25-hydroxycholecalciferol-1-hydroxylase activity in heat stressed laying hens.

The activity of 25-hydroxycholecalciferol-1-hydroxylase was assayed in heat stressed laying hens fed a 3.5% calcium diet with either .625% or .925% phosphorus. The activity of this enzyme in the heat stressed birds was higher than in the control birds (P less than or equal to .07). The phosphorus content of the diets had no effect on enzyme activity.