02653naa a2200205 a 450000100080000000500110000800800410001902400330006010000220009324501010011526000090021652020640022565000160228965000150230565000100232065000100233070000200234070000200236077300670238020758662017-09-19       1958    bl uuuu     u00u1 u    #d7 a10.2527/jas1958.173743x2DOI1 aHARRINGTON, R. B.  aEstimates of some sources of variation in the body weights of crossbred lambs at different ages.  c1958  aThe weights of 300 Dorset X Rambouillet or Dorset X Rambouillet-Panama-Rambouillet crossbred lambs reared in the winters of 1955?56 and 1956?57 were adjusted to constant ages of 45, 60, 75, 90, 105, 120 and 135 days. The effects of breed of dam, birth type, sex, type of rearing and birth weight on the variation in body weight at different ages were estimated by least squares analysis. The data were analyzed on a within-year basis because the same ewes were bred each season and the effects of age of dam and year could not be separated. The results indicate that there was little difference in the rate of gain of the lambs due to differences in the breed of their dams. Differences in lamb weights due to birth type and type of rearing became relatively less important as the lambs grew older. Type of rearing differences were less important among lambs during 1956?57. Male lambs were heavier than female lambs at all ages during both seasons and maintained the same relative importance. Birth weight was the most important source of variation in the lamb weights at different ages. Regression of subsequent weights on birth weight increased steadily from 1.5 lb. at 45 days to 2.6 lb. at 135 days during the 1955?56 season. The regression of corresponding weights on birth weight in 1956?57 increased from 2.0 to 3.0 lb. at 45 and 135 days, respectively. Birth weight accounted for 34 to 44% of the variation at 45 days and from 23 to 33% at 135 days. Where comparable, the differences due to the various sources of variation were found to be in general agreement with those previously reported by other workers. Coefficients of determination (R2) indicated that from 29 to 59% of the variation in the lamb weights at different ages could be accounted for by the factors studied. These coefficients were highly significant (P&lt0.01) at all ages during both seasons. The variation accounted for by these variables became relatively less important as the lambs grew older. This was probably due to the diminishing influence of type of birth and rearing.  aBody weight  aCrossbreds  aLambs  aSheep1 aWHITEMAN, J. V.1 aMORRISON, R. D.  tJournal of Animal Sciencegv. 17, n. 3, p. 743-751, Aug. 1958.