Adding Zinc Could Lead to Better Health

By Sarah Watson, Livestock Editor
Thursday, November 29, 2007 9:58 AM CST

Adding zinc to post-weaning nursery pig diets leads to less incidence of diarrhea according to a study conducted by a University of Missouri.

The study looked at the effect of zinc oxide on Escherichia coli, the main cause of neonatal and post-weaning diarrhea, as well as lactobacilli, a so-called beneficial bacterium in the pigs’ digestive systems, says Marcia Shannon, a member of the Commercial Agriculture swine team.

The objective of the study was to investigate the effect of feeding pharmacological levels of zinc oxide on growth performance and determine the number of excreted E. coli and lactobacilli in the feces.

“There’s lots of reasons why there’s diarrhea in the nursery,” Shannon explains. “The stress of changing the diet as well as the exposure to some disease challenges.”

Decreased daily gain and death are also consequences of diarrhea.

“With high feed costs you want to eliminate that as much as possible,” she says.

The study focused on E. coli because it is the most common cause of post-weaning diarrhea.

“There have been cases where about 70 some percent of diarrhea that is in nursery pigs is E. coli derived or caused by E. coli,” Shannon says. “There is some E. coli that is good E. coli.”

The study did not differentiate the types of E. coli n either good or bad.

“We do know that diarrhea probably represents about 10-12 percent of mortality in nursery pigs,” she explains. “And about 50 percent of the diarrhea is toxic E. coli.”

In future studies, Shannon plans to type the E. coli and not just look at the number E. coli colonies.

In the study 40 crossbred pigs were studied during a four-week period. The pigs were split into four treatment groups, receiving zinc oxide at rates ranging from zero to 3,000 parts per million. Fecal samples were tested weekly for E. coli and lactobacilli.

The lactobacilli, or good bacteria were tested because several of the probiotics are lactobacillus derived, she says.

“A lot of companies market products that usually have lactobacillus in them,” she says. “We wanted to look at different bacteria to see if they change.”

The hypothesis of the study was the number of E. coli colonies would decrease and the number of lactobacillus colonies would increase. The increase in lactobacilli would relate to a healthy gut, she explains.

“That bacteria should be surviving to make that pig grow better,” she says. “That was our hypothesis.”

However, when the study was concluded, there wasn’t a great affect on the lactobacilli colonies, and pharmacological concentrations of 750-3,000 parts per million of zinc oxide did not result in improved growth performance.

However, nursery pigs fed either 1,500 parts per million or 3,000 parts per million of zinc oxide had less incidence of diarrhea when compared to pigs that received no additional zinc or were fed 750 parts per million of zinc as zinc oxide.

“We really don’t know when we feed high levels of zinc why we have a reduction in diarrhea,” she says.

Shannon recommends feeding 1,500 parts per million in the first two weeks in the nursery.

Producers should be aware that only feeding zinc oxide, not any other zinc compounds, was responsible for the reduction in diarrhea, she says. The pigs in the study were fed zinc beyond the trace mineral premix, which typically contains zinc sulfate at 150 parts per million. Zinc sulfate is used in premixes because it is close to 100 percent bio-available, she explains.

Zinc oxide is around 70 percent bio-available.

“I’ve done the study were you’ve fed 3,000 parts per million of zinc sulfate, zinc chloride, zinc acetate, and zinc oxide,” she says. “And the only one to promote growth is zinc oxide.”

Zinc sulfate at 3,000 parts per million doesn’t work the same as zinc oxide at 3,000 parts per million.

“We’re still trying to figure out why that is,” she says. The answer may lie in the bacteria in the gut. “It’s not as bio-available so it’s probably hangs out more in the intestine than in the gut,” she says. “That’s why our thoughts are it’s impacting the bacteria in the gut.”

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