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ARS Home » Plains Area » Mandan, North Dakota » Northern Great Plains Research Laboratory » Research » Publications at this Location » Publication #182120
Title: SUPPLEMENTING A RUMINALLY UNDEGRADABLE PROTEIN SUPPLEMENT TO MAINTAIN ESSENTIAL AMINO ACID SUPPLY TO THE SMALL INTESTINE WHEN FORAGE INTAKE IS RESTRICTED IN BEEF CATTLE

Author
item Scholljegerdes, Eric
item WESTON, TERRILL - UNIVERSITY OF WYOMING
item LUDDEN, PAUL - UNIVERSITY OF WYOMING
item HESS, BRET - UNIVERSITY OF WYOMING

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/26/2005
Publication Date: 9/8/2005
Citation: Scholljegerdes, E.J., Weston, T.R., Ludden, P.A., Hess, B.W. 2005. Supplementing a ruminally undegradable protein supplement to maintain essential amino acid supply to the small intestine when forage intake is restricted in beef cattle. Journal of Animal Science, 83:2151-2161.

Interpretive Summary: Studies evaluating nutrition-reproduction interactions in ruminants often use restricted feed intake to limit the supply of dietary energy. One problem inherent with this approach is that the quantity of microbial protein reaching the small intestine decreases when dietary energy is reduced. Therefore, supply of energy and protein are confounded. One must supply an equal amount of protein and/or essential amino acids to the small intestine across forage intake levels to properly separate the effects of dietary energy and protein on reproduction. Therefore, we fed 12 Angus crossbred cattle fitted with ruminal and intestinal cannulas restricted amounts of forage plus a supplement that is not readily degraded in the rumen, which should supply extra amino acids to the small intestine. We found that balancing the supply of essential amino acids to the intestine of beef cattle consuming restricted amounts of forage can be accomplished by providing a ruminally undegradable protein supplement. However, appropriate adjustments must be made to account for the more extensive ruminal degradation of supplemental protein that occurs when intake is restricted. Therefore, this approach to balancing essential amino acid supply to the small intestine should prove useful as an experimental model to avoid confounding effects of energy with protein status on the physiology of ruminants.

Technical Abstract: Twelve Angus crossbred cattle (8 heifers and 4 steers; average initial BW = 594 +/- 44.4 kg) fitted with ruminal and duodenal cannulas and fed restricted amounts of forage plus a ruminally undegradable protein (RUP) supplement were used in a triplicated 4 × 4 Latin square design experiment to determine intestinal supply of essential AA. Cattle were fed four different levels of chopped (2.54 cm) bromegrass hay (11.4% CP, 57% NDF; OM basis): 30; 55; 80; or 105% of the forage intake required for maintenance. Cattle fed below maintenance were given specified amounts of a RUP supplement (6.8% porcine blood meal, 24.5% hydrolyzed feather meal, and 68.7% menhaden fish meal; DM basis) in an effort to provide duodenal essential AA flow equal to that of cattle fed forage at 105% of maintenance. Experimental periods lasted 21 d (17 d for adaptation followed by 4 d of sampling). Total OM intake and duodenal OM flow increased (linear, P < 0.001) as cattle consumed more forage. However, OM truly digested in the rumen (% of intake) did not change (P = 0.43) as intake increased. True ruminal N degradation (% of intake) tended (linear, P = 0.07) to increase linearly and true ruminal N degradation (g/d) decreased quadratically (P = 0.02) as intake increased from 30 to 105%. Duodenal N flow was equal (P = 0.33) across intake levels even though microbial N flow increased (linear, P < 0.001) as forage OM intake increased. Total and individual essential AA intake decreased (cubic, P < 0.001) as forage intake increased because the supply of non-ammonia non-microbial N flow from RUP was decreased (linear, P < 0.001) by design. Total duodenal flow of essential AA did not differ (P = 0.39) across these levels of forage intake. Although the profile of essential AA reaching the duodenum differed (P 0.02) for all 10 essential AA, the range of each essential AA, as a proportion of total essential AA, was low, being 11.1 to 11.2% of total essential AA for phenylalanine to 12.3 to 14.3% of total essential AA for lysine. Duodenal essential AA flow did not differ (P = 0.10 to 0.65) with forage intake level for 8 of the 10 essential AA; duodenal flow of arginine decreased linearly (P = 0.01) whereas duodenal flow of tryptophan increased linearly (P = 0.002) as forage intake increased from 30 to 105% of maintenance. Balancing intestinal essential AA supply in beef cattle can be accomplished by varying intake of a RUP supplement.