. 8, 1986

2126

ARMENTANO ET AL.

.02 g sample DM/cm 2. Bags were tied in groups of three replicates and weighted with a 300 g length of galvanized chain. For each determination 15 bags were placed into the rumen and removed in triplicate at 1, 2, 12, 24, and 72 h. Twelve additional bags, four for each protein supplement, were not introduced into the rumen and served as 0 h bags for all three cows. Following incubation, bags were soaked in cold running tap water until a clear exudate was obtained, and rinsed in distilled water. Bags were dried to constant weight in a 65°C forced air oven to determine DM recovery. Contents of each bag were ground through a l-ram screen and analyzed for nitrogen as in (14). Inoculum for in vitro incubations was taken from each cow just prior to inserting the in situ bags. Rumen fluid with particulate matter was removed with a cup and transferred into a warm, insulated vessel. All vessels receiving inoculum were preequilibrated with carbon dioxide passed over heated copper wire. Within 30 min of sampling, tureen contents were strained through six layers of cheesecloth into a flask kept at 39°C. Strained rumen fluid (50 ml) and 50 ml of McDougall's buffer (11) were added to 250-ml centrifuge bottles containing enough protein supplement to provide 75 mg of nitrogen per bottle. Four bottles per protein supplement were kept on ice. Two of these bottles contained no added protein supplement and were used to correct for endogneous DM and nitrogen present in the inoculum. The remaining bottles (10 per protein source) were incubated in duplicate for 1, 2, 12, 24, an 72 h at 39°C in a shaking water bath. All bottles were sealed with rubber stoppers equipped with capillary glass tubing capped with a Bunsen valve. Bottles were centrifuged at 200 x g at 4°C. Supernatant (5 ml) was pipetted into 1 ml of 25% metaphosphoric acid and stored a t - 2 0 ° C for ammonia analysis (14). The remaining sample received 2 ml saturated mercuric chloride and was stored at - 2 0 ° C prior to filtration. Samples were thawed and filtered through one layer of tared 59-//polyester placed in a porcelain filtrator funnel, s Filtrand was rinsed with 100 ml distilled water added in small aliquots with constant agitation of the filtrand mat.

5Fisher Scientific, Raleigh, NC. Journal of Dairy Science Vol. 69, No. 8, 1986

Residue was dried and analyzed for nitrogen as previously described for bag contents. Dry matter and nitrogen remaining after specified incubation times were analyzed similarly for the in vitro and in situ study. Residual material present after 72 h was expressed as a fraction of the original material and denoted as fraction C, the resistant fraction. This fraction was subtracted from the fractional residues at all other times and the natural log of these corrected fractions plotted against time. The antilog of the intercept is the slowly degraded fraction (fraction B) and the additive inverse of the slope is the rate of degradation (k) of fraction B. The rapidly degraded fraction (A) is the quantity 1 -- (B + C). All statistical analyses were conducted using Statistical Analyses System (15). The model used in analysis of variance by a general linear model was dependent variable = cow, period, protein supplement. Orthogonal contrasts were used to compare brewers wet and dried grains combined versus soybean meal and to compare brewers wet versus brewers dried grains. In trials 1, 2, and 3 differences were judged significant when the probability of a type 1 error was less than .05. Trial 2

This trial was to determine directly the effect of drying on in situ degradability of brewers wet grains. Brewers wet grains obtained independently of trial 1 were either frozen, dried at 150°C for 19 h, or dried 50°C for 39 h in forced air ovens. In situ rumen degradabilities were determined by the method of Weakley et al (18) using the mathematical treatment described for trial 1. Dacron (pore size of approximately 50/1) was sewn into 6 x 9-cm bags and loaded with approximately 1 g of brewers grain DM. Two ruminally fistulated, lactating Holstein cows were fed 3.5 kg of commercially dried brewers grains, 3.5 kg of a corn based grain mixture, 2.5 kg of alfalfa hay, 11 kg alfalfa haylage, and 7 kg corn silage (as fed basis). Crude protein (CP) content of the total diet DM was 15.7%. Bags were incubated in triplicate for 0, 6, 12, 18, 30, and 84 h with all three treatments being treated simultaneously in each cow. Dry matter was determined by drying at 50°C to constant weight and nitrogen by the Kjeldahl procedure (1). Data from trials 1 and 2 were combined to

RUMINAL DEGRADATION OF PROTEIN SUPPLEMENTS

test the effects of drying on measures of fermentative degradation of brewers grains. Values from both temperatures of drying in trial 2 were averaged prior to statistical analysis which was as previously described using the model: dependent variables = cow, treatment.

Trial 3

The purpose of trial 3 was to obtain data directly on the flux of DM, total nitrogen, and individual amino acids to the small intestine of lactating cows fed diets supplemented with brewers dried grains or soybean meal. Four lactating Holstein cows were equipped with tureen fistulae and duodenal cannulae. Duodenal cannulae were of the solid teflon T-shape design described by Komarek (10) with total flow of duodenal contents restricted to the lumen of the cannula by wrapping teflon felt around the serosal surface of the duodenum. Collections were made from these duodenal cannulae without a diversion gate, The upward deflection of the duodenum aboral to the cannula, the ventral orientation of the outlet tube, and the force of gastric emptying contributed to reasonably homogenous sampling. Cows were fed diets (low protein) of approximately 13% CP with supplemental protein derived from brewer dried grains or soybean meal. A high protein diet (17% CP) with brewers dried grains as the protein supplement

2127

(Table 2) also was fed. Each cow received all three diets in a switchover design. Data were not obtained for one cow on the 17% CP brewers dried grain ration because the cow went off feed during the collection period. Orchard grass labelled with Yb replaced unlabelled orchard grass for 4 d preceding and throughout the 3-d collection period. Coarsely chopped orchard grass hay was labelled with Yb by soaking each kilogram of hay in 3.3 L of .2% (wt/vol) YbC12 (pH = 4) and 6.7 L tap water for 24 h. Thereafter, hay was soaked twice for approximately 2 h each in 10 L tap water and dried in a forced air oven. This procedure resulted in hay containing approximately 3 g Yb/kg. Cows were fed one-sixth of their daily ration at 4-h intervals. Total fecal collections were made for 3 d with urine diverted by a 75 ml Foley catheter as in a study by Polan et al. (14). During the collection period, 11 duodenal samples were taken at 7-h intervals, thereby preventing bias due to possible diurnal variations or time after feeding. Duodenal samples were pooled and lyophilized prior to analysis. Separate aliquots of the first duodenal samples from 11 collections were analyzed for Yb to test for equilibration of marker. A 3-L sample of rumen contents was taken just prior to each collection and an enriched microbial fraction prepared (12). Feces and duodenal samples were analyzed

TABLE 2. Composition of diets fed in trial 3. ~ Diet 2

Component Corn silage Cracked corn Brewers dried grains Soybean meal Orchard grass hay Mineral mixture 3 Dry matter (DM), % as fed Crude protein. % of DM

SBM-LP

BDG-LP

BDG-HP

63.8 6.9 0 15.8 5.5 8.0

45.6 15.0 24.8 0 6.0 8.7

29.8 13.4 43.8 0 6.0 6.9

53.7 13.8

55.9 13.1

66.3 17.1

*Grams per 100 g ration DM. ZSBM-LP = Soybean meal supplemented diet, BDG-LP = brewers dried grains, low protein diet, and BDG-HP = brewers dried grains, high protein diet. 3 Consisted of (per kg): diealcium phosphate, 30 g; tricatcium phosphate, 30 g; limestone, 70 g; sodium bicarbonate, 120 g; Dynamate, 250 g; trace mineralized salt, 33 g; corn meal, 467 g; vitamin A, 50,000 IU; vitamin D, 5200 IU. Journal of Dairy Science Vol. 69, No. 8, 1986

2128

ARMENTANO ET AL.

f o r Yb (7), n i t r o g e n , and DM (14). C y t o s i n e c o n t e n t was d e t e r m i n e d (16) f o r d u o d e n a l and r u m e n m i c r o b i a l samples and f o r selected f e e d samples. Microbial f r a c t i o n s a n d f e e d s w e r e a n a l y z e d f o r n i t r o g e n and DM (14). D u o d e n a l samples w e r e a n a l y z e d f o r a m i n o acid c o m p o s i t i o n as d e s c r i b e d b y Weakley et al. (18). Statistical analysis was by t h e general linear m o d e l p r o c e d u r e o f (15) using t h e m o d e l : d e p e n d e n t variable = c o w , diet. Least squares m e a n s w e r e c o m p u t e d w i t h t h e p r e d i c t e d d i f f e r e n c e s o p t i o n and d i f f e r e n c e s b e t w e e n t h e t w o 13% CP diets, and b e t w e e n t h e t w o b r e w e r s dried grains diets r e p o r t e d accordingly. RESULTS A N D DISCUSSION Trials 1 and 2

Dry m a t t e r intake as p e r c e n t o f b o d y w e i g h t

averaged 3.1% f o r b r e w e r s dried grains, 2.8% f o r b r e w e r s w e t grains, and 3.0% f o r s o y b e a n meal t r e a t m e n t s . A b s o l u t e e s t i m a t e s o f degradat i o n p a r a m e t e r s d i f f e r e d b e t w e e n in vitro and in situ t e c h n i q u e s (Table 3). In vitro measurem e n t s gave c o n s i s t e n t l y l o w e r results for t h e rapidly d e g r a d e d f r a c t i o n A, primarily b e c a u s e w a s h i n g o f residual material was less effective in t h e filter f u n n e l s t h a n in the bags. T h e resistant f r a c t i o n C was o v e r e s t i m a t e d b y t h e in vitro t e c h n i q u e as m i g h t be e x p e c t e d due t o b u i l d u p o f f e r m e n t a t i o n p r o d u c t s . Despite t h e s e differences b e t w e e n in vitro and in situ t e c h n i q u e s , c o r r e l a t i o n s b e t w e e n e s t i m a t e s o f all in situ and in vitro p a r a m e t e r s w e r e positive. Correlations b e t w e e n in vivo and in vitro m e a s u r e s of f r a c t i o n D o f DM ( r = .87) and n i t r o g e n (r = .86) and t h e rate k f o r DM d i s a p p e a r a n c e (r -.76) w e r e significantly greater t h a n zero. The in vitro 72-h a m m o n i a c o n c e n t r a t i o n was signifi-

TABLE 3. In situ and in vitro fermentative degradation of nitrogen and dry matter from brewers dried grains, brewers wet grains, and soybean meal. p3

In situ Dry matter

Nitrogen

In vitro Dry matter

Nitrogen

Feed 2

Fraction or rate 1

BDG

BWG

SBM

Standard error

~DG vs. BWG

A B C k

.20 .42 .38 .039

.29 .41 .30 .048

.44 .55 .01 .121

.02 .03 .02 .009

.08

.01

.77

.07

.10 .58

.01 .02

A B C k

.19 .51 .30 .042

.51 .39 .10 .066

.26 .74 .00 .177

.07 .05 .03 .006

.07 .23 .05 .12

.36 .04 .04 .004

A B C k

.04 ,38 .58 .065

.11 .47 .42 .053

.32 .56 .12 .094

.04 .03 .04 .014

.40 .18 .10 .61

.04 .08 .01 .18

A

,23 .30 .60 .052

.27 .50 .23 .055

.41 .51 .08

.03 .04 .07 .015

.06 .08 .06 .92

.03 .17 .06 .33

B

C k

.077

BG vs. SBM

A = Fraction of feed degraded rapidly, B = fraction of feed degraded slowly, C = fraction of feed undegraded, k = rate of degradation of fraction B, h -1 . 2 BDG = Brewers dried grains, BWG = brewers wet grains, SBM = soybean meal. 3Probability of detecting a treatment difference when no such difference exists either between brewers grains sources (BDG vs. BWG) or between the combined effects of brewers grains and soybean meals (BG vs. SBM). Journal of Dairy Science Vol. 69, No. 8, 1986

RUMINAL DEGRADATION OF PROTEIN SUPPLEMENTS cantly correlated (r = .95) with the in situ measure of nitrogen fraction C and positively correlated (r = .90) with the in situ rate of protein disappearance. Nitrogen f o u n d in the acid detergent fraction of the protein supplem e n t was significantly correlated with in situ estimates of the fraction C (r = .74), fraction B (r = .78), and k (r = .97) for feed nitrogen. Dry m a t t e r disappearance f r o m bags n o t inserted into the r u m e n was 29% for soybean meal, 8% for brewers dried grains, and 17, 25, and 30% for three separate batches o f brewers w e t grains. Grinding of soybean meal and brewers dried grains to 2 m m had no effect on dry m a t t e r loss ( " w a s h o u t " ) f r o m 0 h bags for soybean meal but slightly increased this meas u r e m e n t with brewers dried grains to 10%. F r a c t i o n A for DM consistently was larger than the washout, indicating that the intercept of the degradation curve is partly influenced by r u m e n environment. Alternatively, the intercept m a y be artificially t o o large because no lag t i m e was built into this model. Estimates of lag t i m e can be a c c o m o d a t e d with the linear m o d e l used herein by eliminating prelag values based on confidence intervals of replicated bags; however, such analysis w o u l d require m o r e bags incubated for 0 to 6 h than were included in the present study. Degradation o f DM and protein was quite different for brewers grains than for soybean

2129

meal. Dry m a t t e r f r o m brewers grains was m o r e slowly digested into dispersible constituents, as indicated by smaller B fractions and their m u c h slower rate of degradation. A significant p o r t i o n of the DM f r o m either source of brewers grains essentially was indigestible by r u m e n microorganisms. The predicted undegraded DM (B*r/(r + k) + C), using in situ data and r = .05 h for tureen turnover, was .61, .51, and .18 for brewers dried grains, brewers wet grains, and soybean meal. Nitrogen degradation paralleled DM disappearance e x c e p t for the relatively large a m o u n t of nitrogen that was rapidly degraded in the brewers wet grains. Predicted undegraded nitrogen was .58, .27, and .17 for brewers dried grains, brewers wet grains and soybean meal. Differences of considerable m a g n i t u d e between wet and dried brewers grains in trial 1 were n o t significant. Similar differences were n o t e d in trial 2 w h e n wet grains were dried (Table 4). No differences were due to drying at 50 versus 150°C. When data on drying were p o o l e d for trials 1 and 2, there was a nonsignificant (P<.06) increase of fraction C at the expense of fraction A for b o t h DM and nitrogen. The p r o p o r t i o n o f nitrogen in fraction B also was increased by drying. The overall effect of drying brewers grains was an increase of predicted ruminal excape o f DM from .47 to .57 and of nitrogen escape f r o m .32 to .55.

TABLE 4. Effect of drying temperature on in situ rumen degradability of dry matter and nitrogen from brewers wet grains. Drying method Wet Fraction or rate ~ Dry matter A B

C k , h -1 Nitrogen A B C k,h -1

50°C

150°C

Cow 503

Cow 489

Cow 503

Cow 489

Cow 503

Cow 489

,34 .45 .21 .042

.50 .35 .15 .026

.21 .52 .27 .046

.34 .47 .19 .038

.21 .53 .26 .049

.33

.45 .42 .13 .029

.46 .50 .04 .022

.15 .65 .20 .038

.30 .65 .05 .028

.14 .64 .21 .044

.10 .84 .06 .038

.49 .18 .040

1A = Fraction of feed degraded rapidly, B = fraction of feed degraded slowly, C = fraction of feed undegraded, k = rate of degradation of fraction B, h -1 . Journal of Dairy Science Vol. 69, No. 8, 1986

2130

ARMENTANO ET AL.

Trial 3

Microbial preparations contained beween 34.6 and 65.6/amol cytosine/g DM and averaged 48.1% CP, indicating a relatively pure preparation. Cytosine content (;~mol/g DM) of brewers dried grains (1.6), orchard grass (1.2), and soybean meal (4.8) were low compared with enriched rumen microbial fractions. Differences between 27 duplicated duodenal and enriched rumen samples, digested and chromatographed separately, averaged 3.6%. Rapid ruminal disappearance of feed cytosine (16) combined with ease, sensitivity, and repeatability of assay make cytosine a suitable marker for microbial contribution to digesta. The Yb concentration of the first duodenal samples averaged 85.9% (standard error = 8.6%) of the pooled duodenal contents, indicating adequate equilibration of marker. Absolute flow of nitrogen and DM to the duodenum was not significantly affected by source or amount of protein (Table 5). More of the nitrogen arriving at the duodenum was of microbial origin when feeding soybean meal diet compared with the isonitrogenous brewers grain diet, although microbial nitrogen flow was similar for these two diets. True digestibility of nitrogen was greater for soybean meal than for

comparable brewers grain diets (Table 6). These data support the results of trial 1. Brewers dried grains, when supplied isonitrogenously to soybean meal, increases feed nitrogen flow to the duodenum. This is accomplished with no loss of rumen microbial nitrogen synthesis (Table 5) due to the ability of the rumen to recycle nitrogen effectively on the low protein brewers dried grains diet. This recycling is demonstrated by the negative apparent digestibility of nitrogen in the rumen (Table 6) and is in agreement with the lower plasma urea and urinary nitrogen loss reported for a similar dietary comparison (14). The negative apparent rumen digestibility for nitrogen may indicate that the protein content of diet supplemented with brewers dried grains could be increased to greater than 13% CP with nonprotein nitrogen. Increasing dietary protein above 13% with dried brewers grains did not increase total nitrogen supply to the duodenum. Microbial flow to the duodenum was less for the high protein diet than for the low protein diet. This is an unexpected result because of the increased milk yield shown previously when brewers dried grains were fed at similar concentrations (14). Dried brewers grains may enhance lactation performance due to decreased rumen

TABLE 5. Flow of dry matter and nitrogen through the gastric region of lactating cows. Diet ~ BDG-LP

SBM-LP

BDG-HP

(kg/d) Intake Dry matter Nitrogen Flow to duodenum Dry matter (M)2 Dry matter (T)2 M/T Nitrogen (M) Nitrogen (T) M/T

SE

X

SE

X

SE

14.0 .31

.4 .03

12.9 .27

.4 .02

12.4 .34

.4 .02

1.6 9.0 .18 .12 .26 .46

.1 1.1 .01 .01 .02 .01 a

1.6 11.1 .15 .12 .31 .40

.1 1.1 .01 .01 .02 .01

1.1 9.0 .13 .10 .28 .34

.1 1.3 .01 .01 .03 .02 a

aDiffers from BDG-LP diet (P<.05). 1SBM-LP = Soybean meal-supplemented diet, BDG-LP= brewers dried grains, low protein diet, and BDG-HP = brewers dried grains, high protein diet. 2M = Microbial, T=total. Journal of Dairy Science Vol. 69, No. 8, 1986

RUMINAL DEGRADATION OF PROTEIN SUPPLEMENTS ammonia production, compared with soybean meal, rather than to increased flow of amino acids to the duodenum. These results indicate that the resistance of brewers grains proteins to ruminal degradation might best be used by combining brewers grains with nonprotein nitrogen rather than usng brewers grains to increase amino acid flow to the duodenum on high protein diets. Dry matter and protein presented to the duodenum were equally digestible across treatments despite the greater concentration of acid detergent insoluble nitrogen in brewers grains rations (Table 1). Total tract digestibility of the low protein brewers dried grain diet was decreased due to decreased rumen degradation. The amino acid composition of duodenal contents was similar across treatments (Table 7). Brewers grains diets delivered slightly less lysine to the duodenum. Flow of amino acids tended to be greater with increased dietary protein on brewers dried grain diets, even though total nitrogen was not. The greater microbial nitrogen content on low protein brewers grain diet could increase the proportion of nonamino nitrogen. This may explain part of

2131

the production responses reported (14). Dry matter apparently digested in the rumen as a fraction of total tract digestion was .46, .22, and .53 for soybean meal, low protein brewers grains, and high protein brewers grains diets. The average proportion, .40, is less than the average found in a wide range of similar studies with cannulated animals (9). Measurement of acetate, butyrate, and propionate production in the rumen (3) can be used to estimate that approximately 45% of digestion occurs in the rumen. Measurements of organic acid absorption (8) indicate that they comprise 40 to 45% of absorbed energy in cattle. Data obtained in these trials indicate that brewers dried grains deliver more protein and DM to the duodenum than isonitrogenous amounts of soybean meal. Release of nitrogen from dried brewers grains is slower and more sustained than that from soybean meal. This sustained release may have greater impact when protein supplement is fed less frequently than in trial 3 where feed was delivered as a mixed ration at 4-h intervals. Brewers wet grains had intermediate nitrogen degradation. The large fraction of nitrogen in acid detergent fraction

TABLE 6. Mean digestibility of dry matter and nitrogen in vivo. Diet 1 BDG-LP

SBM-LP

BDG-HP

(%) Dry matter digestibility Total tract Gastric (apparent) Postgastric2 Gastric (true) 3 Nitrogen digestibility Total tract Gastric (apparent) Postgastric2 Gastric (true) 3

SE

X

SE

X

SE

74.9a 34.3 60.9 45.6

2.4 7.6 3.2 7.3

63.8 14.2 57.3 27.0

2.4 7.6 3.2 7.3

70.4 27.6 60.0 36.4

3.0 9.3 3.9 8.9

74.9 13.6 71.5 53.7a

4.1 7.8 2.2 4.6

66.5 -14.3 70.6 30.5

4.1 7.8 2.2 4.6

76.4 16.2 72.1 44.1

5.0 9.6 2.7 5.7

aDiffers from BDG-LP diet (P<.05). 1SBM-LP = Soybean meal-supplemented diet, BDG-LP= brewers dried grains, low protein diet, and BDG-HP = brewers dried grains, high protein diet. Percent of material appearing in duodenum which is absorbed. 3Corrected for microbial contribution. Journal of Dairy Science Vol. 69, No. 8, 1986

2132

A R M E N T A N O ET AL.

TABLE 7. A m i n o acid composition of duodenal dry m a t t e r ) Diet 2 SBM-LP

Lysine Histidine Arginine Threonine Phenylalanine Valine Leucine lsoleucine Methionine Sum ess. AA 3 Sum disp. AA 4 Sum all AA 5

BDG-LP

BDG-HP

X"

SE

X

SE

,X

SE

75.5 26.5 47.7 65.7 51.9 73.1 107.6 75.6 17.1 559.5 700.7 1283.6

6.5 3.5 9.1 3.5 3.5 4.3 4.7 3.3 2.7 29.3 27.5 58.4

61.1 21.5 38.5 61.8 50.4 73.1 109.8 72.9 18.1 507.2 690.5 1197.8

5.3 2.8 7.4 3.5 3.5 4.3 4.7 3.3 2.7 23.8 26.0 47.8

58.3 20.2 58.9 66.5 52.i 80.3 122.1 74.3 20.3 549.8 774.9 1320.8

6.5 3.5 9.1 4.3 4.2 5.2 5.8 4.0 3.3 29.2 33.6 58.5

1 Least square m e a n s and standard error of four cells except for lysine, histidine, arginine, Sum ess., and Sum all for SBM-LP and all values for BDG-HP for which n = 3, ~mol/g duodenal dry matter. 2 SBM-LP = Soybean meal-supplemented diet, BDG--LP = Brewers dried grains, low protein diet, and BDG-HP = Brewers dried grains, high protein diet. Sum of amino acids listed in table. a Sum of aspartate, serine, glutamate, proline, glycine, alanine, and tyrosine. s Sum of amino acids described in f o o t n o t e s 3 and 4.

o f b r e w e r s d r i e d g r a i n s w a s r e l a t e d to d e c r e a s e d fermentative degradation but did not seem to decrease intestinal digestion.

REFERENCES

1 Association of Official Analytical Chemists. 1975. Official m e t h o d of analysis. 12th ed. Assoc. Offic. Anal. Chem., Washington, DC. 2 A r m e n t a n o , L. E., T. A. Herrington, and C. E. Polan. 1983. Ruminal degradation of dried brewers grains, wet brewers grains and soybean meal in situ and in vitro. J. Dairy Sci. 66(Suppl. 1):171. (Abstr.) 3 A r m e n t a n o , L. E., and J. W. Young. 1983. Production and metabolism of volatile f a t t y acids, glucose and CO 2 in steers and the effects of m o n e n s i n on volatile f a t t y acid kinetics. J. Nutr. 113 : 1265. 4 Burroughs, W., D. K. Nelson, and D. R. Mertens. 1975. Protein physiology and its application in the lactating cow: the metabolizable protein standard. J. Anirn. Sci. 41:933. 5 Clark, J. H. 1975. Lactational responses to postruminal administration of proteins and animo acids. J. Dairy Sci. 58:1178. 6 Forster, R. J., D. G. Grieve, J. G. Buchanan-Smith, and G. K. Macleod. 1983. Effect of dietary protein

Journal of Dairy Science Vol. 69, No. 8, 1986

7

8

9

10

11

12

13 14

degradability in cows in early lactation. J. Dairy Sci. 66:1653. Hart, S. P., and C. E. Polan. 1984. Simultaneous extraction and determination of y t t e r b i u m and cobalt ethylenediaminetetraacetate complex in feces. J. Dairy Sci. 67:888. Huntington, G. B., and R. L. Prior. 1983. Digestion and absorption of nutrients by beef heifers fed a high concentration diet. J. Nutr. 113:2280. Johnson, D. E., and W. G. Bergen. 1982. Fraction of organic matter digestion occuring in the rumen: a partial literature s u m m a r y . Pages 113 127 in Protein requirements for cattle. F. N. Owens, ed. Misc. Publ. 109, Oklahoma State Univ., Stillwater. Komarek, R. J. 1981. Intestinal cannulation of cattle and sheep with a T-shaped cannula designed for total digesta collection w i t h o u t externalizing digesta flow. J. Anim. Sci. 53:796. McDougall, E. I. 1948. Studies on r u m i n a n t saliva: 1. The composition and o u t p u t of sheep saliva. Biochem. J. 43:99. Meyer, R. M., E. E. Bartley, C. W. Deyoe, and V. F. Colenbrander. 1967. Feed processing: ration effects on r u m e n microbial protein synthesis and amino acid composition. J. Dairy Sci. 5 O: 1327. Orskov, O. R. 1982. Protein nutrition in ruminants. Academic Press, Inc., New York, NY. Polan, C. E., T. A. Herrington, W. A. Wark, and L. E. A r m e n t a n o . 1985. Milk production response to

R U M I N A L D E G R A D A T I O N OF P R O T E I N SUPPLEMENTS

diets s u p p l e m e n t e d with dried brewers grains, wet brewers grains or soybean meal. J. Dairy Sci. 68:2016. 15 SAS User's Guide. 1979. SAS Inst. Inc., Raleigh, NC. 16 Schelling, G. T., S. E. Koenig, and T. C. Jackson, Jr. 1980. Nucleic acids and purine or pyrimidine bases as markers for protein synthesis in the rumen. Pages 1 - 9 in Protein requirements for cattle. F. N. Owens, ed. Misc. Publ. 109, Oklahoma

2133

State Univ., Stillwater. 17 Stern, M. D., and L. D. Satter. 1980. In vivo estimation of protein degradability in the rumen. Pages 5 7 - 7 1 in Protein requirements for cattle. F. N. Owens, ed. Misc. Publ. 109, Oklahoma State Univ., Stillwater. 18 Weakley, D. C., M. D. Stern, and L. D. Satter. 1983. Factors affecting disappearance of feedstuffs f r o m bags suspended in the rumen. J. Anim. Sci. 56:493.

Journal of Dairy Science Vol. 69, No. 8, 1986