GM 05. Non linear functions to describe circumference scrotal growth in Brazil goats

Resumo

Four functions to characterize scrotal circumference (SC) growth in goats were compared to identify which one was the most suitable for biological interpretation. Animals were 30 goats males, born in EMEPA-PB, João Pessoa, Brazil. At the time of SC measurements, the ages of the animals were 14, 28, 42, 56, 70, 84, 98, 112, 126, 140, 154, 168, 182 and 196 days. The functions used to describe the data were: Brody, SC = A (1 - B exp -kt ); Logistic, SC = A / (1 + B exp -kt ); Gompertz, SC = A exp(-B exp -kt) and Richards SC = A (1 + B exp -kt )m, where SC is the scrotal circumference at age t, A is the estimated SC at maturity, B is the integration constant established by the initial values of SC and t, k is the maturity constant and m is the inflection point parameter for Richards function. Logistic was selected as the best equation to represent SC growth based on the statistics error mean square, coefficient of determination and average prediction error. In addition, it required the lowest number of iterations for convergence and generated the least computing difficulty. For the Logistic function, estimated SC at maturity (A) was 22.26±2 cm at 72 months of age. The maturity index (k) was .012 cm and the inflection point (time of maximum growth) was reached at 81 days of age at an average SC of 11 cm.