China's booming dairy industry has meant a surge in US hay exports, but the country's resistance to imports of some US genetically-modified crops (GMOs) is reducing US exports of hay modified with biotech alfalfa.

US farmers have embraced the GMO technology that helps to kill weeds, fight pests and improve yields. But China has not accepted all GMO agriculture products and has tight restrictions on imports.

Earlier this year, China started testing to determine if US hay imports contained the genetically modified alfalfa developed by Monsanto Co, according to a report in The Wall Street Journal on Monday.

Exports of alfalfa hay from the US to China jumped more than eightfold between 2009 and 2013 to 785,000 tons, the newspaper reported, however, shipments fell 22 percent by weight from August through October as US exporters reacted to the Chinese testing, the WSJ said.

The result has been about a 12 percent decline in US hay prices, in part because the drop in demand from China increased domestic supplies, according to the article.

A combination of dwindling access to water and arable land forced China to turn to the US to help feed the country's growing herd of dairy cows. Packed with fiber and protein, alfalfa hay is a prime food source for dairy cows.

"China is merely enforcing a rule that all exporters should know and follow: Unapproved genetically-engineered (GE) products are not allowed into the country," wrote John Szczepanski, director

at the US Forage Export Council/National Hay Association in Nashville, Tennessee in an e-mail to China Daily.

"Chinese regulations on GE alfalfa are not having a major effect on US forage exports where China represents about a quarter of all overseas sales," said Szczepanski.

Dan Undersander, an extension and forage agronomist at the University of Wisconsin in Madison, said that only about 5 percent of US hay production is exported. ``It (China's testing procedure) will be significant in Washington, Oregon, and California, but not generally across the US," he said.

"We are hoping that some methodology and certification can be arranged for testing in the US so that hay does not have to be shipped to China before the testing occurs. The current situation makes hay growers reluctant to ship hay to China. If not, this will significantly cut US hay exports," he wrote in an e-mail to China Daily.

Gregory P. DeWitt, marketing and communications manager at ACX Global, the largest hay exporter in North America, said there was a decrease in shipments over the past few months as the industry sought to better understand exactly what needed to be done to make sure it was in compliance with Chinese protocols.

"This may have softened demand in the domestic markets, but demand in China has not changed. Just as with any product, (the) industry must adapt to the needs of the customer. If export customers won't accept GMO alfalfa, then exporters must source non-GMO product," he said in an e-mail.

Undersander said the new tests that China is using are much more sensitive than previous tests.

"Some (hay) will test positive for GM hay if pollen from a nearby corn field blew onto the alfalfa. The important issue is that non-GM hay under some circumstances is testing positive on arrival in China. This hurts the US hay industry because the hay can't be delivered and cannot be returned to the U.S. because China has contagious disease in dairy cattle (Hoof and Mouth and Brucellosis). Fortunately other countries in southeast Asia (Vietnam, Japan, and Korea) accept GM alfalfa so the shipments can be diverted there," he said.

DeWitt said the US is not the only supplier of alfalfa hay to China. "China also imports forage and roughage products from Canada, Australia, and Spain. There are a limited number of countries from which China sources animal feed to supplement its domestic supply, but there may be a number of countries awaiting regulatory approval in China," he said.

DeWitt said that US exporters will adjust to the Chinese market.

"China is among the largest markets for US hay; so, of course it will affect exports. Again, it comes back to industry sourcing product as demanded by the customer. It is our understanding the Chinese government is aware of the need for regulatory approval and that it might take at least a year," he said. "In the meantime, we strictly adhere to China's zero-tolerance policy and do our best to please our customers in all markets with properly sourced product."

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