What non-return rates can tell us, phantom cows and what to do next
As mating rolls on, your herd’s data can tell you a lot about how things are tracking — from heat detection right through to conception. One key number to watch is the Non-Return Rate (NRR). NRR is the percentage of inseminations where cows have not been re-inseminated within 24 days — in other words, cows that seem to have conceived and not come back on heat.
Understanding NRR
Low NRR (< 64%) – a warning sign
A low NRR usually means fewer cows are getting in-calf.
Common causes include:
- Cows not in top condition (low energy, transition issues, cow health)
- Heat detection or AI timing not quite right
- Insemination or semen-handling issues.
What to do:
- Talk to your veterinarian, review and correct:- Heat detection and return analysis- Cow health- Insemination timing and technique.
- Consider an early scan, and look at whether the mating strategy or length needs adjusting.
High NRR (> 75%) – not always good news
A high NRR can look great on paper – but sometimes it hides problems. Some cows appear to have conceived, but they have
lost the embryo early on and do not show another heat for a while. These “phantom cows” make the NRR look higher than it really is, and the issue only shows up at scanning, which can be very frustrating!
What to do:
- Talk to your veterinarian and- Consider an early pregnancy scan to confirm how things are really tracking.- Consider treating phantom/non cycling cows.
Interpreting Return Analysis (RA)
A return analysis shows how long after insemination cows are being re-inseminated. It is a powerful way to pinpoint where in the reproductive process things may be breaking down.
When plotted as a bar chart, the distribution usually forms a cluster around 18–24 days, which represents normal returns. Cows returning in this window are those that did not conceive at their last insemination.
A healthy herd should show a strong green bar at 18–24 days, minimal short returns, and only small red/yellow bars in the early or long-return zones.
Estimating phantom cows – How many are hiding in your herd?
So how many phantom cows might be sitting quietly in your herd right now?
A quick estimate can be made using your submission rate, non-return rate (NRR), and what we know from field data.
Example:
- Herd size: 1,000 cows
- Mated in the first two weeks:60% → 600 cows
- Non-returning (>24 days since mating, not returned): 65% → 390 cows
- Estimated phantom cow rate: 4–9%*.
That is around 16–35 cows that appear to be pregnant but are unlikely to be so.
Turning numbers into action With wearables providing accurate heat data, NRR becomes much more powerful. It is no longer just a blunt number – it is an early warning tool that helps flag when things are not going to plan, so that you can step in early and allow for timely intervention.