I have written before about working on improving birth weight values. My goal is a spread of birth weights between seven and eleven pounds. Different people have different ideals, based on their management systems. I want my lambs to have big enough frames that they are not at risk of chilling on cold, rainy days; but not so big that they risk difficult births, because I’m not always present to assist. It looks like I’ve made some progress there, here are my numbers from this year.

I believe the first thing to do to move the curve is to look at BWT (birth weight) Estimated Breeding Values (EBVs) from NSIP metrics. When choosing which ewes to retain last fall, I did pay attention to that number, and gave it fairly high priority. I scaled back on using my ram that has the poorest values. I painfully let go of some otherwise very nice ewes because they had lower BWT metrics than average for me. They will do well in someone else’s barn lambing scenario.

Last year I convinced myself that increasing feed earlier in late gestation wouldn’t help, according to the data I had so far. I looked at whether the late-born lambs, which had 1-3 weeks of extra feed invested in them during gestation, were heavier at birth. They were not, and there was actually a negative correlation there. So I wasn’t going to change my feeding protocol, convinced it wouldn’t help. But I overrode that decision because I had some lean ewes in winter, and my yearling ewes were smaller than I wanted. I wanted to give them a good boost at the end of pregnancy. And I’m guessing it did have some effect.

In past years, I’ve just escalated feed in the last 30 days of pregnancy, leading up to the first day lambs are due. This time, I started ramping them up on grain ten weeks prior to lambing, bringing them up to 1.5 lbs. per head per day over three weeks. So they had seven full weeks of high grain before the onset of lambing (and more if they lambed later than the first day). I used a “dry” rolled corn-barley mix (no molasses), which is only about 10% protein, same as my hay. So, it’s not a “hot” feed like soybean meal (which is about 50% protein). Rather, it is just something to give them extra calories as they are able to take in less  feed volume when their bellies are full of lambs.

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Here is a graph of birth weight distributions from the last four lambing seasons. The mean for all prior years together was 7.7 lbs, and the mean for this year was 8.7 lbs, so a good increase there. This year’s (blue) bell curve is centered very nicely between the goal posts. It’s still a little wide, I’d like the shape of the curve to look more like 2011 (the green curve), where variation is narrow. But this is good progress, especially in a short period of time. The lamb group looks nice and uniform this year, I am very pleased.

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