Viacom Inc., owner of the MTV network and Paramount Pictures, said third-quarter profit gained 37 percent on rising advertising sales at cable channels. Net income climbed to $574 million, or 97 cents a share, in the period ended June 30, from $420 million, or 69 cents, a year earlier, New York-based Viacom said today in a statement. Excluding costs to cut jobs, Viacom’s earnings of 99 cents a share beat the 86-cent average of 25 analysts’ estimates. Higher domestic ad sales at Nickelodeon, MTV and Comedy Central drove earnings growth. Viacom’s sales rose 15 percent to $3.77 billion, exceeding the $3.49 billion average of 21 analysts’ estimates compiled by Bloomberg. Profit at Viacom’s cable networks rose 27 percent to $1.03 billion from a year earlier on sales of $2.39 billion, the company said. Domestic advertising sales increased 12 percent.