Abstract
Aim of the study: To adjust nonlinear Gompertz model to describe the body growth and feed intake (FI) of free-range chickens of the CPK (Color Plumé) strain, receiving different levels of digestible lysine (dig-Lys), from 21 to 77 days of age.Area of study: São Cristovão, Sergipe, Brazil.Material and methods: A total of 432 one-day-old unsexed chickens were used in the study. At 21 days of age, the birds were assigned to four treatments (0.85%; 0.97%; 1.09%; 1.21%) of dig-Lys, in a completely randomized design with four replicates, with 27 birds per experimental unit. The Gompertz model was used to estimate bird growth curves related to body weight (BW) and FI at each Lys level.Main results: The tests of comparison between the parameters of the Gompertz model for each Lys level showed that parameter A varied, while parameters B (0.0329) and C (45.819) did not differ significantly. In parameter A, the dig-Lys level of 0.97% provided the highest BW estimate at maturity and maximum BW at the inflection point.Research highlights: Use of non-linear models to predict nutritional requirements, helps farmers to optimize management decisions and, thus, maximize their profit. According to Gompertz model, it was possible to infer that the inclusion of 0.97% dig-Lys in the diet of mixed batches of free-range chickens of the CPK strain meets their nutritional requirements.
Highlights
Free-range chicken farming is an activity that represents an economic alternative for small and big entrepreneurs, considering that consumers seeks products with different characteristics from those found in the conventional fast-growing chickens
Associated with this result, the Gompertz equation derivation allowed to verify that the maximum body weight (BWe) of the birds related to the dietary treatment with 0.97% of digestible lysine (dig-Lys) was higher (BWe=1916.6g), but with WGe (58.6g) lower when compared to treatment with 0.85% of dig-Lys
Determination coefficients higher than 99% were observed and a high correlation (DW statistics) between observed and estimated data was obtained for body weight (BW) at the dig-Lys level of 0.97% (Table 2)
Summary
Free-range chicken farming is an activity that represents an economic alternative for small and big entrepreneurs, considering that consumers seeks products with different characteristics from those found in the conventional fast-growing chickens. Free-range chickens have a slower growth rate and, slaughtered at older ages, which in turn requires nutritional adjustments to improve their growth. Diets for chickens reared in free-range systems usually include corn and soybean meal as main energy and protein sources (Ferreira et al, 2014); these ingredients may not be sufficient to meet the nutritional requirements of these animals, especially in terms of essential amino acids such as Lys and methionine.
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