Improving the efficiency of feed utilization in poultry by selection. 1. Genetic parameters of anatomy of the gastro-intestinal tract and digestive efficiency

Genetic parameters were estimated for 630 broiler chickens of the eighth generation of a divergent selection experiment on AMEn. Birds were reared until 23 d of age and fed a wheat-based diet. The traits measured were body weight (BW), feed conversion ratio (FCR), AMEn, weights of crop, liver, gizzard and proventriculus, and weight, length and density of the duodenum, jejunum and ileum.The heritability estimates of BW, FCR and AMEn were moderate. The heritability estimates were higher for the GIT characteristics except for the weights of the proventriculus and liver. Gizzard weight was negatively correlated with density (weight to length ratio) of duodenum, jejunum and ileum. Proventriculus and gizzard weights were more strongly correlated with AMEn than with FCR, which was not the case for intestine weight and density.GIT traits were largely dependent on genetics and that selecting on AMEn or FCR would modify them. Phenotypic observations carried out in the divergent lines selected on AMEn were consistent with estimated genetic correlations between AMEn and GIT traits.Improving feed efficiency is a major factor in reducing the costs of poultry production and the environmental impact of chicken production. Many genetic studies have shown that feed efficiency could be improved by selecting on growth, FCR (feed conversion ratio) or feed intake, which are heritable [1]. Mignon-Grasteau et al. [2] recently showed that the ability of the animal to digest its feed could also be used as a selection criterion. Following this study, two lines (D+ and D-) were divergently selected on digestive efficiency assessed by the AMEn (Apparent Metabolisable Energy corrected for zero nitrogen retention) of a wheat-based diet, measured at 3 weeks of age. After 7 generations of selection, D+ and D- lines differed by about 30 to 40% on the selection criterion, but presented similar body weights [3]. Mignon-Grasteau et al. [2] and Rougière et al. [4] also showed that levels of starch, prot