Effect of the progestogen, allylestriol, on the bursal development of the chicken

Fertile eggs were dipped on the fifth day of incubation into varying concentrations of allylestriol (AE), a synthetic progesterone, and testosterone propionate (TP). Concentrations of AE higher than 0.1% inhibited hatchability. The AE inhibited the differentiation of the bursal mesenchyme and follicular development and subsequently resulted in bursectomy. The AE caused bursectomy in 40-50 times lower concentrations than did TP. An unusual lymphocyte accumulation occurred around the postcapillary venules in the bursal mesenchyme of AE-treated birds. This observation suggested that inhibition of mesenchyme differentiation may lead to a modification in bursal function. The AE modification of bursal development was compared to those produced by TP. We demonstrated that AE caused immunosuppression of the B-cell system.