By Rodney Kott, Extension Sheep Specialist, Animal & Range Sciences Department, Montana State University

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A good breeding program will result in a flock of sheep that has a high reproductive rate, good lamb survival and good lamb growth rates. The genetic potential of a sheep flock can be increased through selection and crossbreeding. Progress in selection for economic traits is slow and requires patience and time compared to the improvement that can be realized by crossbreeding. Different breeds of sheep are superior in different traits. Not all economically important traits can be found in one breed. Crossbreeding can be used to incorporate the strengths of different breeds into a sheep producers program. In addition to the improvement that can be realized through the use of complementary breeds, are the advantages obtained from heterosis or hybrid vigor. In general, crossbreeds tend to be more vigorous, more fertile and grow faster than the average of the purebreds included in the cross.

Crossbreeding has been used to improve the genetic producing ability of the ewe flock by combining breeds that complement each other. The Finn sheep has been successfully utilized to increase the reproductive rate in our domestic breeds of sheep. As a general rule of thumb each 1 percent of Finn breeding that a ewe has will result in a 1 percent higher lamb crop than the base breed. In addition, Finn X ewes have a greater chance to breed as a lamb and lamb at one year of age. Smut-faced ewes (Blackface X Whiteface) ewes are sometimes used in farmflock situations as they are more vigorous, live longer, more fertile and have lambs that are more vigorous and have higher livibilities. The major drawback to crossbred ewes is a significantly lower valued wool clip produced.

Using crossbreeding in a terminal crossing program is common among sheep producers. The most common terminal crossing program involves crossing blackface rams with whiteface ewes. By doing this we can maintain a whiteface ewe flock that in well-adapted to the local environment, modest is size (to control maintenance costs — big sheep eat more) and produces a high quality wool crop while taking advantage of the larger faster growing ram breeds. Most research data shows that crossing blackface rams with whiteface ewes will result in a 15 to 20 percent increase in lamb production through a combination of increased lamb crop born, increased lamb survivability and increased lamb growth rate.

In a terminal crossbreeding program all lambs from the cross are marketed. A very important part of designing such a system involves consideration of how to obtain or produce replacement stock. Probably the simplest is to buy replacement stock, provided high quality replacements are available at a reasonable price. If replacement ewes are going to be raised, about 20 to 40 percent of the ewes would need to be mated to whitefaced rams to produce suitable numbers of replacement ewes from within the flock.

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