Apologies, the wording of my post probably gives the wrong impression. Betdaq seed their own markets and the only way they can do that without getting raped by the arbers is to have a bot which constantly monitors the BF markets and keeps them in tandem. I said it 'feeds off' the BF market which suggests it back/lays but I simply meant it gets it's information from the BF markets.
The Betdaq market usually moves first and the BF market follows, this might sound weird considering the size of the two exchanges, but this happens for two reasons. Firstly, the vast majority of on-course bookmakers use Betdaq to hedge their bets, so when a horse is backed on course to chunky money then the books quickly hedge their liabilities on Betdaq (and often it'll be several books rather then just one), which leads to the second reason - the liquidity on Betdaq is far lower than on BF so the money coming from on-course books will shorten the price on Betdaq several ticks at a time, whereas on BF there is more money so this takes longer to be taken (by the bots run by arbers over the two exchanges), hence the delay in BF following Betdaq.