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Comparison of the Growth Performance of Lambs from Western and Dorset X Western Ewes¹

Oklahoma State University³, Stillwater

Abstract

One-hundred-twenty purchased Western ewes (predominately Rambouillets) and 120 raised Dorset x Western ewes were compared on the basis of the growth performance of their lambs when both ewe breed groups were bred to the same rams and managed for fall-lambing. The lamb growth variables studied were birth weight (BW), rate of gain from birth to 70 days (RGB70), 70-day weight (70DW), rate of gain from 70 days to market (RG70M) and market age (MA). Each variable was analyzed separately for the two ewe breed groups by least squares procedure. The results of the least squares analyses revealed that for each variable separately, the mean values changed from year to year for the data from the two ewe breed groups. However, within each year, the mean values were quite similar for the data from both breed groups. This was also evident for the age of dam, type of birth and rearing (type of birth for BW) and sex of lamb mean values. These results indicate that the least squares constants were similar for the data from the two breed groups, since the overall means for each of the variables were quite similar. The overall means for BW, RGB 70, 70DW, RG70M and MA were 4.10, 4.06 kg.; 0.281, 0.28.2 kg.; 23.9, 23.8 kg.; 0.24S, 0.250 kg. and 156.4, 155.5 days for the lambs from the Western and Dorset crossbred ewes, respectively. For each of the variables, the difference between the overall means for the data from the two breed groups was not significant. It appears that neither ewe breed group has any advantage over the other relative to the growth rate of their lambs when the ewes are bred to the same rams.

¹ Journal Article 1767 of the Oklahoma Agricultural Experiment Station, Stillwater.

² Present address: Department of Animal Science, University of Kentucky, Lexington.

³ Department of Animal Science in cooperation with the A.H.R.D., A.R.S., U.S.D.A.