Estimation of microbial protein synthesis efficiency in sheep using purine nitrogen index and nitrogen capture efficiency

Abstract

An experiment was conducted to evaluate the efficiency of utilization of rumen degradable nitrogen (RDN) for optimum microbial protein synthesis in sheep by the use of possible potential parameters such as purine nitrogen index (PNI) and nitrogen capture efficiency (NCE), which was estimated from purine derivatives excretion in spot urine samples. Sheep (36) were divided into 4 groups of 9 each and the animals in all groups were fed finger millet straw (FMS) as a basal diet and groundnut cake (GNC) as a nitrogen source. The animals in group 1(G1) were fed with ad lib. FMS. Animals in groups 2, 3 and 4 (G2, G3 and G4) were offered GNC@ 14, 18, and 23 g RDN/kg digestible organic matter (DOM) along with FMS. The experimental feeding was continued for 1 month followed by a metabolism trial of 7days. A total of 4 spot urine samples from each sheep were collected at 6 h intervals each day during last week of 1 month feeding period. The total purine derivatives (mmol/litre) excretion and purine derivatives; creatinine (PDC) index recorded were 17.52 and 38.07; 20.53 and 50.09; 24.30 and 51.10 and 18.65 and 39.17, respectively in G1, 2, 3 and 4, respectively. The microbial purine absorption, the calculated microbial nitrogen (MN) supply (g/d) was comparable among the RDN supplemented groups (G2, G3 and G4). PNI and NCE values recorded were 0.19 and 1.40; 0.19 and 1.05and 0.13 and 0.62, respectively in G2, G3 and G4. The results indicated that 14 g RDN from GNC may be adequate for optimum microbial protein synthesis in sheep fed on FMS based diet. Further, PNI and NCE estimated in spot urine of sheep fed ad lib. appeared to be useful in evaluation of ruminant diets.