EFFECT OF CONCENTRATION OF MIXED-FUNCTION OXIDASE ON CONCENTRATION OFESTROGEN, RATE OF EGG LAY, EGGSHELL THICKNESS, AND PLASMA CALCIUM IN LAYING HENS

The objective of this study was to investigate the effect of induction or depression of mixed-function oxidases (MFO) by xenobiotics on the peripheral concentration of estrogens, plasma Ca, rate of egg lay, and eggshell thickness in laying hens. In Exp. 1, 100 mg of phenobarbital (PB) administered orally each day for 3 or 7 d reduced concentrations of estrone and estradiol (E2) in serum. In Exp. 2, 25, 50, or 100 mg of PB was administered orally to laying hens for 3 or 7 d. Treatment w ith 100 mg of PB for 3 d or with 25, 50, or 100 mg for 7 d significant ly increased liver:body weight ratios. Microsomal protein increased af ter 7 d of 50 or 100 mg of PB administration. Feeding PB decreased con centration of E2 and total plasma Ca in a dose- and period-dependent m anner. Concentration of E2 was reduced to 10% of control, whereas hepa tic cytochrome P-450 increased significantly with dose. The correlatio n between concentration of E2 and P-450 was negative and significant. Total Ca in the plasma was highly, positively correlated with concentr ation of E2. Eggshells were thinner from hens treated with 100 mg of P B for both 3 or 7 d than those from control hens. Rate of egg lay was reduced by 100 mg of PB for 7 d. In Exp. 3, .5 mL Of CCl4 given orally for 1 d decreased P-450 and increased E2. These data indicate that ef fects on rate of egg lay, eggshell thickness, and plasma Ca by xenobio tics may be mediated through modification of MFO and the consequent ch ange in concentration of estrogen.