DIGESTION AND UTILIZATION OF PROTEIN IN THE WEST AFRICAN DWARF SHEEP

Abstract

West African dwarf sheep maintained on Cynodon nlemfuensis/Centrosema pubescens hay and concentrate supplements were used to study intake and digestibility of dry matter and nitrogen metabolism. Levels of ruminal metabolites of nitrogenous origin and blood urea were examined on the rations fed to the sheep. [15N] ammonium chloride and [15N] urea were used to study the production of ammonia and its utilization in the rumen, and the flow of blood urea into the digestive tract. Shredded paper impregnated with chromic oxide was used to partition digestibility in the stomach and intestines of the sheep. The results for the West African dwarf sheep were compared with those of other breeds of sheep in intake and digestibility of organic matter and nitrogen metabolism. The intake of dry matter by the West African dwarf sheep was similar to that of other breeds when expressed per metabolic size. Nitrogen retention values were high and this shows that absorbed N was being utilized efficiently. The metabolic faecal N values of 3.0 to 3.7g N/kg dry matter intake and the endogenous urinary N value of 0.0238 g/day/WKg 0.734 were obtained for this class of livestock. The biological values of the rations ranged from 85.7 to 100.0%. The digestible crude protein requirement for maintenance over the experimental period was 0.74g/day/Wkg, 0.734 by the N balance mehod, and 0,22g/day/Wkg 0.734 by the factorial method. The levels of nitrogenous metabolites in the rumen varied with levels of dietary crude protein. Ruminal ammonia was highly correlated (r = 0.99) with blood urea. The amino acids present in lowest concentration in bacterial and protozoal protein are methionine and histidine while there are high levels of lysine and leucine. Isotopic studies with [15N] ammonium chloride and urea shows that 4-7% of [15N] ammonium chloride administered into the rumen was recovered in the faeces, and 3.1% was recovered in milk. Also 30.5% of [15N] urea administered into the blood was recovered in the urine and the isotope was not recovered in the faeces. Ruminal ammonia contributed 26 – 33% of the bacterial N and 15 – 19% of protozoal N ten hours after feeding. Urea was synthesized in the body at the rate of 9.4 to 10.1g/day, and 4.7 to 7.3g/day were degraded in the digestive tract of the sheep. The chromic oxide - impregnated paper method showed that 72.5% of digestible dry matter and 72.6% of digestive organic matter of the rations were digested in the stomach. The corresponding values for small intestine were 10.1% and 11.4% for dry matter and organic matter respectively, while in the ceacum and colon, the values were 17.5% and 16.0% for dry matter and organic matter respectively. Substantial amount of N of endogenous origin were secreted in the proximal small intestine but were efficiently absorbed before the distal portion was reached. The results show that the West African dwarf sheep utilize the hay and supplement rations efficiently and are adapted for survival in areas where the intake of N might be inadequate.