Influence of increasing dietary calcium and magnesium levels on performance, mineral metabolism, and egg mineral content of laying hens

The effects of increasing dietary magnesium level from .17 to .77% and calcium level from 3 to 4.2% for laying hens over a 7-week period was investigated. Increasing either dietary magnesium or calcium level had no significant effect (P greater than .05) on feed consumption, egg production, egg weight, or egg shell deformation. Increasing dietary magnesium level had no significant effect on calcium retention, although there was a significant (P less than .01) reduction in the percentage of magnesium retained. Egg shell calcium content was significantly (P less than .01) reduced and shell magnesium significantly (P less than .05) increased in response to increase in dietary magnesium content. Increasing dietary magnesium level also significantly (P less than .01) reduced bone calcium and zinc contents while concomitantly increasing bone magnesium levels. Bone ash and calcium were significantly (P less than .05) increased and bone magnesium reduced when the calcium content of the diet was increased. Plasma calcium was significantly (P less than .01) increased in dietary calcium level and significantly decreased with increased dietary magnesium. The converse was true for plasma magnesium in response to increases in dietary calcium and magnesium. Significant positive correlations were observed between mineral contents of diet and bone, bone and plasma, and plasma and shell. A negative correlation was observed between shell magnesium level and egg shell quality as assessed by deformation. An antagonistic relationship seems to exist between calcium and magnesium, and this is discussed in relation to skeletal integrity and egg shell quality.