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Wool Yields in the Small Side-Sample as Related to Individual Whole-Fleece Yields in Four Breed-Groups of Sheep

U. S. Department of Agriculture

Abstract

The percentage yields of small side samples from 45 Rambouillet, 40 Targhee, 44 Corriedale, and 45 Columbia yearling ewes were compared to the percentage yields of the whole fleeces for the purpose of establishing a yield prediction index for these breed groups. Highly significant group differences were found in the side sample yields. Fineness of fiber, density index, or weight of whole fleece did not account for the group differences.

The regression rate was highly uniform in sampling error and nearly equivalent to ß = 1, when the groups were considered separately or in combination. The average within-group regression rate was 1.08 ± .062, and was found to be applicable to all 4 groups. The average within-group standard error of estimate was ± 1.18 per cent which lowers the error of estimation by 44.53 per cent from estimation based on the sample alone. The complete prediction index is expressed in the form of a regression equation in which the group level is fixed by the a value of the respective breed group.

On the basis of the results obtained, the whole fleece yield, , is calculated from the small sample yield, , using the formula,
. The values for a are –2.86, –1.62, –0.84, and +0.73, respectively, for the Rambouillet, Targhee, Corriedale, and Columbia groups. The value of b_y·x is 1.08 for all groups.

A graph illustrates the relationship between the breed averages and gives the respective breed regressions from which whole fleece values can be read directly when small sample yields are known.

¹ The authors are respectively, animal husbandman, associate animal fiber technologist, senior animal husbandman, and former junior statistician, Bureau of Animal Industry, United States Department of Agriculture. The authors express appreciation for helpful assistance to Julius E. Nordby and John I. Hardy of the Bureau of Animal Industry, and to Robert H. Burns (now with Wyoming Agr. Exp. Sta.), Warner M. Buck, and George C. LeCompte of the Agricultural Marketing Service, United States Department of Agriculture.