PREDICTION OF VOLUNTARY DRY-MATTER INTAKE, DIGESTIBLE DRY-MATTER INTAKE AND GROWTH-RATE OF CATTLE FROM THE DEGRADATION CHARACTERISTICS OF TROPICAL FOODS

An experiment using twenty-five bulls aged between 1 and 1.5 years and weighing 117 to 209 kg was carried out to estimate voluntary dry-matter intake (DMI), digestible dry-matter intake (DDMI), dry-matter apparent digestibility (DMD) and growth rate when the bulls were given 18 foods available from smallholder dairy farms on the slopes of Mount Kilimanjaro, Tanzania. The animals were randomly allocated to five groups of five animals each. Foods were then randomly allocated to the five groups for four periods of 60 days each during which DMI was measured. A digestion trial was made at the completion of each measurement. Outflow rates of solids from the rumen were determined by giving the animals 200 g Cr-mordanted fibre of each food and grab faecal samples were obtained. Dry matter (DM) degradation characteristics of the foods were determined in sacco in the rumen of three Boran steers fed on guatemala grass and the water soluble fraction (A) was measured. DMI varied from 2.2 kg for banana pseudostem to 4.77 kg/day for urea-treated maize stover. DMD ranged from 549 for untreated maize stover to 767 g/kg DM for banana pseudostem and growth rate ranged from 72 for banana leaves to 275 g/day for urea-treated maize stover. Potential degradability (defined by A + B) (where B is the insoluble fraction degradable with time) for the DM ranged from 617 g for banana leaves to 874 g/kg DM for banana pseudostem and the degradation rate (c) ranged from 0.0168 for banana leaves to 0.0440 per h for green maize stover. The separate use of degradation characteristics A, B and c in multiple regression to predict DMI, DDMI, and growth rates gave better results than when A + B or (A + B) + c were used. Multiple correlation coefficients between degradation characteristics and DMI, DDMI and group rate were r = 0.90, 0.93 and 0.93 respectively. The results indicate that DMI, DDMI and growth rates by cattle fed on crop residues and forages could be predicted well using the rumen degradation characteristics of the foods.