Progesterone-induced delay of the onset of lay in the prepubertal pullet.

Thirty-six 119-day-old White Leghorn pullets were administered either a 2 cm progesterone (P4) implant or an empty (control) implant. Plasma samples drawn at 7, 14, and 43 days postimplant were assayed for P4 and luteinizing hormone (LH), and the day of first egg production and total egg production to 200 days of age was recorded. Treatment with P4 significantly elevated plasma concentrations of P4 at all sampling intervals and depressed plasma LH at the sampling intervals 14 and 42 days postimplant. In addition, P4 treatment significantly delayed the mean time of the onset of egg production by greater than 16 days and decreased the total number of eggs laid to 200 days of age. It is suggested that P4 can inhibit LH secretion in the prepubertal pullet. However, from the present study, it is not possible to determine whether the decrease in plasma LH in P4-implanted birds is directly or indirectly related to the delayed onset of egg production.