Introduction of East Friesian dairy sheep into the Norwegian sheep population

Abstract The litter size in the Norwegian crossbred (NC) sheep population has increased considerably in recent years and consequently there is a need to improve maternal ability. East Friesian (EF) dairy sheep were introduced by artificial insemination with semen from four Swedish pure-bred rams into two research flocks of the Agricultural University of Norway in 1985. The flocks differed in producing level. Different breed combinations of lambs (1/2 EF, 3/8 EF, 1/4 EF, 1/8 EF, 1/16 EF) with various degrees of EF in the dam (0 EF, 1/8 EF, 1/4 EF, 1/2 EF) were produced and compared to NC lambs for live weight, ultrasonic-scanning results and carcass traits. Ewes of 1/2 EF, 1/4 EF and 1/8 EF were compared to NC ewes for litter size, mature and fleece weights. The groups varied considerably in size. Data from 1988 to 1992 were used, and a least square analysis was carried out in order to test for significant differences. The direct effect of growth reduced as the proportion of EF increased in the crosses. This was seen in the lamb weights and in the mature weight of ewes. A moderate degree of EF in the dam (1/8) seemed to have a positive effect on lamb growth and litter size, indicating that maternal ability in EF is beneficial in improving productivity. An optimal degree of EF in lambs and in dams was observed where the advantage of the superior maternal ability, higher fertility and lower ewe weights of the EF could be exploited without reducing the direct growth capacity and muscling of the lambs very much. This optimal level of EF seems to be higher in lower producing flocks then in high producing flocks.