Here is a bit of information that was new to me.
Blind Quarters
The Horn Fly Issue
While growing, heifers are on pasture where horn flies can be a constant irritation. Horn flies take 20 to 40 blood meals per day. As heifers develop, estrogen and progesterone levels increase. It has been documented that, as estrogen levels increase so does
horn fly irritation and that cattle in standing heat are vulnerable. The horn fly impact on mastitis and blind quarters is two-fold.
First, horn flies tend to feed on the blood vessels in the skin of the teat causing irritation. Scabs eventually develop where the bacteria that cause the mastitis (staph aureus) can incubate. Second, as horn flies move around the teat and feed from cow to cow, the bacteria travels with them. The spread bacteria enter the teat orifice and move upward in the quarter destroying milk-producing tissues.
As much as 50% of mastitis is caused by horn flies.
Horn flies should be controlled throughout maturation to lower the risk of blind quarters during udder development.