Everybody can and should do whatever they might feel is best for their own operation obviously. And if you don't ever want to mess with a bull on your operation, that's a personal preference... and if you have a cow/calf operation, that leaves you with these artificial "tools". Maybe you "need" to have genetics that are only available through AI... that's OK too. I'm just one who's not very eager to "mess with" the natural hormonal processes of the herd or individuals within it, and feel that the more we do this kind of thing, the more we're asking for problems. Now, that having been said, my custom grazed herd owner relies on this whole program heavily, because he's doing embryo implants.
My point though is, by using the "approved protocol" for artificially supplied hormone estrus synchronization along with AI, you're not really gaining all that much in actual "time" (to get the whole herd moved forward for a calving window),
IF THAT IS YOUR PRIMARY BASIS FOR DOING IT, (and remember that is the question posted for this thread).
JSV has suggested her program is to "breed on observed heat for 5 days"... out of a 21 day cycle (so 25% of the cycle)... so that means that there's 16 days left for any that haven't been observed in heat. If the herd is evenly distributed in their cycles, that means that out of 100 head, 25 got bred (NOT conceived), and 75 didn't. "Then GNRH everything else".... so generally, that will mean 75% (75 head out of 100) gets GNRH.
If the cow or heifer has large follicles (at least 10 mm in diameter) present on the ovary, GnRH will induce ovulation of these follicles about 24 to 30 hours after GnRH injection... so let's assume that 33% of the remaining 75 is there... so another 25 head that you observe in heat and breed... which gets you to 50% of the herd has been bred through 2 shots, all within 7-8 days. We've now got 50 of the 100 head bred (NOT conceived), and 50 still remaining unbred and open. Then JSV has suggested watching these 50 for 18-24 days (one normal cycle),
or wait a week and Lutalyse them again.... let's assume the latter, so we can try to artificially move them up as much as possible. So that means a 7 day wait, plus 1.5 days, or 8.5 days to a timed breeding event on the remaining ones. We were already at 6.5 days to breeding for the first group, plus optimally out to 7-8 days for the second group of "synchro treated animals", so now we're at 14.5 days to breeding on this last group from day one of our 21 day cycle, and we've now gotten all 100 of them bred (NOT conceived).
Let's assume that you're achieving a really excellent confirmed pregnancy rate of 75% at first service with your AI program (according to generally recognized research, not realistic with synchronized timed breeding...)
Understanding CIDR, "Overall pregnancy rates should exceed 55% of all cows synchronized, which is generally better than any heat detection protocol, Lamb adds."
Therefore, we should have 75 cows pregnant through these first two series, and we should have 25 left open... It's not mentioned in the JSV suggested protocol if we'll go back in on these 25 and try another round of synchronizing or not, so I will just leave it at that, and assume that we'll let them cycle normally after this, and then AI them again. We will have 75 out of 100 that will calve within a 15 day window essentially. But you've also now "forced" those who didn't "catch" from the synchronized AI breeding to be coming back in 21 days from this second breeding point... because you've "moved" their cycle... AND, you've used a "reduced fertility breeding method" (AI vs. natural) to try to get them bred, for BOTH cycles you've just performed (or for all three...). Let's assume that we'll AI breed them on their next natural heat too, and let's assume that they'll be cycling spread out "normally" over the course of the next 21 days (which they won't, because we've "moved" their cycle with the synchronization shots... most will be 18-21 days after that last breeding opportunity)... so 25 cows, spread out over the next 21 days, of which 75% will "take" again... so that's another 19 cows that will "take", spreading our calving window out to 14.5 + 21 = 35.5 days... and we'll have a remaining 6 that won't settle on that round and will be "outside of that window", or that just won't settle at all and will become culls???? 94% in 35.5 days... not a bad pregnancy rate or calving window for all AI... but of course, this is theoretical.
Now let's look at typical... BUT AGAIN THEORETICAL, ALL NATURAL SERVICE. If everything else is "right" nutritionally, fertility and condition wise, (as we have been assuming for the synchronized group in the example), we probably should have be able to achieve at least 90% conception or better (90 cows) with a natural service system through our normal first 21 day cycle. We would have 70% of the remaining 10 cows second cycle occurring then in that next 14.5 days (to get to the same 35.5 days in the previous example)... so 7 of the remaining 10 animals should cycle naturally again and get bred naturally again within that period, with a 90%+ settle rate. 7 animals x .90 = 6.3.... let's call it 6. We have 4 animals left that will then be calving "outside of that 35.5 day window", or that just won't settle at all, and will become culls. And we've achieved this "higher percentage of calves within our 35.5 day calving window, with NO ADDITIONAL HANDLING, no observation required, no hormone/drug costs, no additional "tool costs" to catch/observe heats, and no vet fees, etc. (
but of course, WITH a bull cost).
Synchronization along with AI IS a "tool"... no doubt, but it's definitely not "THE tool", on it's own, to achieve a tighter calving window, or to dramatically make a difference in "moving a cow up" very much (what this thread is about), as opposed to simply using no synchro and natural service. I'm still a believer in focusing on the nutrition/condition and then genetic fertility, more than I am in these "artificial tools" as the "cure".
