Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/16/1998
Publication Date: N/A
Interpretive Summary: For cattle consuming high-grain diets, an optimal amount of ruminally degraded nitrogen can be fed which will enhance fermentation in the rumen, increase amino acid flow to the duodenum, and increase net portal appearance of amino acids without affecting energy use by the portal- drained viscera. When the ruminally degraded nitrogen requirement has been nmet, no further benefit to additional ruminally degraded nitrogen will be observed. Feeding ruminally degraded nitrogen and escape protein may increase amino acid absorption when compared with feeding ruminally degraded nitrogen alone at the same level of crude protein. However, exceeding the crude protein requirement may result in increased nitrogen excretion because of lower nitrogen recycling to the portal-drained viscera when ruminally degraded nitrogen and escape protein are fed.
Technical Abstract: Seven MARC III heifers fitted with hepatic portal, mesenteric venous, and carotid catheters, and an abomasal cannula were used in a 7 x 5 incomplete Latin square design experiment. The objective was to evaluate the effects of increasing levels of ruminally degradable N (RDN) with or without the addition of abomasally infused casein on portal-drained viscera (PDV) flux of nutrients. Treatments consisted of dietary CP percentage levels of 9.5 (control), control plus .72% dietary urea (11.5U), control plus 1.44% dietary urea (13.5U), control plus abomasally infused casein (250 g/d; 11.5C, or control plus .72% dietary urea and abomasally infused casein (250 g/d; 13.5UC). All diets contained (DM basis) 80% ground corn, 15% corn silage, and 5% dry supplement, and were provided ad libitum. Nitrogen intake increased (linear, P<.001) as CP increased from 9.5 to 13.5%. Portal-drained visceral release of ammonia N increased (linear, P<.10) as RDN increased, and was greater (P<.05) when protein was fed compared to heifers fed control (P<.10). Urea N removal by PDV was not affected (P>.10) by level of RDN, but was greatest when 11.5C was fed and least when 13.5UC was fed. Net alpha- amino N (AAN) release by PDV was greatest when 13.5UC was fed (309 mmol/h), least when 9.5% CP was fed (112 mmol/h) and intermediate for the other groups (205 to 252 mmol/h). These data suggest that removal of N by the PDV may promote microbial protein synthesis when dietary RDN is low. When RDN needs have been met and amino acids are deficient for the host, escape protein should be fed to increase amino acid absorption.