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

Abstract

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.