What makes Romanov unique in crossbreeding activities?
In cross-breeding systems, the use of F1 ewes requires simultaneous breeding of purebred and F1 offspring, a situation that requires an intensification of management and increases in cost of production (Sierra, 1985; Galal et al., 1993). This is probably the main reason why commercial sheep farmers are increasingly interested in the use of synthetic lines instead of first crosses. Generally, F1 animals tend to be better than subsequent inter se crosses. While there are numerous reports on the performance of F2 animals, empirical results on F3+ generations are limited. Due to recombination loss, this heterotic superiority in the F1 animals is expected to break down in subsequent generations, which is confirmed by findings of Syrstad (1989), who reported considerable declines for all relevant dairy traits when comparing the F2 with the F1 generation. Like in other farm animal species, F1 animals are reported to show the highest heterosis, which is lost in subsequent inter se matings. Bou
