I have found a huge variation on calving dates from my ET calves. I am not sure if they are much different than pasture bred or AI bred females as I have also found differences in calving dates from females that were synchronized and AI bred. One two different occasions I have had 18 days from the first born to the last born from embryos from the same flush and implanted on the same day. The first time this happened I had six ET full sibs born. The first one born was on the expected due date and the rest followed, most of which were in the next few days after the first. In this case, all 6 were heifers and all were born unassisted, although there was some increase in BW in the later born calves.
The second time this happened, again there was 18 days from first to last born. There was 4 ET full sibs and the first born was a heifer, followed by a bull calf and then two more heifers. Over the years, I have always thought that I had far more bull calves past their due date than heifer calves but that seems to be tossed out the window when it comes to ET calves. All ET calves here are parentage verified so they is no chance the later calves were from a later breeding. I also never put a clean up bull with my recips for at least 2 months after putting embryos in.
I have mentioned this before but I am wondering what affect the recip cow has on the due date of the ET calf. Most everything I read says the calf's genetics will be the biggest influence on the gestation date. I had one black Simmental/ Angus recip that had 7 ET calves here. Every year she had an ET calf, she was the last recip to calve. She was the recip that carried both of the ET calves that were 18 days past to expected due date. Both times she calved unassisted with a heifer calf. Makes me wonder if she was the reason for the delayed birth.
I know many people worry and eventually induce females when they feel they are overdue. After an experience at Bar 5 Simmental in the 1980s, I have never induced another cow and probably never will. Bar 5 decided that they were going to calve on Tuesdays and Thursdays so that they could hire their local vet to be at the farm. I never saw so many assisted births and c- sections as well as weak calves and retained placentas in the cows. Most of the cows took longer to cycle and get rebred and the next year's calf crop was more spread out. I like to think that Mother Nature knows best in most of these calving situations.
Right now, I am down to 6 cows left to calve and I am probably going to jinx myself by saying this. This is the first time in my life that I can say that I have not assisted a single cow or heifer at birth. Before calving started I purchased some new calving chains and a handle and they are still in the plastic container they were in when I bought them. I normally don't have to assist many, but usually there is a malpresentation ( backwards or a foot back etc). I know there were some of this year's calf crop that went over their projected calving date by several days and I also know a few were before their projected calving date, as I had recorded breeding dates on most of my cows and heifers last year.
