Gestation length correlations

[SheepGirl]

Is there a correlation between number of days bred and the age of the dam, the birth type, birth weights, or sex of the lambs?

According to Sheep 201:

The average gestation length in sheep varies from 142 to 152 days. The average is 147 days. Individual pregnancies may vary from 138 to 159 days. There are breed differences in gestation length. The earlier maturing breeds (e.g. Finnsheep) tend to have shorter pregnancies than the late maturing breeds (e.g. Rambouillet). Ewes carrying multiple births tend to have shorter gestations. Male lambs and heavy birth weight lambs are usually carried longer than female lambs.

According to Montana Farm Flock Sheep Production Handbook:

Average gestation length or length of pregnancy for sheep varies from 144 to 151 days (about 147 days; figure 11). Individual pregnancies may vary from 138 to 159 days. Generally the earlier maturing meat breeds and the high prolific breeds such as the Finn have shorter gestation lengths (144 to 145 days), while the slower maturing finewool breeds (Rambouillet) have longer periods (150 to 151). Typically multiple lamb baring ewes will have slightly shorter gestation periods. It is not unusual for individual ewes within breeds to vary in gestation length by 3 to 5 days.

Here is some statistical information for those of you who like to look at this kind of stuff. If you have your own information, please feel free to add it.

RAW DATA

ORGANIZED DATA
AGE
1 yr - 144, 144, 147 (145)
2 yr - 143, 145 (144)
3 yr - 143
4 yr - 145
5 yr - 145
6 yr - 143
7 yr - 145
8 yr - 146

BIRTH TYPE
1 - 144, 144, 145, 145, 147 (145)
2 - 143, 143, 143, 145 (143.5)
3 - 145, 146 (145.5)

SEX
Ewe - 143, 143, 143, 143, 143, 145, 145, 145, 145, 146 (144.1)
Ram - 143, 144, 144, 145, 145, 145, 146, 146, 147 (145)

BIRTH WEIGHT
< 5.0 lbs - 143
5.1-6.0 lbs - 145
6.1-7.0 lbs - 143, 145, 146 (144.7)
7.1-8.0 lbs - 143, 145, 146 (144.7)
8.1-9.0 lbs - 145, 145, 145, 146 (145.3)
9.1-10.0 lbs - 144, 147 (145.5)
10.1-11.0 lbs - 144
> 11.1 lbs - 145

Over the next week or two, I will be adding six more ewes onto this data as they lamb. My first ewe is due as early as Feb 21 (day 143) -- she is a 9 year old ewe, with likely just a single or a small set of twins.

 

[HoneyDreameMomma]

That's a really cool idea! Makes me want to try it from a goat perspective, but I wouldn't get much data this year. We had our bucks in the pasture with the does for over month, and we can only confirm the exact day for half our girls.

 

[Goat Whisperer]

Very interesting!