HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Atkinson, R. L. Articles by Ludden, P. A. PubMed PubMed Citation Articles by Atkinson, R. L. Articles by Ludden, P. A.

Effects of ruminal protein degradability and frequency of supplementation on nitrogen retention, apparent digestibility, and nutrient flux across visceral tissues in lambs fed low-quality forage

R. L. Atkinson^*, C. D. Toone^*, T. J. Robinson^*, D. L. Harmon and P. A. Ludden^*

^* Department of Animal Science, University of Wyoming, Laramie 82071 Department of Animal & Food Sciences, University of Kentucky, Lexington 40546

ludden{at}uwyo.edu

Abstract

Two experiments were conducted to determine the effect of ruminal protein degradability and supplementation frequency on intake, apparent digestibility, N retention, and nutrient flux across visceral tissues of lambs fed a low-quality forage diet. In both experiments, wethers were fed a basal diet of mature crested wheatgrass hay (4.2% CP) for ad libitum consumption plus 1 of 4 supplements: 1) a high ruminally degradable protein (RDP) supplement provided daily (RDP-D), 2) the high RDP supplement provided on alternate d (RDP-A), 3) a high ruminally undegradable supplement (RUP) provided on alternate d (RUP-A), or 4) a 50:50 mixture of the RDP and RUP supplements provided on alternate d (MIX-A). In Exp. 1, 12 lambs (29.9 ± 2.7 kg initial BW) were used. Forage OM, NDF, and ADF intake were not affected by treatment. Total tract digestibilities (OM, NDF, ADF, and N) were unaffected by treatment. Neither protein degradability nor supplementation frequency had an effect on N retention. In Exp. 2, 15 lambs (34 ± 4 kg initial BW) fitted with indwelling catheters were used. Release of ammonia N by the portal-drained viscera (PDV) was reduced (P = 0.004) in alternate day supplemented lambs compared with RDP-D. Consequently, hepatic uptake of ammonia N was least (P = 0.003) in all alternate-day lambs. Alpha-amino nitrogen (AAN) release by the PDV and hepatic uptake of AAN were not affected by treatment or supplementation frequency. Additionally, hepatic output and PDV uptake of urea N were not affected by treatment. Hepatic N uptake (ammonia N + AAN) accounted for urea synthesized by the liver in all treatments; however, hepatic urea synthesis was approximately 4.5 fold less for RUP-A lambs. This suggests that the provision of amino acids as RUP may provide a delay in ureagenesis, thus altering the timing of N recycling.

Key Words: lambs • low-quality forage • protein degradability • nitrogen balance • nitrogen recycling • nutrient flux