ricky1, I think you got that definition here:http://cancerweb.ncl.ac.uk/cgi-bin/omd?milk+fever
Unfortunately this site is just an automated dictionary - and usually IMHO not very useful for medical terms for genealogists.
Milk Fever nowadays refers to a disease of cows.
Formerly, and sometimes now, it would refer to mastitis, ie infection/inflammation of the lactating breast in humans.
However, it is usually in historical/genealogical terms taken to mean puerperal fever, which is an infection in a recently-delivered woman.
Commonly this would be an overwhelming sepsis which killed women pre-antibiotics. Often this would be via the umbilical cord being cut with a dirty instrument (this is a very common cause of maternal mortality in the developing world today), leading to tetanus. or the labour being prolonged allowing infection via the intr-uterine route. Or almost any other serious infection.
Hope this helps.
Just seen two last posts - google is not your friend in this case, sorry!