Probably the easiest error to make in the early years of shepherding is to provide the wrong level of nutrition to the gestating ewes. This is typically a “rookie mistake” that occurs once or twice as the shepherd learns the intricacies of gestational requirements. Unfortunately this learning curve can occur at the expense of the sheep, since errors can result in the loss of of the lambs and perhaps even the pregnant ewe.
Sheep gestation follows many of the same patterns as human pregnancy. Although it’s shorter in length, we still divide it into three trimesters. In humans, each trimester lasts about three months, while in sheep it lasts about 50 days. Each breed of sheep will have its own length of gestation — running from 142 to 156 days — but to simplify the math for feeding, using 150 days simplifies the trimester calculations.
We seldom look at the gestational age of a specific ewe unless she is having some particular difficulty. We calculate the current trimester by the gestational age of the fetuses carried by the flock as a whole. Our flock was bred this year between September 17th and October 29th, meaning that the first trimester would end for our ewes between November 6th and December 19th. Yet the breeding crayon marks proved that the median date of breeding (when the most markings occurred) was around October 6th. This means that our flock’s first trimester ended about 50 days after this date, around Nov. 25th. Based on this calculation, their final trimester will begin on January 14th. Both of these dates are critically important when it comes to nutrition, and trimesters should be calculated by all shepherds in some way.
In the first trimester, a bred ewe is essentially fed the same maintenance nutrition as an unbred ewe, except she requires a little greater quantity. Good nutrition allows her body to maintain its condition and also provide for the growth of her embryos. During the first trimester, the placenta and umbilical cord are created. Poor nutrition during this period can lead to undersized structures that cannot provide the full level of nutrition as the fetus nears term. Low birth weight lambs are typically the result of poor nutrition in the first trimester, and these lambs can be very high risk.
The first trimester can be a good time to help out a bred ewe lamb who is still small in size. Providing the young ewe (still a lamb herself) with a high level of nutrition can aid her growth. A higher level of nutrition in later trimesters is more likely to increase the size of the lamb(s) she carries, which is not necessarily a good thing for a small ewe lamb who must deliver vaginally.
With basic fetal structures already in place, the second trimester is a period of growth. For wool producers, this is the time when the wool follicles evolve, so good nutrition is critical. The ewes require a small increase in nutrition through this stage from, say, 3.5 to 4 lbs of good quality hay in the first trimester to 4 to 4.5 lbs in the second trimester (Feed quantities are based on the open weight of the ewe and should be calculated for your specific breed – these quantities work well for our breeds). Ewes that are carrying multiples will need all the nutrition they can get through the first and second trimesters, since by the end of the second trimester, the fetuses will begin to crowd the rumen, limiting the ewes’ intake at a time when they need it most. These ewes end up in our high-nutrition group for this reason, along with the bred ewe lambs. These girls get protein-rich alfalfa hay through the first two trimesters.
Nutritional needs really begin to ramp up for all ewes in the third (final) trimester, since this is the period of greatest fetal growth. No matter whether the ewe is over- or under-conditioned (shepherd-speak for fat or thin), her level of nutrition at this point must increase to head off disaster. The lambs will pull their needed nutrition from the ewe regardless of her intake; if she doesn’t eat enough, it will be her own body that suffers as her body fat is burned to provide what is lacking.
As the demands of the lambs continue to increase and the ewe’s body begins to burn fat in greater quantities, the burned fat produces byproducts that flood the ewe’s system, causing an illness called pregnancy toxemia. The byproducts suppress the appetite, creating an even bigger discrepancy between nutritional need and intake. The pregnancy toxemia deepens, and the ewe eventually goes off feed altogether, with no energy at that point to stand or move. Untreated, pregnancy toxemia will ultimately lead to death of the ewe and of every lamb she carries. Treatment is only successful in the early stages of the illness by the shepherd’s focused intervention or just before the due date when labor is induced early (and often unsuccessfully). This is a tragedy better avoided than treated. Pregnancy toxemia is mostly a disease of inexperience; new shepherds often don’t realize the critical nature of third trimester feeding until tragedy strikes.
To avoid toxemia in our flock, we increase the nutritional level of all of our ewes in the final trimester. The high-nutrition group (bred ewe lambs and adult ewes who carry multiples), which has been eating alfalfa hay to this point, begins an additional ration of grain — extra nutrition in a small, nutrient-dense package. The other ewes, who have been eating high quality second- or third-cutting grass hay, are switched to higher protein alfalfa hay at the beginning of this final trimester. Because of shrinking space in the rumen due to growing fetal size, if the alfalfa is not high quality, add a bit of grain to their ration. At this stage, I would rather overfeed than underfeed. Most well-producing ewes will lose weight during lactation.
Keep in mind that if you shear anytime during the last trimester, the wool loss will increase their nutritional needs as their metabolism shifts to produce greater body heat. Depending on temperatures, shearing can create a need for up to 25% more feed at a time when rumen capacity is at an all-time low. When in doubt during this last trimester, feed more or better; there is a limit to how much they can fit into their already large bellies!
During gestation, ewes are in the process of creating our future flock. A strong, healthy, and low-trouble flock needs the appropriate levels of good quality feed as building blocks to build that future. Gestation requires you to be informed and to not cut corners. After all, lives hang in the balance.