. . "The apparatus of claim 19 wherein the simultaneous equations have the form: W=Ae (--e (--k(t--t*))) where W is the current body weight of the animal, A is the weight of the animal at physical maturity, t is the current age of the animal, and t* is the age at which the animal achieves its maximum rate of growth, and k is a growth rate factor, k and t* being statistically related. 21." . . .