CHICAGO (Reuters) - U.S. cattle producers have started rebuilding the nation's herd or are close to doing so, Tyson Foods ( TSN ) CEO Donnie King said on Wednesday, after supplies dwindled to a 74-year low.

Tight cattle inventories have driven up beef prices for U.S. consumers and forced meatpackers, including Tyson and rivals like Cargill and JBS, to pay more for livestock to slaughter.

Farmers slashed their herds by sending more animals to slaughter instead of keeping them to reproduce following a years-long drought that reduced grazing lands and raised prices for livestock feed. Ongoing dryness over the past year had discouraged producers from starting the rebuilding process, which can take roughly two years.

"Everybody is hesitant, including me, to call that we are now in rebuild," King said on a webcast of BMO's Farm to Market Conference. "If we're not, we're very close."

Tyson reported an adjusted operating loss of $181 million in its beef business in the six months that ended on March 29.