For decades, New Zealand farmers watched their animals stumble. From the mid to late 1900s, cows and sheep grazing lush perennial ryegrass would suddenly stagger, collapse, and injure themselves. The condition became known as ryegrass staggers, and for years its cause remained unknown. 

Researchers discovered safer endophytes in grass, helping reduce the risk of ryegrass staggers in livestock.

The breakthrough came in 1981, when scientists discovered a microscopic fungus living inside ryegrass – an Epichloë endophyte – was responsible. Endophytes were essential for protecting pasture from insects, but some produced toxins that harmed livestock. Removing them altogether wasn’t an option. Without endophytes, pastures would fail under relentless pest pressure.

Instead, scientists took a bold new approach, searching for safer endophytes. Drawing on expertise across biology, chemistry, plant breeding and animal science, the team screened ryegrass seed from around the world. After years of research, they found something extraordinary – AR37.

Developed by researchers for commercial use through Grasslanz Technology, AR37 proved to be a rare win-win. It protected ryegrass from five of the six major pasture insect pests, boosted pasture growth by around 12 percent, and dramatically reduced ryegrass staggers. Together, these benefits delivered healthier animals, increased milk and meat production, and an estimated $3.6 billion return to the New Zealand economy.

Today, the science continues, looking at whether gene‑editing tools can be used to make precise DNA changes to endophytes – improving plant protection and further reducing harm to livestock as climates change.