Control of intramammary infections in goats: impact on somatic cell counts.

Udder-half infections were recorded throughout a lactation for 1,060 goats belonging to eight commercial herds. Bacteriological examination from aseptic milk samples and somatic cell counts (SCC) determined by Fossomatic cell counting were performed at the beginning, the middle, and the end of lactation. Coagulase-negative staphylococci (CNS) were the prevalent microorganisms isolated. Geometric means of SCC for uninfected halves or halves infected by CNS or major pathogens were 272 x 10(3) cells/mL, 932,000 x 10(3) cells/mL and 2,443,000 x 10(3) cells/mL, respectively. Two field trials were carried out for evaluation of effectiveness of systematic treatment at drying-off (1 syringe by half) by a combination of penicillin, nafcillin, and dihydrostreptomycin labeled for bovines. In the first trial, all goats (n = 217) of two herds were treated immediately after the last milking, and two herds (n = 196) were used as untreated controls. In the second trial, 215 goats were treated at drying-off. There were no untreated controls. Dry period cures were determined by bacteriological examination of udder-half milk samples collected aseptically at drying-off and 2 wk after parturition. Impact of treatment on SCC was determined from composite milk samples collected monthly after kidding. At parturition, in the first trial, 40 of 202 (19.8%) udder halves were spontaneously cured in the control group vs 169 of 217 (77.9%) in the treatment group. In the second trial, 141 out of 215 treated halves were cured. During the first 75 d in lactation, geometric mean SCC was significantly lower for treated goats than for control goats. After 75 d, SCC for treated and control goats were similar. These data suggest that other methods are required to prevent new intramammary infections throughout the lactation in order to keep a low SCC in goat milk. To determine whether this could be accomplished through teat dipping, half of the goats in five commercial herds were dipped (n = 294) after morning and evening milkings through the lactation (10 mo) with a teat dip product containing nisin. Undipped goats (n = 292) served as a control group. No difference was found for SCC in milk between the dipped and undipped groups. It was concluded that systematic treatment of goats at drying-off is an efficient method for the cure of subclinical mastitis and control of SCC at the beginning of the following lactation and that effectiveness of postmilking teat disinfection remains to be demonstrated.

Efficacy of a germicidal post milking barrier-type teat dip in preventing intramammary infections.

Five commercial dairy herds with 269 lactating cows participated for 12 months in a field trial to determine the effectiveness of a barrier teat dip containing chlorous acid/chlorine dioxide germicide. The right quarters of the cows in two herds and the left quarters of the cows in three herds were dipped in the experimental teat dip after the removal of the milking machine. The other quarters were dipped in a conventional 0.5 per cent iodophor product. Compared with this control product, teat dipping with the experimental dip reduced the number of new intramammary infections by 18.8 per cent, infections with major pathogens by 13.6 per cent, infections with minor pathogens by 16.8 per cent and clinical mastitis by 33.3 per cent. Statistical analysis indicated a trend towards decreased intramammary infections with coliforms and coagulase-negative staphylococci when the experimental teat dip was used. It was concluded that under the conditions of this investigation it was effective in preventing new infections due to both contagious and some environmental pathogens. However, the data suggested that it could adversely affect the condition of the skin of the teat when it was used after incorrect preparation of the udder.

The contribution of mammary infections by coagulase-negative staphylococci to the herd bulk milk somatic cell count.

Quarter foremilk samples were taken at 2-3 weekly intervals for several years in an experimental herd comprising about 45 cows. The samples were submitted to bacteriological analysis and somatic cell counting. The most prevalent quarter infections from 1982 to 1988 were by coagulase-negative staphylococci (15-20% of all the quarters sampled). Most of these (75.6%) persisted until drying-off. Dry cow therapy eliminated 86.5% of these infections. Comparison of udder quarters within cows, involving 775 samples from pairs of non-infected quarters and quarters infected by coagulase-negative staphylococci, yielded geometric means of somatic cell counts of 210,000 and 420,000 cells/ml, respectively. The correlation (r = 0.87) between the herd bulk milk somatic cell count (SCC) and its estimation from the quarter milk somatic cell count performed on the same day allowed us to evaluate the contribution of the different categories of quarters, according to their infection status, to the herd bulk milk SCC. Quarters infected by a major pathogen (8.5% of samples) gave rise to 46.6% of the total number of cells, while quarters infected by coagulase-negative staphylococci (17.8% of samples) gave rise to 18.1%. Although coagulase-negative staphylococci represented only a secondary source of somatic cells as compared to major pathogens, they were not a negligible source considering the threshold of 300,000 somatic cells advocated for herd milk of good quality.

Evaluation of three rapid tests for identification of Staphylococcus aureus isolated in bovine milk.

In order to develop a routine and rapid method for the identification of Staphylococcus aureus isolated from bovine milk, three tests were evaluated with 200 strains isolated from different regions. Tests were performed with colonies isolated from the initial agar plate medium. Clumping factor reations were positive with 93.5% of the strains, beta hemolysin with 76% and protein A with 56% of them. It was found the three tests were never all negative for any particular strain. A scheme for rapid identification is proposed.