Effect of dietary protein degradability on microbial protein supply to the Small intestine of sheep

D. S. DJOUVINOV

Thracian University, Faculty of Veterinary Medicine, BG-6000 Stara Zagora, Bulgaria

Abstract

DJOUVINOV, D.S., 1999. Effect of dietary protein degradability on microbial protein supply to the small intestine of sheep. Bulg. J. Agric. Sci., 5: 435-441

Eight castrated male lambs were fed three experimental diets at two levels according to a balanced changeover design. The diets differed in the proportions of quickly (QDN), slowly (SDN) and digestible undegradable nitrogen (DUN) of total N (diets Q, S and U, respectively), and in rumen degradable N (RDN):fermentable metabolizable energy (FME) ratio. Microbial N (MN) supply to the small intestine was estimated from the purine derivatives excretion in urine. Daily amounts of MN were significantly affected by the feeding level, but not by the diet. The efficiency of utilisation of effective rumen degradable N (ERDN) for MN synthesis was 0.51, 0.95 and 0.46 for diets Q, S and U, respecitively. The value of 0.51 for diet with high QDN content was lower than the AFRC prediction of 0.8. Diet S (synchronised for SDN and FME) confirmed the assumption that SDN can be incorporated into MN with efficiency 1.0. Feeding diet U led to reduction in food intake and digestibility in the sheep, most likely due to their inability to sustain the microbial activity in the rumen. This in turn, suggests the limited capacity of sheep to recycle endogenous N which seems to be lower compared to the value adopted by AFRC (1993).

Key words: protein degradability, dry matter intake, digestibility, purine derivatives, microbial nitrogen.
Abbreviations: ADIN = acid detergent insoluble nitrogen, AOMD = apparent organic matter digestibility, CP = crude protein, DM = dry matter, DUN = digestible undegradable nitrogen, ED = effective degradability, ERDN = effective rumen degradable nitrogen, FME = fermentable metabolizable energy, LW = live weight, ME = metabolizable energy, MN = microbial nitrogen, N = nitrogen, NDF = neutral detergent fibre, QDN = quickly degradable N, RDN = rumen degradable N, SDN = slowly degradable N.