Mineral composition of tropical forages and metabolic blood profiles of grazing cattle and sheep on calcium-dominated Caribbean soils
AbstractGrass sand legume species were analysed for mineral composition and blood was obtained for blood profiling from cattle and sheep grazing virgin pasture on a Ca-dominated limestone soil. The land upon which the forages were grown was in native forest, and had not previously been used for animal production. Fertilizer containing additional Mg, Mn, B and Cu was used to supply 107 kg N, 105.1 kg P and 88.9 kg K at planting. Annual dressings of 336 kg N, 146.6 kg P and 195.1 kg K/ha were applied to pure grass stands but without N to grasslegume mixtures. The mineral content of the legume (glycine, Glycine wightii; siratro. Macroptilium atropurpureum; greenleaf desmodium, Desmodium intortum: centro, Centrosema pubescens; alfalfa, Medicago sativa) ranged from 1.83 to 2.75 per cent Ca, 1.10 to 3.05 per cent K, and 0.36 to 0.59 per cent Mg. Ca/P ratio for legumes were high, ranging from 6.8 to 9.5, whereas those for Guinea grass (Panicum maximum) ranged from 2.1 to 3.2. Legume species were also high in phosphorus and iron. Selenium levels were deficient and Cu and Mo levels were high for both grass and legume species, with the exception of a relatively low Mo content for siratro. The Cu:Mo ratio ranged from a critically low 3.6 for guinea grass to 30.4 for siratro: S contents ranged from 0.13 to 0.33 per cent for non-irrigated Guinea grass and alfalfa, respectively. Circulating blood component levels of cattle and sheep were comparable to those of healthy, productive animals maintained on established grass land in temperate areas. However, post-mortem analyses of both calf and sheep liver tissue confirmed the Se deficiency and Cu toxicity indicated by analyses of the forage.