Response of Male Broiler Chickens to Dietary Lysine:True Metabolizable Energy (Nitrogen-Corrected) Ratios During Three Consecutive Fourteen-Day Periods from Hatching

Abstract

An experiment was conducted to estimate the changes in body composition associated with the concentration of dietary lysine, independent of energy intake. A secondary objective was to determine whether the treatment effects on body composition could be inferred by using the initial body weight of the birds as a covariate, rather than data from groups initially slaughtered. The experiment comprised three phases, based on the age of the birds: 1 to 15, 15 to 29, and 29 to 43 days. The same 56 dietary treatments, arranged as an 8-by-7 factorial, were used in each phase.The dietary treatments consisted of eight ratios for bioavailable lysine and TMEn with seven levels of cellulose dilution, the latter being used to ensure a range of TMEn intakes. The experimental units were groups of 4 chicks in Phase 1 and individual birds in Phases 2 and 3. The comparative slaughter procedure was used. The initial slaughter populations comprised 30 groups of 4 birds for Phase 1 and 40 individual birds for Phase 2 and Phase 3. The intakes of bioavailable lysine and bioavailable energy (ITMEn) were measured, and the body weights were recorded. The carcasses were assayed for dry matter, energy, protein, lipids, and ash.The gains in body weight, water content, and protein content reached maxima at ratios for lysine to TMEn of between .76 and .86 g per mJ,661 mJ = .239 Meal. independent of the phase. The gains in dry matter, energy intake, and lipid content per unit of ITMEn were independent of the lysine:TMEn ratio and of the phase (P>.05). The phase affected the regression coefficients for gains in body weight and body water (P<.01) but not for protein (P>.05). Phase effects were most apparent in the intercepts of the regression lines where the differences reflected variations in body-maintenance requirements for energy. A covariance analysis provided estimates for the rates of response very similar to those obtained by using data from the initial slaughter groups. Both experimental approaches depend for precision and accuracy on a strong relationship between body weight and composition; such does not appear to exist for total carcass energy and lipid content