Estimation of (co) variance component and genetic parameters for total weight of lamb weaned per ewe joined in Zandi sheep

This study was undertaken to estimate genetic parameters for total weight of weaned lambs per ewe joined (TWW/EJ) in first to 4^th parities. Data were obtained from 1912 ewes collected during 17 years (1990-2006) by the Zandi sheep breeding station in the Khojir Tehran province. Analysis was carried out by Restricted Maximum Likelihood procedures using univariate and multivariate animal models. Heritability obtained for total weight of lamb weaned per ewe joined (TWW/EJ) in parity one through parity four as 0.065±0.04, 0.100± 0.06, 0.110±0.07 and 0.159±0.05, respectively. In the univariate analysis, two models including genetic additive effects and service sire effect were used. Results showed that effects mentioned above had a minor importance in phenotypic appearances of the studied trait. Random effect variances due to service sire for these traits were low. Additive genetic correlations of total weight of lamb weaned per ewe joined among different parities moderate to high and positive, ranging from 0.454 (between first and 4^th parity) to 0.723 (between first and 2^th parity). The corresponding estimations for phenotypic correlations ranged from 0.034 (between first and 3^rd parity) to 0.414 (between first and 2^rd parity). Considering high genetic correlations between first and subsequent parities, selection for increasing reproductive performance can be based on total weight of lambs weaned per ewe exposed at first parity.