Abstract A study was conducted at a farm near Colima, Mexico, to evaluate the reproductive performance of 60 hair sheep and 30 F1 crossbreds (Rambouillet or Dorset×Rambouillet) with progesterone and gonadotropin treatments. Sheep grazing was supplemented with a protein bank of Leucaena leucocephala. Ewes were supplied with a concentrate of 3 Mcal ME/kg and 18% CP 1 month before and 1 month after lambing. Oestrus synchronization or induction was performed with progesterone and gonadotropins. Females were bred 48–69 h after sponge retrieval. Of the treated sheep 97% showed oestrus. Average fertility was 66%. Seasonally low lambing rate was from March to July in the absence of hormone treatments. Hormone treated sheep (hair sheep and crossbreds) showed increased ( P<0.01) fertility in 8 out of 12 months. Higher difference in fertility was due to treatment in January to May. Fertility was highest from June to December. Overall prolificacy of treated ewes was 1.93±0.32 versus 1.79±0.21 for controls. Hormone treated ewes had a greater percentage of twins, triplets and quadruplets than controls. Overall yield of lambs from treated ewes was 29.86 kg per year compared to 19.99 kg for controls, however since controls had more single lambs, overall birth weight was in favour of controls (2.20 versus 1.85). It is concluded that crosses of Rambouillet or Rambouillet×Dorset males with Pelibuey and Barbados Blackbelly hair ewes increased lamb crop, birth weight, and number of parturitions per ewe per year under tropical conditions in Mexico.