Different service schedules on the fertility and litter size of Pelibuey and Blackbelly ewes under tropical conditions

The effects of the number and time of services after oestrus detection on t he fertility and litter size (LS) of Pelibuey (PB) and Blackbelly(BB) ewes were determined. The data covered three breeding years. Ewes grazed native pasture and were fed a grain and molasses based supplement during the dry s eason (February-May) of each year. The fertility analysis included data on 537 PB ewes and 238 BB and that on litter size, data of 430 PB ewes and 189 BB. One, two or three services were studied at 0, 12 or 24 hr after oestru s detection. Contrast procedures were used to compare the frequency and tim e of service. The fertility of the PB ewes receiving only one service was 1 0 and 13% lower than those with 2 or 3 services (P < 0.01) but there was no effect on LS. In BB ewes there were no differences in fertility with 1, 2 or 3 services, except in LS. BB ewes with two services had a larger LS (1.8 0) than those with one (1.54). There was no significant (P < 0.05) differen ce in fertility in PB or BB ewes according to the time of service. It is co ncluded that two services per ewe improved fertility of PB ewes and litter size of BB awes.