| The objectives of this study were to determine the efficacy of a new intramammary dry cow antibiotic formulation for eliminating existing mastitis and preventing new intramammary infections (IMI) during the dry period, and to identify important risk factors for both elimination and prevention of IMI in the dry period. The impact of milk production and other important management strategies on the efficiency of the drying-off process were also studied.;Administration of intramammary tilmicosin phosphate at the end of lactation, as compared to a positive control, significantly reduced existing infections caused by Staphylococcus aureus, and was as efficacious in eliminating infections caused by mastitis pathogens other than S. aureus. Furthermore, when compared to an intramammary negative control placebo, intramammary tilmicosin reduced the rate of new IMI that occurred during the dry period. It was concluded that intramammary tilmicosin phosphate was an effective dry cow antibiotic formulation.;The probability of curing S. aureus in the non-lactating period, was decreased when somatic cell counts prior to drying-off were increased, when multiple positive culture results of that organism were obtained, and when the infection occurred in a hind quarter. The probability for a quarter that was uninfected at the time of drying-off to develop new IMI, was increased with higher levels of milk production, increased dry period length, and greater parity.;There was considerable variation in both the decline, from two weeks prior to drying-off, and the actual level of milk production on the day of drying-off. There was a significant relationship between the level of milk production and the rate at which the teat canal keratin plug formed during the dry period. Teats that did not form a teat canal keratin plug were significantly more likely to develop new IMI in the dry period. In addition, teat-ends that had a visible crack were significantly more likely to develop new IMI than teat-ends without cracks. These findings reinforce the importance of the teat as the first line of defence to new IMI. |
