Six horses have died on a Wairarapa property, whose owner has got "out of his depth" and has too many of the animals, the SPCA says.
Of the 19 horses on the property, two died last year and another four in the past six weeks.
At least one had the parasitic condition worm burden, contracted after the horses were allowed to roam freely over the property and get to poor pasture.
The SPCA says charges have not yet been laid against the man, who lives a considerable distance from the property, because he is co-operating.
An SPCA senior inspector, Val Ball, says the man obviously cares about the horses but has got out of his depth, and did not realise how bad the situation had become.
The landowner is required to drench the remaining animals and surrender three further malnourished horses this week, or face six months in prison or a fine of $25,000.