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Fetus size -vs- Breeding Date

Old 12-21-2004, 05:54 PM
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Default Fetus size -vs- Breeding Date

Just wondering if anyone in here is educated on the size of a deer fetus in corresponding with it's age? A friend of mine harvested a doe on Sunday night December 19th and I was assisting with the field dressing. Inside, I found a "fetus" the size of my thumb (I guess about 2" or so). I was just wondering how long ago breeding took place?
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Old 12-21-2004, 06:24 PM
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Default RE: Fetus size -vs- Breeding Date

As memory serves (I don't have my old textbook with me now), the gestation for deer (full-term) is anywhere from 195-210 days, with an average gestation of 205 days, so I will take a guess and say that your friends doe was bred approximately 1.5 months ago (40 days).
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Old 12-21-2004, 07:42 PM
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Default RE: Fetus size -vs- Breeding Date

This is from my text on Research and Management Techniques for Wildilfe and Habitats in the "Sexing and Aging" chapter.

There are a few techniques that have proven to be reasonably accurate. These include "Crown to rump" measurments as Rose has mentioned.

You can also use a combination of physical characterisitcs, crown-rump measurement, hind foot, and hind leg measurements in mm to more accurately ascertain fetus age.

So using only the crown to rump measurement 2" = 50.8 mm

According to a table from Larson and Taber (1980) of fetal crown-rump measurements from Whitetails in NY, 40 days would seem a bit young. Mean crown-rump measurements for 45-52 day old fetuses were 37.8 mm, substantially lower than 50mm. 53-60 day old fetuses mean was 62.7 mm which is closer to the actual measurement (50) than 37.8.

I would place my estimate closer to 50 days. This would be made more accurate by knowing if the eyelids were formed and mouth was open or closed.

Assuming a constant fetal growth rate, Hamilton et al. (1985) determined the age of a fetus from a doe killed on Dec. 15 to be 51 days. So we would expect the fetal age to be somewhere around there to account for variations in conception during the rut.

Of course these kinds of measurements do vary among populations and among individuals at different nutritional levels but they are fairly accurate.
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Old 12-21-2004, 08:13 PM
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Default RE: Fetus size -vs- Breeding Date

I figured I should have done exact measurements and so on. I will say that the mouth was closed, but I do remember it seemed to have good detail. In other words, I could easily see the mouth, the eyelids, ear openings, and it even seemed that you could tell where the legs were jointed and where the hoofs would be.

For what it's worth, I hunt in North Central Texas (not South Texas) and depending what chart or who you ask, our rut is normally around the 2nd-3rd week in November. I shot a Buck last season on November 8th that was HEAVY in rut.

This year has been VERY wet for us and we have had a total Bumper crop of acorns along with every other thing in the world for them to eat. It has been a unique year and rumor has it that the rut may have been "off" this year. I hunted in the same geographical area last year and rut sign was "heavy"...This year.....NONE!! But buck sitings and bucks shot way outnumber does seen or killed.

All of that is why I'm trying to narrow down some dates.... Thank you again.
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Old 12-21-2004, 08:15 PM
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Default RE: Fetus size -vs- Breeding Date

Brutal--Excellent post, Good job.
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