Statistical evaluation of somatic cell counts in bovine milk at calving, during lactation and at drying-off (by official recording)

A survey was carried out to evaluate the importance of postpartum intra-mammary infections (IMI), on the basis of somatic cell count (SCC), by characterising the behaviour of Linear Score (LS) in cows at calving, during lactation and at drying-off.Throughout 2007, a follow-up was made of 25,216 Friesian cow lactations from 1984 farms within Galician Official Milk Recording (Northwest Spain) selected by simple random sampling. SCC values were calculated from milk taken at each of the monthly tests performed on every sampled animal. Data indicated that the number of observations where LS was higher than 4 (LS > 4) as well as the mean LS during lactation and the LS at drying-off significantly increased when LS at the beginning of lactation was greater than 4. Likewise, this study showed that the probability of an animal drying-off with LS > 4 was significantly higher when the LS increased at the start of lactation.