In many religions it is taboo to eat certain animals. Most pagan or tribal cultures, where the spirit of each person in the tribe reflects the nature of an animal and the relationships between people in the tribe are as important as the symbiotic relationships between animals in their environment, it is taboo to eat one's own totem, or the animal in which one's spirit flows.

In Judaism legged mammals without cloven hooves, such as pigs, rabbits, dogs and elephants, are taboo. This is not for any direct spiritual reason, but rather an understanding that these animals are statically and traditionally more likely to carry diseases that can affect humans than cattle, sheep or goats. So the Jews, a tribe from the warm climate of Northern Africa, decided not to eat the meat of animals prone to bacterial infection and, being a society with religion at its core, taught that this was Gods decree. Take one look at the seafood forbidden by Jewish tradition and it becomes obvious that the primary role of these bans is protection from food poisoning.

The write-up above suggests that Hinduism forbade the eating of cattle for similar reasons, citing mad cows disease (the other diseases listed have little to do with cattle except via fleas).
This is quite ridiculous. We know that battery cattle ‘farmers’ feeding mashed cows to cows caused the outbreaks of mad cows disease. According to modern science, this cannibalism is an efficient way of transmitting diseases and, according to traditional Chinese medicine, force any animal into cannibalism and they will go mad. This forced cannibalism is a phenomenon of the twentieth & twenty first centuries and Hinduism and cattle are much older than that. The belief that cows are sacred, and therefore taboo, comes down to a simple equation:

(living cow == (milk = yoghurt & cheese) + (dung = fuel) + docile freind + work)   >   (dead cow == meat)

...or cows are worth much more alive than dead.