Red, yes I have seen some correlation on sex of calf versus times of the A-I.
Although it's fairly hard to prove, over time and many thousands of services, I have noticed one distinct thing.
The male and female sperm cells swim as fast as they can after being deposited in the tract. Here is the key factor.
Male cells swim slightly FASTER than females cells do -- ""BUT"" they never live as long. So at least in theory, the earlier you breed your cow/hfr in the cycle, the better tha chance of getting a hfr, but also, the earlier you breed, the better the chance of the cow NOT settling due to later ovulation. I know this gets confusing some times, so here is a run down start to finish of the events needed for conception.
Pre-Estrous -- the period of time before the cow will stand, she head butts and tries to ride, bot won't stand -- aprox 6 hours time.
Standing for others COWS, but not the bull as yet. About 12 hours average, then she will stand for the bull (Nature finds a way) This is getting close to 18 hours now already.
Post -Estrous -- no longer standing, but still tries to ride a little, and plays around some. Getting tired, and will go lay down soon, another 3-6 hours total time. A-I insemeniation is best done within the next few hours.
Ovulation takes place -- about 6 hours after post estrous, or aproaching the 30th hours from her very first signs.
Semen will last 20-24 hours in the cow, but is incapable of fertilization for the first 6 hours while it washes off the cryo-protectants needed for freezing.
Assuming all is well, breeding the cow about 18 hours after first stand will accomplish the best conception rate, if I myself get in a hurry here on both my own cows and the donors, settled cows and fertile eggs go DOWN.
If you are trying for hfrs, and I do here on my own as well, but also I MAKE myself breed them on the time line above, you would need to breed them a little sooner than I mention -- and hope for the best.
How much longer the feamle cells live versus the males is a guess, but they do swim slower and live longer -- almost like us humans. Over the centuries, it is almost a given the women live longer than thier male partners. Some say men are faster in life, who knows, I have been called slow more than once -- hehehe!
If I were to make a graff of the bull/hfr thing, with breeding early versus late -- the hfr ratio would out weight the bulls by 10 percent. In nature, the average is 51% bulls, 49 % hfrs. It takes a little luck and alot of well planned timeing with extreme accuracy to try and deviate that average, but it can be done. One year I bred everything really late due to the fact they came in heat in the afternoon, and bred around 10 AM in the morning. We had ALL bulls that year.
The next year -- things worked out where most of the cows were AM heats, and was out there breeding in the dark -- but it still averaged 3-4 hours earlier than the previous year -- we had 9 hfrs and 2 bulls that year!!! Small herd yes, but BIG results! We A-I every cow, no bulls on the place at all.
Try breeding an hour after her last stand for a hfr, this is still late enough to get her settled if she lets the egg go on time, and will give the female cells and extra hour or two to get there and have an equal chance at beating out a male cell. If you WANT bulls, wait an extra few hours, say 4-6 hours at least after all activity is done, and use good semen, your bull ratio will go up slightly -- but it does take numbers to see the difference in a bigger way!
Thanks for question -- most of us don't have the patience to go thru all this, but this is all I do, so what the heck hey???
Good night all -- Terry
