PARIS — For years, the animal rights movement, scorned by both politicians and the public in the land of foie gras, struggled to gain traction in France, Europe’s biggest producer and consumer of red meat, where one billion animals are slaughtered a year.

“Animal welfare has never really been a crowd-pleasing cause among French politicians, although the public agrees that animals shouldn’t be mistreated,” said Sébastien Arsac, co-founder of one of the country’s most vocal animal rights organizations, L214 Éthique et Animaux.

So when Mr. Arsac and the organization’s other co-founder, Brigitte Gothière, heard Emmanuel Macron, now president, pledge basic safeguards for animal welfare during the 2017 election campaign, they thought they had found an ally. Mr. Macron promised to set up closed-circuit televisions in slaughterhouses and to ban the sale of eggs from caged hens by 2022, two of L214’s top priorities.

But while French lawmakers are debating a law on agriculture and nutrition this week, Mr. Macron’s government has watered down the former campaign promises, dashing L214’s hopes that they could make inroads with the support of political leaders.