BEIJING – China’s huge pig herd is rebounding rapidly after being decimated by disease but pork output will take much longer to restore given the low quality of the new herd, experts and analysts said.

China’s pork output fell to its lowest level in 16 years last year after African swine fever swept through farms nationwide from 2018 onward.

With as many as 60% of its breeding sows gone by the second half of 2019, production of market pigs plunged and pork prices soared to new highs, where they have hovered for much of this year.

But after Beijing called last September for an urgent rebuilding of pork supplies and producers have poured billions of yuan into new farms, triggering a rapid rebound.

In July, the herd grew for the first time in more than two years, and in August it jumped by 31% over the same month last year, said the Ministry of Agriculture and Rural Affairs.

Some producers have even suggested that the rebuild may be overdone.

But the large numbers mask a less-productive herd. With such a severe shortage of breeding stock, many new farms are keeping back females that would normally have been slaughtered for meat to use as breeders.

Also known as “three-way cross” females, they are bred for meat and their different genetics produce significantly smaller litters, experts said.

They now make up at least half of the breeding herd, from almost none earlier, estimated Stephen Wilson, chief executive of leading livestock genetics firm Genus PLC.

“Even though numerically the sow herd is growing, it’s growing in a low-quality way,” he said.

The sow herd grew for the first time in June, and surged 37% in August on a year ago, shows ministry data. But the increase is coming from a low base, said Pan Chenjun, senior analyst at Rabobank.

In August 2019, the herd was almost at its lowest level after heavy losses to African swine fever earlier in the year.

“If you take out the 50% of three-way cross females, it’s really not that much,” Pan said.

Three-way cross females typically have two pigs fewer per litter, or about five fewer a year based on around 2.4 litters over 12 months.