Purine derivative excretion and ruminal microbial yield in growing lambs fed raw and dry roasted legume seeds as protein supplements

Urinary excretion of purine derivatives was used to estimate the microbial N supply to growing lambs in an experiment designed to examine the effect of raw and dry roasting whole lupin (lupinus angustifolius) seeds (WLS) and whole faba (vicia faba) beans (WFB) as protein supplements. Lambs were fed a fixed quantity of oat straw and alfalfa hay plus a daily legume seeds of either of the following: no legume seeds (CTRL), raw WLS, roasted WLS, raw WFB, or roasted WFB. Legume seeds were dry roasted at 150 °C for 45 min. Diets were isonitrogenous 15.9% CP. In supplemented diets, about 55% of protein was supplied by WLS or WFB protein. Excretions of the purine derivative allantoin, uric acid plus hypoxanthine and xanthine, were measured after total urine collection during an N balance trial to estimate microbial N supply to the duodenum. Lambs fed the five dietary treatments with similar total DM (1158 g per day) and CP intakes (185 g per day), but different UDP (rumen undegraded feed protein, from 57 to 106 g per day), DVE (truly digested protein in the small intestine, from 46 to 91 g per day) and OEB (degraded protein balance, from 3 to 45 g per day) values differed (P<0.05) in urinary excretion of uric acid plus hypoxanthine plus xanthine (1.7 in CTRL versus 2.7 mmol per day in supplemented groups) but did not differ in urinary excretion of allantoin (average: 10.5 mmol per day), total purine derivatives (average: 13.0 mmol per day), total purine derivatives absorption (average: 15.4 mmol per day), microbial CP supply (average: 69.8 g CP per day) to the duodenum and efficiency of microbial synthesis (average: 23.7 g of N/kg DOMR (digestible OM fermented in the rumen)) to growing lambs. Dry roasting and supplementation of WLS and WFB did not affect flow of microbial N into the duodenum.