Crossbreeding In Sheep
By: Angie Bailey, Jason Canup and Jorge Lucena
Breed diversity is an important aspect in any livestock breeding program, but is extremely critical in the sheep industry. This is most likely do to the diversity of the animal. Sheep vary immensely from breed to breed. Many breeds such as the Merino, Rambouillet, Polypay, Finn and Romanov are classified as ewe breeds due to their excellence in maternal ability. Others such as the Suffolk, Hampshire, and Southdowns are classified as terminal breeds and are classified by fast growth and good carcass quality. Yet, still others are known as dual purpose breeds because they are somewhat balanced, rather then excelling, in terminal and maternal characteristics. These breeds include the Dorset, Columbia, and Montadale.
As a producer it is necessary to know which breed best fits into which production system. Perhaps none of the above mentioned breeds is ideal for what a producer's goals happen to be. This will encourage the producer to practice a method known as crossbreeding. This is accomplished by mating ewes and rams of two or more purebreds in an attempt to develop offspring of superior quality. The goal is to have individuals who complement each other in such a way that the offspring benefit from the increased heterosis between the two.
Many types of crossbreeding systems are available for producers to choose from. The most easily managed and widely used of these is the simple cross approach. In this system ewes of one breed are simply mated to rams of another complementary breed. The resulting offspring will contain 50% of their genes from each breed and take full advantage of heterosis. However, the difficulty in this type of system is that no purebred replacements are produced and they must be purchased elsewhere.
Another type of crossbreeding program is the rotational system. Rams of two or three different breeds are used in altering generations when this plan is implemented. Heterosis increases with the number of different ram breeds being presented to the flock. However, this system increases management concerns by forcing ewes to be separated into different flocks during the breeding season. Also, variation in breed composition can create different managerial requirements among flocks, but this approach does generate its own replacements, resulting in little or no need to purchase ewes for this purpose.
The final type of crossbreeding system that is widely used is the terminal system. In this approach rams of a specialized sire breed are mated to ewes from one of the above systems to produce terminally sired market lambs that express 100 percent lamb heterosis. This system is widely used to maximize meat production efficiency. Again, replacement ewes must be purchased elsewhere because all lambs are sent to market.
Crossbreeding is a production tool that may not fit into every producer's personal goals, but when used correctly can be very efficient and cost-effective. The selection of which breeds to put into these systems should be made only after careful forethought. Production resources and limitations should be identified prior to any decisions about what approach would be most effective to a given herd. Also, an understanding of the traits that most impact efficiency in the production system should be determined with target levels established for ach trait. Finally, it is absolutely essential to select breeds and determine breed composition that achieve the target lambing rate of the system. If all of the above criteria are analyzed and applied correctly any producer can improve his or her herd productivity by implementing a crossbreeding system.
Pictures provided by Dr. Jerry Fitch, Oklahoma State University
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