Factors Affecting Birth Weights of Crossbred Lambs

Suffolk and Southdown rams were mated to ewes of predominantly Hampshire, Border Leicester, Romney and Cheviot breeds. The resulting 280 lambs were weighed to the nearest one-tenth of a pound soon after birth. Analyses were conducted to determine the effect of breeds, breed-cross interaction, birth type, sex and birth type-sex interaction on birth weights of the lambs. There was no consistent difference in birth weights of lambs sired by Suffolk and Southdown rams. Lambs from Border Leicester-cross ewes were significantly heavier than those from Cheviot-cross ewes. Hampshire-cross ewes produced lambs which were heavier than those from Cheviot-cross ewes when all lambs were sired by Suffolk rams. There were no significant differences among birth weights of lambs from Hampshire, Border Leicester and Romney-cross ewes nor between those from Romney and Cheviot-cross ewes. Birth type contributed the most consistent of all effects on birth weights. Singles were from 1.92 to 2.40 lb. heavier at birth than were the twins. Moreover, year differences in birth weights were apparent. Consistent but small differences existed between the birth weights of ram and ewe lambs.