Coagulase-negative staphylococci and mammary gland infections in cows

Coagulase-negative staphylococci (CNS) are the most frequently isolated bac teria from bovine mammary gland milk samples. The objective of this study w as to determine the type of inflammation evoked by CNS in the mammary gland of cows during their first lactation. Twenty-four Israeli-Holstein heifers in their first lactation were tested for bacteriological status, somatic c ell count (SCC) and differential leucocyte count in milk 60-120 days postpa rturition and every 50-60 days after until drying off. Following the first testing, the 96 quarters of the 24 heifers were classified as follows: 69.8 % as no bacterial growth (NBG), 27.1% infected with CNS and 3.1% infected w ith Staphylococcus aureus. During lactation, 84.5% quarters had no change i n their classification, 6.2% were newly infected with other pathogens, 3.1% were classified as self-cured and in 6.2% sporadic bacteria mere isolated. Among the CNS, S. intermedius, S. chromogenes and S. haemolyticus were the most frequently isolated. Milk from CNS-infected quarters had significantl y higher SCC than milli from NBG quarters. An analysis of the leucocyte pat tern in milk from CNS vs. NBG quarters revealed a significant increase in p olymorphonuclears and a significant decrease in the percentage of total lym phocytes and lymphocytes bearing CD4(+) or CD8(+). The high percentage of C NS-infected quarters that remained unchanged in their bacterial status duri ng the first lactation, indicates that those CNS have the ability to elude the immune system and persist in the mammary gland for a long time. The per sisting infection, resulting to some extent from an increase of SCC by some CNS strains, suggests that in the near future control steps will have to b e taken into consideration, in order to enhance the improvement of milk qua lity.