Nutritional interventions show promise in preparing pigs' immune systems to better deal with porcine circovirus-associated disease challenges.

There is considerable debate among nutritionists and veterinarians as to what health, management and nutritional measures are available to maintain pig performance in the presence of porcine circovirus-associated disease (PCVAD).

Outside of vaccination — and the PCV2 vaccines remain in limited supply — there are three plans of attack:

1. Improving management practices, such as stocking rate; all-in, all-out pig flow; ventilation; intensive cleaning/disinfecting, etc.

2. Controlling other swine diseases, such as porcine reproductive and respiratory syndrome (PRRS) and salmonella.

3. Modifying nutritional programs, including the feeding of plasma proteins and yeast cell wall products containing mannans and glucans, as well as elevated levels of vitamins and trace minerals.

Improved management practices and the control of secondary diseases would reduce environmental and physiological stressors, which may initiate onset of PCVAD.

Modifying nutritional programs prior to the disease outbreak may improve the pig's ability to deal with a health challenge.

This article will focus primarily on the use of nutritional intervention to better prepare the immune system to deal with a PCVAD challenge.

Early Field Trials

Recognizing that pigs diagnosed with PCVAD can be immunologically impaired, a local veterinary group suggested supplementing water-soluble vitamin C as a water suspension. Several large production systems began using the water-soluble vitamin C manufactured by DSM Nutritional Products as a part of their disease control strategy.

With an initial positive response, the focus turned to finding the most cost-effective method of supplementing vitamin C. In addition, we began investigating combinations of vitamin C with other nutritional additives, including higher than normal levels of vitamin E, because of its role as an antioxidant.

We also tried the yeast cell wall product, Bio-Mos (Alltech, Inc.), because previous research demonstrated that sows fed the product had increased immunoglobulins in their colostrum. One system using Bio-Mos has reported lower losses due to PCVAD than other systems in the same area.

Vitamin C will be discussed in greater detail due to the initial responses. However, the feeding of elevated vitamin E, the feeding of yeast products and the control of secondary diseases are equally important.

Focus on Vitamin C

It is well accepted that pigs do not necessarily have a vitamin C requirement, due to adequate biosynthesis from glucose. However, research has shown improvements in boar fertility when diets were supplemented with the vitamin, and several nursery trials have shown benefits from early addition of vitamin C.

In the finishing phase, vitamin C supplementation has largely been thought to be unnecessary. For the most part, this is true for a healthy population. However, disease can cause a negative impact on liver function and other factors necessary for vitamin C biosynthesis.

During periods of stress, such as immunological challenges, it has been reported that pigs may have lower levels of an enzyme needed for the biosynthesis of vitamin C. At the tissue level, vitamin C acts as an antioxidant, thus playing a role in immune function due to its ability to scavenge free radicals.

Vitamin C in the form of pure ascorbic acid is not heat stable and should only be used in mash feeds. A heat-stabilized form of vitamin C (Stay-C from DSM) should be used when feeding pelleted diets.

And due to its interaction with iron in the water, pure ascorbic acid can become bound when added to water systems. Therefore, a stabilized form of vitamin C, also available from DSM, is required.

A statistical approach to measuring the effect of the nutritional interventions on PCVAD is often difficult because the expression of the disease can vary among barns, by sites, by pig flow and possibly by genetics.

Recognizing these statistical limitations, we are sharing the following field observations, which demonstrate a possible benefit from supplementing vitamin C, adding vitamin E and/or Bio-Mos in an effort to reduce mortalities and improve pig performance in the presence of PCVAD.

Case Study No. 1

Vitamin C was first used by production system “A” in North Carolina during June and July 2006. At a four-barn site diagnosed with PCVAD, two barns were treated via the water supply, while the other two barns received no vitamin C and served as controls.

The treated barns were initially supplemented with stabilized vitamin C at 500 ppm for 6-8 hours, then dropped to 250 ppm for 4-5 weeks.

The results of this field trial are shown in Table 1. While a statistical analysis is not possible, the numerical response encouraged further investigation and the vitamin C supplementation continued.

Although water supplementation has the advantage of treating individual barns, we knew supplementing vitamin C in the diet would be more cost effective. Therefore, during August and September 2006, stabilized vitamin C was added to the feed (100-125 ppm) instead.

Vitamin C was added to the feed when pigs were placed on the finishing floors (3-4 weeks prior to an anticipated PCVAD outbreak). Switching from the normal finishing vitamin premix to the sow-pig vitamin premix also increased vitamin E levels.

Overall, with the reduction in mortalities and culls, this large system plans to continue supplementing vitamin C and increasing vitamin E levels until an adequate supply of PCV2 vaccine is available.