Birth weight (BW) data on 1650 lambs, weaning weight (WW)on 1611 and yearling weight (YW) on 1077 lambs which had been collected during the 8- year periode (1982..1990) in Jafar-abad Sheep Breeding and Improvement Research Station for estimating the effecet of some environmental factors,genetic and phenotipic parameters were analysed with least squares method. the means and standard deviation for BW, 1-month weight (1MW),2MW, 3MW,4MW,5MW, 6MW, 9MW and 12MW were 4.44 ±0.48, 11.13±2.34, 15.25±3.36, 19.81±4.38, 22.89±4.87, 27.74±5.35, 32.23±5.88, 35.34±5.98 and 38.87±7.06 Kg respectively. Also the mean of daily gain from birth to 3-month age and birth to 6-month age were 171 and 154 grams respectively. The year,sex and type of birth effects on all mentioned traits were highly significant (P <0.0001) . The male lambs were heavier than the female lambs at BW(0.285Kg), WW (2.250Kg) and YW(3.200Kg), and differences between single and twin lambs in BW,WW and YWO.321,3.242 and 3.000 Kg respectively. Age of dam had no effect (p>O.OS) on 13W,WW and YW.In the analysis , sex with year and type of birth with year (p
0.927 ±0.477 and 0.825 ±0.363 respectively .Phenotypic and environmental correlations for BW, WW and YW were 0.163, 0.107 (BW WW)0.147 0.051(BW...YW) and 0.569, 0.552 (WWXW)respectively.
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