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Rotational crossbreeding systems breed heifers sired by one breed to bulls from another breed. Heifer offspring are then bred to the next breed in the rotation, etc. Composite systems result in a "new" breed consisting of fixed proportions of "old" breeds. Both systems produce their own replacement heifers rather than requiring the purchase of F1 heifers or special matings. Both systems have potential advantages for producers of slaughter beef because a high level of heterosis (hybrid vigor) is present in cows and calves. High levels of heterosis increase efficiency and reduce the cost of producing beef.
The level of heterosis in rotational crossbreeding systems and composites increases as the number of breeds increases. All available breeds would be used if the level of heterosis was the only factor considered. However, not all breeds are equally efficient in a given beef production situation. A producer with a straightbred herd should use the most efficient breed. Likewise, the two breeds with highest efficiency would generally be used in a two-breed rotation or composite, the three best breeds in a three-breed rotation or composite, etc. Increasing the number of breeds has the advantage of increased heterosis, but at the cost of decreased average efficiency of the breeds in the rotations or composites.
Two problems may arise in adapting rotational crossbreeding systems to farm and ranch management. Bulls from all breeds in the rotation will need to be available each yr so that cows can be bred to the appropriate breed. Also, cows will need to be identified for their breed of sire so that the next breed they are bred to is known. These conditions are not too restrictive when artificial insemination is used. However, only one or two bulls may be needed by small herds using natural service sires. This makes it costly to maintain extra bulls and breeding pastures. In extensive production situations, identification and sorting of cows and having extra breeding pastures available can pose management problems, making it difficult to use rotational crossbreeding.