It would be great if you can post pictures so that we can easily determine the insect whether it is fleas or another. If the cow is getting red colored rashes then there is highest possibility that it is a mite or flea. These pesky pests are nowadays becoming a serious problem for all the pet owners. According to me you should contact to pest exterminator NYC or other who can come and detect the pest and can do pest control to eliminate pest completely.
Whelps can be anything from skin irritations to bigger things. Biting flies leave a small black scabbed over bump and it's not something I usually worry about. If you can find Permetherin concentrate and mix it with a carrier like diesel or mineral oil you can spray and fend off the flies for a little while.