Latest figures from Beef + Lamb's Economic Service show there was an increase of nearly 40% in the number of lambs born from hoggets this season.
Hoggets are young sheep, aged between one and two years and this season 1.41 million lambs were born from them.
Executive director Rob Davison said favourable feed conditions nationwide meant hoggets were in good enough shape to breed and farmers also took the opportunity this season to cull their older breeding stock.
Nearly 27 million lambs have been tailed this spring and lamb numbers are up by almost two million (1.9 million) on last year due, to a combination of the good spring weather, improved fertility in the national flock and favourable feed conditions leaving sheep in top condition.
However, the lamb crop is still the third lowest since the early 1950s.