proles (n.)

1640s, "producing young or fruit;" 1650s, "producing offspring or fruit in abundance;" from French prolifique (16c.), from Medieval Latin prolificus, from Latin proles "offspring" + combining form of facere "to make, to do" (from PIE root *dhe- "to set, put"). Latin proles is contracted from *pro-oles, from PIE *pro-al-, from *pro- "forth" (see pro-) + root *al- (2) "to grow, nourish." Related: Prolifical (c. 1600).

Prolific is in common use, but to make a satisfactory noun from it has passed the wit of man. [Fowler]

Gower (1393) has prolificacioun, from Medieval Latin prolificationem; prolificacy (1796) and prolificness (1690s) also have been tried.