Estimates of genetic parameters for different body weights andmuscle and fat depths of Karayaka lambs

Abstract

In the current paper the direct additive and maternal genetic effects on birth, weaning (at 90 days of age), and scanning (at 20 weeks of age) weights and muscle and fat depths of the ribeye area in Karayaka lambs were investigated. Analyses were carried out by the restricted maximum likelihood approach, fitting 6 animal models with various combinations of direct and maternal effects. The best model was chosen after testing for improvement in the log-likelihood values. Direct heritability (h 2 d) for all traits decreased when maternal genetic effects were included in the models. The maternal heritability (h 2 m) ranged from 0.15 to 0.22 for birth weight, from 0.04 to 0.14 for weaning weight, and from 0.08 to 0.16 for scanning weight. The effects of h 2 m on muscle depth and fat depth of the ribeye area were not considered due to their insignificance. The permanent environmental effect of the dam was significant for birth, weaning, and scanning weights. Moderate negative genetic correlations (r am) between the direct and maternal genetic effects were observed, which were significant for birth (-0.179 and-0.221), weaning (-0.310 and-0.415), and scanning (-0.116 and-0.141) weights. As a result, h 2 d and h 2 m can be used as selection criteria for birth, weaning, and scanning weights in Karayaka lambs.

Estimated variance components and breeding values for pre-weaning growth criteria in Romney sheep

“…Supakorn et al (2013) reported that in Thailand sheep populations, estimated direct and maternal heritabilities from multivariate analysis of the model for birth weight were 0.32±0.06 and 0.23±0.02, respectively. Aksoy et al (2016) reported that in Karayaka lamps, the direct heritability of birth weight was 0.44±0.063. When the maternal genetic effects were considered in models, the direct heritability for birth weight decreased from 0.36 to 0.24.…”

Genetic trends of body weight and some scanning traits of Karayaka lambs

“…Therefore, usually Karayaka male lambs are grown and fattened for meat production. Karayaka breed is highly tolerant to extreme rainy environmental conditions, but profitability in Karayaka sheep farming is limited because of insufficient biological and socio-economic knowledge (Aksoy et al 2016).…”

“…Body weight is the major component of meat production and is affected by genetic and environmental factors (Aksoy et al 2016, Khan et al 2017. The goal of lamb breeders is to develope this significant trait (Ulutas et al 2010;Malik et al 2017).…”

“…Many researchers employed this technique on sheep to produced leaner meat (Ulutas et al 2008, Simm et al 2002, Kvame and Vangen 2007. Also, estimates of the heritability and genetic correlations of live weight (Khan et al 2015) and ultrasound muscle dimensions (Clarke et al 1998, Ulutas et al 2008Aksoy et al 2016), especially in longisismus-dorsi muscle, are more valuable indicators to the genetic improvement of carcass yield and composition through selection based on live animal.…”

“…Body weight, weaning weight, slaughter weight and carcass composition traits (fat and muscle depths) are very important traits in the sheep industry (Aksoy et al 2016;Malik et al 2017). The selective breeding organization for Karayaka native sheep breed was started in 2006 and the general aim of this breeding program was to increase the productive characteristics of Karayaka native sheep breed.…”