Bovine mastitis in Finland in 1988 and 1995--changes in prevalence and antimicrobial resistance.

Two surveys were carried out (during 1988 and 1995) to estimate the prevalence of bovine mastitis in Finland. In 1988, 17,111 quarter milk samples were obtained from 4495 cows, and in 1995 the corresponding figures were 10,410 and 2648. Antimicrobial susceptibility of mastitis pathogens was studied. Prevalence of mastitis on cow basis decreased from 47.8% in 1988 to 37.8% in 1995. Staphylococci was the largest group of pathogens isolated. The proportion of Staphylococcus aureus decreased and that of coagulase-negative staphylococci (CNS) increased. The proportion of strains resistant to at least one antibacterial drug increased with regard to S. aureus from 36.9% in 1988, to 63.6% in 1995 and with CNS from 26.6% to 49.7%. Most of the increase in antibacterial resistance was due to a higher number of beta-lactamase producing strains. Multiresistance also increased, but it was proportional to the overall increase in resistance. All the predominant mastitis streptococci were susceptible to beta-lactams tested.