We have considered, as general models for the evolution of animal
size in a random environment, stochastic differential equations of the form dY(t)=b( A-Y(t))dt+\sigma dW(t), where Y(t)=g(X(t)), X(t) is the size of an animal at time t, g
is a strictly increasing function, A=g(a) where a is the asymptotic size, b>0 is a rate of approach to A, s measures the effect of random environmental fluctuations on
growth, and W(t) is the Wiener process. The transient and stationary behaviours of this stochastic differential equation
model are well-known. We have considered the
stochastic Bertalanffy-Richards model (g(x)=x^c with c>0) and the stochastic Gompertz model (g(x)=ln x). We have studied
the problems of parameter estimation for one path and also considered the extension of the estimation
methods to the case of several paths, assumed to be independent. We used numerical techniques to obtain the parameters estimates through maximum likelihood methods
as well as bootstrap methods. The data used for illustration is
the weight of "mertolengo" cattle of the "rosilho" strand
