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Feral and conventional growth performances were compared using Marismeña cattle as a model. Marismeña calves are commonly reared under feral conditions in one of the most important reserves of Europe (Doñana National Park, Spain). Data recording in these natural conditions faces compromises as animals are only handled once per year. This fact has to be saved to obtain efficient estimations for the biological growth curve of cattle reared under feral conditions. On the one hand, we assessed the inference of the theoretical influence of human management on cattle growth. On the other hand, we studied the fitness of the best growth curve, in both feral and conventional systems to use the physiological meaning of the parameters obtained from their study as selection criteria related to the adaptability of potential breeding males and females. Fitting of Brody's, von Bertalanffy, Verhulst, logistic, Gompertz and Richards’ models was tested as these models are the most representative ones for cattle growth. In general, Brody's and Richards’ models presented the best fitting values for the biological curve. According to the biological curve parameters, males and females presented asymptotic weights of 641.71 kg and 403.55 kg, respectively. As expected, the results of the commercial growth curve severely differed from those of the biological curve. The best fitting biological curve was not representative for cattle reared under commercial conditions. The logistic model was the best fitting one for feral females, Gompertz model for feral males, and Verhulst for intensive males and females, respectively. Seasonal oscillations in feeding may be responsible for the earlier achievement of the best performance in feral cattle (7 and 10 months for males and females, respectively), while such best performances were reached at 11 months in intensive calves, what becomes relevant for management and slaughtering decision-making. The study of the biological curve in Marismeña feral breed is very illustrative as this is the first time that feral cattle's growth is approached. Knowledge on the biological growth curve parameters could be used to interpret the strong relation between feral animals and their environment. This research could infer a model to quantify the effects of human management on livestock development, as feral resources offer unique opportunities to study domestic livestock without any human influence.

We examined commercial growth curves of three sheep genotypes in a Second-Grade cooperative context, with Spanish Merino used as a maternal base, Fleischschaf as a paternal base, and crossbred (Fleischschaf × Merino) lambs as the commercial product. We included weight-age data collected from 2013 to 2016 for 9846 lambs of both sexes belonging to 14 herds across the three genotypes. Five of the most-cited models (Brody, von Bertalanffy, Verhulst, Logistic, and Gompertz) were applied to the data, using the determinative coefficient, mean square error, number of iterations, Akaike information coefficient, and the biological coherence of the estimated parameters as best-fitting criteria. The dataset included lamb weights at different ages and sexes, grouped across nine age levels, for a total of 23,299 wt records. Models were fitted according to non-linear regression. The von Bertalanffy model was found to best fit lambs of both sexes for the Spanish Merino breed, whereas the Verhulst model best fit Fleischschaf and crossbred lambs. Parameters of the best-fit curve and derived parameters (inflection age and weight, asymptotic value, growth rate, maturity degree) were estimated for all sex-genetic groups to examine capacities for use as complementary selection criteria in the breeding program, resulting in promising traits for this purpose. Our findings demonstrate that current crossbreeding strategies implemented at the OVISO cooperative, which seek complementarities and/or heterosis, are not achieving the expected results; therefore, we recommend a new strategy for the breeding program. We also found that artificially conceived Spanish Merino lambs exhibited better performance than those conceived naturally, likely due to superior genetics of carefully selected sires.