Me: So I’m trying to schedule this dairy farm welfare elective, but the day all the interested students are free to do it, the faculty member has a herd check scheduled. He thinks it will be fine, we can use the herd check as a starting point, but you know how these things go.
The Boy: No. What’s a herd check?
Me: Rectalling a hundred cows to tell if they are pregnant.
The boy makes a face.
Me: It’s not so bad, it’s just kind of boring, and I’ll be doing plenty of that on my Ambulatory rotation, I don’t need to be doing it during my elective week.
The Boy: So all the cows get bred at once, that’s why you do a hundred?
Me: Well, it depends on how you run your farm, but no, for this particular farm, Dr. Maolain visits them every week. So he’s checking a hundred cows a week. Well, I don’t know that it’s a hundred, actually.
The Boy: So he’s checking all the cows?
Me: Just the ones who were bred recently. Actually, knowing when to breed them is a whole Thing. They come into heat every 21 days, but they are only in heat for less than a day. The best way to know when to inseminate them (which almost everyone does artificially) is to watch them to see when they are in heat. But it is a real pain to watch all your cows all the time. So you can also use hormones to sync them, and to narrow the window for when they will come into heat.
The Boy: How long after you breed them can you tell that they are pregnant?
Me: That was a test question. It was a lot of tests ago, though. I don’t remember.
But I have looked it up for you (and as a review for me). There are four positive signs of pregnancy in a cow that you can feel per rectum: fetal membrane slip (day 30), the amniotic vesicle (day 30), placentomes (day 75), and the fetus (starts at day 65, but by mid-gestation may be too deep in the abdomen to reach with your arm). If you can feel at least one, you can say that the cow is pregnant. The fetal membrane slip is supposed to feel like the seam on womens’ stockings; it is the allantois inside the uterus. The amniotic vesicle is the sac enclosing the fetus (and it is apparently not recommended for veterinary students to go poking at it, but people who know what they are doing are OK).
Placentomes are where the cow uterus connects to the placenta, and there is seriously not a Wikipedia article on it for me to point you at! Bizarre. Different kinds of animals have different ways of getting nutrients from the mom to the baby during pregnancy, and that is why cows have placentomes and we don’t. (If you want to know more about that, comment! I might could write a post on it.)