The efficacy of a high magnesium grass cultivar in controlling hypomagnesaemia in grazing animals

A cultivar of Italian ryegrass (Bb 2067), specifically bred for high magnesium content, was assessed for its efficacy in alleviating the incidence of hypomagnesaemia in lactating ewes. Pasture and animal management was regulated to maximize the potential for the development of hypomagnesaemia. The incidence of clinical hypomagnesaemia in ewes grazing the control pasture (cv. RvP) was 21% within the first 10 days and this was accompanied by a significant fall of 35% in serum magnesium concentration. The incidence in ewes grazing the high magnesium cultivar was only 2·5% and there was no significant change in the serum magnesium concentration. The mean magnesium content of Bb 2067 herbage (1·45 gkg DM-1) was 48% higher than cv. RvP (0·93 g kg DM-1) while calcium and phosphorus were 15% and 30% higher. The mean dry matter intake of ewes grazing Bb 2067 was higher than that of ewes grazing RvP, and although the difference was not statistically significant there were significantly increased intakes of magnesium, calcium and phosphorus for ewes grazing Bb 2067 compared with RvP. Ewes grazing Bb 2067 ingested more than the recommended allowance of magnesium and were close to sufficiency for calcium and phosphorus, while those grazing RvP were in serious deficit for all three minerals. There was no significant difference in the ewe body weight loss between the treatments but lamb liveweight gain was significantly greater on the Bb 2067 pastures compared with those on cv. RvP. It was concluded that the high magnesium grass provided an effective means of controlling hypomagnesaemia under grazing despite the extreme predisposing conditions imposed in this trial.