Early ultrasound scanning is safe and useful

from Dairy Exporter December 2020

A child’s perspective

Story by: Karen Trebilcock

Mating has gone pretty well, you think, although more than a few cows came up twice for artificial insemination (AI) and one came up three times.

Not unusual, but the calving report will show the cow holding to the last insemination and you know that doesn’t always happen.

Sometimes the cow will be pregnant to the first one.

And with the new wintering rules requiring no calves to be born on crop you’re worried because you know you won’t have accurate calving dates.

Also there were a lot of cows in the herd that came up only once for AI. Was the technician that good that they got almost all of them in calf? What to do? The answer is to get your cows pregnancy scanned. And the earlier you do it, the better the accuracy of aging the calf and so predicting the calving date. Vets use a rectal ultrasound machine and either a screen or goggles, and it’s a quick process either done during milking on rotary platforms or between milkings in herringbone dairies.

Ultrasound uses soundwaves, not radiation. The soundwaves bounce off what is inside, producing a black and white image. Black is fluid and white is bones, and various shades of grey are the sides of the uterus and other structures.

There are no harmful side effects for the cow, the calf or for anyone standing nearby.

If no calf is detected, vets can then do a manual check through the rectal wall of the uterus to see if there is a calf or not, because pregnancies of less than six weeks can be hard to detect with ultrasound.

Scanning at this time also finds your phantom pregnancies.

These are cows that come on heat, are inseminated, then never come on heat again so it’s assumed they’re pregnant – but they’re not.

It’s not unusual to have between 5% and 15% of a herd with phantom pregnancies and it’s now acknowledged as one of the reasons why we have such poor six-week in-calf rates.

The causes of phantom cows are still being figured out but cows that calve late, so have less time between calving and coming on heat, are more at risk as are heifers and cows more than seven years old.

Non-cycling cows that have been inseminated as part of a PG or a CIDR programme also have a higher chance of being a phantom.

A general rule is that 70% of cows should hold to the first insemination. If your non-return rate is higher than that, especially if a large number of those cows had CIDRs or PG shots, then you need to do an early scan to check.

The phantom cows can be found at 35 to 42 days after insemination and given a single dose PG or a CIDR to get them back cycling.

Scanning can be done at weekly intervals, so cows inseminated in week one, two and three of mating can be scanned in weeks six, seven and eight. This gives you time to get the cow cycling again and in calf before mating ends.

The earlier you do it, the better the accuracy of aging the calf and so predicting the calving date.

Think about using compact calving or short gestation length dairy semen on these cows so they will calve earlier and will be less likely to become phantom cows again next season.

Or, if you’ve stopped AI, you now won’t have to guess how much bull power you need to finish the job.

However, if you are going to intervene with phantom cows, you have to trust your records because a cow pregnant for only a couple of weeks will probably show up as empty with the scan and the PG or CIDR will abort the calf.

If you have tag double-ups or dirty tags that are impossible to read, don’t do it. And it’s probably not something to do after the bulls have gone out as those matings can never be accurately recorded.

Early scans, between 35 days and 90 days from conception, also accurately age the calf so you can confidently split your herd into calving dates come spring.

Any earlier or later than these dates and it’s too hard to tell. Before 35 days the scanner might not pick up the pregnancy and after 90 days the foetus starts to drop down into the cow’s abdomen as it grows.

The calf is aged by the amount of fluid in the uterus, the presence of the amnion (also known as the birth sack) and the cotyledons and placentomes in the uterus.

Cotyledons and placentomes are part of the placenta and allow the exchange of oxygen and nutrients between the calf and its mum.

From day 60, when the calf is the size of a mouse, the skull or the trunk diameter is usually measured to age it using a grid on the ultrasound screen.

After about day 90, when it’s snuggled down deep into the cow’s abdomen, the calf’s head is often out of reach of the rectal scanner.

Depending on the skill of the person doing the scan, the aging of the calf is usually within 10%. That means a 100-day pregnancy is called between 90 and 110 days, a 40-day pregnancy is between 36 and 44 days.

This means the earlier you do the scan, the more accurate the aging.

Early scans can also diagnose reproductive issues such as uterine infections, mummified calves or cysts that are stopping the cow getting in calf.

Again, if you do the scan early, there is time to do something about it and the cow won’t be destined for the works or to become a carry-over.

A final scan can be done around the time of drying off to find any cows that have aborted. It’s too late to age the calf, and far too late to do something about getting the cow pregnant, but it’s a useful tool if you don’t want the expense of wintering empty cows.

Another way to find out whether a cow is pregnant or not is milk testing. Pregnancy-associated glycoproteins (PAGs) can be detected in milk from day 28 of a pregnancy.

However, the amount of PAGs won’t age the calf, and, if an animal has recently aborted it will take two weeks for their PAGs to drop, which can mean a false positive. For more information, talk to your vet.