Twitchy horse, deficiency or ?

[ahlam1399]

My mare has started to sometimes twitch like she has a fly on her, she is also swishing her tail. She is in a stable, in a rug, in the middle of winter so there are no flies on her. I?m just wondering if it could be some sort of vit / min deficiency or something else. She is a TB fed speedibeet, grass chaff and a balancer. She has ad lib hay. She is not doing it all the time, it?s just caught my eye as being a bit odd when I see her do it. She is currently on box rest due to a cut leg but is being a perfect patient and doesn?t seem agitated. She has also done the twitching and swishing when not on box rest.

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