In the grey dawn the game was turned and the branch broken by our best piqueur. A rare day's hunting lies before us.
Google says piqueur is a French word means whipper in English. But I still can't understand the words piqueur and game here.
I find in old English , game has the meaning of wild animals or birds that people hunt for sport or food. It's uncountable. Probably it's correct for this context.
[Edit] More specific context of this sentence are:
And then, if he lived near to a cover, there would be the more hares and rabbits to eat out his harvest, and the more hunters to tramper it down. My lord has a new horn from England. He has laid out seven francs in decorating it with silver and gold, and fitting it with a silken leash to hang about his shoulder. The hounds have been on a pilgrimage to the shrine of Saint Mesmer, or Saint Hubert in the Ardennesm, or some other holy intercessor who has made a speciality of the health of hunting-dogs. In the grey dawn the game was turned and the branch broken by our best piqueur. A rare day's hunting lies before us. Wind a jolly flourish, sound the bien-aller with all your lungs. Jacques must stand by, hat in hand, while the quarry and hound and huntsman sweep across his field, and a year's sparing and labouring is as though it had not been.——The Essential Travel Writings, Robert Louis Stevenson