Foreword: I’m holding two Fertility Field Days in South West Victoria in early December – one in Irrewillipe, and the other at Bessiebelle. We’ll be doing case study reproductive investigations with my two very gracious host farmers, and it should be a great day out! For more details, check out the flyer here and let me know if you’d like to come along.
If only it was this easy…
Although most farmers I meet do some form of early pregnancy testing, I occasionally run into the odd person who looks at me blankly when I ask them about it. ‘Preg testing?’ they ask me, ‘I don’t really do that.’
Hmm. I usually just nod politely and move away, but I’m puzzled on the inside. Why? Well, when I think of all the benefits that farmers are missing out on – often due to just a few misconceptions about pregnancy testing – it makes no sense why you wouldn’t take advantage of a cheap and essential service.
So… I think it’s time to clear up a few misunderstandings about pregnancy testing, and reiterate why we do this practice. There are heaps of things in dairy farming which are a matter of preference or system-specific, meaning they’re worth it on some farms, but not on others. I’d never prescribe to a farmer things like: what breed they should run, what genetics they must choose, whether to use sexed semen or not, or if they should use a synchronization protocol for this reason.
However, and yes, I’m going to bold this because it’s so incredibly important, early pregnancy testing is NOT one of those things. Early pregnancy testing has a place on ALL farms.
Let me explain.
Firstly, the ‘early’ in ‘early pregnancy testing’ is key to the whole business. Often the farmers I meet who no longer pregnancy test talk about inaccuracy. ‘The vet,’ they complain, ‘makes so many mistakes that I can’t trust the information.’ (These are generally the same farmers I discover are withholding dates during pregnancy testing so that they can ‘test’ the vet and avoid ‘giving them hints’. Hmm. More on this later.)
So, what is ‘early’ pregnancy testing? This is pregnancy testing done no later than 15 weeks after the start of mating – it doesn’t matter whether it’s done by ultrasound or rectal palpation (we won’t go into milk or blood testing in this article, as they lack the ability to age the fetus). Very early pregnancy testing can be done fairly reliably from as early as 35 days, but this is separate to ‘ordinary’ early pregnancy testing and has its own risks and uses which could fill an entire other blog post.
So, why is 15 weeks the cut-off point for early pregnancy testing? Well, as the fetus becomes bigger and heavier, it begins to ‘drop’ off the cow’s pelvic rim and sink deeply into the abdomen. This varies between individuals, but on average, the uterus drops over by 10 weeks, and can no longer be pulled back over the pelvis into reach for easy palpation by 13 weeks.
Rectal examination at 3 months (13 weeks) where fetus has dropped off pelvic brim, and 5 months, where the fetus has sunken deeply into the abdomen. Click image to see larger version. Source: University of Dublin.
Between five and seven months, the vet may be completely unable to directly palpate the developing fetus, and must rely on secondary signs of pregnancy, such as fremitus (the vibrations of the uterine artery), and cotyledon size (the little balls of placenta that provide a site of blood exchange for the fetus).
This makes it much harder to age the pregnancy. Without the ability to feel and size the fetus directly, the vet must estimate when aging older pregnancies. Relative changes that occur in early pregnancy are also more marked than in late pregnancy, making it easier to determine age. So, let’s re-emphasize: one of the main reasons we should pregnancy test early is for increased accuracy.
Secondly, doing early pregnancy testing gives you a wealth of information, including:
- Accurate pregnancy aging, allowing you to calculate accurate dry off and calving dates. This is the key to effective transition management – without accurate calving dates, it’s impossible to guarantee that cows have enough time on transition feed leading up to calving.
- How many AI replacement heifers you have
- Which cows are empty and can be re-joined
- Which cows have serious uterine abnormalities which need to be addressed
- Which cows are empty and need to be sold or milked through.
As much as we hope that our cows are going to tell us when they’re about to calve – they really can’t. Not only do cows find it difficult to read English, but humans also find it difficult to ‘read’ cows. Some farmers use failure to return to heat, dropping milk production or other physical signs to determine pregnancy status. However, this is really inaccurate (due in part to individual variation). For example, some cows do not return to heat despite not being pregnant (such as ‘phantom’ cows, or cows with health problems), and some show heats despite being pregnant (weird, but true). Physical signs also come too late to be truly useful for management purposes.
In summary, pregnancy testing is cheap and pays itself back many times over. Do yourself a favour and give it a go.
A great article on this from Dr Rob Bonanno is worth reading for a vet’s perspective.
This case study article from Dairy Australia shows things from a farmer’s perspective.
Leave a Reply