Quite so, which rather makes the point I was suggesting, ie that daylight might not be the governing factor.
Those who offer supplementary feeding here in Scotland, be that to either roe deer (à la Zobel) or red deer (- a common undertaking on many highland estates) are generally doing so in order to maintain their deer in favourable condition, and see them through until the spring rather than trying to produce freaks, just saying. I’m unaware of anyone here in Scotland using growth promoters on red deer in the spring and summer (or indeed outwith the season, come to that) when the antlers here are being developed; that said, I understand that it is quite an industry in USA and NZ.