Describing and Comparing of Growth Pattern of Morphometric Traits in Isfahan Native Chickens Using Three Nonlinear Models

The objective of the present study was to characterize the growth pattern of morphometric traits of Isfahan native chickens. For conducting this research, 200 (112 males and 88 females) of Isfahan native chickens were reared for 12 weeks. At day 1, each chicken was weighed and marked with color plastic tags attached on the one leg and then weighed weekly. At weeks 3, 6, 9 and 12 morphometric traits such as breast width and length, thigh diameter and length, shank diameter and its length were measured. Flexible growth and fixed point of inflection functions were evaluated for their ability to describe the relationship between morphometric traits and age. Three non-linear growth functions (Gompertz, Logestic and Richards), were used for this purpose. Based on models fitting criteria and statistical parameters, all three models gave a good fit to the data (r2adj≤ 0.90), but the Gompertz function gave the best fit to the data. The results indicated that male broilers had a higher final body size than the females. In general, males had higher asymptotic body size and lower growth rate than females. Females reached to maximum growth rate faster than males and had a lower body size in the inflection point. The correlation between body weight and morphometric traits at week 12 for both sexes were positive and significant (p < 0.05) and the correlation values were moderate to high (0.03<r<0.82). In conclusion, based on the differences in the growth pattern of chicken sexes it advised that in the rearing of