Genex Sexed Straws am/pm or 24hrs ?

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Well-known member
Oct 11, 2018
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New Mexico
I had a cow standing this morning. I have sexed Net Worth from Genex. Does someone know the protocol on when to use it ? My ai tech said 24 hours after standing heat?
I just breed them when they quit standing, but I haven't used sexed semen. Seem to get 50/50 over time. My recollection is earlier is better odds for heifers. So 24 hours after onset of standing heat? I dunno - have had cows stand for 18 hours and others stand for 3 hours.
I still believe in the old rule of see them in heat in the morning, breed in the afternoon, see in the afternoon, breed in the morning... and with the sexed semen, I have heard 2 thoughts.. but sooner rather than later is what I have heard since the female carrying sperm live longer and will meet the egg, further up the reproductive tract when the male carrying sperm will die off before they get there...
But it also has a lot to do with the ph of the repro tract too... and the general thoughts are the more alkaline the female tract, the better the capacitation (maturing) of the sperm, the better motility and so they will swim farther, live the female carrying sperm should "outlast" the male carrying sperm to reach the egg. The later the breeding, the closer the egg is so the sperm do not have to live as long or travel as the male carrying sperm win the race.

But then again, some years it seems we have 2/3 bull calves to 1/3 females and other years more females... so diet may play a part in the body's reproductive tract ph also...

I have always bred early for the hope of a female calf... JUST MY WAY....No scientific studies in that...
Never used any sexed semen, but I believe the time window is 18 to 24 hours after they first start standing. The issue is when did they first stand? Likely they started standing a few hours before you notice unless you watch continuously. ST genetics says 18 to 22 hours after first standing. Since it is sexed semen, the conventional thinking about time of insemination affecting sex of calf seems to not apply.