Seasonal variation of body condition in feral horses at Tornquist Park, Southern Pampas, Argentina

Monitoring the body condition of feral horses is important for animal welfare considerations and to anticipate population densities that affect the ecosystem. Monthly adult body condition scores (BCS) were estimated in a population of feral horses in an Argentine grassland nature reserve in 2001 and 2002, when the population reached maximum historical density approaching estimated carrying capacity. Monthly mean BCS showed a seasonal pattern. Female BCS was higher throughout 2001 with respect to 2002, while males only showed this pattern between wet seasons. BCS was higher for males than for females throughout the study and also higher during the wet season for both sexes. Mean monthly BCS of males was correlated to precipitation of the previous month, which is known to determine grass productivity in the area. Lower BCS values for females can be explained by the additional energy expenditure associated with pregnancy and lactation. In many cases, continuous monitoring of body condition is not possible and then it is important to identify times of the year when it is a more sensitive indicator of the population’s proximity to carrying capacity. For the area, this would be during the peak of rainfall in autumn or the minimum of rainfall in winter. The estimates corresponding to females would be especially accurate considering their dependence to density and rainfall. The implementation of management measures guided by BCS could avoid reaching population levels close to carrying capacity, reducing the negative impacts on the environment and on the welfare of the horses themselves.