Revista Brasileira de Zootecnia
versão On-line ISSN 1806-9290
SIQUEIRA, Jefferson Costa de; SAKOMURA, Nilva Kazue; NASCIMENTO, Dáphinne Cardoso Nagib e FERNANDES, João Batista Kochenborger. Mathematical models to estimate digestible lysine of ISA Label broilers. R. Bras. Zootec. [online]. 2009, vol.38, n.9, pp. 1732-1737. ISSN 1806-9290. http://dx.doi.org/10.1590/S1516-35982009000900013.
The objective of this study was to evaluate different models in the adjustment of weight gain (WG) responses, obtained in an experiment carried out with ISA Label birds from 1 to 28 days of age. A total of 480 male and female chicks were distributed in a completely randomized design, in a 4 X 2 factorial arrangement (lysine levels X sex), with three replications of 20 birds each. The basal diet was formulated to meet the chick requirements, except for lysine. This diet was supplemented with L-lysine HCl replacing the L-glutamic acid and resulting in experimental diets containing 0.85, 0.97, 1.09 and 1.21% digestible lysine. The weight gain response was adjusted to lysine levels according to following models: Linear Response Plateau (LRP), segmented regression with two slopes, quadratic and exponential. The first interception of the quadratic model on the LRP plateau was used to estimate the optimum lysine level. The lysine levels estimated according to LRP, segmented regression and quadratic models were 0.999, 1.010 and 1.116%, respectively. The digestible lysine level estimated by the combination of quadratic with LRP models was 1.041%. The exponential model provided an estimate of digestible lysine digestible of 1.066%, considering 95% of the asymptotic response. Based on the economic approach this model generated estimates of 1.000 and 1.030%, when the L-lysine cost was R$ 8.50 and R$ 6.50, respectively. Considering the limitations of each one of the proposed models, procedure to estimate the digestible lysine by the interception of quadratic equation with LRP plateau was the most adequate to optmize the weight gain of the birds when economic variables were not considered.
Palavras-chave : broilers; digestible lysine; dose-response; regression models.