Infusion of either a long-acting
antibiotic preparation (cefalonium) or the same
antibiotic preparation combined with an internal teat sealant (
bismuth subnitrite) were compared for the effect on new intramammary
infections at calving and clinical
mastitis in the first 100 d of lactation, in relation to dry period length. For all cows, a significant reduction in the incidence of new
infections in quarters at calving (3.7 vs. 7.3%) was found for the combination treatment group (150 cows) compared with the
antibiotic-alone treatment (133 cows). With a dry period of 10 wk or longer, significantly fewer new quarter
infections (3.8 vs. 11.4%) were found in those cows receiving the combination treatment compared with
antibiotic treatment alone. When the dry period was less than 10 wk, the incidence of new
infections in quarters treated with the combination treatment was lower than for the
antibiotic treatment alone (3.7 vs. 6%) but this was not a statistically significant difference. Fewer
infections caused by Streptococcus uberis and
coagulase-negative staphylococci were found in cows receiving the combination treatment compared with the
antibiotic treatment alone (not significant). Coliform isolates were less likely in cows receiving the combination treatment with the longer dry period but the numbers of new intramammary coliform
infections were low for both dry period categories. Few
infections were caused by
coagulase-negative staphylococci. The incidence of clinical
mastitis in the first 100 d of lactation in quarters infected at calving was significantly lower (4 vs. 15 cases) for the combination treatment than for the
antibiotic treatment alone for both dry period lengths. The clinical incidence in quarters in which a pathogen was not detected in either of the samples taken after calving was comparable between groups. No significant difference was found in the total clinical incidence after calving for both groups irrespective of dry period length.