Staphylococci are the main pathogens responsible for mastitis in dairy sheep flocks. Implementation of a mastitis control program is an essential step in improving milk quality and disease prevention. One of the measures included in these control programs is vaccination. The objective of this study was to evaluate the impact of vaccinating against Staphylococcal mastitis (composed by a Staphylococcus aureus inactivated, expressing Biofilm strain.) on milk yield. The relationship between subclinical mastitis and milk yield is well described in the literature. Mastitis is strongly correlated with a decline in milk yield.