Because they’re animals. They may be domesticated, but they’re still animals, they don’t know the intentions of a farmer even if they’re trying to help.
Animals only begin to understand/trust human intentions if they’ve spent A LOT of time with humans. Like in direct contact being touched.
Farm animals don’t get that, because they’re one of dozens or hundreds of animals. The farmer can’t spend that time with all of them.
So they stay skittish/suspicious of the farmers
I grew up out in the country, and my experience (which is of course just an anecdote) is that most grazing cows would be pretty curious of people coming up to the fences. They’d only really be scared if you make very sudden movements. They are very much herd animals, though, and panic and fear seems to spread to others very rapidly. If one gets scared by something, nearby animals are very likely to follow.
It depends on how well socialized they are, which often depends a lot on how big the farm is. On some farms, people interact a lot more with their animals than others do. Cows are relatively smart, and have no problems remembering which humans are nice and which aren’t.
Cows only think 2 things. “Oooh, what is that, can we eat it?” or “Aaaaaaaa! What is that? Run away!”
If cows are used to being fed by people, they will see people and approach them and demand food. If not, they will avoid the scary things.
Beef animals on pasture are often unused to humans on foot. They are also wary of change – if you usually arrive in a truck, they will be wary of someone in a car. Prey animals have to be on guard.
Latest Answers