Animal genetics company Livestock Improvement Corporation has told its farmer shareholders bacterial contamination was the most likely cause of faulty semen used in 1127 herds in October 2023.
Cows did get in calf from the inseminations on the affected days, but at a considerably lower rate than LIC would expect.
Credit and goodwill packages were offered to farmers to support recovery.
Following the faulty batch, an independent review was carried out to formally assess the way LIC took action.
The review found areas of improvement when it came to managing risk, responding to events and communicating effectively.
It highlighted recommendations around quality control checks and testing, technical knowledge and training, traceability and production hygiene, facilities and work processes.
LIC has told farmer shareholders it is committed to implementing all of the recommendations.
Chief executive David Chin said: "While LIC was able to narrow it down to a possible cause, it was not possible to identify the exact root cause of the bacterial contamination. We considered every possibility, from the bull farm to on-farm insemination, and were able to rule out many possible causes by process of elimination.
"We are now focused on implementing the recommendations that stemmed from the investigation to reduce the likelihood of this ever happening again."
LIC will have more than half the recommendations in place by March, and many improvements had already been made.
Chin acknowledged that for impacted farmers, the full extent of the situation was only now coming to light as they completed pregnancy testing.
LIC was disappointed it had not delivered to the high standard that farmers expected, he said.
"We are not closing the book on this. As a farmer-owned co-op, we are always looking at ways we can improve our processes to deliver farmers the right tools to breed the most sustainable and profitable herds - now and into the future."