بررسی منحنی رشد مرغ شاخدار خاکستری مرواریدی با مدل‌های مختلف غیر‌خطی

Introduction: In low-income and marginalized rural communities, poultry species play a vital role as sources of animal protein and household income. The guinea fowl belonging to the Galliformes order and the Numididae family, is particularly important in these communities. Understanding the growth characteristics and patterns of guinea fowl can be crucial in successfully raising them as a profitable enterprise. This knowledge can help in developing appropriate nutritional and feeding regimens to optimize feed usage and increase profitability. Growth is a complex process that involves physiological and morphological changes from hatching to maturity. It is defined as the increase in body weight and organ size over time and age. This growth can be described using mathematical non-linear models that capture biologically significant parameters. Since growth patterns vary significantly between species and genotypes, it is important to analyze growth for each specific species. While various models have been introduced in different studies to describe the growth curve of different species, research on the growth pattern of guinea fowl is limited. Therefore, this study aims to evaluate different non-linear models to determine the most suitable model for describing the growth pattern in both male and female pearl grey guinea keets.
Materials and methods: The present study was conducted on pearl grey guinea keets raised at the Special Domestic Animals Institute, Research Institute of Zabol, Zabol. A total of 129 one-day-old keets (70 males and 59 females) were obtained from the hatchery and then identified by wing-banded numbers. All keets were individually weighed every week until 28 days of age and then every two weeks until 168 days of age using a sensitive digital electronic weighing scale. After data editing, Gompertz, Richards, Logistic, Weibull, and Lopez models were fitted to describe the growth curve of female and male keets. Four goodness of fit criteria including mean square error (MSE), Akaike information criterion (AIC), Bayesian information criterion (BIC), and adjusted determination coefficient (R_Adj^2) were used to compare the studied models and select the best model to describe the growth pattern in both sexes. All models were fitted to the body weight of male and female keets using the nlme package of R software, and model parameters were obtained for both sexes.
Results and discussion: Male keets had higher body weight than female keets at all ages. The difference in body weight between the two sexes was not significant until the eighth week (P<0.05), but from 10 to 20 weeks of age, a significant difference was observed (P<0.05). The highest and lowest values for the initial and final weight parameters were related to the logistic model in both sexes. Male keets had higher maturing index (k), shape parameter (m), age and weight at the inflection point, and absolute growth rate at 1, 12, and 24 weeks of age compared to female keets. Based on goodness of fit criteria, the Lopez model was found to be the best model among those studied to describe the growth pattern in male and female keets. When comparing actual body weight with predicted values from the studied models, the Lopez model closely matched the actual values at most ages, indicating that the Lopez model provided a more accurate prediction of body weight in both male and female keets compared to other models.
Conclusions: Based on the findings of the present study, the Lopez model was determined to be the best model in describing the growth pattern in female and male keets. Understanding the growth pattern in both sexes can assist in developing nutritional programs to meet nutritional needs at various ages. Overall, additional research is needed to investigate the model parameters and explore the potential of incorporating them into selection programs to attain the desired growth curve.