Animal growth is a complex and dynamic process that involves physiological and morphological changes from hatching to maturity. It is defined as the increase in body size per time unit. Mathematical functions, called growth models, have been used to explain growth patterns. The aim of this study was to compare the Gompertz-Laird, logistic, Richards, and Von Bertalanffy growth models to determine which best fits the data of the Creole chickens ( CC ). Three hundred forty-seven CC were individually weighed from hatching until 177 D of age. Birds were fed a starter diet (0–18 D of age; 19% crude protein ( CP ) and 3,000 kcal of ME/kg) and grower diet (19–177 D of age; 18% CP and 2,800 kcal of ME/kg). Data were analyzed using PROC NLIN to fit the nonlinear growth curve. The coefficient of determination ( R 2 ), Akaike information criteria ( AIC ), and Bayesian information criteria ( BIC ) were used to compare the goodness of fit of the models. The Von Bertalanffy (R 2 : 0.9382, 0.9415; AIC: 2,224.1, 2,424.8; BIC: 2,233.5, 2,434.3, for females and males, respectively) was the model that best explained growth of the birds. On the other hand, both the Gompertz-Laird and logistic models overestimated hatching BW and underestimated the final BW of CC. Females reached age of maximum growth faster than males. The asymptotic weight was higher in males (3,011 g) than in females (2,011 g). Body weight at inflection point was 892 g at 64 D of age for males and 596 g at 54 D for females. In conclusion, the best fit of the data was obtained with the Von Bertalanffy growth model; the information is intended to serve as the basis for utilizing CC.

A study was conducted to characterize the backyard chicken production system in Campeche State, Mexico, as the basis of a program for utilizing local poultry genetic resources. A total of 260 surveys were administered in person. The housewives undertake backyard production activities. Farmers have, on average, 0.20 ± 0.1 hectares for raising local chickens (LC). Flock size was 24.4 ± 1.3 birds per household. The number of egg/hen/year was 45.8 ± 1.6. Confined and semi-confined production systems are used. Farmers fed chickens with corn, whereas chicks were fed with commercial feed. During the rainy season, flu and diarrheal diseases are more frequently observed. Body size is the main trait for acquiring/selecting breeders within/outside the flock. Selection of eggs for incubation is based on size and freshness. Families consume LC meat 3.5 ± 0.2 times a month and 17.0 ± 1.0 eggs a week. Farmers sell 1.6 ± 0.2 birds per month and 7.6 ± 0.7 eggs per week to get $8.99 ± 0.93 and $3.82 ± 0.33 USD, respectively. Feed shortages, diseases, predators, and lack of technical assistance services were the major constraints for LC backyard production. In conclusion, backyard chicken production based on LC provides a readily available source of animal protein and cash income for households in Campeche State, Mexico.

Objetivo: Evaluar el crecimiento de pollos de engorda criados en pastoreo o confinamiento, mediante los modelos Gompertz, Logístico y Richards, e identificar el más adecuado. Metodología: Ciento diez pollos de engorda mixtos Ross 308 se distribuyeron en dos sistemas de crianza: pastoreo o confinamiento. Semanalmente se obtuvo el peso corporal de cada ave, hasta los 56 d de edad. Tres modelos de crecimiento (Gompertz, Logístico y Richards) fueron considerados y se compararon con base en tres criterios de bondad de ajuste (coeficiente de determinación, criterio de información de Akaike y criterio de información Bayesiano). Resultados: Las tasas de crecimiento inicial (L) y exponencial (K) de los modelos Gompertz y Logístico, respectivamente, fueron mayores en las aves en confinamiento (L = 0.1232, K = 0.0779) respecto a las criadas en pastoreo (L = 0.0944, K = 0.0657). El máximo crecimiento relativo (K) del modelo Richards fue menor en pollos en confinamiento (0.0129) que en pastoreo (0.0153). Con los tres modelos, se estimaron mayores pesos asintóticos (WA) para los pollos en confinamiento (3,967.1 a 9,095.5) respecto a las aves en pastoreo (2,461.7 a 5,192.6). De acuerdo a los criterios considerados, el modelo Richards es el que tiene un mejor ajuste.         Implicaciones del estudio: Los resultados obtenidos sólo son válidos para pollos de engorda mixtos Ross 308 y bajo las condiciones de manejo especificadas. Conclusión: El crecimiento de pollos de engorda criados en confinamiento o pastoreo, puede describirse con los modelos Gompertz, Logístico y Richards, sin embargo, este último tiene un mejor ajuste.