All 3 of mine are kept in short hair. Boo is a good boy and will stand still for me so I just shave his body in the summertime and leave the hair on his legs and head longer.
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Gracie Ruth matts real bad too, so she stays in a short cut. I use to do a Lamb cut on her, but it just wasn't flattering. The last time Lisa cut her body and the upper part of her legs to about 1/2" and then left the lower half of her legs long. Lisa calls them boots, DH says it looks like she has bell bottoms on.
I just call it cute! Here she is in the Lamb cut.
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Yogi is in a modified Lamb cut. I say modified because Lisa does extra work to layer his hair so that it will lay nicely and not stick out like he's been electrocuted .
Which the hair on his face has a tendency to do.
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You really need to work those mats out because otherwise they'll probably just need to shave her. If you don't already have, you'll need to get a nice metal 'flea' comb, these are the best at working the mats out. You can get some detangler at the pet stores or I use Corn Starch, it works really good to help loosen the mats so that you can comb them out. Just take a pinch and rub it into the mat and work on it a little with the comb. Rub some more in, if needed, until you work the mat all out. I've never tried but have heard you can put a little hair conditioner on the mat to help loosen it. But unless you just want to have her shaved and then start from there, you really need to work those mats out.