I had our grass tested again last fall, but for some reason they didn’t send the results, and I forgot to ask about it until now. They were able to quickly retrieve them for me. High time to be looking over the numbers, since the sheep will be back on grass in a few more weeks. I did some different testing this year, and as always, was surprised and enlightened by the results. I’m back to changing my ration plans again. I think I can improve my lamb growth, and I continue to have some ewes which stay too thin for no obvious reason. So I keep looking at ways to improve. This year, I tested for selenium in our forage, which I hadn’t done before.
Pretty much “everyone” says all northwest soils are too low in selenium, and that we must all always supplement. Nearly every brand of mineral supplement carried by stores here contains added selenium, and feed store employees seem to always recommend using it. I’ve heard veterinarians, feed mill nutrition experts, and WSU researchers all echo this set-in-stone fact in talking about the Western range, from Spokane to Medford. Many producers, in addition to year-round feed supplementation, also juice pregnant ewes and does with an injection of extra Se right before parturition; as extra insurance against white muscle disease in lambs and kids.
I’ve heard this low-Se theory so many times, it almost didn’t seem worth the bother to test soil or forage. At the lab I use, Se testing is $13 extra per sample. I have had a few lamb liver samples come back high-normal, and one very high, which got me curious. So I decided to see what the grass was contributing, compared to my supplements.
Imagine my surprise to see that both fields tested fairly high. At 1.25 and 1.39 mg/kg, respectively, that’s a sweet spot in the recommended range of 0.1 to 2.0. And, it would imply that I probably need no supplementation whatsoever during the grazing season. So much for “common knowledge!”
A Thin Line
Since there is Se in my mineral supplements, this means it’s possible my sheep have sometimes been getting too much. When I do the calculations, it all depends on how much supplement they eat. Since I feed free choice, I only know averages and not individual consumption rates, and I can’t control if one sheep is overdoing it. And that is the trickiness of Se. The recommended range is decidedly narrow. Both toxicity and deficiency can be lethal, and both have similar symptoms. It’s desirable to keep selenium on the high end, because it contributes to rapid growth. But too much can cause the reverse, resulting in poor growth.
I feel fairly confident that I’ve never had a death related to selenium- I’ve not seen the foaming bloody mouth nor “blind staggers” from an acute case. And most of my liver samples imply that my sheep are typically landing within the normal range, so nothing to get excited about, yet.
Nagging Little Problems
In searching the web on this topic, there is much more information available on deficiency than excess. But here are a couple of interesting articles: Irish Veterinary Journal and Cornell. The things that jump out at me regarding low-grade selenium excess are: lameness, foot pain, hoof tissue deformities, anemia, and ill thrift—all of which I see in some sheep, some of the time; usually during summer when the grass is most lush and they are eating full tilt. There is also mention of sulfur balancing out Se (we have a lot of sulfur in our grass, so it could be offsetting the fact that they’re pushing the limit on the latter). And Se toxicity is often accompanied by Molybdenum-induced copper deficiency; just another angle to this complicated web of mineral interactions.
I had not run across this selenium tie-in to hoof health before, probably because I was so brainwashed to think it wasn’t possible here!
And, several sources mention selenium toxicity can cause abortion. I had some strange perished fetuses last year that turned up in the afterbirth alongside healthy lambs. Judging by their tiny size, they perished right around the time I had switched to using the Cattlemen’s supplement, which is quite high in Se. I wondered if the sheep had gorged on the supplement when it was novel, and whether some excess there was a contributor to fetal mortality. Who knows, but just another clue there to think about.
What’s got me curious is wondering why our fields don’t obey the common regional theme? I don’t know. One guess is that possibly river flooding brings nutrients to these fields that the majority Western soils don’t enjoy. The above-mentioned article about Ireland cites both floodplain and peaty swamps as selenium hotbeds, and we do have underlying peat soils in this valley. Another guess is that these century-old farm fields have had enough selenium added to them, either specifically (less likely) or by virtue of manure from selenium-fed animals, that over time the soil profile has been augmented. I read that sheep do excrete extra Se in feces, but also that Se in that form isn’t very bioavailable to plants. So, hmm, how knows?
Back to the Math
So, there I go, back to my spreadsheet again to re-jigger my mineral supps before the sheep go back to grazing for the summer! It seems it’s a moving target getting their nutrition optimized just so!