The response of broiler breeder hens to dietary lysine and methionine

Abstract

1. Broiler breeder hens were used in an experiment lasting 10 weeks (29 to 38 weeks of age) to measure the responses to dietary lysine and methionine, the main objective being to determine whether the coefficients of response to these amino acids were the same for broiler breeders and for laying pullets.

2. The hens were offered 150 g/d of one of 20 dietary treatments, 10 being lysine‐limiting and 10 being methionine‐limiting. The diets were mixed by diluting one of two concentrate (summit) mixes with a protein‐free dilution mixture. The lysine‐limiting summit diet was designed to supply approximately 1300 mg lysine/ bird d, while the other supplied 520 mg methionine/bird d, when fed at 150 g/bird d.

3. Birds on the 5 lowest concentrations of both lysine and methionine did not consume the allotted amount of food, the amount decreasing, in a curvilinear fashion, to approximately 105 g/bird d.

4. The minimum egg weight recorded was 0.8 of the maximum, whereas the rate of lay of birds fed on the diets with the lowest amino acid concentrations was 0.2 of the maximum.

5. Using the Reading Model, the coefficients of response were calculated to be. (for lysine) 16.88 E and 11.2 W, and for methionine, 7.03 E and 1.52 W, where E = egg output, g/bird d, and W = body mass, kg/bird. An average, individual, broiler breeder of 3 kg, producing 45 g of egg output per day, would need 793 mg of lysine and 321 mg of methionine daily. This intake of methionine is similar to that estimated by means of coefficients used for laying pullets, but the lysine requirement would be underestimated by 0.18 if the coefficients for laying pullets were used.

6. The coefficients for maintenance for both lysine and methionine, determined in this experiment, are considerably lower than values published previously, whilst the coefficients for egg output are, in both cases, higher. The resultant flock response curves therefore differed significantly from those in which the coefficients of response for laying pullets were used.

7. The possible reasons for these differences are discussed in terms of the difficulties experienced in fitting the Reading Model, namely, in estimating values for the parameters used; in the varying food intakes on different treatments; in considering the large proportion of birds laying fewer than one egg every second day; and in the large lipid reserves in broiler breeders that contribute substantially to body weight but that should not be considered in determining maintenance requirements for amino acids.