DAIRY 101 SCANNING
40 days following conception.
50 days following conception.
65 days following conception.
Early ultrasound scanning is safe and useful Story by: Karen Trebilcock
M
ating 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 78
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
Dairy Exporter | www.nzfarmlife.co.nz | December 2020
