The national newspaper ad for Go Vegan World, a vegan campaign group, in February featured a photo of a cow behind a piece of barbed wire and the headline "Humane milk is a myth. Don't buy it."
Smaller text stated: "I went vegan the day I visited a dairy. The mothers, still bloody from birth, searched and called frantically for their babies.
"Their daughters, fresh from their mothers' wombs but separated from them, trembled and cried piteously, drinking milk from rubber teats on the wall instead of their mothers' nurturing bodies. All because humans take their milk."
The Advertising Standards Authority (ASA) said seven complainants, some of whom had experience of working in the dairy industry, and who believed that the ad did not accurately describe the way that dairy cattle were generally treated in the UK, challenged whether the ads' claims were misleading and could be substantiated.
Go Vegan World said the ad did not state or imply that calves were separated from their mothers prior to the 12 to 24 hours recommended by the Department for Environment, Food and Rural Affairs (Defra).
But in any case, they believed the exact timing of the separation was irrelevant to the ad, which commented on the injustice of separating cow and calf, claiming later separation actually caused more distress.
They believed most people would consider separation at 25 hours as unjust as separation at 24 hours.
Clearing the ad, the ASA said it understood the complainants were concerned the ad implied a significant number of dairy farms did not comply with animal welfare standards in place in the UK, and milk production was therefore "inhumane" in that sense.
But it concluded: "We understood that Defra recommended that calves should be kept with their mothers for at least 12 and preferably 24 hours after birth.
"Although the language used to express the claims was emotional and hard-hitting, we understood it was the case that calves were generally separated from their mothers very soon after birth, and we therefore concluded that the ad was unlikely to materially mislead readers."