Comparison of lysine requirements amongst eight stocks of laying fowl

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Abstract
An experiment is described in which eight commercial stocks of laying hens were each fed from 25 to 70 weeks of age on six diets of differing lysine contents. The stocks had a range in mean body weight from 1.8 to 2.6 kg and a range in peak egg output from 43 to 51 g/bird d. Three groups of 21 pullets each were used for each stock × diet combination. The different lysine contents of the diets were produced by varying the total protein content, using cereals and sesame meal as the principal sources of protein. It was confirmed in a separate trial that lysine was the first limiting amino acid in the diets used. Clear responses to changes in the intake of lysine were demonstrated. Net efficiency of lysine utilisation changed with age in each stock and maximum efficiency was obtained at the time of peak output (36 to 47 weeks of age). An analysis of responses obtained during this period showed small but significant differences between stocks in the amount of lysine required per g of egg produced and/or the amount required per kg of body weight maintained. In spite of these differences, the relationship between lysine intake (L — mg available lysine/bird d), egg output (E = g egg produced/bird d) and body weight (W = mean body weight, kg) could be expressed adequately for all stocks by the equation: This equation is assumed to be applicable to individual birds but not to flock averages. The integration of the responses expected from all the individuals of a flock leads to the prediction of a sigmoid response curve. A method is presented for deriving this response curve and for determining the optimum intake of lysine for any flock for which performance and the price structure can be specified. For prices of 40 p/kg for eggs and 160 p/kg for the marginal cost of supplying lysine, the optimal lysine intakes for the eight stocks examined range from 820 to 920 mg/bird d.