Benchmarks for evaluation and comparison of udder health status using monthly individual somatic cell count.

The objectives of this study were to propose benchmarks for the interpretation of herd udder health using monthly individual somatic cell counts (SCC) from dairy herds in Quebec, Canada and to evaluate the association of risk factors with intramammary infection (IMI) dynamics relative to these benchmarks. The mean and percentiles of indices related to udder infection status [e.g., proportion of healthy or chronically infected cows, cows cured and new IMI (NIMI) rate] during lactation and over the dry period were calculated using a threshold of ≥ 200 000 cells/mL at test day. Mean NIMI proportion and proportion of cows cured during lactation were 0.11 and 0.27. Benchmarks of 0.70 and 0.03 for healthy and chronically infected cows over the dry period were proposed. Season and herd mean SCC were risk factors influencing IMI dynamics during lactation and over the dry period.