A liquid supplement is a relative novelty in the US where most probiotic supplements are sold freeze dried.
"Our product has the advantage that it is sold as a high quality fresh liquid which is attractive to horse owners," he said.
Mr Prassinos said the company would have a majority shareholding in the joint venture and retain all intellectual property rights.
"It will still be our company and our brand, and we will continue to develop the microbial isolates here in New Zealand.
"We will provide the technology and ingredients for the Denver company to manufacture and distribute the end product."
The chance to break into the US market was a huge opportunity.
"We're a small bootstrap start-up with a small resource, operating on monthly cash flow, about to make headway internationally - so we're excited.
"We believe we have the finest probiotic in the world and we will accept any challenge to prove ourselves wrong."
A memorandum of understanding has been signed between the two parties and Mr Prassinos will fly to Denver shortly to begin due diligence and cement the deal. He estimates EquiBrew will be on shop shelves in the US mid-year. It is stocked by 40 Kiwi retailers.