CONTRIBUTION OF DIETARY PURINE-BASES TO DUODENAL DIGESTA IN SHEEP - IN-SITU STUDIES OF PURINE DEGRADABILITY CORRECTED FOR MICROBIAL-CONTAMINATION

The dietary contribution of purine bases (PB) to duodenal flow was eva luated by the in situ method after correcting for microbial contaminat ion using N-15 as microbial marker and rumen solid associated bacteria as reference sample. Four ruminally fistulated sheep were offered at 4 h intervals a mixed diet 2:1 vetch-oat hay:concentrate, and 179 mg o f (((NH4)-N-15)(2)SO4) were continuously infused in the rumen during a minimum of 5 days prior to incubation and rumen sampling. The followi ng feeds were tested: meat meal (MM), fish meal (FM), gluten feed (GF) , barley grain (BG), corn grain (CG), sunflower meal (SFM), soya bean meal (SBM), dry brewery distilled grain (DBDG), alfalfa hay (AH) and b arley straw (BS). The largest residual proportion of microbial purine bases was found in BS followed by AH, CG, BG, DBDG, GF, SFM, MM, SBM a nd FM, in that order, For all feeds, the extent of degradation of diet ary purine bases at the studied fractional outflow rates increased aft er the correction for microbial contamination. Apparent and true degra dability were significantly different (P < 0.05) in DBDG, CG, AH, GF a nd MM, ranging the feeds in that descending order; whereas they did no t differ in BG, SBM, SFM and FM, Correction for contamination of feeds by microbial purine bases did not substantially affect the proportion of dietary purines escaping ruminal degradation ranging from 5 to 17% for AH, BG, GF, SFM, CG, from 11 to 23% for MM, SBM and from 20 to 40 % for FM and DBDG when fractional rates of outflow from the rumen of 0 .02-0.08 were assumed.