16/10/2025
Late Non-Cyclers and Phantom Cows – To Treat or Not to Treat?
There has been a resurgence of interest in treating non-cyclers in the 2nd round. It has been long established that the Return on Investment is far greater for cows treated pre-mating, with the empty rate being little impacted by the end of a 12 weeks mating period.
However, a lot of farms are now utilizing shorter mating windows, and many farms with collars are doing AI only. This gives us a few more options!
Greg Chambers did a rather elegant study on scanning herds before the end of mating to identify Phantom Cows (i.e. those that have been mated and not returned on heat but did not conceive).
He found that approximately 9% of the cows scanned were phantoms.
Treating these phantom cows gave them an increased chance of getting in calf by 1.7 X
Mark Challoner utilized a massive data set to do a mathematical analysis.
He estimated the prevalence of phantom cows to be 20% at day 29 and 8% at day 65 of mating
He calculated that scanning at 10 days before the end of mating and treating phantom cows gave an average ROI of 3.8:1 and an empty rate decrease of 1.4% for the herd.
The idea of utilizing non-cycler treatment for the later cows / cows not mated in the first round, was also assessed.
It was found that there was a positive ROI for treating between days 24 and 35 of mating, peaking at 2:1 on day 29. This meant cows had a chance for a return to heat if they did not hold to the fixed time AI.
The length of mating had an impact on the profitability of late intervention: it had a greater benefit if the mating period was 70 days or less.
