Wise Sheep

Plants have quite a struggle to get the best spots with plenty of light and water to put down roots and get established in the good life. As if that weren’t enough, many members of the animal kingdom are addicted to herbivory and will suck the sap or chew the leaves. A defensive mechanism of the plants is to produce tannins. These polyphenols are a good insect deterrent but are not so effective against vertebrate munchers.

The arms race is on and mammalian herbivores, as well as some marsupials, produce some proline rich salivary proteins that bind to the polyphenols and take them out of the picture – up to a point, that is. Being stuck with a diet that is high in tannins is not a pleasant option.

So what is a sheep to do if she is stuck in a pen with a high tannin diet? She’ll rely on chemistry and self-medicate with high molecular weight polyethylene glycol, PEG, as available in over the counter laxatives. That of course means that she will have to raid her shepherd’s bathroom cabinet. Sanga et al of Utah State U have reported on a study of this behavior (1). The big question they wanted answered was what did they tell their offspring?

Two groups of ewes were picked and one group was fed tannin-rich feed and the other was on normal rations. The tannin-rich group quickly learned to self medicate and now the scene was set. The alternative to PEG was a placebo in the form of grape pomace. When both groups were subsequently stuck on the high-tannin feed and offered PEG or pomace, the wise old gals munched away heartily and choose PEG dessert. Not so with the naïve ones they didn’t eat much were a bit slow on the laxatives.

After their lambs were weaned, the ones with wise moms had no trouble and got stuck into PEG dessert and even the ones with the relatively naïve moms tried that route too. A group of young lambs on their own had trouble as no one had told them to eat their PEG.

I guess it is a reminder to us all to talk to our kids about the junk food their eating and to keep our bathroom cabinets stocked up.

  1. U.Sanga, F.D.Provenza & J.J.Villalba, Animal Behavior, 82, 219, (2011).

One Response so far.

  1. hmmm, didn't know PEG was in laxatives.

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