Characterization of the lactation curve of f1 Holstein-Zebu cows

The objective was to find a function to describe the lactation curve of grazing Holstein - Zebu cows (n=23) in tropical Mexico. Twelve were based on the general nonlinear function A*?(1)(x)*?(2)(x): A, a positive scalar; ?(1), a positive monotonically increasing function with asymptote ?(1) = 1; ?(2), is a monotonically decreasing function with asymptote ?(2)=0 and initial value of 1; and x is lactation time (days). For ?(1), the Mitscherlitsch, Michaelis-Menten, generalized saturation kinetics, logistic, Gompertz and hyperbolic tangent equations were used, whilst for ?(2), they were the exponential and inverse linear. A gamma function, the more used, and the addition of two logistic equations, the more biologically explicit, were also included. The smaller value of the Akaike information criterion corrected (AIC(c)) indicated the latter was the one with the best fit, so its use to study factors affecting the lactation curve is suggested.