Risk factors for a high somatic cell count at the first milk recording in a large sample of UK dairy herds

Abstract

The dry period is important for the cure of existing intramammary infection (IMI) and the acquisition of new IMI. Somatic cell count (SCC) at both the last milk recording before drying off and at the first milk recording following calving can be used on farm to describe the dynamics of IMI during the dry period. The aims were to quantify the association between the main risk factors collected from milk recording data and the occurrence of a high SCC in early lactation as well as to partition the observed variation into the prevalence of high SCC in within-herd and between-herd variation. Milk recording data collected between 2004 and 2006 from 2,000 herds in England and Wales were used. Cows with an SCC ≥200,000 cells/mL were classified as high, and other cows as low. The median prevalences of the high classification were 42 and 21% at the last milk recording before drying off and the first milk recording following calving, respectively. Cows classified high or producing more milk before drying off as well as cows of greater parity or recorded in early lactation were more likely classified high at the first recording following calving. Cows from herds in which the prevalences of the high classification or the probability of remaining or becoming high over the dry period were elevated during the previous year were more likely classified as high at the first recording following calving. Half of the variability in the proportion of cows with a high SCC after calving originated at the herd level. The other half was unexplained within herd, but by between-year variability. Most cow-level predictors were important in explaining individual cow performance, but accounted for little of the overall between-herd variability. Of the predictors identified as important at the cow level, only milk yield at drying off was important in explaining the between-herd variability.