E F F E C T OF EXCESS D I E T A R Y P R O T E I N ON FEED I N T A K E A N D N I T R O G E N M E T A B O L I S M IN STEERS l Constantine L. Fenderson 2'3 and Werner G. Bergen 2

SUMMARY

INTRODUCTION

Growing Holstein steers were fed four rations containing from 10 to 40% protein. Soybean meal and isolated soy protein concentrates were used as supplemental protein sources. Extensive ruminal bypass of the soy protein was anticipated and this study was designed to elucidate the role of high protein availability (e.g., amino acids absorbed from the small intestine substantially above the animal's amino acid requirements) on feed intake in steers. Steer dry matter intake for the two high (32.5 and 40,0%) protein rations was depressed primarily during days 2 and 3 with a subsequent recovery to initial intake levels between days 5 to 10. Overall, plasma amino acid levels were not markedly influenced by dietary protein level and hence in this study an "aminostatic" control of feed intake in steers could not be demonstrated. Steers fed the two high protein rations had very high ruminal ammonia levels and elevated plasma urea nitrogen concentrations. It was concluded that, although for all rations the protein requirements of the steers were met, extensive degradation of the dietary protein negated the experimental design of achieving extensive ruminal protein bypass and an excessive absorption of amino acids from the small intestine. The steers, despite ruminal ammonia levels in excess of 100 mg/100 ml rumen liquor, did not exhibit any signs of ammonia toxicity. Apparently excessive levels o f ruminal ammonia arising from breakdown of performed protein can be tolerated by ruminants when their amino acid requirements are met. (Key Words: Steers, Excess Protein, Ammonia, Amino Acids, Feed Intake.)

The effect of feeding low or adequate protein rations on feed intake, productive performance and nitrogen metabolism in ruminants has been studies (Bergen et al., 1973; Leibholz, 1970). A number of workers have studied the effect of high protein intakes by infusing protein directly into the abomasum or duodenum, by feeding incremental levels of formaldehyde-treated proteins to sheep and by bottle feeding incremental levels of protein to nursing lambs. In all these studies the plasma essential amino acids were markedly elevated but nonessential amino acids remained unchanged (Bergen and Potter, 1975; Potter and Bergen, 1974; Weston, 1971; Hogan et al., 1968). Studies, similar to the above have not been widely conducted with growing steers. The objective of this study was to examine the effect of excessive protein intake on nitrogen metabolism (plasma free amino acid and urea concentrations and ruminal ammonia levels) and feed intake of growing steers. Rations containing 10 to 40% protein were formulated. Soybean meal or soy protein isolates were included in the rations at appropriate levels in an attempt to vary the amount of absorbable protein in the small intestine.

EXPERIMENTAL PROCEDURES

Four Holstein steers (average body weight 299 kg; average starting weight 237 kg to average final weight 360 kg) fitted with rumen cannulae, were randomly allotted to a 4 • 4 latin square experiment. In the experiment four pelleted rations containing 10.7, 20.2, 32.5 and 40.0% protein (N • 6.25) (table 1) were fed to the steers in four, 14-day treatment periods. Each treatment period was preceeded by an t Michigan Agricultural Experiment Station Journal l 1-day adjustment period during which the Article No. 7448. steers were fed the low protein (10.7%) ration. 2 Ruminant Nutrition Laboratory, Department of The steers were housed indoors in 2.5 • .9 Animal Husbandry. m metal stalls. The steers had free access to 3Present address: Tennessee State University, water and were fed ad libitum twice daily at Nashville 37203. 1323 JOURNAL OF ANIMAL SCIENCE, Vol. 42, No. 5, 1976

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Michigan State University, East Lansing 48824

FENDERSON AND BERGEN

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TABLE 1. COMPOSITION OF PELLETED EXPERIMENTAL RATIONSa Rations 1

2

3

Oats, grain (4) 4-03-309 Sugarcane molasses, (5) 5-05-604 Corn, dent, yellow, grain, gr. 2 US mn wt 54 (4) 4-02-93 Soybean, seeds, solv-extd, grnd, mx 7% fiber (5) 5-04-604 Isolated soybean protein (70%) b Isolated soybean protein (90%) b Corn, cob, grnd, (1) 1-03-782 Limestone, grnd, mn 33% Calcium, (6) 6-02-632 c Trace mineral salt d,e Crude protein f

10.0 5.0

10.0 5.0

7.5 5.0

75.0

50.0

30.0

209

5.0 30.0 . . . . . . ... 2.0 " 2[0 1.0 1.0 2.0 2.0 10.7 20.2

32.5 20.0 2.0 1.0 2.0 32.5

22.5 30.0 10.0 2.0 1.0 2.0 40.0

39

3.6

919

112.0

9

7.5 5.0

Mcal/kg Calculated digestible energy

3.8

3.7 g/Mcal

Crude protein-digestible energy ratio

29.0

54.2

acontained per 454 kg: vitamin A palmitate (Pfizer Co., Terre Haute, Ind.), 1,000,0OO IU; ergocalciferol (Fleishmann irradiated yeast), 125,000 IU; and alpha tocopheryl acetate (Eastman Kodak, Rochester, N. Y.), 22,500 1U. bcentral Soya, Decatur, Indiana. CCalcium Carbonate Co., Quincy, Illinois. dContained in percent: Zn, mn .35 ; Mn, mn .2 ; Fe, mn .2 ; Mg, mn .15 ; Cu, mn .03 ; Co, mn .05 ; Iodine, nan .007; NaCI, mx 98.5. elntemational Mineral Co., Libertyville, Illinois. fAnalyzed with the micro Kjetdahl procedure using Cu as a catalyst.

12-hr intervals. U n c o n s u m e d feed was r e m o v e d before each feeding and weighted to q u a n t i t a t e daily feed intake. During each experimental period, b l o o d and r u m e n samples were collected before the morning feeding on days 1, 2, 3, 5, 7, 10 and 14. The blood samples were drawn f r o m the right jugular vein. Blood plasma and protein free filtrates were prepared and stored at - 7 0 C for urea-nitrogen and amino acid analyses, respectively (Bergen et al., 1973). The r u m e n samples (chilled on ice) were strained through 2 layers o f cheesecloth and the r u m e n liquor was frozen and stored at - 7 0 C. R u m e n a m m o n i a and plasma urea nitrogen concentrations were analyzed according to the microdiffusion procedure of C o n w a y (1950). Ration protein (N x 6.25) c o n t e n t was determ i n e d according to the m i c r o Kjeldahl procedure using Cu as catalyst. Results were analyzed by the analysis of variance p r o c e d u r e (Steel and

Torrie, 1960). Mean separation was achieved by Duncan's multiple range test (Steel and Torrie, 1960). All results in this study were analyzed on a t r e a t m e n t basis (protein level, ignoring time effects) and also within t r e a t m e n t s to evaluate time effects 9 The f o u r rations (table 1) were f o r m u l a t e d to contain four levels o f absorbable protein. Since a considerable p r o p o r t i o n of dietary soy protein bypasses ruminal degradation [anywhere f r o m 30% (Burroughs et al., 1975) to 60% (Hume, 1 9 7 4 ) ] , the i n c o r p o r a t i o n of incremental levels of soybean meal and soy isolates should result in the passage of various levels of absorbable nitrogen (amino acids) to the small intestine. Actual protein passage to the small intestine was not assessed in this s t u d y however. RESULTS

Feed

Intake and Feeding Behavior.

The

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Ingredients

EXCESS PROTEIN FOR STEERS

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TABLE 2. EFFECT OF DIETARY PROTEIN LEVEL ON DRY MATTER AND PROTEIN INTAKE IN STEERS a Rations 1

2

Dry matter Protein

9,0 1,0 b

8.4 1.7 bc

3

4

SEM

7.1 2.3 c

5.0 2.0 c

1.1 .2

kg/day

aMean daily intakes for the total 14-day period. b'CValues in the same row not sharing common superscript are different (P . 0 5 ) w i t h ration p r o t e i n c o u n t .

m a t t e r and p r o t e i n intake d r o p p e d precipitously ( P < . 0 5 ) for ration 4 on days 2 and 3 a n d the s u b s e q u e n t recovery in f e e d intake was m u c h slower t h a n for ration 3 and m a x i m u m intake was n o t r e a c h e d for the steers f e d ration 4 until day 14. Steers f e d rations 1 a n d 2 t e n d e d t o c o n s u m e a major p o r t i o n o f their feed i m m e d i ately after f e e d i n g and e x h i b i t e d " m e a l e a t i n g " behavior. The steers fed rations 3 and 4 did n o t c o n s u m e m u c h f e e d at any one time, but t e n d e d to eat small a m o u n t s n o w and t h e n and e x h i b i t e d " n i b b l i n g " f e e d i n g behavior.

The daily p a t t e r n s o f dry m a t t e r and p r o t e i n intake for each ration within 14-day periods are p r e s e n t e d in table 3. Protein and dry m a t t e r intake r e m a i n e d u n c h a n g e d for the low p r o t e i n ration (ration 1) t h r o u g h o u t t h e f e e d i n g period. For ration 2 t h e r e was a significant ( P < . 0 5 ) d r o p in dry m a t t e r and p r o t e i n intake on day 2 with a s u b s e q u e n t recovery by day 3. Protein and dry m a t t e r intake declined ( P < . 0 5 ) m a r k e d l y for ration 3 on days 2 and 3 with a s u b s e q u e n t intake recovery by day 5. Dry

Rumen A m m o n i a and Plasma Urea and Am i n o Acids. The mean overall results for r u m e n a m m o n i a and plasma urea and a m i n o acids c o n c e n t r a t i o n s are p r e s e n t e d in table 4. The stepwise elevation in ration p r o t e i n level caused significant ( P < . 0 5 ) increases in r u m i n a l a m m o n i a and plasma urea-nitrogen. Total plasma essential and n o n e s s e n t i a l a m i n o acid con-

TABLE 3. DAILY PATTERN OF DRY MATTER AND PROTEIN INTAKE IN STEERS a Days Parameter

1

2

3

5

7

10

14

SEM

kg/day Dry matter Ration 1 Ration 2 Ration 3 Ration 4

8.5 7.5 bc 7.7 c 5.7 cde

8.6 6.4 b 5.1 b 3.3 bc

8.8 7.5 bc 5.0 b 2.3 b

8.7 8.7 c 7.7 c 4.8 cd

9.3 9.5 c 7.8 c 5.3 cde

9.2 9.7 c 8.2 c 6.1 def

9.4 9.6 c 8.3 c 7.4 ef

.3 .3 .3 .3

Protein Ration Ration Ration Ration

.9 1.5 bc 2.5 c 2.3 c

.9 1.3 b 1.7 b 1,3 b

.9 1.5 bc 1.6 b .9 b

.9 1.8 bc 2.5 c 2.0 c

1.0 1.9 bc 2.5 c 2.1 c

1.0 2.0 c 2.7 c 2. 5cd

1.0 2.0 c 2.9 c 3.0 d

,1 ,1 ,1 .1

1 2 3 4

aEach value daily mean intake per steer. b'c'd'e'fvalues in the same row not sharing common superscript are different (P