The use of spray-dried porcine plasma, an ingredient in weanling rations derived from the blood of slaughtered pigs, has been used without incident in the hog sector since the 1990s.
But it has now come under intense scrutiny as a possible cause of the PED outbreak in Canada that began on Jan 22.
“It’s real common in starter diets when pigs are weaned pretty early,” said Dr. Gary Cromwell, a retired professor of swine nutrition at the University of Kentucky.
“There’s really good solid evidence that it gets those pigs started off a lot faster. It has some real benefits at that stage.”
The blood, collected from large slaughter plants, is transported in chilled tanker trucks to a processing plant where the plasma and red blood cell components are separated and then spray-dried.
Dried blood plasma is “fairly expensive, said Cromwell, and is only used in the Phase 1 diets of very young pigs weighing less than five pounds for about 10 days.
The dried red blood cells, which are rich in protein and amino acids, are fed to piglets later on, in so-called Phase 2 diets that cover an additional two to three weeks.
Cromwell said that newly weaned piglets have difficulty adapting to solid food, and typically lose weight for the first two to three days post-weaning before gaining it back within five to seven days. But if plasma is fed, the piglets have a vastly reduced “growth lag” during the transition, continue growing sooner, and gain at the same rate as they did while nursing on the sow.
Researchers are unsure exactly why it works, but Cromwell said that immunoglobulins in the product appear to enhance immunity in piglets, but bovine blood plasma seems to work just as well.
Whether the spray-drying process is able to kill all the pathogens in the plasma, Cromwell wouldn’t comment, saying it was not his area of expertise.
More from the Manitoba Co-operator website: Manitoba PEDv case not linked to feed: CVO
Dr. Pat Halbur, a professor at Iowa State University’s veterinary diagnostics department, noted that his department had found in 2009 that porcine circovirus 2 could survive a spray-drying process and infect pigs.
“We determined — in the lab spray dryer — that the circovirus in the plasma was infectious,” said Halbur.
However, the results of that study were challenged on the grounds that the “tabletop” spray-drying apparatus they used did not accurately reflect the commercial processing method, and a followup study in 2011 that “more closely mimicked” the commercial process found that the final product “did not contain infectious virus.”
“If (PED) is spread through the feed, we need to understand what component of the feed contains it,” said Halbur.
Cross-contamination from some other source offers a likely explanation, he added, because even if PED could survive the spray-drying process, steam treatment during the pelleting stage that follows should kill any remaining virus.
Could this be a BSE moment for the hog industry, one that demonstrates the folly of feeding pig parts to pigs?
“That’s possible,” said Halbur. “But I’m not convinced yet that it has been proven ineffective here. We have a lot of work to do to confirm that it is related to spreading this disease.”