I am a Christian who is researching how other religions influenced Christianity throughout its history. Having found that some of my fellow believers in the Hebrew Roots movement hold the belief that Acts 10 (Peter's Vision) references a rabbinic law in which no clean animals can have interactions with unclean animals without themselves becoming unclean, I decided to look a bit deeper. I could not find any Oral Torah law that states this, and the proponents of this theory do not provide one themselves. I am not an expert on the Talmud or any previous writings of a similar nature, so I wanted to ask if a law like this existed, at least during the 1st century, that I have just not heard about.
You'd have to define your terms better, but a live kosher animal (let's say a cow) remains kosher even if it touches a pig. Whatever you're describing doesn't ring any bells.
Off the top of my head, the only way to make a live kosher animal non-kosher is either to injure it in a way that would eventually be life-threatening, or various odd practices involving idolatry. Even if a cow was um, "abused" by a lonely man, it's still kosher -- though no longer fit to be used as a sacrifice. (Sadly this one came up with a men's prison in upstate New York where they also worked at a dairy farm.)
There is a law against buying "mystery milk" from a non-Jew; a Jew should observe the milking. (Today many would argue that the combination of economics and enforcement in many countries qualifies ... but that's a different story.) Certainly a farm containing both cows and pigs would prevent a Jew from buying a bucket of milk from the farmer, as how do we know it's all cow milk in this bucket? If we somehow are certain that the only mammals in a 50-mile radius are kosher species ... there is room for discussion. But I think that's still far beyond what you're describing.
As far as the mainstream Judaism as it appears in the Talmud, that's about as far as we can help you here. There are Jewish scholars who specialize in the history of that time period who could probably help you more, who are well-versed in New Testament and its context vis-a-vis Judaism at the time -- Malka Simkovich and Lawrence Schiffman are two names who come to mind -- and they would probably be a good resource on this. For instance, there were a lot of schisms going on at the time, so this may have been a teaching of some group that didn't become the one that wrote the Talmud. (E.g. the Sadducees not the Pharisees.)