Serratia species isolated from bovine intramammary infections.

Intramammary infections from which Serratia spp. were isolated were studied over a 32-mo period in a research dairy herd consisting of approximately 120 lactating cows. A total of 29 Serratia spp. intramammary infections were detected and accounted for 9% of all Gram-negative bacterial intramammary infections. Serratia marcescens was the most common Serratia spp. isolated. Origin of intramammary infections was 48.3% during the first half of the dry period, 31% during the last half of the dry period, and 20.7% during lactation. A total of 64% of intramammary infections that were first detected during the first half of the dry period persisted to calving. Geometric mean number of lactation days infected for all infections was 55. Intramammary infections that originated during the first half of the dry period were present in lactation for a significantly greater number of days compared with intramammary infections new during the last half of the dry period or lactation. A total of 48% of infections were clinical. Serratia spp. intramammary infections tended to be of long duration compared with other Gram-negative bacterial intramammary infections and were highly associated with the dry period.