Farmers are devastated they have to destroy thousands of cows to stop the spread of mycoplasma bovis.

The Ministry for Primary Industries will cull 4000 cows from five infected properties in the South Canterbury and North Otago region.

Cattle from two farms have already been dealt with.

Federated Farmers South Canterbury dairy chairman Ryan O'Sullivan told Rachel Smalley owners' livelihoods are being taken away.

He said one of the farms affected is owned by a young sharemilking couple who have put everything into it.

LISTEN ABOVE AS RYAN O'SULLIVAN SPEAKS WITH RACHEL SMALLEY