The rules are being toughened up when it comes to the treatment of bobby calves.

The Government has announced a string of changes, including a requirement that calves are at least four days old before they're transported for sale or slaughter.

LISTEN ABOVE: SAFE executive director Hans Kriek speaks with Larry Williams

The changes also include a ban on transporting young calves by sea, including over the Cook Strait.

It's also now prohibited to kill calves through blunt force trauma, unless in an emergency.

Primary Industries Minister Nathan Guy said there needs to be a strict code for animal welfare, not only for the animals, but also for consumers and our export market.

He said the regulations should be in place before the 2016 calving season.

Dairy New Zealand spokesperson Jenny Jago said the changes make it clear to everyone in the supply chain what they need to do.

"Farmers like it to be clear what those expectations are, and I think they address some of the areas that were raised as concerns."

However, SAFE spokeswoman Mandy Carter said the real battle is how to monitor compliance within the industry.

"There were actually already rules in place about how animals need to be treated in New Zealand, and those people were quite happy to break those laws, so how are we going to make sure they're not going to break new rules."

She said it seems "nonsense" that they're proposing changes that are already laws.