Animal model evaluation of dairy traits in US sheep breeds, their crosses and three synthetic populations

Multi-trait animal model procedures allowed simultaneous estimation of year of record, age of ewe, litter size and genetic group, and the prediction o f direct additive genetic merit, and non-genetic permanent maternal environ mental effects of the dams with multiple lactations. Mixed model methodolog y was used to obtain estimated breeding values and estimated producing abil ity for total milk yield and percentages of fat, protein and lactose in the Dorset (D), Finnsheep (F), Lincoln (L) and Rambouillet (Ra) breeds and som e of their crosses, the Romanov, Suffolk and Targhee breeds and three synth etic populations derived from crossbred foundations: Synthetic I (FXL), Syn thetic II (DXRa) and Synthetic III (FXL)X(DXRa). Ranking of breeds was base d on the mean values of mixed model solutions for direct additive genetic m erit as deviations from their respective groups and non-genetic permanent m aternal environmental effects of the dams. Among the purebreds, Suffolk ewe s produced the highest volume of milk while the Finnish Landrace and Romano v ewes produced the lowest volume (6.8 vs -14.5 and -11.5, respectively). P roductivity of synthetic populations was comparable to that of their purebr ed parents but lower than the crossbred parents. Crossbred ewes exceeded th eir purebred parents in milk yield (0.32 vs -6.15), possibly due to heteros is. In contrast, the percentages of fat (-0.07 vs -0.02), protein (-0.04 vs 0.02) and lactose content (0.01 vs -0.07) in the crossbred ewes were simil ar to those in the purebred ewes. Increased milk production in sheep could be beneficial in raising more lambs from multiple births common in the shee p breeds with a genetic background of the Finnsheep and Romanov inheritance . The genetic variation between and within domestic breeds reported here in dicates an opportunity to develop higher milk producing strains for a comme rcial dairy sheep industry in North America. However, importation of Europe an dairy sheep breeds is an alternative approach which might achieve that g oal more rapidly and which is now being evaluated. Published by Elsevier Sc ience Ireland Ltd.