Apart from the fact that it has somewhere between 19-21% sugar content, there is absolutely no reason not to. Better option is fodder beet, though as less sugary.
Usually the sugar is extracted from sugarbeet - products such as Speedibeet are particularlty low in sugar. Sugarbeet tends to be fairly high in energy, but it's released slowly so it doesn't tend to cause fizziness. It's great for gaining/maintaining condition, especially in winter as it is also high in fibre.