The loss of opsonic activity of bovine milk whey following depletion of IgA.

The role of the IgA antibody to Streptococcus agalactiae found in the whey of milks 12 hours after the first intramammary infection of six Friesian first lactation heifers was assessed using an in vitro bactericidal assay. The mean percentage kill of the streptococci by neutrophils in the presence of these wheys was 36.2% while the equivalent figure for the non-infected quarter whey was 0%. When the IgA antibody was absorbed from the infected quarter wheys using class specific IgA antiserum cross linked with glutaraldehyde the percentage kill of the test system fell to 0%. Elution of the absorbed antibody partially restored the activity to a mean percentage kill of 18.2%. The results indicated that the IgA antibody found in infected quarter whey during the acute stages of intramammary infection with Streptococcus agalactiae was responsible for the opsonic activity which pertained at that time.

Clinical features of consecutive intramammary infections with Streptococcus agalactiae in vaccinated and non-vaccinated heifers.

The clinical, haematological and functional changes which followed three consecutive intramammary infections of Streptococcus agalactiae in the first lactation of eight heifers, four of which were systemically hyperimmune to the organism, are described. Irrespective of whether it was a vaccinated or non-vaccinated heifer or first, second or third infection the clinical features during the first 24 hours were characterised by elevated temperatures with hard, swollen and painful infected quarters. First infections were almost all of short duration because of self cure, while second or third infections were prolonged, with intermittent excretion of bacteria and low cell counts. Milk yields of infected quarters were depressed, ranging from 8 per cent in short infections to 31 per cent in chronic infections. All blood parameters remained within normal limits with the exception of total and differential white cell counts, which showed a change from a quantitative to a qualitative response by the third infection. The most significant finding was the absence of any real difference between the systemically hyperimmune and the non-vaccinated heifers, suggesting that circulating antibody has little effect against intramammary infection.

Enzyme-linked immunosorbent assay for Streptococcus agalactiae antibodies in bovine milk.

An enzyme-linked immunosorbent assay (ELISA) for the detection of Streptococcus agalactiae antibodies in bovine milk was developed using whole bacterial cells as antigen. Microtitre wells were coated overnight at room temperature with a 1:64 dilution of antigen in 0.05M carbonate-bicarbonate buffer at pH 9.6. After washing, milk whey samples diluted 1:40 were added, incubated overnight and again washed. After incubation with rabbit antibovine serum, bound antibody was detected with alkaline phosphatase conjugated sheep antirabbit serum. Using the ELISA, the levels of Str agalactiae antibodies in the individual quarters of the mammary glands of cows in a severely infected dairy herd were measured. A high proportion of cows had specific antibody to Str agalactiae in one or more quarters. Using ELISA in association with electronic cell count and bacterial isolation, it was possible to identify latent and subclinical carriers of infection.