The influence of herbage mass on the calcium and magnesium content of diets selected by sheep and calves: A dissertation submitted in partial fulfilment of the requirements for the degree of Bachelor of Agricultural Science in the University of Canterbury

Abstract

A grazing trial was run on a ryegrass/white clover swazd. Four herbage masses were offered (1800 - 5100 kg DM.ha⁻¹), to two animal species, calves and lambs. Oesophageal fistular bolus samples were·taken for two daily intervals for 4 sampling periods. Bolus samples were dissected into leaf, stem and dead material before being analysed for Ca and Mg concentrations. Pregrazing sward cuts were analysised in a similar way. Results show there was a significant decline in magnesium concentration in the diets of sheep (9%) and calves (33%) with increasing herbage mass on offer. This was related to lower concentrations of magnesium in the sward at the higher herbage masses and the diet selection of the animals over the range of herbage masses. Calcium concentrations of dietary intake was affected by the clover content in the diet. Both Ca in the diet selected and clover % eaten increased with progressive time on the sward for calves whereas the calcium content of the diet selected and clover proportion decline with time on the sward for sheep. Dietary mineral concentrations and intake data have been used to calculate daily mineral intakes and these have been compared to A.R.C. suggested requirements. On this basis calves feeding on a herbage mass of 5000 kg DM.ha⁻¹ have insufficient magnesium and calcium intakes.