Nutritive evaluation of grain Amaranth (Amaranthus spp.) in broiler chicken diets
Studies were carried out to determine the nutritive value of grain amaranth as a feed ingredient for broiler chickens and assess the extent to which it could replace maize in broiler diets. Three grain species were evaluated namely, Amaranthus cruentus L., Amaranthus hypochondriacus L. and Amaranthus caudatus L .. In the preliminary study, the chemical attributes of the grain were assessed. The average crude protein and metabolisable energy contents of the three grain species were 15.80% and 3310 kcal/kg, respectively. The mean lysine and sulphur amino acid levels were 0.78 and 0.67%, respectively. The mean tannin and trypsin inhibitor contents were 0.093% and 0.65 trypsin inhibitor units/mg, respectively. A. caudatus species had superior nutrient composition but contained the highest levels of antinutritional factors. In Experiment I, raw grain from each of the three species was incorporated in broiler starter diets at 20, 40 and 60% levels. Chick body weight and feed intake at four weeks of age declined (P<0.05) while pancreas weights increased with increasing levels of dietary amaranth. The 20% A. hypochondriacus diet however gave similar (P>0.05) chick performance to that of the maize-soyabean meal control diet. Upon thermal extrusion of grain amaranth in Experiment 2, chick performance markedly improved, with the 20 and 40% A. hypochondriacus and A. cruentus grain diets showing similar (P>0.05) body weight, feed intake and feed efficiency as the maize-soya bean meal control diet. In Experiment 3, inclusion of lysine, lysine plus methionine and casein in 40% raw and 60% thermal processed A. hypochondriacus diets showed similar (P>0.05) chick performance between the thermal processed amaranth diet containing casein and the maize-soya bean meal control diet. The latter diet however, resulted in higher (P<0.05) essential amino acid availability. Casein increased the levels of various essential amino acids in the amaranth diets. Chicks on thermal processed amaranth diets were heavier and consumed more feed than those on diets containing raw grain amaranth. The low zinc retention from all the diets indicated interference with absorption of this mineral. In Experiment 4, casein and ethylene diamine tetraacetate (EDTA) were separately added to 40% raw and 40% thermal processed A. hypochondriacus diets. Chicks on the processed amaranth diets gave higher (P<0.05) body weight, feed intake and nitrogen retention. Inclusion of EDTA in amaranth diets failed to increase (P>0.05) mineral retention but the tissue mineral content of chicks was adequate. In Experiment 5, 20 and 40% A. hypochondriacus diets with or without molasses were fed either as raw grain mash diets or in steam pelleted form. Chick body weight was higher (P<0.05) for the pelleted and maize control diets at 4 weeks of age. However, continued feeding up to 8 weeks of age resulted in similar (P>0.05) chick body weights for all the diets including the maize control. Pelleting improved (P<0.05) body weight and feed efficiency and increased (P<0.05) carcass fat but molasses inclusion had no ~ffect (P>0.05) on feed intake or body weight. Histopathological studies of chick organs did not show changes attributable to amaranth feeding. Growth depression in chicks fed on raw amaranth diets mainly resul ted from reduced feed intake accompanied by low protein digestibili ty. Raw and thermal processed A. hypochondriacus grain can effectively replace maize up to 20 and 40% of broiler starter diets, respectively.