Abstracts Biological Sciences

The effect of genotype, drying conditions and microbial enzyme supplementation of the nutritive value of hybrid and open pollinated maize grain for broiler feeding.

by Kwazi Cyril Khumalo

Three experiments were conducted to examine the effects of tannin inclusion in the diet; heat treatment of maize; and maize genotype and sex of broilers; on the nutritive value of maize-soyabean based diets, as affected by dietary enzyme supplementation. In Experiment 1, six hundred day-old Ross male chicks were given 5 main diets. The 5 main diets were based on hybrid yellow maize and a commercial soyabean concentrate and supplemented with tannin at 0, 5, 15, 20 or 25 g/kg. In addition each diet was either supplemented with Avizyme 1502 (Finnfeeds International, UK) at 1 g/kg diet, or not. The birds were given experimental feed from day one to day 22 and the experiment was a completely randomised design with 5x2 factorial arrangement of treatments, and 6 replicates. The inclusion of tannin in the diet significantly reduced feed intake (P<O.OOO), weight gain (P<O.OOO) and feed conversion efficiency. The feed conversion efficiency followed a curvilinear response to dietary tannin level, from a low at the lowest tannin level, to a peak at tannin level of between 10 and 15 g!kg , whereafter it started declining with further increase in dietary tannin. Tannin inclusion also significantly reduced the digestibility of protein (P<O.OI), gross energy (P<0.05), and phosphorus (P<0.05). A similar trend was seen in terms of ileal digestibility of amino acids. The jejunum tissue protein was significantly reduced due to tannin inclusion in the diet. The activity of the digestive enzymes was not significantly affected by tannin inclusion in the diet. Avizyme 1502 supplementation in the diet significantly (P<0.05) improved weight gain of the birds. There was a non-significant increase in the food intake and feed conversion efficiency of broilers on diets containing tannin, due to Avizyme 1502 supplementation. Avizyme 1502 did not have a significant effect on tissue protein content, activity of the digestive enzymes (except for alkaline phosphatase, of which the activity was significantly (P<0.05) reduced due to enzyme addition), nutrient digestibility (protein, gross energy, phosphorus and calcium) and amino acid digestibility in this experiment. In Experiment 2, three hundred and twenty day-old Ross male chicks were given four main diets. The four main diets were based on a commercial soyabean concentrate and hybrid yellow maize that was sun-dried (control) or oven-dried at temperatures of 85°C, 95°C or 105°C. The oven-dried maize were dried for 24 hours. Each diet was in addition either supplemented with Avizyme 1502 at 1 g/kg diet, or was left without the Avizyme supplement. The birds were given experimental feed from day one to day 28 and the experiment was a completely randomised design with 4x2 factorial arrangement of treatments, and six replicates. Heat treatment of maize significantly (P<0.05) improved food intake and feed conversion efficiency. Above a drying temperature of 95°C, heat negatively affected these variables. The digestibility of phosphorus and calcium were also improved by heat treatment of maize. Heat did…