The Sporting Magazine (1792 - 1870) is considered the first general sporting magazine, though in its later decades it gave considerable emphasis to fox hunting. But it published all manner of sporting-related material, from news stories to poetry to calendars of upcoming sporting events. The subtitle of this magazine was "Monthly Calendar of the Transactions of the Turf, the Chace, and every other Diversion interesting to the Man of Pleasure, Enterprize and Spirit." [more at Wikipedia]
The November, 1861, issue, in an article on "Wild Fowl Shooting in November," makes a reference to a Newfoundland as a gun dog. The author, identified only as "D. G.", is describing the use of a double-barreled gun to kill large numbers of ducks at a time:
To recover the wounded fugitives, he [the hunter] must depend in a great measure upon a steady and persevering retriever. The writer was, some years since, in possession of a double-gun, manufactured by Moore of Regent-street. The same was calculated to throw half-a-pound of shot from each barrel. Upon one occasion, whilst walking along the shore at Pylewell, near Lymington, accompanied by his dog "Tippoo," a Newfoundland animal of indomitable courage, and under the best course of training, his ear was attracted by the near gaggling of geese. . . . There must have been some scores of them in company. In a kneeling position, with the right-hand barrel, he raked the floating phalanx with a close volley of No. B shot, and let drive the contents of the second barrel among the noisy group, whilst in the act of taking wing. A gentle wind from the westward conducted the killed birds towards the beach, whilst his canine fidus Achates redeemed such as had been crippled; so that he managed to pick up, out of his twain shots, fifteen head of geese and one pintail widgeon.