How do you figure breed adjustment on gestation length for ET?

[RSC]

I have some ET calves coming and the date I have as a calving date is the standard ABS date.  If you have a PB Maine embryo in a PB angus recip how do you adjust the expected gestation length?  Does the genetics of the calf decide the gestation length or can the breeding of the recip contribute some as well? 

Thanks for any insite.

RSC

 

[sjcattleco]

I have some ET calves coming and the date I have as a calving date is the standard ABS date.  If you have a PB Maine embryo in a PB angus recip how do you adjust the expected gestation length?  Does the genetics of the calf decide the gestation length or can the breeding of the recip contribute some as well? 

Thanks for any insite.

RSC

figure on about 276 days instead of 283.

 

[xxcc]

I'm no ET authority, but have had 14 embryos delivered live here over a three year period...7 different matings...2 50/50 Angus Maine, 5 fullblood Maine, the balance purebred Charolais.  To clarify sjcc's response, i would venture to say the 276 day period is transfer date to expected delivery date.

all of my gestation lengths have been all over the board, depending on gender.  My vet tells me that it is the calf that decides when the pregnancy is over.  I've had one Charolais come a week early and two Fullblood Maines up to 11 days over (based on age of embryo, i.e. bred on date to delivery date).  both fullbloods were huge and came out the side.  when they came, they were FAT.  one was so muscled up in the neck, he looked like he might make a hell of a bull if I turned out on cows a week later.  Maybe I was playing with fire, but the sires to the two Maine calves were import bulls from France.  Flushmates to the calves were born with ease.  I don't know what the deal is.

my best experience with recips has been Red Angus cows.  Mind you these are commercial Montana red angus and probably have some hereford way back there.  talking with some other canadian fullblood maine breeders, i would not recommend fullblood Maine, any type of Charoais or Simmental as a recip.  once I thought that was the answer, but I am sold on big old deep body, big pelvic area, heavy milking Red Angus or Red Angus cross recips.

just my two bits.

 

[Jill]

You know I was just think about this last night.  Our embryo's are always put in all at the same time and date, and this year same matings, but the calves will vary up to 3 weeks.  My earliest embryo calf came on Feb.18th and I am still waiting on several, I know they aren't bred to the bull because we wait 2 heats after transplant.  Our recips are purebred Angus, Maine, Maintainer and cross.  The embryologist puts an ear tag in that is 9 months from the date of transplant and that is usually in the middle somewhere.  I guess what I'm saying I don't have an answer, but do have the same question.

 

[RSC]

You know I was just think about this last night.  Our embryo's are always put in all at the same time and date, and this year same matings, but the calves will vary up to 3 weeks.  My earliest embryo calf came on Feb.18th and I am still waiting on several, I know they aren't bred to the bull because we wait 2 heats after transplant.  Our recips are purebred Angus, Maine, Maintainer and cross.  The embryologist puts an ear tag in that is 9 months from the date of transplant and that is usually in the middle somewhere.  I guess what I'm saying I don't have an answer, but do have the same question.

Jill,  It is an interesting thing to try an figure out!  If you using the standard AI on a cow, the Old ABS Barn Record sheet gives you breed adjustmant to estimate calving date.  So does the genetics of the pregancy alone determine the gestation length or does the genetics of the dam carrying the pregnancy come into the equation as well?  I do like the idea of using Red Angus as recips.

RSC

 

[DL]

It is biology and biology doesn't always read the book and cows don't always read the tables.

North Dakota study
462 cows were inseminated to calve on March 1st
only 87 calves on the expected date
the first calf arrived Feb 11th and the last March 19th

80% calved within an 11 day window
95% within a 19 day window
98% within a 28 day window
there are always outliers on either side of the middle of the bell shaped curve

Be that as it may when I calculate the due date for ET calves I figure the embryo was 7 days old when implanted and therefore use the date 7 days prior to implantation for the "insemination" date and look on the gestation chart for the calving date

With nature you can't always be precise 

 

[justintime]

This is an interesting topic in that I have tried to find some trends over the years in regards to expected calving dates on ET calves. Quite frankly, I see no trend at all. Three years ago we implanted 18 embryos. We used up a big bunch of our luck and got 17 pregnancies. We used up even more luck and got 18 heifer calves from 17 pregnancies ( the first embryo split to give us identical twin heifers). The twins came a few days early as twins often do. But from the next recip to calve until the 17th calved, was 18 days. The first, second, fifth, 11th, 14th and 17th recips all had full sib heifers yet there was 18 days between the first and last... and 15 lb difference BW between the first and last. All the calves DNA'd correctly. Two years ago it was much the same with 4 pregnancies from the same flush being 20 days apart. Both the first and last of these were heifers as well, with the middle two being bulls. I usually find that bull calves will go longer term than heifers usually. In 2007, we had 15 ET calves, of which 6 were Salute's- all from the same flush. This time the embryos were put into recips in two groups, 24 days apart. Four were put into the first group of recips, 2 in the second group. One of the recips from the second group calved before the last one from the first group. Again all DNA'd correctly. It seems strange that embryos from the same flush could vary so much in gestation time.
I do think that the recip may have a much larger role in when the calf is born. I also think the calf may have a part in this. Of course the genetics have some role as well, as does the weather and a few other things. All this certainly makes a lot of extra trips to the barn.  I find that the gestation length of ET calves is no different than most everything else involved in ET. It seems that just about every time I think I am starting to understand how to have a great flush, I have a complete bomb and I am left scratching my head when it is done. ET  has a great way in keeping you humble.