Farmers who scan their cows early to see if they are pregnant have the advantage of being able to get a cow that has slipped back in calf. Karen Trebilcock reports.
During early pregnancy scans, farmers will often hear the word ‘slipping’ from the vets.
It’s describing a pregnancy that has ended, for whatever reason, and the foetus is no longer alive.
“Actual conception rates, sperm fertilising egg, can be as high as 90% in cows but losses can occur at any stage, particularly early on, so that we end up with our 60% target,” said vet Jason Darwen of Clutha Vets.
A pregnancy could be detected from about 28 days by manual palpation or ultrasound scanning.
“At 35 days we’re looking for something that is about a centimetre long from crown to rump if it was stretched out and we’re looking for a heartbeat to confirm it’s alive.
“At that stage it is just a very quick flutter,” he said.
“Unfortunately, some of these early detected pregnancies will not survive, and we consider it normal to lose up to 5% of pregnancies diagnosed between 28 and 42 days (four to six weeks), so we always recommend rechecking these cows at a later stage.”
He said if a herd was not scanned early, the cows would eventually show up as late or empty, and the farmer would never know that the cow had been in calf and slipped.
“Some of these cows may show up with long return intervals between services with no explanation.”
Farmers started doing early pregnancy scans at least 15 years ago and for about 5% of Clutha Vets’ dairy farmers it was now routine.
“The original reason was to pick up phantom pregnancies – cows that had been mated and had not come back on heat but were not pregnant. We have the option of treating these cows with appropriate hormonal interventions at this stage.”
Cows that were recorded as having been mated but did not have a viable pregnancy at scanning could be given a PG (prostaglandin) injection if they have a corpus luteum (CL) on the ovary. This may bring them back on heat in a few days.
“It means the farmer can do something quickly and hopefully get the cow back in calf,” Jason said.
“For farmers who only scan after mating is finished it’s too late for them to do anything if there is a high empty rate.
“If they scan early they can leave the bull in or keep going with AB. For some clients it can be better to have late calving cows than empty ones.”
Allan Bote, farm manager at Braeburn Dairies at Clydevale in Otago for the past six years, has done early pregnancy scanning since the farm owner, Mark Shore, decided to go no-bull five years ago. They used to mate for 15 to 16 weeks using a combination of AB and natural mating but now use AB for 11 weeks only.
“We had to adapt when they phased out inductions,” Allan said.
Planned start of calving is August 3 with all of the 800 to 850 cows milking by the end of October. They do an early scan eight weeks after the start of mating and this year decided to use AB for another week, until January 17, after the early scan showed not enough cows were in calf.
A final scan to find empties for culling is done six weeks after the end of mating and, if Allan has seen cows riding that scanned as pregnant at the end of the season, he will do a final one in May.
The farm uses Friesian straws for its replacements and finishes with beef breeds Speckle Park and Stabilizer instead of short gestation dairy because it wants to avoid putting calves on the bobby truck.
Jason said the number of slipping pregnancies (dead foetuses) at Braeburn was not unusual, and no particular reason has been found there for calves slipping.
With few farms doing early pregnancy scans, and with farms doing them at different stages of pregnancy, it was difficult to benchmark calves slipping between farms and from one season to the next.
“Certainly if there are an unusual number on a farm we’d go looking for causes,” he said.
“BVD can cause early embryonic loss, but the vast majority of our herds, including Braeburn, are regularly monitored for BVD using bulk milk testing.
“If cows are not stressed, if they are healthy and happy and well fed, then you are doing everything right. A few early pregnancies slipping is just part of mating.”
“We do get the odd hiccup with BVD in the district. A lot of the herds haven’t had any exposure for years so any introduction has a significant effect.”
Salmonella, M. bovis, and other pathogens could also cause cows to lose a pregnancy, he said.
“Macrocarpa and mouldy balage will do it as well, but that usually happens in late pregnancy.
“If cows are not stressed, if they are healthy and happy and well fed, then you are doing everything right. A few early pregnancies slipping is just part of mating.”
Allan said the herd was fed grain daily throughout the season on the rotary platform while milking to smooth out grass quality and quantity issuesduring mating and early pregnancy.
“One of the hardest things is you’re mating at the time of the year when the weather here can be very changeable,” Allan said.
“It means grass quality is very changeable too.”
Jason said it was unlikely that a farmer would notice an early foetus slipping.
“In those early stages it’s smaller than a grape, so the only way to detect it is by doing early scans.”
As a PG shot would abort a foetus, care was always taken to make sure the cow was not pregnant before it was used.
“It’s a very thorough process. If we scan a cow empty we always do a manual check as well before using PG.
“When you are scanning you’re never 100% sure you are seeing all of the uterus.”
He said sometimes they would find a dead foetus in one horn of the uterus, but a viable one in the other.
He said scanning did not cause pregnancy losses. Ultrasound was widely used across a wide range of species, including humans.
However, inseminating a pregnant cow could cause an abortion so farmers picking cows for AI later in the mating season needed to make sure they were genuinely on heat.
“We don’t just look at the tail paint,” Allan said. “We look at all of the data we have on the cow, such as when she was last inseminated, and we look for other signs of riding such as rub marks.
“If it’s been wet or there are trees in the paddock the cows could have rubbed against we are very careful, and we redo the tail paint every week so it is always fresh.”
Early pregnancy scanning also improves detection of twins and occasionally triplets.
Of the 400 cows scanned eight weeks after mating started at Braeburn this season, there were 16 sets of twins.
“We can’t sex a foetus until it is 60 days old so we have no idea if they will be freemartins,” Jason said.
