WHY DO bulk cell counts go up in summer? Not, as previously thought, because more cows are in late lactation or there are more new infections.

Instead, preliminary research by vet Martin Green at Warwick University and the Bristol Vet School shows all cows have a small rise in their cell count in summer. “This could be a physiological response to changes such as turnout, nutrition, stress or walking long distances to grazing,” says Mr Green.

Summer readings

Having studied 41,726 cell count records for 5386 cows in 33 herds over a period of 12 months, Mr Green says more cell counts remained high in summer compared with previous readings. This suggests existing infections lasted longer, contributed to a higher bulk cell count and there were fewer cures.

“The differences between summer and winter cell counts could be due to a different type of mastitis-causing bacteria, differences in treatment or detection routines,” he adds.