It's the barnyard equivalent of L'Air du Temps, a kind of sows' Shalimar. A two-second spray of it under a lady pig's nose stirs her romantically, and the end result is a lot more little pigs than would otherwise be the case.

The substance is called, bluntly, "Boar Mate." It simulates the odor of a sexually aroused male pig and, says its U.S. distributor, "simply prompts what comes naturally." Use of the aphrodisiac often enables a hog farmer to reduce by as much as half the number of days between weaning one litter and re-breeding, thus increasing a sow's "production" by up to 20 percent.

Sam Kennedy III of Clear Lake, Iowa, a 28-year-old international authority on swine, introduced Boar Mate to this country in March. Already he is predicting 1979 sales of $3 million (a $7 aerosol container is good for 40 applications).

Boar Mate was developed by British livestock researchers and has been marketed in Europe since 1972. Surprisingly, experiments indicate, as Kennedy delicately puts it, "human females are not indifferent to its sensual odor." At Guy's Hospital in London scientists sprayed chairs in the visiting room randomly with Boar Mate, and when women arrived for treatment they chose those chairs over others. The active ingredient in the pig perfume is androstenone, and other British tests show that men with high levels of this chemical (measured in urine samples) tend to be married, father more children and occupy positions of power in industry. (Aggressive young criminals also have an excess of androstenone.)

Kennedy warns strongly against human use of Boar Mate. A bachelor and Boy Scout troop leader, he lets his own social life slide as he travels to Europe or South America eight or 10 times a year to lecture on hog production. He does manage to hunt, fish, trap and keep bees and, as pilot of the Cessna leased by his company, Agricultural Waste Controls Ltd., he sometimes flies dates over to Minneapolis for dinner and back. Such pleasure trips are rare: The business really hogs Sam's time.