Surely a high non-return rate (NRR) is what we are after, isn’t it? Well yes of course it is, as NRR is the earliest proxy of conception rate we have; however a high NRR doesn’t necessarily mean that conception rates are high.
The NRR is the percentage of inseminations where the cows did not return to heat. In the Fertility Focus Report (FFR) it refers specifically to the AB period, so once natural mating starts (if you record your natural matings), the NRR is not calculated to include those, therefore you would need to do the maths yourself if you want to monitor the NRR right through the mating period.
The FFR NRR, can be generated once you have 50 return inseminations entered into the herd improvement software – so we are seeing these come through now on our clients’ Fertility Focus Reports (NRR is not reported in any other place in the MINDALIVE suite of reports).
Once you’ve done about 18 days of AB, you need to start looking at your daily NRR and seeing how it is tracking over a few days. Remember cows’ heat cycles are 18-24 days, the average being 21 days, so you can’t just look at the returns on one day, you need to monitor the returns for a few days.
NRRs quoted by the AB technicians often don’t include groups of cows like CIDR cows and short returns, therefore it is not really giving you an idea of how your overall herd mating performance is tracking. The FFR NRR is a 1-24 day NRR, which means short returns, CIDR cows and long returns are all included in the calculation, which is therefore much closer to your overall herd conception rate. Our target for this NRR is above 64% (from the FRR below).
The NRR reported in the FFR is reliant on the returns being detected. So other than a true conception (i.e. cow is in calf and not cycling anymore) the other reasons she may not return are:
- Not detected on heat (quiet heat, heat detection fatigue in the staff, missed being drafted)
- Early embryonic loss i.e. cow not on heat in the normal 18-24d window because she is pregnant, but returning at 30-40d because she has had an embryonic death
- Phantom cow – not in calf but has stopped cycling (this is common in non-cycling cows or cows in suboptimal body condition)
If you are unhappy with how your NRR is tracking (either too high >75% or too low <64%) there are some options around what you can do. These might include increasing bull power to cope with the extra non-pregnant cows or scanning cows that were inseminated during week 1 of AB to check actual conception rates. Taking action now will lead to a better outcome. Please give us a call to help you figure out what might be going on and together we can come up with a plan.