EFFECT OF STAGE OF MATURITY AND FORAGE BOTANICAL COMPOSITION AT ENSILAGE ON NUTRITIVE VALUE OF COLUMBUS GRASS (SORGHUM ALMUM) SILAGE

Abstract:

A study was conducted on field grown columbus grass (Sorghum almum)at the National Animal Production Research Institute (NAPRI), Shika, Ahmadu Bello University, Zaria, Nigeria during the rainy season of 1992. The objective of the trial was to determine the ensiling characteristics of the forage at five maturity stages and evaluate the nutritive potentials of the resultant silages in ruminant feeding systems. Forage sown on 30th July, 1992 was harvested at pasture stages of 50, 60, 70, 80, and 90 days post-planting and ensiled fresh in laboratory silos. Following an incubation period of 21 days the resultant silage was scored for colour and aroma. The pH was determined and sample analyzed for nutrient constituents. The forage declined in moisture content (85.1 to 54.6%) and leafiness (46.0 to 26.0%) with time to maturity. Bloom content and fodder yield rose (10.3 to 95.1% and 1.3-8.40t DM/ha) with time to maturity. Fodder accumulation was rapid with mean daily increment of 177.0kg DM/ha within the growing period. Forage materials at all phenological stages resulted in satisfactory silages with agreeable colour and aroma. The materials consolidated well and fermentation was complete with moderately acidic pH values (4.6 to 4.1) . The HCN concentration was low and declined with stage of maturity (244.0 to 183.0 mg HCN/kg DM) . Plant factors favouring digestibility such as CP, EE and carotene declined with stage of maturity, while structural constituents (NDF and ADF) showed positive relations. Silages of the late vegetative to the hard dough stages declined in contents of N, P, K, Na and Fe. There was no consistent trend in concentrations of Ca, Mg and Cu, while the concentration of the Mn was fairly constant. Based on ruminant nutritional standards the nutrient composition of the silages are apparently sufficient in supplying the requirement of N, Ca, Mg, Mn, Fe, Cu and carotene for production. The silages are deficient in P and border-line in Na concentration. Results in this study indicate that satisfactory silages were obtained from columbus grass (S. almum) at varying phenological stages from the late vegetative to the hard dough stages (i.e., 50 to 90 days post-planting) . As a compromise between fodder yield and nutritional quality, the soft dough stage (ca 80 days post-planting) is recommended as the optimum stage of harvesting the forage material for ensiling. Such silage could however be deficient in N, P, and Na relative to the requirements of ruminant for productive functions. Supplementation of these nutrients may thus be essential. Animal studies involving feeding trials are advocated to elucidate and further define the limits of the S. almum silage in ruminant feeding systems.