Genetic parameter estimates for growth traits in Iran-Black sheep

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 (r am ) was positive for all traits and ranged from 0.3690.27 for BW to 0.9990.98 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 (r a1,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 r a1,a2 . Phenotypic and environmental correlations for all traits were generally lower than direct genetic correlations.

Influence of non-genetic factors on the maternal ability of Santa Inês ewes

“…The variation in results among different studies, even within the same breed, is justified by the fact that the weights at birth and weaning are greatly influenced by different environmental effects, especially the maternal environment (KAMJOO et al, 2014), and by the management adopted on each farm. In the present study, some factors that probably influenced lamb performance were reproductive management, the supplementation of the dams before lambing, and the use of creep feeding for the lambs.…”

“…The positive and moderate correlation observed between BW and WW was also expected, as the dams received supplemented feed during part of the pregnancy and the lambs had access to creep feeding before weaning. Many publications have reported moderate to high positive correlations between these two traits in different sheep breeds (HANFORD et al, 2003;BARROS et al, 2004;EL-AWADY, 2011;SAVAR-SOFLA et al, 2011;KAMJOO et al, 2014 EKIZ (2005), in mammalian species, growth traits, in particular until weaning, are substantially influenced by the environment provided by the dam.…”

Genetic analysis of reproductive characteristics in Iran-Black sheep

“…Mating ratio was one breeding ram to 10-12 ewes. Lambing began in mid-January and ended in February (Kamjoo et al, 2014). Lambs were weighed and ear-tagged shortly after birth and weaned at 90 days of age.…”

“…Further, to design the effective selection programs for improving the efficiency of ewe production, the knowledge of genetic parameters for ewe traits and the genetic relationships among the traits are of significant importance. Therefore, estimates for genetic parameters, selection criterion, response to selection, and construction of selection indexes are needed (Kamjoo, Baneh, Yousefi, Mandal, & Rahimi, 2014). Previous studies have shown that reproductive traits are not only influenced by the genes of the individual and the environment in which it is raised, but also by the service sire and the maternal environment (Maghsoudi, Torshizi, & Jahanshahi, 2009;Mokhtari, Rashidi, & Esmailizadeh, 2010).…”

Effect of mother’s age on body weight of lambs from birth to weaning in various strains of domestic sheep Pramenka

“…Also, effects of the lamb weight and age of the ewe were found to be important for the reproductive performance of ewes and for the lamb's growth rate (ACTAŞ et al, 2015). Body weight and growth traits of lambs are known to be affected by the direct and maternal genetic effects as well as by environmental effects (KAMJOO et al, 2014).…”