Effects of genetic potential on the lysine requirement and economic results of simulated broiler flocks

The effect of lysine dietary concentration (expressed as g of lysine per kg of feed) on growth from 20 to 40 days of age in male broiler flocks was studied by simulating flock performance. A total of 17 sets of parameters was considered. Different hypotheses were made on the means, variances and covariances of initial body weight (20 d of age), live weight gain (20 to 40 d), lipid content of gain and of a factor affecting the energy requirement for maintenance. The effect of dietary lysine concentration on individual live weight gain was simulated according to a "broken line" model which resulted in a curvilinear variation of flock performance with lysine concentration, as usually observed. The lipid content of gain was the major characteristic of the genotype accounting for the mean lysine requirement of flocks: the latter increased by 1.935 g per kg of feed, i.e. 20.1%, when the former decreased from 21 to 13%. Growth rate and the factor affecting energy requirement for maintenance also exerted significant effects: when weight gain increased from 1550 to 1950 g, the lysine requirement increased by 6%. Lean and efficient flocks required diets with a higher lysine concentration. Heterogeneity for fatness also tended to increase the variability of lysine requirement. The minimum feeding cost per kg of gain was reached on average when the mean weight gain of flocks was 97.9% of maximum gain, flock feed conversion ratio (FCR) was about 100.7% of the minimum FCR, and when the lysine requirement of 65.8% of individuals was satisfied. chicken / growth / lysine / requirement / adiposity / simulation Rsum -tude, par simulation, des influences respectives de plusieurs caractristiques gntiques sur le besoin en lysine et les rsultats conomiques de troupeaux de poulets de chair. L'effet sur la croissance de la concentration du rgime en lysine digestible a t tudi par simulation, chez des poulets mles entre 20 et 40 jours. Cette concentration tait exprime en g par kg d'aliment et 17 situations ont t considres. Les hypothses initiales portaient sur les distributions du poids vif 20 jours, du gain de poids, de la teneur en lipides du gain de poids et d'un facteur caractrisant le besoin nergtique d'entretien. Les moyennes, carts types et corrlations entre ces paramtres diffraient. En simulant le gain de poids de chaque individu en fonction de la teneur du rgime en lysine selon un modle dit en ligne brise , nous avons observ une rponse curvilinaire du troupeau. La teneur en lipides du gain de poids est le paramtre d'origine gntique influenant le plus le besoin en lysine : ce dernier augmente de 1,935 g par kg d'aliment (soit 20,1%) quand le premier