An agricultural professor says the government must try and find out what actually happens to the thousands of sheep being sent to Mexico, once they arrive.
The 50,000 sheep and 3000 cattle are being sent to Mexico for breeding and left Timaru on board the livestock carrier Nada, over a week ago.
New Zealand bans live sheep exports for slaughter, but not for breeding purposes.
An agri-food systems professor at Lincoln University, Keith Woodford, said in his experience the animals would quickly be killed and end up on the barbecue at village festivals.
He said the Government needed to send New Zealand veterinarians to work with the Mexican authorities and find out what was really happening to the sheep.
"The New Zealand Government needs to get over there, it needs to work with the federal government in Mexico to find out what is really happening over there, one way or the other.
"When you look at how the animals have been elected, and the types of animals they are, it doesn't add up," Professor Woodford said.
"Essentially, these are all animals that would have otherwise gone to slaughter in New Zealand, rather than being breeding animals here."
He recommended that the Government get permission to send New Zealand veterinarians to monitor the unloading, as some of the animals could have become ill travelling through the tropics on the voyage.
Professor Woodford said that would be the only way to know how many had died on the voyage.
In his experience with previous exports, he said the sheep would be distributed to small farmers.
"Typically as a gift from the state governments that are doing the importing.
"So this of course gains some, I suppose you might say 'tick', from the local people ... but history tends to say within a very short time, they tend to end up being killed, and they go on to the barbecue, and this is at local village parties and festivals and so-on."
Previously, the Ministry for Primary Industry has said the exporter - Mexican-owned, Christchurch-based Livestock and Agricultural Products - had signed a statutory declaration that the animals are not intended for slaughter.
Professor Woodford said he was not convinced by that.
"I've worked on a lot of international development projects over many years, and this just does not seem to be the way that one sets up a big rural development project aiming at increasing the long-term sustainability of the small farms," he said.
"You have to do a whole lot of other things, as well as just provide some animals, if you really want to get a sustainable improvement."