First use of 'mercy dogs' by British troops Flanders?

[kerry]

Dear All,

I've Googled this but can't find a start month as to when British Forces in the Ypres Salient started to use so-called mercy dogs to help locate wounded lying in No Man's Land. I read that the French used them near Boesinghe in April 1915 and that a School was set up in 1917 but I also read that an officer began training dogs for this specific purpose, before the start of hostilities.

Does anyone know if such dogs would have been used in early May 1915 or would that have been too early for their deployment and use to carry water etc to our stranded wounded beyond the wire?

Thanks in advance.

Edited 6 April by kerry
Missing info.