Modeling the growth of tissues in broiler chickens

The development of the animal?s body occurs in three stages: visceral organs, structural tissues and muscle deposition. The knowledgement of the tissue?s development is the first step to model nutritional requirements. Thus, the aim of this study was to determine the growth of the broiler?s tissues using the Gompertz equation. For this trial, 136 male chicks (Cobb 500^(R)) were allocated in individual cages and raised until 70 days of age. The diets were formulated according to the recommendations in the Brazilian Tables. Tissues (liver, tibia and pectoral muscle) were collected in 10 successive slaughters (four broilers slaughtered per week) to obtain the tissue weights (g). For the collection of tissues, the liver was completely extracted, the bone of the right tibia was removed and its value was multiplied by two to make up the total weight of the tibias and the pectoral muscle was completely removed. For the description of tissue?s growth curves, the weights (g) of the tissues were adjusted by Gompertz equation: . Where: Wt is the tissue weight (g) at time t (day); Wm is the mature weight of the tissue (g); B is the maturity rate of the tissue (day^-1) and t* is the time (day) at witch growth rate is maximum. Growth rates (GR) are obtained by the derivative of the Gompertz equation: and it was used to determine when the tissue showed maximum growth for each day. Respectively, the parameters for liver, tibia and pectoral muscle were presented as: Wm (g) = 93.37, 43.41 and 2098.94; B (day^-1) = 0.059, 0.0478 and 0.0412; t*(days) = 20.53, 32.78 and 43.97, and R? = 0.91, 0.98 and 0.99. The GR (g/day) values for the liver, tibia and pectoral muscle were 2.02 (21 days), 0.76 (35 days) and 31.68 (42 days), respectively. Organs such as liver reached its higher growth rate earlier than others tissues; structural tissues such as tibia are required to support muscles and to protect soft organs; in the final stage, the pectoral muscle was the last tissue to achieve the maximum growth rate. Based on the results, the model reflects the physiological development stages of the broiler and can be used to demonstrate growth of individual tissues and develop nutritional strategies to maximize the growth rate of these tissues.