Nitrogen Metabolism in Dairy Cattle. II. Soybran Flakes versus Oats as Principal Sources of Digestible Carbohydrates for Nitrogen Utilization1

NITROGEN METABOLISM IN DAIRY CATTLE. II. SOYBRAN FLAKES VERSUS OATS AS PRINCIPAL SOURCES OF DIGESTIBLE CARBOHYDRATES FOR NITROGEN UTILIZATION 1 H. R. CONRAD AND J. W. HIBBS Department of Dairy Science, Ohio Agricultural Experiment Station, Wooster SUMMARY

Nitrogen metabolism, feed intake, and milk production were studied using six lactating dairy cows in a 3 X 3 Latin-square design. Soybran flakes and soybean oil meal were compared to either (1) soybran flakes, ground shelled corn, and soybean oil meal or (2) ground whole oats, ground shelled corn, and soybean oil meal as the principal sources of digestible nutrients. The two soybran flake mixtures were also compared to an alfalfa hay and grain concentrate ration, using six dairy heifers. The percentages of cellulose, starch, pentosans, polyuronides, and sugars were determined for each ration. Apparent protein digestibility reflected differences in the protein content of the complete rations. Cellulose digestibility was unusually high in the soybran flake rations, 77 to 79%. Higher average yields of milk nitrogen and larger positive nitrogen balances resulted in greater nitrogen efficiency in cows fed soybran flakes. However, differences in digestible dry matter intake were correlated with the differences in nitrogen utilization, and adjusting for digestible dry matter intake accounted for the differences in nitrogen efficiency. Abrupt shifts to high levels of cereal grain in the ration depressed milk yield because of lowered feed intake. It was concluded that cellulose is equal to starch for supporting nitrogen metabolism in growing or lactating dairy cattle, provided the cellulose can be digested.

This study is concerned with the efficiency of nitrogen utilization in lactating cows when the principal feed sources of digestible energy were either cellulose and hemicelluloses of soybran flakes or starch of ground whole oats. In a previous study, it was shown that the nitrogen from freshly cut forages was utilized more efficiently by dairy cows than nitrogen from ensiled forages. Differences occurred primarily at high levels of protein equivalent in the ration, since below 15% protein equivalent in the ration, silage and freshly cut forage nitrogen were utilized with the same efficiency. But, utilization of silage nitrogen for milk and body retention declined in efficiency at higher levels of protein equivalent; whereas, freshly cut forage nitrogen was used efficiently at all levels of protein equivalent measured up to 24.6% (5). Head (11) has made similar observations in England, but found that most of the extra nitrogen utilized went for body retention. Adding cereal grain to forage rations increased the efficiency of nitrogen utilization markedly (5, 10). Holdaway et al. (13) showed that nitrogen efficiency decreased sharply when high levels of protein supplement were included in the grain concentrate. EI-Shazly (9), Cuthbertson and Chalmers (8), and McDonald (18) have demonstrated, using sheep, that efficiency of protein utilization decreases with Received for publication May 29, 1961. 1

Journal Article No. 65-61, The Ohio Agricultural Experiment Station.

1903

H. R. CONRAD AND J. W. ttIBBS

1904

i n c r e a s e d s o l u b i l i t y of the p r o t e i n i n the r u m i n a l contents. A m a j o r r o u t e of n i t r o g e n loss arose f r o m the passage of a m m o n i a d i r e c t l y across t h e r u m e n wall (8, 19). Because the n o n p r o t e i n n i t r o g e n of ensiled f o r a g e was f o u n d to be t h r e e or f o u r times t h e a m o u n t c o n t a i n e d i n f r e s h l y cut forage, i t was c o n c l u d e d t h a t a n i n c r e a s e i n r e l a t i v e c o n t e n t of soluble n i t r o g e n a n d a s i m u l t a n e o u s decrease i n soluble c a r b o h y d r a t e d u r i n g f e r m e n t a t i o n caused the r e d u c t i o n i n efficiency of n i t r o g e n u t i l i z a t i o n below t h a t o b t a i n e d w i t h f r e s h l y c u t forage (4). To o b t a i n specific i n f o r m a t i o n on the significance of f o r a g e - t y p e p l a n t carboh y d r a t e s to n i t r o g e n u t i l i z a t i o n i n d a i r y cattle, i t was t h o u g h t advisable to s i m u l a t e i n a r a t i o n f r o m n a t u r a l sources c a r b o h y d r a t e s f o u n d i n f r e s h l y c u t forage, a n d to d e t e r m i n e t h e i r a b i l i t y to s u p p o r t n i t r o g e n u t i l i z a t i o n i n l a c t a t i n g cows i n c o m p a r i s o n w i t h the c a r b o h y d r a t e s of cereal g r a i n . EXPERIMENTAL PROCEDURE S o y b e a n oil m e a l c o n t a i n i n g 50% p r o t e i n was used as the m a j o r source of n i t r o g e n . T h e c a r b o h y d r a t e s were f u r n i s h e d f r o m s o y b r a n flakes or g r o u n d whole oats, g r o u n d shelled corn, a n d molasses. V t a m i n A a n d D s u p p l e m e n t , def l u o r i n a t e d rock phosphate, salt a n d trace m i n e r a l s were i n c l u d e d i n each r a t i o n . The f o r m u l a e f o r two s o y b r a n flake m i x t u r e s a n d the oats m i x t u r e are shown i n T a b l e 1. The r a t i o n s were f o r m u l a t e d to be either h i g h or v e r y h i g h i n p r o t e i n TABLE 1 Ingredients and chemical composition of experimental concentrate mb:tures ~Mixture 1

Soybran flakes Ground whole oats Ground shelled corn Soybean oil meal l~Io]asses Salt Defluorinated rock phosphate

62.7 ...... ...... 33.3 3.0 0.5 0.5

Dry matter Organic matter Crude protein Cellulose Pentosans Polyuronides Fat Ash Starch

86.3 79.3 25.4 26.5 12.0 10.6 2.25 7.0 1.2

Mixture 2

Mixture 3 (%)

Ingredients ~ 62.7 ...... ...... 62.7 16.7 16.7 16.6 16.6 3.0 3.0 0.5 0.5 0.5 0.5 Average chemical analysis 86.5 87.2 81.0 82.2 18.1 24.3 29.2 8.5 12.5 6.0 10.1 0.3 2.63 3.92 5.5 5.0 12.0 40.1

Mixed hay

...... ...... ...... ...... ...... ...... ...... 84.3 76.6 10.4 34.2 19.4 6.2 0.89 7.7 ....

Micro-ingredients included the trace minerals iodine, copper, iron, zinc, manganese, and cobalt. One thousand I.U. of vitamin A and 500 I.U. of vitamin D were added per pound Of mixture. c o n t e n t , so t h a t a n excess of p r o t e i n was a v a i l a b l e a n d so t h a t two levels of p r o t e i n were used w i t h s o y b r a n flakes. The p r o t e i n c o n t e n t of the v e r y h i g h p r o t e i n s o y b r a n flake r a t i o n , M i x t u r e 1 - - T a b l e 1, was raised b y s u b s t i t u t i n g

1905

N I T R O G E N M E T A B O L I S I ~ I N DAII~Y CATTLE. I I .

soybean oil meal for the ground shelled corn. Likewise, Mixture 3, the control ration, was made by substituting ground whole oats for the soybran flakes, which made the protein content of Mixture 3 approximately equal to Mixture 1, Table 1. These mixtures were fed to appetite to six cows with a limited amount of low-quality, grass-legume hay cut on J u n e 19. The six milking cows were fed the various rations in accordance with a Latin-square experimental design, using sequences described by Coehran and Cox (3), for estimating residual effects. Separate collections of feces and urine (4) were made during the third week of each 3-wk. feeding period. Feed intake, feed refused, and milk produced were measured daily. D r y matter, total nitrogen, ether extract, and ash were determined by conventional procedures (24). Cellulose was determined by the procedure of Crampton and Maynard (6). Polyuronides were estimated as the galacturonic acid equivalent of carbon dioxide produced from boiling 1.5 hr. with 19% hydrochloric acid at 145 ° C. (17). Pentosans were determined colorimetrically (1), using a perchloric acid extract of finely ground plant tissue (21). I n another experiment using two 6-8-mo.-old dairy heifers soybran flake Mixtures 1 and 2 were fed with mixed hay and compared to an alfalfa h a y - g r a i n concentrate ration. Digestibility and nitrogen utilization were measured. The grain concentrate was composed of 17% soybean oil meal, 50% ground shelled corn, 21% ground whole oats, 1% iodized salt, and 1% steamed bonemeal. RESULTS

Chemical analyses of samples taken from the various feeds eaten by the experimental cows showed the protein content to be : Ration 1, 24.7% ; Ration 2, 17.6%; and Ration 3, 21.2% (Table 2). Distribution of the major component TABLE 2 Protein and carbohydrate composition of complete rations consumed ~ (Dry basis) Ration I Protein Cellulose Pentosans Polyuronides Starch Sugars

24.7 32.7 15.9 11.2 ...... 1.5"

Ration 2 (%) 17.6 34.7 16.4 10.9 9.1 ~ 1.5 a

!~ation 3 21.2 22.8 14.1 3.4 23.2 a 1.8 ~

a Starch and sugar values calculated and based on percentages of cereal grain in the ration and average values taken from tables on composition of cereal grains (22). carbohydrates in the various rations are also shown. The major carbohydrates varied from 32.7% cellulose and no starch in Ration 1 to 22.8% cellulose and 23.2% starch in Ration 3. The total pentosan content was approximately the same for each ration, but polyuronide content was three times higher in the soybran flake rations than in the oats ration.

]906

H . R. 0 0 N R A D

A N D 3. W. t t I B B S

TABLE

3

Comparison of digestibility of rations, efficiency of nitrogen utilization, feed intake, a n d milk production by cows when either soybran flakes or ground whole, oats provided the major carbohydrate components of the ration and were fed with mixed h a y Comple¢e Experimental Rations Ration 1 D r y m a t t e r digested ( % ) Cellulose digested ( % ) Total digestible n u t r i e n t s ( % ) Digestible dry m a t t e r / i , 0 0 0 lb. B.W. (lb/day) Experimental ration consumed (lb/day) Mixed h a y consumed (lb/day) A p p a r e n t protein digestion ( % ) Nitrogen utilization 1. N i t r o g e n intake (g/day) 2. A p p a r e n t nitrogen absorbed (g/day) 3. Fecal nitrogen (g/day) 4. Urine nitrogen (g/day) 5. Milk nitrogen (g/day) 6. N i t r o g e n balance (g/day) 7. Total nitrogen used (g/day) Nitrogen efficiency (%)~ Nitrogen efficiency a d j u s t e d (%)b Milk N (%) Absorbed N Urine nitrogen ( % )

Milk (Ib/day) 4% F.C.M. (lb/day) Milk protein ( % )

Ration 2

Ration 3

L.S.D. P < 0.05

76.6 78.9 72.1 21.7 29.2 9.1 78.4

75.3 76.6 71.9 22.9 30.3 9.2 72.5

69.3 55.8 66..7 19.0 20.2 15.8 77.9

5.7 10.1

596 467 129 291 106 70 176 29.1 28.2

4.50' 326 124 168 100 58 158 35..0 33.4

482 375 107 234 91 50 141 2.8..3 30.8

...... ...... ...... N.S. N.S. N.S. 6.1 2.4

22.7

30.7

24.2

2.8

48.8 47.1 41.8 3.08

37.3 46.0 41.2 3.04

4,8.6 43.1 40.3 2,.89

8.9 3.9 N.S. N,S.

3.1 ...... 4.7

* Per cent of intake used for milk protein and nitrogen retention. b N i t r o g e n efficiency a d j u s t e d for differences in digestible dry m a t t e r intake by analysis of covariance.

Results of digestion and nitrogen balance trials are summarized (Table 3). Although all rations were offered free-choice, the cows ate less experimental mixture and more hay when fed Mixture 3 than when Mixture 1 or 2 was fed. Attempts to raise the level of grain consumption in cows fed Mixture 3, by limiting the amount of hay fed, resulted in increased amounts of refused grain and in one animal becoming bloated. Consequently, the average total protein content of Ration 3 was lower than had been anticipated, because of the low protein content of the extra hay used. Apparent protein digestibility did not differ markedly among the complete rations, but reflected the differences in the protein content of Rations 1 and 2 (Table 3). Cellulose digestibility was unusually high in the soybran flake-mixed hay ration and both dry matter and cellulose digestibility were significantly less during the periods when oats and mixed hay were fed (P < 0.01). Comparisons of the nitrogen efficiency values indicated the effective usage of nitrogen in cows fed soybran flake rations (Table 3). The per cent protein content of the ration and nitrogen efficiency percentages deviated from the theoretically expected inverse relationship, suggesting a direct ration effect. Nitrogen efficiency percentages were 29.1, 35.0, and 28.3, respectively, for Ra-

1907

NITROGEN 1VIETABOLISM IN DAIRY CATTLE. II.

tions 1, 2, and 3; whereas, the protein contents were 24.7, 17.6, and 21.2. However, associated with the lower protein anabolism in cows fed the oats-mixed hay ration was a lower digestible dry matter intake. That differences in feed consumption were partly responsible for the differences in nitrogen utilization was suggested by the positive correlation coefficient, r = 0.554, between digestible dry matter intake and the amount of nitrogen used. When the mean nitrogen efficiency percentage of each ration was adjusted by analysis o~ covarianee (23), for the observed differences in digestible dry matter intake, the adjusted means in contrast to the true means were found to be inversely related to the per cent protein content of the rations and each differed significantly from the other. Milk production was highest during the period of soybran flake feeding. There were no notable differences among the groups in the amount of 4% fat-corrected milk produced. Milk protein showed a slight average decline but was not significant (Table 3). The results with heifers showed no marked differences in nitrogen retention between soybran flake rations and the alfalfa hay-grain concentrate ration (Table 4). TABLE 4 Digestibility and nitrogen utilization in dairy heifers fed rations high in soybran flakes compared with heifers fed a l f a l f a h a y a n d grain concentrate Soybran flakes Ration 1 No. of animals Av. body weight (lb.) Dry m a t t e r digestibility ( % ) Protein digestibility ( % ) Nitrogen balance (g/day/lO0 ~b.) Nitrogen efficiency ( % ) Feed intake Experimental mixture (tb/day) Mixed h a y (lb/day) A l f a l f a h a y (lb/day) Grain concentrate (lb/day)

Soybran flakes Ration 2

Alfalfa h a y and grain

2 464, 73.4 77.8 16.9 44.6

2 445 74.8 71.5 11.0 40.1

2 404 72.4 74.6 12'.5 34,.6

7.5 2.3

9.2 1.6 ......

. ..... 9.7 4.0

DISCUSSION" OF RESULTS

Rations consisting of soybran flakes, soybean oil meal, a small amount of ground corn and molasses, and limited hay effectively supported nitrogen utilization in dairy cows; whereas, substituting ground whole oats for the soybran flakes reduced nitrogen utilization. This was true even though the cellulose content of the soybran flake ration was higher than percentages usually found in a typical forage-grain type ration. For example, a ration consisting of 20% grain and 80% alfalfa-grass forage contained 20% protein, 24% cellulose, 12% polyuronides, 5% pentosans, 6% starch, and 3% sugars, compared to Ration 2, Table 2, which contained 18% protein, 30% cellulose, 9% polyuronides, 14% pentosans, 6% starch, and 1.3% sugars. Convincingly demonstrated by the results is the principle that the carbohydrates in a ration, largely through effects on feed intake, effectively alter the

1908

H. R. CONRAD AND J. W. HIBBS

efficiency of nitrogen utilization and determine the optimum amount of nitrogen that may be used efficiently in a ration. Moreover, the results form a basis for postulating that cellulose, pentosns, and polyuronides are useful for efficient utilization of the protein contained in soybean oil meal. In this regard, Bryant and Robinson (2) have shown that certain cellulose-digesting tureen microorganisms require ammonia nitrogen and thus possibly serve as nitrogen conservers in the rumen. Cunningham et al. (7) raised the protein content of the ration of young calves to 24% of the total calories without diminishing the efficiency of nitrogen utilization by simultaneously increasing the energy intake. Itibbs and Conrad (12) found that high-roughage pellets with a nutritive ratio of 1 : 3.9 supported higher body weight gains in young calves than similar rations with wider nutritive ratios. The high nitrogen efficiency found in dairy cows fed freshly cut forage high in protein was discussed in the introduction to this paper (5). In lactating cows, Logan et al. (15) found that cows fed a high-protein, highenergy ration produced more milk and gain in body weight than control cows fed a normal protein high-energy ration, provided they also consumed more digestible nutrients daily. Because of these results, and the results of this experiment, it is postulated that many sources of nitrogen fed to dairy cattle could be used efficiently up to 18% total protein in the ration if the carbohydrate mixtures which would support maximum digestible dry matter intake were always used. The reduced yield in milk of cows fed the oats and mixed hay ration has been noted in the results. The question may be raised as to whether this represents a temporary condition effeeted by the abrupt shift to a high level of starch and more hay in the diet, which depressed ruminal cellulose digestion and feed intake. That the conditions of lowered milk yields and nitrogen utilization are temporary is suggested by the finding that suboptimum digestible dry matter intake occurred simultaneously. Because of the present emphasis on high-grain feeding in certain areas, a more expeditious experimental desigu involving total lactation studies is needed to clarify this effect. The observations made on digestibility of soybran flakes are in agreement with the results obtained by Quicke et al. (22) and Loosli (16). It appears that optimum nitrogen retention was obtained in growing heifers using the ration high in cellulose and devoid of starch, but that the cellulose fraction was known to be unusually high in digestibility. Thus, it is concluded that cellulose is equal to starch for supporting nitrogen metabolism, provided the cellulose can be digested. This conclusion is in line with the findings reported by Kellner (14). ACKXOWLEDGMENTS The authors are indebted to D. G. Anderson and :R. L. Johnson for technical assistance, to J o h n ]King of the D e p a r t m e n t of Animal Science for m a k i n g the p e n t o s a n analyses, a n d to Dr. C. R. Weaver, Station Statistician, for suggesting an appropriate experimental design. Wo are especially g r a t e f u l to Dr. Leo Curtin of 1YfcMillen l%ed 5fills, Decatur, Indiana, who supplied the experimental rations and provided for their formulation.

NITROGEN METABOI~ISI~I IN DAII%Y CATTLE. II.

1909

REFEREN CES (1) BRGWN, A. H. Determination of Pentose in the Presence of Large Quantities of Glucose. Archiv. Bioehem. and Biophys., 11: 269. 1946. (2) BRYANT, M. P., AND ROBINSON, I. M. Nutrition of Rumlnal Cellulolytic Bacteria. J. Dairy Sci., 43: 876. 1960. (3) C0atIR~N, W. G., AN]) Cox, GE~TRU])~ M. Experimental Designs. 2nd ed., p. 465. John Wiley and Sons, Inc., New York. 1957. (4) CONm~D, If. R., IIIBBS, J. W., AN]) P~AT% A. D. Nitrogen Metabolism in Dairy Cattle. Ohio Agr. Expt. Sta., Research Bull. 861. 1960. (5) C0,NRAD, If. R., HIBBS, J. W., PI%ATT, A. D., AN]) DAVIS, R. R. Nitrogen Metabolism in Dairy Cattle. I. The Influence of Grain and Meadow Crops Harvested as Hay, Silage, or Soilage on Efficiency of Nitrogen Utilization. J. Dairy Sci., 44: 85. 1961. (6) CP~A~P~0~r, E. W., ANO MAYNAm~, L. A. The Relation of Cellulose Content to the Nutritive Value of Animal Feeds. J. Nutrition, 15: 383. 1937. (7) CUNNINGtIAI~/I, H. M., IIASKELL, S. R., MII~ES, V. J., LOGAN, V. S., AN]) Bl~ISSOlg, G. J. F u r t h e r Studies on the Protein and Energy Requirements of Young Dairy Calves. Can. J. Animal Sei., 38: 33,. 1958. (8) CUTHB~TSON, D. P., AND CHALME~S, M. I. Utilization of a Casein Supplement Administered to Ewes by Ruminal and Duodenal Fistulae. Biochem. J., 46: 17. 1952. (9) EL SHAZr~Y, K. Studies on the Nutritive Value of Some Common E g y p t i a n Feeding Stuffs. I. Nitrogen Retention and l~umlnal Ammonia Curves. J. Agr. Sci., 51: 149. 1958. (10) GRAY, F. V., PII~RI~, A. F., AN]) WF~LLEU, R. A. The Digestion of Foodstuffs in the Stomach of the, Sheep and the Passage of Digesta Through Its Compartments. II. Nitrogenous Compounds. Brit. J. Nutrition, 12:413. 1958. (11) IIF~AD, M. J. Grass, Nitrogen and the Metabolism of the Dairy Cow. Soc. Chem. Ind. Monograph 9, 191. 1959. (]2) IIIBBS, J. W., AND CON]~A~, H. R. IIigh Roughage System for Raising Calves Based on the E a r l y Development of Rumen Function. V I I I . Effect of Rumen Inoculations and Chlortetracycline on Performance of Calves Fed High Roughage Pellets. J. Dairy Sci., 4.1: 1230. ]95.8. (]3) HOLDAWAY, C. W., E ~ ' , W. B., AN]) HA~RXS, W. G. The Comparative Value of P e a n u t Meal, Cottonseed Meal, and Soybean Meal as Sources of P~otein for Milk Production. Virginia Agr. Expt. Sta., Tech Bull. 28. ]925. (14) ]~ELLNEI% O. The Scientific F e e d i n g of F a r m Animals. Julius Sprunger. Translated from German by William Goodwin, Macmillan Company, New York. 1913. (15) LOC~AlV,V. S., 1VflI~S, V., AND HASKELL, S. l~,. The Effect of R.elative Protein and Energy Content of Dairy Rations on Production and Composition of Milk. Canadian 3-. Animal Sci., 3~9: 226. 1959. (16) LOOSLI, J. K. Citrus Pulp and Soybran Flakes. Hoard's Dairyman, 105: 1104. 19'60. (17) McCR~A])Y, R. M., S w ] ~ s o ~ , If. A., AND McC~AY, W. D. Determination of IIronic Acids. Ind. Eng. Chem., Anal. Ed., 18: 290. 1946. (18) MoDo~AL]), I. W. The Absorption of Ammonia from the R umen of the Sheep. Riochem. J., 42': 584. 1948. (19) Me'DOnALD, I. W. The Extent of Conversion of Food Protein to Microbial Protein in the Rumen of the Sheep. J. Physiol., ]07: 21. 1948. (2'0) MILL~, D. F. Composition of Cereal Grains and Forages. National Academy of Sciences~National Research Council, Pub]. 585. 1958. (2~1) I~EIL,SEIN~, J. P. Rapid Determination of Starch. Ind. Eng. Chem., Anal. Ed., 15: 176. ]943. (22) QUIOKE, G. V., BENTb]~T, O. G., SCOTT, H. W., JOttNSOlV, R. R., AN]) MOXON, A. L. Digestibility o~ Soybean Hulls and Flakes and the in Vitro Digestibility of the Cellulose in Various Milling By-Products. J. Dairy Sci., 42: 185. 1959. (2'3,) SNF~ECOa, G. W. Statistical Methods. 5th ed. Iowa State Ilniverslty Press, Ames. 1956. (24) TRmBOLD, II. O. Quantitative Analysis with Application to Agricultural and Food Products. D. Van Nostrand Company, Inc., New York. 1946.