Well, you know cows don't read the newspaper. They hang out with farmers. I think we have a nocebo effect in domestic animals. Moerman intends to research this intriguing area further before publishing, but the working hypothesis is that the farmers' concern about their cows, who for all they knew had been gobbling pure poison, was somehow communicated to the cows, who responded by slacking off on the milk production. He also points out a difference between nocebo and placebo.
Rats are apparently as vulnerable as cows.
In one experiment, which didn't set out to be about nocebo, rats were given sweetened water to drink and then given shots of cyclophosphamide, which causes nausea and also induces sometimes fatal immunosuppression. To the experimenters' surprise, rats who only got one shot of cyclophosphamide but kept on being fed the sweetened water continued dying at a high rate. I think not. OK, a little. But just as placebo has limits, just as flu viruses laugh scornfully when I tell them I took my vitamins, so they should go away, there are limits to nocebo as well.