SummaryA total of 59 mastitis staphylococcic strains were tested for growth agglutination upon supplementation of growth media with ovine and bovine milk whey and mammary secretions from dry cows. Differences were observed when comparing bacterial species or origins (ovine vs. bovine) of bacteria and whey. All of the ovine and bovineS. aureusstrains tested, but only 4 among 22 other ovine mastitis staphylococcic strains, showed growth agglutination in Todd Hewitt broth (THB) supplemented with ≥ 30 % (v/v) ovine milk whey. None of the strains agglutinated during growth in regular THB medium. Ovine whey had an agglutination induction capacity higher than bovine whey (P< 0.005), concerning the number of responsive ovine and bovineS. aureusstrains. There were no differences between whey samples from different ewes with regard to their capacity to induce agglutination. OvineS. aureusstrains were more responsive than bovine strains of this bacterial species, concerning the number of responsive strains (P <0.001) to bovine whey (≥ 30 % in THB), the proportion of responsive strains at low (10%) ovine whey concentrations (P<0.001), and the strength of reaction (precipitation timing and clump sizes). Secretions from dry cows systematically induced agglutination in all of the bovine and ovineS. aureusstrains tested.