The present work analyzes the most important mechanisms of stress on animal reproduction. Genetic selection for certain productive characteristics added to the metabolic demands imposed by thc current production systems create a marked susceptibility to illness, as well as the reduction on reproductive function.It is important to begin to create conscience on the use of rational practices and thc search of better productive systems based on better knowledge of ethology and the animal well-being. This gains bigger importance, when in the future the organizations of animals rights will mark our professional activity.