Comparison of different mathematical functions for fitting growth curves of ascitic and healthy broiler chickens

Abstract

Ascites syndrome (AS) causes major economic losses in commercial meattype chickens. The objectives of the current study were to select the best non-linear growth curve functions (GCFs) of the ascitic and healthy chickens, and to investigate the association of ascites incidence with the growth pattern. A total of 5584 body weight (BW) records belonging to 823 chickens (381 male and 442 female) from a paternal pure Arian broiler line were used. The birds were categorized into; healthy male and female, ascitic male and female.Five GCFs including Logistic, Gompertz, Lopez, Richards, and Von baretanalffy were fitted to the BW records of all groups, separately. After the estimation of growth curve parameters for all the chicks individually, the effect of sex and health status on the growth curve parameters were assessed. The results revealed that the Richards function is the best for all the groups. Comparison of the growth curves showed that the ascitic chickens reach the inflection point of the curve earlier than their healthy counterparts (P<0.05). The average growth rate of the healthy birds in the rearing period was significantly higher than that of the ascitic birds (P<0.05), thereby suggesting that there is no direct relationship between the rapid growth rate and the incidence of ascites. Therefore, genetic improvement of the used population for both rapid growth rate and reduced ascites incidence may be possible and the utilization of growth curve parameters in the selection index might be beneficial.