image

Lambing is almost over here, I have one late ewe left to deliver whom I think is due next weekend. Total count so far is 64 lambs, which is low, but not terrible. I have eight open ewes, six of which are yearlings. So now it’s time to pour over data and start making decisions about which sheep to keep, sell, and cull; as well as decisions about management changes for next year.

I’ve written before about lamb birth weights, as I’m very interested in keeping them between the goal posts of 7-11 pounds, with 9 being about the mean. Last year I nailed it almost perfectly (solid green line in the graph). Lamb birth weights is a Goldilocks problem: you don’t want them too big or too small, they need to be just right. Big lambs cause troubled deliveries, little lambs are at risk of chilling, and are correlated with slower growth later.

Some people don’t think this is an important trait, and I agree for systems where lambs are creep-fed (which compensates for lower birth weights and poor milk) and where birthing is highly managed. But, for me, semi-unattended pasture lambing makes birth weight pretty important. I don’t want ewes sitting out there straining for hours to get a lamb out if I’m not there to pull it. And I don’t want tiny lambs chilling in our cold rain. And because my lambs don’t have the help of creep feed, they need good enough size out of the gate to get good early growth on milk and pasture alone.

This year, birth weights were a little low (solid blue line), and the spread was wider; which is not preferable, but it’s still very close to my goal. I don’t think I had as good of hay quality this last winter, and that is probably the main reason birth weights are a little lower than last year. I’m also using two new rams, both of which I think might be on the low side for birth weight; but I don’t yet have enough data to know for sure. Plus, I still have a lot of young ewes: about half my population is age one or two.

I’m reasonably happy with this year’s result. I’d rather have the curve vary a little to the left than start moving too far to the right. Larger birth weights are a natural genetic consequence of selecting for better lamb growth over time. And, as my ewe population’s median age increases, I’ll see a shift to the right on birth weights due to that. So, I know I’ll have to work to keep the bell curve centered near 9 pounds. This is done via genetic selection as well as careful management of ewe pregnancy nutrition.

No big actions needed heading into next year. I want to try to feed the ewes a little better if I can. And I’ll keep watching the impact of the new rams on the birth weight trait; and watching the top-end NSIP metrics to ensure that I’m not breeding big-to-big there, and risking getting too big!

Advertisements