Model comparison and estimation of genetic parameters for body weight in commercial broilers

Abstract

Maniatis, G., Demiris, N., Kranis, A., Banos, G. and Kominakis, A. 2013. Model comparison and estimation of genetic parameters for body weight in commercial broilers. Can. J. Anim. Sci. 93: 67–77. The availability of powerful computing and advances in algorithmic efficiency allow for the consideration of increasingly complex models. Consequently, the development and application of appropriate statistical procedures for model evaluation is becoming increasingly important. This paper is concerned with the application of an alternative model determination criterion (conditional Akaike Information Criterion, cAIC) in a large dataset comprising 203 323 body weights of broilers, pertaining to 7 (BW7) and 35 (BW35) days of age. Seven univariate and seven bivariate models were applied. Direct genetic, maternal genetic and maternal environmental (c2) effects were estimated via REML. The model evaluation criteria included conditional Akaike Information Criterion (cAIC), Bayesian Information Criterion (BIC) and the standard Akaike Information Criterion (henceforth marginal; mAIC). According to cAIC the best-fitting model included direct genetic, maternal genetic and c2 effects. Maternal heritabilities were low (0.10 and 0.03) compared to the direct heritabilities (0.17 and 0.21), while c2 was 0.05 and 0.04 for BW7 and BW35, respectively. BIC and mAIC favoured a model that additionally included a direct-maternal genetic covariance, resulting in highly negative direct-maternal genetic correlations (−0.47 and −0.64 for BW7 and BW35, respectively) and higher direct heritabilities (0.25 and 0.28 for BW7 and BW35, respectively). Results suggest that cAIC can select different animal models than mAIC and BIC with different biological properties.

Genetic analysis on body weight at different ages in broiler chicken raised in commercial environment

“…The decrease in the permanent environmental maternal effect with increasing age was also found for meat quail (Barbieri et al, ) and local Venda chicken (Norris & Ngambi, ). In comparisons, the permanent environmental maternal effect at the corresponding age in our study is lower than other studies (Begli et al, ; Dana et al, ; Jasouri et al, ; Maniatis et al, ; Zonuz, Alijani, Rafat, Abbasi, & Kia, ). This may be due to the raising environment.…”

“…In our study, the correlations between early and late BWs were relatively low, ranging from 0.320 to 0.572 for BWs between weeks 1–2 and 5–6. Maniatis et al () found a genetic correlation of 0.17 between BWs at weeks 1 and 5. The genetic correlations for BWs were 0.66 between weeks 2 and 6, 0.46 between weeks 2 and 8, and 0.26 between weeks 2 and 10 (Begli et al, ).…”

“…Begli et al () showed that the ratio of the permanent environmental maternal variance to the total phenotypic variance for BW of F2 chicken crossed between commercial broilers and native fowls increased slightly from 0.10 at week 2 to 0.12 at week 6, and then reduced to 0.07 at week 10. Maniatis et al () showed that the ratio of the permanent environmental maternal variance to the total phenotypic variance was 0.12 for BW at week 1 and 0.05 for BW at week 5 of commercial broiler chicken. The decrease in the permanent environmental maternal effect with increasing age was also found for meat quail (Barbieri et al, ) and local Venda chicken (Norris & Ngambi, ).…”

“…Optimal modelling plays a key role in improving the accuracy of predicted breeding values for traits of interest, and thereby increasing genetic gain in breeding programmes. Apart from direct additive genetic effects, other factors including maternal effects, sex‐by‐genotype interaction and heterogeneous residual variances have been accounted for when modelling body weight (BW) in poultry, (Barbieri et al, ; Begli, Torshizi, Masoudi, Ehsani, & Jensen, ; Grosso et al, ; Maniatis, Demiris, Kranis, Banos, & Kominakis, ; Mebratie et al, ). However, the method used for including those factors in BW modelling varies across studies.…”

“…Maternal effects are often ignored for egg production traits that are expressed relatively late in life, but the effects are considered to be important for growth traits in broiler chicken, especially at juvenile stage that broilers are usually selected in breeding programmes (Besbes & Ducrocq, 2003). Two commonly modelled maternal effects for BW traits are additive genetic and permanent environmental effects of the dam (Barbieri et al, 2015;Maniatis et al, 2013;Norris & Ngambi, 2006). The maternal effects reduce as chicken are older (Barbieri et al, 2015;Maniatis et al, 2013;Norris & Ngambi, 2006).…”