Low birth weight lambs

In the shepherding world, not all lambs are created equal. When we first started our flock, our newborn lambs weighed an average of about eight pounds, with as many above that weight as below. As I began my shepherding journey, collecting data as we went, I soon realized that those lambs who weighed less than eight pounds were at much greater risk of death than those who weighed more. After crying through the loss of several pint-sized lambs, I vowed to figure out a way to save them — and over the years, we have.

Romeldale Natasha with tiny twins Odessa (3.7 lbs) and Oleg (3.3 lbs) in 2015

The problem is that small lambs have a large surface area but a very small stomach volume. They must continually consume first colostrum and then milk in order to remain alive in our cold Iowa spring temperatures, even if they’re tucked within our barns. It is far too easy for these little ones to nurse, immediately fall asleep, and digest everything in short order. This means that they need to get up and nurse again within an hour or two. Their mothers don’t realize how often they must feed to survive, and usually the lambs are still napping when their stomachs are empty. When this happens, they fall into a deeper sleep — due to hypothermia — and they just never awaken. I come to the lambing barn in the morning to find that they died during the chilly night, despite the heat lamps and all.

Romney Harmony with good-sized triplets in 2013: Meia (11.2 lbs), Mikko (10.4 lbs) and Mia (9.0 lbs)

Larger lambs have larger tummies and can take in more milk in one nursing. By the time they are becoming empty, their mothers are getting tight with milk and awaken them to nurse. The system works better for them than for their smaller flockmates. The only way to get around this issue was to increase birth weights. Yet this alone is not the answer, since increased birth weights bring problems of their own. With larger lambs, the ewes must have a larger pelvic girdle to allow a big lamb to pass through unassisted. They must also be capable of feeding multiples, and feeding three big lambs requires a lot more milk than feeding three tiny babes.

To raise our birth weights so that few would fall below the eight-pound threshold, I began a multi-pronged approach: bring in rams who father bigger lambs, feed our ewes well during the first trimester when the placenta is forming (think of this as the lamb drinking out of a straw — the bigger and better the straw, the more the lamb can drink), select for ewes who produce larger lambs without assistance, shear the ewes 2-8 weeks before lambing (this adds two days of gestation, creating lambs nearly a pound larger than they would have been), and provide more energy in the ewes’ feed (more carbs like corn) in late gestation. This last point actually has two important roles, since high-energy feeds will not only increase birth weights but will also improve the quantity and quality of colostrum, the first milk that comes in to feed the newborn lambs. Any ewes who were too small in the pelvis were culled in favor of those who could deliver the larger lambs.

It took five years, but we eventually stabilized our birth weights at an average of 11.2 pounds. We have about as many lambs born above eleven pounds as below, and very few of the small ones fall below eight pounds. It does still happen, but anytime we have a newborn lamb weigh in at under eight, we consider them high-risk and we invest a lot of time and effort into trying to keep them alive. If the same dam produces such small lambs two years in a row without a good reason, she is on our possible cull list, since I cannot invest all that time and effort in this one ewe — it takes me away from being available to the rest of our productive flock.

Another problem is that these small lambs are usually born with a poor suck reflex, so they need a lot of encouragement to nurse. They also lose heat easily, so I have to make sure that they not only nurse constantly but that they don’t get chilled. One would think that a heat lamp would be the answer, but that isn’t the case; setting the heat lamp low enough for a small lamb means that the ewe can too easily singe her wool. We have used heating pads in the past with some success, but I must make sure they are not set too high and that the ewe doesn’t get caught in the cord or chew it. Honestly, the whole thing is complicated, and the lambs don’t always survive even after I’ve invested a lot of time and energy.

There are no low birth weight lambs in our barn at this time. We still have only Nypsi’s twins, who weighed in at nine and nearly eleven pounds — smaller than our average but able to tough it out in the barn on their own. Because this is lambing season for many shepherds, I thought I’d share some wisdom. And as always, I welcome any comments or questions from you!

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  • Janice says:

    Interesting topic! I’m curious about why shearing date increases gestation time. I wouldn’t think that would matter.

    • Dee says:

      I’m thinking it has to do with the extra heat of pregnancy, which is more easily dispersed once the wool has been sheared. I think when they are overheated and uncomfortable, their bodies go into labor sooner “to set things right.” I dont know if this is the case, but when we moved our shearing date from after lambing to before, our average gestation increased by about two days. Shortly after that, I happened to read a study performed in Australia that showed that shearing before lambing increased gestation length by something like 42 hours – very close to the two days that my own work had revealed. We now always shear about two weeks before our first lambs arrive.

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