GROWTH-CURVES OF ZEBU MALES ON A FEEDING SYSTEM BASED ON PASTURES

From data of monthly weighings in performance tests under grazing cond itions of Zebu males, the liveweight development of two animal populat ions including two dynamic periods of time was studied through a growt h model. There were 13373 observations corresponding to 1217 animals i n 5 years of the study. The Initial weight considered was at 8 months of age and each animal had 11 observations. For growth representation a multiplicative model including the effect of the growth curve was us ed: [A(exp) (bt + ct(2) + dt(3)], the effect of the animal [V(k)], the effect of the bimester [M(i)], that of the year [Y(j)] and the year x bimester interaction [MY(ij)]. The model was the following: P-ijkn = A(exp) (bt(ijkn) + ct(ijkn)(2) + dt(ijkn)(3)) M(i)Y(j) (MY)(ij) V-k E( ijkn) The curves of both populations showed high levels of adjustment with coefficients of determination of 0.972 and 0.967, respectively. T he inflection points were at 555 and 475 days with maximum instant gai ns of 703 g/day and 746 g/day, respectively. The effector bimester and the year x bimester interaction were significant (P < 0.001). There w as a poorer performance in the dry season bimesters, especially in Mar ch-April It is concluded that the use of models which study growth and the factors affecting it is an important way of arriving at criteria which allow to improve the efficiency of animal performance and the ne ed of continuing the development of models which consider not only the parallel effects to the growth curve but also the perpendicullar ones such as the sire effect.