Results of a crossbreeding experiment with sheep for different systems of fat lamb production. I. Reproductive traits

A crossbreeding experiment with sheep was carried out at two of the University's experimental stations between 1969 and 1973. On farm I ewes of five groups of different first crosses were tested against the indigenous purebred Merinoland sheep for five lambing periods. The ewes were kept under an accelerated lambing programme, the lambs were reared artificially. On farm II the same domestic breed was tested against three first cross lines with spring lambing and ewes suckling their lambs for 5 to 8 weeks. Each test group consisted of at least 50 ewes made up of 10 halfsib groups. 10 rams of each of four exotic fat lamb sire lines were hand-mated to the ewes. In addition, purebred and special control matings were carried out. All ewes in the experiment were of the same age.The data were analyzed by least squares procedures for different reproductive traits (gestation length, litter size for lambs born and reared, litter weight, score for lambing difficulties) and by simple one-way classifications for various others (lambs born and reared per ewe and year, lambing frequency, body weight, fleece weight, wool income).Since no significant interactions among main effects were detected for any trait, the presentation of the results emphasizes the general combining ability of the sire and dam lines. No significant differences were found between sire lines on both farms in all traits except gestation length. For the most important reproductive traits the differences between the dam lines were highly significant, the Finnish Landrace crosses being the best in both lambing frequency and number of lambs per litter. The superiority of these crosses cannot be maintained for the number of lambs reared and slaughtered, if, like in farm II, facilities are not available to rear lambs of large litters without high losses.