Meeting nutritional requirements of mature broiler breeder hens.
The overall objectives of this study were to compare the response of broiler breeder hens to dietary lysine at peak rate of lay and late in the laying cycle when rate of lay has declined, to compare the coefficients of response to those previously published, to determine whether there is any interaction between the response to lysine and to energy, and to compare the responses to lysine when broiler breeders are fed either wheat- or maize-based diets. Two experiments lasting 10 weeks were conducted on individually caged broiler breeder hens. In the first experiment, birds from 36 to 46 weeks of age were used, whilst in the second experiment birds from 52 to 62 weeks of age were used. In the first experiment each hen was offered 160 g/d of one of 12 dietary treatments, six dietary lysine concentrations based on both maize and wheat. In the second experiment each hen was offered 150 g/d of one of 12 dietary treatments, consisting of six concentrations of lysine at two different dietary energy levels (low and high) . All the diets in both experiments were produced by diluting one of the concentrate (summit) mixes with the appropriate protein-free dilution diet. Each lysine-limiting diet was designed to supply approximately 1350 mg lysine/bird d when fed at 160 and 150g/bird d for the first and second experiment, respectively, whilst the most diluted feed supplied only 270 mg lysine/bird d. In both experiments birds fed the highest contents of lysine consumed virtually all of the food allocated to them. However, birds on the most diluted diets consumed less than half of the daily intake of the birds on the summit feeds. By fitting the Reading Model to the data from each experiment, the coefficients of response were calculated to be 8.44E and 0.01W for wheat-based diets, 7.75E and 0.02W for maize-based diets, 10.23E and 4.57W for low energy series diets, and 9.29E and 0.01W for high energy series diets. The pooled data for both energy series produced coefficients of 9.41E and 0.00W. Since Bowmaker (1986) estimated the body weight coefficient for broiler breeders to be 11.2 it was then decided to use an assumed body weight coefficient of 10 and the 'a' coefficient was recalculated using the equation: a = (I-bW)/ E. The overall a coefficient became 15 and 13 for wheat- and maize-based diets, and 16 and 18 for low and high-energy series with a mean of 17. On the bases of the coefficients from the Reading Model a broiler breeder hen weighing 3 kg and producing 45 g of egg output per day would need 380, 349 and 423 mg of lysine/d from wheat and maize-based diets, and pooled energy series, respectively. Both the low and high-energy series curves had the same shape, implying there was no interaction between the response to lysine and to energy. Using the calculated 'a' coefficients, because they accounted for maintenance requirements, and assuming an egg contains 8.3 mg lysine/g, the efficiency of utilization of lysine for egg production is estimated as being 0.55, 0.64 and 0.49 for wheat- and maize-based diets, and pooled energy series data, respectively. The efficiency derived for the older flock is lower than the one derived for a younger flock indicating that the efficiency of utilization of the limiting amino acid for egg production declines with age in broiler breeder hens. Broiler breeder hens that were fed maize-based diets were more efficient than those fed on wheat-based diets.