EFFECTS OF DIETARY MAGNESIUM EXCESS IN WHITE LEGHORN HENS

The effects of excess dietary magnesium on White Leghorn laying hens w ere investigated in two experiments and a third experiment looked at t he effect of dietary phosphorus on excess magnesium in the diet. In Ex periment 1, magnesium levels of 0.15, 0.8, and 1.2% were fed in a diet containing 2.5% calcium to hens 30 wk of age for 5 wk. A control diet with 3.5% calcium and 0.15% magnesium was also fed. In Experiment 2, hens 65 wk of age fed 3.5% calcium were fed dietary magnesium levels o f 0.15, 0.36, 0.53, 0.76, and 0.91% for 4 wk. In these two experiments , excess magnesium reduced egg production, decreased feed consumption, decreased body weight, decreased percentage eggshell, reduced plasma calcium, and increased plasma magnesium and tibia magnesium but change s seen in tibia weight, percentage ash, and tibia calcium and phosphor us were variable. More changes from feeding excess magnesium were seen in the young, high producing hens in Experiment I, In Experiment 3, h ens 50 wk of age were fed a marginal calcium level (2.5%) with an exce ss of magnesium (0.8%) and a control level of available phosphorus (0. 45%) and this was compared to a low (0.25%) and a high level (0.9%) of available phosphorus for a 4-wk experimental period. At the end of th e experimental period, hens fed low phosphorus had lower egg productio n and lower feed consumption than the hens fed higher levels of phosph orus. Body weight was lower in the hens fed the two lower levels of ph osphorus. Percentage eggshell was lower than the controls when fed low phosphorus and higher when fed high phosphorus. These results suggest that high phosphorus diets are better than low phosphorus diets when excess magnesium is fed to laying hens. Further study is needed to inv estigate the role of phosphorus when excess magnesium is fed.