Yesterday I was lecturing to vet students at the Ontario Veterinary College in Guelph. The topic? Clinical cases in canine/feline obstetrics: should I be afraid if a breeder calls in the middle of the night for this? What was the purpose of this talk? Show the students that they SHOULD NOT be afraid to face these situations because we now have in veterinary medicine the tools to answer all these questions.
Interesting discussion then, and during the talk one of the student asked me a very good question. “OK, I don’t know much about obstetrics in canines yet, but can’t we determine the due date in the bitch to make things easier for everybody?” I told her that was an excellent question… because today we can!
Pregnancy length in the bitch is 63±1 days from the day of ovulation. This is important because most of the time when I speak with our breeder partners, they will determine the pregnancy length from the day of 1st breeding… while in this case, pregnancy length can go from 58 to 72 days. Large range here: more difficult to accurately predict the due date. As you see, this is another reason why performing a timing of ovulation can be so valuable. Not only will it optimize the fertility of your animals, but moreover if you know when the bitch ovulated, you can almost tell when parturition will take place!
And we can be even more accurate than that depending on the size of the bitch. You can see here a graph I borrowed from my former sidekick Dr Fernando Mir at the Alfort Vet School. Small dogs will usually deliver earlier (around 62 days post-ovulation) while larger dogs will tend to deliver around 64 days post-ovulation.
Influence of the size on the pregnancy length (from Mir et al 2011)
And what happens if you did not do a timing of ovulation? Well, we still have ways to estimate the due date (it will however then only be an estimate we will definitely lose in accuracy):
– We can do what we call biometric measures under ultrasounds (typically we will measure the size of the skulls – what we call the biparietal diameter): these measures are entered in an equation that will give us an approximative due date (different equations are available depending on the size of the animal, if your vet is interested in this they can reach out to me).
– More expensive but an interesting tool when we are dealing with an at-risk bitch, we can assay progesterone. 24h before parturition progesterone levels will drop below 2ng/mL: when we have this result, we know that parturition is about to start and if needed, we know that we can safely perform a C-section because it means that the bitch is soon due.