Abstract:
EFFECT OF TWO SOURCES OF FAT ON DIGESTION IN SHEEP FED ROUGHAGE DIETS M. van Houtert and J.V. Nolan Fat, a dense source of energy, offers potential as a supplementarv feed to improve productivitva. of ruminants consuming high-fibre roughages. -4 level of fat in roughage diets of more than Z&-3%, however, generally results in a decreased fibre digestibilit,y in the rumen (Palmquist 1988). Calcium salts of long chain fatty acids (CaLCFA) and fat, prills are considered to be ruminally inert.. ln sheep fed straw-based diets, supplementation with CaLCFA increased live-weight, gain ( LWG), whereas supplementation with fat, prills only increased LW G when fed together with a protein meal (Van Houtert. and Leng 1986, 19~7). Mature rumen-cannulated sheep were offered a roughage-based diets with CaLCFA or fat prills to enable comparison of their effects on digest,ion. In Exp.1, sheep were offered a rice straw-based diet for 6 weeks with 0 (n=5) or 45 (n=4) g/d CaLCFA. In Exp 2, four groups of four sheep were offered an oaten chaff- based diet for 5 weeks, supplemented with fat prills (F`) and/or formaldehyde- treated cottonseed meal (C; see Table). Measurements of in vivo and in sacco digestibility of straw (Exp.1) or oat,en chaff (Exp.2), concentrations of NHs-N and volatile fatty acids (VF,4) and numbers of protozoa in rumen fluid were made. Supplementation with CaLCF,4 tended to increase in vivo DM digestibility, but had little effect on in succo degradability, nor feed intake nor on metabolite concentrations in rumen fluid. Numbers of protozoa in rumen fluid were depressed. Supplementation with fat prills depressed feed intake in the absence, but not in the presence of protein meal in the diet, reduced digestibility, both in vivo and in sacco and resulted in a higher ratio of propionate to acetate in rumen Auid VFA; concentration of NHa-N and numbers of protozoa in rumen fluid varied widely but not significantly between diets. Fat prills, in contrast to CaLCFA, cannot be regarded as a run-&ally inert source of LCFA for sheep offered roughage-based diets. PALMQUIST! D.L. (1988). In Feed S cience, p.293 [E.R.Brskov, ed.] Amsterdam: Elsevier Science Publishers. VAN HOUTERT, M. & LENG, R.A. (1986). In R ice Straw and Related Feeds in Ruminant Rations, p.282 [M.N.M. Ibrahim and J.B. Schiere: editors 3. Wageningen: Agricultural University. VAN HOUTERT, Mr & LENG, R.A. (1987). In R ecent Advances in Animal Nutrition in AustruZiu, p.3a [D.J.Farrell ed.] Armidale: University of sew England. tDept. of Biochemistry, Microbiology and Nutrition, University of New England, Armidale NSW 2351, Australia. . 30A