Phantom cows are cows mated, then not observed in oestrus within 24 days of mating. They are diagnosed when the cow is 35-42 days pregnant. Practically, this means if cows are mated in weeks one, two, and three and have not returned to oestrus, they are pregnancy tested in weeks six, seven, and eight of mating.
The research work was done by Emma Cuttance and Winston Mason, dairy cattle vets at VetEnt, and presented to vets at this year’s Zoetis dairy summit.
Cuttance said phantom cows were perplexing because they left farmers and veterinarians asking themselves what it was that caused the cows to be the way they were, and what could be done to avoid it happening.
Typically veterinarians find pregnancy testing results show 5-15% more cows empty than the farmer anticipated. These are often the phantom cows that had not been discovered earlier.
“We wanted to research how to provide more value to farmers by finding the risk factors for the prevalence of phantom cows in herds,” Cuttance said.
Along with identifying pre-disposing factors, the work aimed to find if intervention and treatment were beneficial, and what the outcome was of that treatment.
Much of the work to date has been based on research that was 10 years old and done overseas.
This trial involved studying phantom cows diagnosed from the first 21 days of mating from 14 herds, 10 in the Waikato and 4 in Canterbury.
Once phantom cows in the herds were identified, they were subjected to an ovarian ultrasound to determine the status of their ovaries.
Phantom cows were classed in four categories: CL+ if they had a corpus luteum (CL), large follicle if they had follicles more than 10mm in diameter, small/no follicle if there were no follicles or follicles less than 10mm and no CL, and cystic if follicles were more than 25mm in diameter.
In the first year all phantom cows were left untreated. In year two their treatment depended on their ovarian status.
CL+ cows were randomly assigned to either no treatment, or an injection of prostaglandin. Those cows were then mated naturally.
Small/no follicle and large follicle cows were given either a 10-day progesterone synchronisation programme then AI, or left untreated and mated naturally.
The results revealed that phantom cows comprised 9.1% of the non-returns of the first 21 days of mating.
“That number was very much in line with what we have seen in practice over the past seven years, and less than Australia where the figure is 18-19%.”
Despite the variance between Australian and NZ figures, the number was still significant enough to cause concern, Cuttance said.
Compared to all other cows in the herd, including cows mated in the first three weeks and returned to oestrus and cows not mated in the first three weeks, untreated phantom cows from the first three weeks of mating took about 20 days longer to get in-calf, and had a 10% higher empty rate.
The work helped to define risk factors that are likely to contribute to cows becoming phantoms within a herd.
Cows treated for anoestrus before the start of mating, along with first lactation heifers, cows older than seven years, and purebred cows were all more likely to be phantom. Lighter body condition score (BCS), less than or equal to 4, and a smaller interval from calving to first mating also increased the odds of being phantom.
“This does not mean that farmers should not treat non-cycling cows or farmers should have a later mating, it simply means that by working on improving overall reproductive performance by having a compact calving, cows in ideal BCS, less non-cycling cows etc, this would also reduce the prevalence of phantom cows as well as improve overall reproductive performance.”
Treating the CL+ cows with prostaglandin and large follicle cows with a progesterone programme did not significantly improve the reproductive results for them.
Treatment of small/no follicle cows with a progesterone programme resulted in a reduction of 15 days in the time from the start of mating to conception, and a 43% lower empty rate compared to cows of the same status not treated at all.
Cuttance said the research results meant it might be possible to develop a predictive tool that could help gauge a farm’s risk profile for phantom cow presence.
Identifying small/no follicle cows and treating them delivered a return of about $250 a treated cow.
“The predisposing factors to a cow being a phantom cow are similar to what we know already about poor reproductive performance, namely BCS, large numbers of non-cycling cows, younger cows and breed factors.
“It appears that treatment for small/no follicle phantom cows is effective and worth exploring.”
