It doesn't generally increase in Summer. So that's knocked that article on the head.
There are some units where it might though. All year round housing is one, but still relatively a minority sport.
The other is for block Autumn calving cows where most are near drying off in mid-Summer.
Then there's units where cows graze in very forested areas where there are sh!t-loads of flies and where the fly management is lax.
Generally though, cell counts tend not to rise in Summer.
I don’t believe you are correct here. Firstly if you ring kingshay or your milk buyer. They will tell you that cell counts generally rise all summer then drop off at housing.
Also a 200k cow study in the states showed that as the temperature increases so did scc even on units with large amounts of cooling/ventilation.