Efficacy of a biological response modifier in preventing Staphylococcus aureus intramammary infections after calving

A change in the epidemiology of mastitis in recent years has emphasized the role of the udder immune system in the pathogenesis of Staphylococcus aure us. Therefore, if the bovine or udder immune capability could be enhanced, susceptibility to Staph. aureus could be reduced and antibiotic efficacy co uld be increased. Immune system defense mechanisms could be enhanced by vac cination and by biological response modifiers. Within this latter group, a biological response modifier obtained from Parapox ovis that was attenuated over 200 tissue culture passages was recently developed and commercialized in some European countries. This study reports the results of a field tria l on the efficacy of this biological response modifier in reducing Staph. a ureus intramammary infection (IMI) after calving in primiparous and pluripa rous cows. The trial included 106 cows sampled six times (55 cows from herd A and 51 from herd B) for a total of 2544 quarter milk samples. The analys is of IMI prevalence showed that 25.09% of samples were bacteriologically p ositive in the placebo group, and 23.17% of the positive samples were obser ved in the biological response modifier group. Staphylococcus aureus IMI ha d a frequency of 11.44% in the placebo group and 6.00% in the biological re sponse modifier group. The dynamic of the hazards showed significantly lowe r rates in the biological response modifier group than in the placebo group (risk ratio = 0.47). Treatment with the parapox-containing biological resp onse modifier showed significant reduction of Staph. aureus IMI around calv ing, and this reduction was attributed to an increase in immune defenses.