Studying Growth Pattern and Body Weight Gain of Isfahan Native Chickens

Native chickens are playing an important role in rural economy in most of the developing and underdeveloped countries. One of the sources that provides protein in developing countries, is native chicken. So, they should be taken in to consideration in poultry improvement programs. Mathematical functions called ‘growth functions’ have been used to relate body weight to age or cumulative feed intake. Growth models summarize information needed to understand the biological phenomenon of growth; an important component in livestock production systems. They are used to determine the age-live weight relationship of animals and each its own characteristics and mathematical limitation.
Little is known about the productive performance of native chickens, so the objective of the present study was to characterize growth performance and growth curve of Isfahan native chickens under a confined system.  The chickens of this study included 230 of Isfahan native chickens which were reared for 12 weeks. The birds were raised under the same condition in the rearing period. Feed and water were provided ad libitum. Temperature and air humidity in the hall were measured and controlled automatically day and night. The average temperature was 25°C (max 32°, min 18°) and air humidity was 60-65%. During raising period, chickens were vaccinated and dewormed following the sanitary program of the region. The lighting program consisted of 24 h from 1 day to 12 weeks of age. At 1-day of age, each chick was weighed and marked with color plastic tags attached on the on the right leg. The chickens were individually weighed weekly until the end of the experiment. Some morphometric traits were measured at weeks 3, 6, 9 and 12. Morphometric traits were included breast width, breast length, thigh diameter, thigh length, shank diameter and shank length. Those measurements were done on day 84 with the help of a field assistant, so the birds each time were held in comfortable position and measurements taken in particular order for above mentioned times for accuracy. The chickens were slaughtered and after determining their sex, divided into economics parts. The carcass traits evaluated included live-weight at 12 weeks of age, carcass weight, carcass yield, and primal cuts (breast, thighs, wings and back and neck) weight. Flexible growth and fixed point of inflection functions were evaluated for their ability to describe the relationship between live-weight and age. For Three non-linear growth functions (Gompertz, Logestic and Richard), were used for this purpose. The accuracy of the used functions was determined by determination coefficient (R2), root mean square error (RMSE) and Akaike’s information criterion (AIC). Statistical analysis of data collected in this study was performed using the SAS statistical program v9.1.  Based on goodness of fit criteria and statistical analysis, the flexible growth functions fit the data better than the functions with a fixed point of inflection. Richard’s function gave the best fit to the data with r2adj= 0.96 for both sexes. The results indicated that male broilers had a higher final body weight than the female broilers. Sex had significant influence on live weight from the second week until the last week and no significant influence on live weight of first week. Chicken sex had significant influence on carcass and abdominal fat weight, yields of thighs, breast and wings and no significant influence on carcass yield. Male chickens were found to have higher live body weight, carcass weight, yields of thighs, whereas yields of breast and wings were higher in female chickens. Breast width of males in every week numerically was higher than females, but this difference was statistically significant at weeks of 6 and 9. Length of the breast at weeks 6, 9 and 12 was significantly higher than females. Thigh diameter of males numerically was higher than females but this difference was statistically significant at weeks 6, 9 and 12 only. Length and diameter of the shank in males was significantly higher than females in each week.  The male chickens had superior growth performance and higher potential for selection and breeding. Comparison of tree growth functions in terms of goodness of fit criteria revealed that the Richard’s function was the most appropriate function for describing the age-related changes in body weight of native chickens. Special attention should be paid to characterization of the growth pattern of birds under different environmental conditions. The development of growth curves for native chickens may be useful in selecting chickens that have rapid growth at early ages.