Abstract
The present study was conducted to estimate variance components and genetic parameters for growth traits of Iran-Black sheep, maintained at the Abbasabad sheep breeding station, located in northeast of Mashhad, (Razavi Khorasan province of Iran) over a period of 24 years (1981 through 2004). Records of 4607 lambs descended from 155 rams, and 1227 ewes were used in the study. Traits included for the present study were birth weight (BW), weaning weight (WW), weight at 6 months (W6), weight at 9 months (W9), and yearling weight (YW). Analyses were carried out by restricted maximum likelihood (REML) fitting an animal model and ignoring or including maternal genetic or permanent environmental effects. Six different animal models were fitted for all traits. The most appropriate model was chosen after testing the improvement of the log-likelihood values. Heritability estimates for weight at birth; weaning; and 6, 9, and 12 months of age were 0.04, 0.14, 0.16, 0.19, and 0.18, respectively. Maternal heritability of body weight declined from 0.33 at birth to 0.04 at six months of age. The maternal permanent environmental component accounted for 6% to 15% to the total variance for all traits under study. The direct-maternal genetic correlation (ram) was positive for all traits and ranged from 0.36±0.27 for BW to 0.99±0.98 for YW, but was never significant. The results showed that modest rates of genetic progress appear possible for all weights. Results also suggest that maternal additive effects were only important in early stages of growth, whereas a permanent environmental maternal effect existed at all ages up to 12 months of age, probably as a carry-over effect of maternal influences present at weaning. Direct genetic correlations (ra1,a2) between traits were positive and ranged from 0.82 (BW-WW) to 0.99 (W6-YW). The estimates of correlation between permanent environmental maternal effect among traits were close to those of ra1,a2. Phenotypic and environmental correlations for all traits were generally lower than direct genetic correlations.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
