Estimation by calcium analysis of the proportion of grass in oesophageal fistula samples from cattle grazing grass-stylo pastures

Abstract

Variation in calcium (Ca) concentration in tropical grasses and Stylosanthes species growing in paddocks with and without superphosphate fertilizer was examined at six intervals over one year on whole plant tops and on hand-plucked samples. Variation in Ca concentration between plant parts was also measured on one sampling date. Extrusa samples obtained from cattle fitted with oesophageal fistulae in two grazing experiments were used to examine the relation between the Ca concentration and the botanical composition determined by the microscope-hit method. The concentration of Ca was 2.2 to 5.2 times greater in legumes than in grasses. While it decreased in legumes with increasing plant maturity, it remained relatively constant in the grasses, especially in those receiving fertilizer. Calcium concentration did not vary greatly between plant parts in the grasses, but the legume stems had lower (0.77 per cent Ca) concentrations than legume leaves (1.58 per cent Ca). The relationships found in the two grazing experiments did not differ, and the resulting combined equation describing it was : y = 128.4 - 82.0x (n = 40; r2 = 0.822; S y . x = 12.6) where y = per cent grass and x = per cent Ca.