PKE in calves is okay if fed for a short period or smaller quantities over a longer period as part of a balanced diet (1kg for example). For short-term feed deficits they shouldn’t be fed more than 50% of their diet in PKE, so at the moment a maximum of 3-3.5kgDM for a 180kg calf. If you are or need to feed more than 50% of the diet in PKE there should be some higher protein feed added to the PKE such as DDG or canola meal. At higher levels of PKE in the diet, calves also need to be getting a couple of kgs of effective fibre as well (long chop good quality perennial silage, or very good quality hay) as I’m pretty sure no one has any stalky grass left now we’ve had enough rain to mush what was there. Maize can also be in their diet but once again only as a part of a balanced mix (it’s low in protein and high in starch so it’s not an ideal feed for calves on its own).
Also remember that with grass now growing the calves will start eating it – sounds obvious but is actually annoying! Autumn grass doesn’t lead to good growth rates in calves – lots of water and not much else in it. So often calves will look poorly in the autumn despite being apparently well fed on pasture as the energy density just isn’t there. Good quality supplements can reduce this affect.
Also the move to grazing can be stressful for calves, and knock their growth. Finding out what they were eating before they left and trying to continue this for a while before transitioning to grass alone will minimise this effect and in turn prevent disease.