In this, study 3072 records of productive traits related to 1096 ewes in Chaharmahal -O- Bakhtiari province during the period of 1991 to 2000 were used to study of the biological efficiency. The least square mean (±s.e) of total weight of lambs at birth, r lambs born per kg body weight of ewe, gr lambs born per kg metabolic weight (BW)°5 of ewe, total weight of lambs weaned, gr lambs weaned per kg body weight of ewe and gr lambs weaned per kg metabolic weight of ewe were 5.81±0.01, 102±0, 279±1, 31.96±0.12, 561±2 and 1540±6 per ewe joined, respectively. The effect of joining year, age of ewe at joining, type of birth and sex of lambs were significant (P< 0.01 or 0.05) for all the traits. Total weight of lambs at birth and when weaned increased with age of ewe up to 5 years old and thereafter declined, while the maximum of the other traits of ewe occurred for ewes at 2 years of age and declined for older ewes. Performance of ewe in twin births were 41 to 62 percent higher than that in single births. Direct heritabilities for, the various traits per ewe lambing and joined were 0.09±0.03 to 0.21±0.04 and 0.03±0.03 to 0.13±0.03 and repeatability estimates were 0.17 to 0.31 and 0.09 to 0.24 respectively. Phenotypic and genetic correlations between traits of related to total birth weight and traits of related to total weaning weight were low to medium, while high phenotypic and genetic correlations were estimated between gr lambs weaned per kg metabolic weight and total weaning weight per ewe lambing and joined.
)