Phantom cows haunt herd fertility
Zoetis New Zealand.
Phantom cows haunt herd fertility.
Work by a leading veterinary researcher is helping farmers shed light on the vexed problem of “phantom cows” and the impact they have on a herd’s reproductive performance.
Dr Scott McDougall has been summarising recent research on the problem to vets around the country this spring, through the Zoetis spring road show.
A phantom cow is a cow that is not detected in oestrus (heat) by 25 days after insemination, but which is then determined to not be pregnant at pregnancy testing.
“You are left with this concern, what is it about these cows that causes them to be this way, and how can we better avoid them?”
Typically a vet may find at pregnancy testing time 5-15% more empty cows than the farmer may have expected, as a result of the phantom cows not being discovered earlier.
Dr McDougall described a complex mix of physiological, pathological and managerial factors that make detecting and reducing phantom cow incidence a challenging one.
“Short returns” that is cows that ovulate (and show heat) 10-14 days after a first mating occur in perhaps 75% of cows that are bred at the first ovulation after calving.
Such cows have a very low chance of getting pregnant. However from the farmer’s point of view they have no way of knowing whether the heat they observe is in a cow having a first ovulation and heat after calving or not.
Add in risks of embryonic mortality and poor heat detection, and it was understandable farmers were getting higher than expected incidences of phantom cows.
“United Kingdom research shows us around a third of cows didn’t follow the text book when it came to having normal ovulation cycles.”
He said using techniques like fixed time AI introduced an even higher risk of phantom cows occurring, with around 43% of treated non-cyclers that did not conceive to the first breeding not returning to heat at 18-24 days after mating in one NZ study.
“But for farmers using that technique, in their eyes those cows have been bred, and haven’t returned to heat and are assumed to be in-calf, but in reality they have not conceived.”
Dr McDougall’s advice to vets and farmers was to look hard at a herd’s non return rate at week five of mating. If the non-return rate was more than 70%, particularly where that group included treated for non cycling “alarm bells should be ringing.”
“Realistically the first service conception after a non-cycler treatment rate is about 40% and only about 50% in cycling cows, so if you get 70% not returning in week five, it can’t be correct, there must be cows in trouble there.”
Minimising the risk of phantom cows occurring involved the familiar InCalf messages of feeding prior to calving, having a 5 to 5.5 body condition score (BCS) at calving, and adequate feed levels post calving.
The use of re-synchrony programmes without pregnancy testing was an option, but Dr McDougall cautioned that using progesterone alone had a negative effect on first pregnancies.
Confirming pregnancies using early pregnancy detection before initiating treatment was an option. But as these treatments may affect existing pregnancies, accurate early pregnancy testing is critical.
A South Island trial with 1800 cows conducted by Oamaru veterinarian Mat O’Sullivan found re-synchronising had the best effect in low body condition score phantom cows (BCS 4.5 or less) whether or not they had been treated as non-cyclers earlier in the breeding season..
When resynchronised the thinner phantom cows experienced a significant increase in their 10 week in calf rate, which lifted from 25% on average without treatment, to 60% following re-synchronising.