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Does PRRS influence weaned pigs’ nutritional response?

In the past 30 years, the growth and body composition of US market hogs has changed dramatically, but the same cannot be said for dietary vitamin and mineral levels.

27 July 2019, at 2:34pm

“Baseline serum vitamin and mineral levels for nursery pig is primarily based on 30-year-old data,” Jacob Baker, veterinary student at Iowa State University, told Pig Health Today. But the health status of the herd and role of disease may influence the pig’s actual dietary needs.

Because porcine reproductive and respiratory syndrome (PPRS) is such a significant disease in the US swine industry, Baker wanted to evaluate the effect of PRRS virus challenge on vitamin and mineral levels.1

“By understanding what is happening on a physiological basis, diet changes or other interventions may help reduce losses caused by disease,” Baker said.

For the study

Four pigs were selected from 10 litters out of a PRRS-positive-stable sow farm and then allocated to either a non-challenged control group or a PRRS-challenged group. Pre-weaning blood tests confirmed the pigs were negative for PRRS by polymerase chain reaction test.

The control and challenged groups were housed in separate facilities, 20 miles apart. Both groups received the same nursery diet.

At 7 days post-weaning, pigs in the challenge group received an intra-muscular injection of PRRS virus-184, with exposure confirmed 2 days later. Notably, the sow herd had not previously encountered this virus.

Baker collected serum samples and weighed pigs at the time of the PRRS virus challenge and 3 weeks later, at the trial’s conclusion. Pigs in the control group also were confirmed PRRS-negative at that time. All pigs were euthanized to collect liver tissue and second-rib samples for further testing.

The findings

The PRRS-challenged pigs had lower levels of vitamin A in serum and higher levels in their livers versus the control pigs. This shift in vitamin levels makes it less available to the pig for growth, which may explain the difference in average daily gain between the control group at 0.75 lbs. and the challenged pigs at 0.40 lbs., Baker said.

Conversely, the PRRS-challenged pigs had more vitamin E in their blood and less in their liver than the controls. This suggests that the vitamin was mobilized from the liver to support an immune response in the challenged pigs.

Looking at calcium, the challenged pigs had higher levels in serum and lower levels in their ribs compared to control pigs. “The challenged pigs may have been mobilizing calcium from bone reserves for T-cell proliferation and maturation,” he noted. In general, the challenged pigs had larger increases and higher levels of most minerals in their blood at the close of the trail.

“This study suggests that metabolism of vitamins and minerals in PRRS-infected pigs is altered,” Baker concluded.

He added that more research is needed to determine whether dietary adjustments are warranted to address the production parameters of diseased pigs.

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