The influence of iodine teat dipping and an external teat sealant in heifers on bacterial isolation from quarter milk culture obtained post-calving

A longitudinal observational 2 year field study including 178 dairy herds was conducted in Norway. The aim of the study was to investigate the influence of iodine post milking teat dipping (PMTD) and an external teat sealant (ETS) in first calvers (heifers) on bacterial isolation from milk culture post-calving. Every heifer was either sampled in connection with a clinical mastitis (CM) event at calving or otherwise approximately 6 days post-calving. Milk culture results were available from 3218 individual heifers and 12,872 quarter milk samples. Separate multivariable logistic regression models were used for each bacterium. Neither use of PMTD nor ETS did decrease the risk of bacterial isolation post-calving. However, if iodine PMTD had been used, there was an increased risk of clinical mastitis (Odd ratio (OR) = 1.6 (0.9–2.7)) and an increased risk of isolation of coagulase negative staphylococci OR = 1.5 (1.0–2.1). If ETS had been used, there was an increased risk of isolation of coliform bacteria (coliform and Escherichia coli) (OR = 2.9 (1.2–7.3)). There was significantly less Streptococcus dysgalactiae during the summer and autumn compared to the winter and spring. There was a significant herd effect for Streptococcus uberis and for coliforms with an OR = 5.1 (2.1–12) and 4.5 (2.7–7.6) respectively.