Yes pigweed is highly toxic and poisonous to cattle and other livestock as well as goats, sheep, and swine.
If you have pigweed growing in the fields where goats, sheep, swine and cattle are grazing then be sure to kill off the pigweed or remove the pigweed somehow to keep your livestock and cattle from ingesting it.
However sometimes cows have eaten the smaller younger pigweed plants and haven't gotten sick but some cows have gotten sick and even died when eating the older bigger pigweed.
It's best to try and keep the fields or any part of the yards free of pigweed if possible when you have cattle, sheep and swine.