Book excerpt: Three prolific wool-breeds (Finnsheep, Combo-6 and Booroola Merino) and 2 hair-breeds (St. Croix and Barbados) were evaluated. Suffolk and Targhee ewes were exposed to rams (3 rams per breed per year) of these 5 breeds. Results indicated that ewes mated to hair-breed rams had higher fertility and their lambs had higher survival to weaning than ewes mated to wool-breed rams, suggesting a better reproductive performance of ewes mated to hair-breed rams. F$sb1$ ewe lambs resulting from the previous matings were mated to Dorset rams. F$sb1$ ewe lambs from hair-breed sires reached puberty later, were lighter at breeding and had a shorter breeding to lambing interval than F$sb1$ ewe lambs from wool-breed sires. Hair-breed-sired F$sb1$ ewe lambs had higher fertility, less lambs born per ewe lambing and weaned more of lamb per ewe lamb exposed than F$sb1$ ewe lambs sired by wool-breed rams suggesting a superior adaptability of the hair-breeds over the wool-breeds to the environment in southern Illinois. These F$sb1$ ewe lambs were also mated to Dorset rams when they were 1$sp{1/2}$ and 2$sp{1/2}$ years old. F$sb1$ ewes from hair-breed sires were lighter at breeding, ovulated less and conceived to a ram earlier than F$sb1$ ewes from wool-breed sires. Adult F$sb1$ ewes from hair-breed sires had higher fertility, higher ewe productivity and their lambs had higher survival and weighed less at weaning than those from wool-breed sires. These results together with those from Suffolk and Targhee ewes and F$sb1$ ewe lambs suggest that the productivity of ewes mated to or sired by hair-breed rams is superior to that of ewes mated to or sired by wool-breed rams.