Sheep farmer Takanori Nishikawa, from Bibai, Hokkaido, is finding growing demand for premium lamb and mutton raised on asparagus.

Nishikawa, 46, is not a farmer by birth. He owns a construction company inherited from his father.

He had no experience of animal husbandry when eight years ago a local farmer brought asparagus roots as feed for his father's three pet sheep. The roots are usually removed from the plant before shipment and thrown away.

He realized that a diet of asparagus might result in tastier meat than that of animals raised on compound feed and hay, and he set about turning it into a business.

Sure enough, the mutton tasted sweeter than imported meat. He attributes this to the level of sugar in asparagus.

Less than 1 percent of lamb and mutton consumed in Japan is produced domestically and even in Hokkaido, where mutton dishes are popular, imports account for most of the meat consumed.

Bibai, a city in the central part of Hokkaido, once flourished as a coal mining town, but its fortunes have declined and its population of 23,000 is down to a quarter of the peak.

Nishikawa manages the construction company his father, Iwao, 71, founded.

Ever eager to improve feeding methods and meat quality, Nishikawa is a regular visitor to restaurant owners to consult them. He has also developed processed mutton products and organized promotional events.

Nishikawa's flock now comprises 180 head of sheep and demand is rising for his produce.

During the season when fresh asparagus is unavailable, the farm uses feed made from the fermentation of dried asparagus mixed with rice and wheat bran.

And in a neat twist, the sheep droppings are shipped to the asparagus farmers' fields as fertilizer.