Did I say tomorrow? I meant the day after tomorrow. 🙂
Since I rely on my vet to inseminate my cows, and since my vet isn’t always available when I want him, I’ve always been a little panicky about calling him as soon as my cows show signs of being in heat. The first time he came out, he stuck his long, gloved arm in there, and said, “She’s only just coming into heat. That’s great. And breeding her now will increase your odds of getting a heifer.”
So I learned how to tell when my cow was in heat (yeah!) and I inadvertently learned how to get heifers. I don’t always want heifers, but I get ’em anyway, because I’m panicky about calling the vet as soon as my girls show signs of being in heat.
This stuff here has to do with human fertility. The female releases an egg at ovulation, and the egg always carries an x chromosome. The male’s sperm can have either an x or a y chromosome, and that is what determines the gender of the baby; two x chromosomes is a girl, an x and a y is a boy. Now the sperm are longer lived than the egg, so the egg can be fertilized by sperm donated at least a couple of days in advance. (Chickens are good for as long as three weeks!) Male “y” sperm are lighter and faster, but they die more quickly. Female “x” sperm are bigger and slower, but they live longer. If the sperm are introduced when the egg is ready, those male sperm have an advantage over the females, but if the sperm are applied before the egg is released, it is more likely that the males will die before they can achieve fertilization, giving the females a wide-open shot.
I figure cows are mammals, too, and even though their cycle is shorter, and their fertile period is much shorter, it works basically the same. Susanna got it right when she said, “NFP for cows!”
When a cow first shows signs of heat, she is moo-ey, restless and less interested in grazing. She will mount the other cows (or you!) and the other cows will try to mount her, but she will move out of the way. You may also notice a soft vulva and perhaps some mucus. I usually notice this behavior first thing in the morning, but my vet won’t answer the phone until eight. Very tense for me. And he always asks if the cow in question is in standing heat. Standing heat is when the cow will allow the other cows to mount her. She will stand for it, perhaps looking over her shoulder to watch, but make no effort to get out of the way. I always say “yes”, even though the answer is really no. He’ll only come if I say yes, and by breeding at the first signs of oncoming heat, we are favoring the female sperm, who are more likely to still be alive when the cow’s egg is released later in the day.
We’ve had six calves born on our farm, and all but one have been heifers. The one bull was born to a half-Brown Swiss cow who never showed any obvious heat signs. I could only tell she was in heat when she was in standing heat, and I was not surprised to see her bull-calf earlier this month. That cow is going into the freezer next month because she’s all around harder to breed and her gestation lasted three weeks longer than for my full-blooded Jerseys. And she’s huge and slightly stubborn, which scares my backup milkers.
Now most experienced farmer-types laugh at me when I tell them this stuff. They tend to be men, though; perhaps they just don’t have the appropriate appreciation for female fertility cycles. And most of them won’t breed till standing heat because they want to make sure the pregnancy “sticks” the first time, but the only cow we’ve had to breed twice is that Brown Swiss. If you wait till she stands, you’ve waited too long. 🙂
So there you have it. Bottom line: Call your AI tech or vet as soon as you suspect your cow is going into heat, and dramatically increase your odds of having girls.