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.

Case Study No. 2

Current raw performance data for pigs in production system “B” are shown in Table 2. Pigs at locations “O” and “W” were not fed extra vitamins or Bio-Mos, but were vaccinated for PCVAD in the nursery. Pigs at location “M” were fed vitamin C and extra vitamin E, but received no vaccines. Due to the timing of the initiation of the Bio-Mos feeding, only a portion of the younger “M” pigs received Bio-Mos. Pigs at location H-5 were fed vitamin C, extra vitamin E and Bio-Mos for the first 6-8 weeks on the finishing floor and were vaccinated for PRRS.

The performance numbers for locations O and W are a strong indication that the PCVAD vaccine was effective in reducing death losses. At location M, feeding the extra vitamins did not reduce death loss when pigs were not vaccinated for PRRS. No conclusions can be drawn relative to Bio-Mos at this site.

Vaccinating for PRRS and feeding diets containing vitamin C, extra vitamin E and Bio-Mos at location H-5 may reduce production losses from PCVAD, but have not eliminated those losses. Death losses at several H-5 barns have increased in the past few weeks, but are still lower than previous closeouts for this location.

In the future, barns at the H-5 site will have vitamin C available to add to the water at the first signs of a PCVAD break. Pigs continue to drink during a health challenge, plus vitamin C levels in water are four times higher than in the feed. This will be in addition to the use of the feed additives mentioned.

The data for site H-5 looks promising, but demonstrates that the nutritional intervention is not invincible.

Case Study No. 3

Production system “C” has fed a yeast cell wall product (Bio-Mos) to the sow herd for several years. When faced with increased death loss and culls on the finishing floors as a result of PCVAD, they decided to add Bio-Mos to the late-nursery and early-finishing diets.

While overall mortalities and culls were reduced, occasionally a site would still break with PCVAD. These breaks were often associated with increased stress due to overstocking.

Vitamin C was added to the water for 3-4 weeks at these sites, which reduced death loss and cull rates. Management at this operation emphasizes that the vitamin C must be in the water early in order to have an impact.

Estimated Costs

Tables 3 and 4 provide estimated costs for some of the programs discussed.

The first 4-6 weeks on the finishing floor is a critical time for preparing pigs for the physiological challenge that lies ahead, should their barn become infected with PCVAD. It is important to stay out in front of the disease when using nutritional interventions. Therefore, the feed additives are fed for the first 6-8 weeks or in the first 175-225 lb. of the finishing feed budget. This results in a cost of $0.50 to $0.70/pig for the additional vitamin C, vitamin E and Bio-Mos. Should it become necessary to treat individual barns with the water-soluble vitamin C, then the cost/pig would increase.

Experience has shown that PCVAD can inflict heavy production and financial losses, and that these losses are even more severe in the presence of other health challenges. Acknowledging that PCVAD is a multi-faceted issue, and approaching it as such, it is possible that neither management practices, nor nutritional interventions, will ward off PCVAD losses under the most severe, multiple-disease circumstances.

Not the Last Word

The task of determining the most effective nutritional interventions to reduce production losses due to PCVAD continues. While initial efforts focused on individual water and feed additives, future efforts will focus on a combination of additives, inclusion levels and timing of their use.

Nutritional additives are not a silver bullet and should not be thought of as a replacement for a vaccination program. Still, these early field trials indicate that the supplementation of vitamin C, vitamin E and/or yeast cell wall material has reduced mortalities and culls in some systems.

Based on what is currently known, health care providers and production managers in these case studies have requested that vitamin C, elevated levels of vitamin E and Bio-Mos remain a part of the nutritional program in herds experiencing a PCVAD challenge. While the field evidence is still anecdotal, these supplements may be a practice to consider until vaccines are more readily available.

Table 1. Vitamin C in Water (Case Study No. 1)

Treatment No. Placed ADG Feed
% Culls % Mortality
Control (No vitamin C) 1,856 1.48 2.52 15.9 8.8
Vitamin C (in water) 1,825 1.63 2.36 9.5 4.7
Table 2. Performance as of Dec. 24, 2006 (Case Study No. 2)
Treatment Location
Barn No.(s) Weeks on
Death and Culls
Death and Culls, %
Vaccinated PCVAD O 1-4 barns closed 4,167 384 9.2
Vaccinated PCVAD W 1-4 16-19 4,174 249 6.0
Vitamins; no vaccines M 1-8 13-18 5,106 1,601 31.4
Vitamins + Bio-Mos +PRRS Vac. H-5 1-6 9-13 6,265 793 12.7
Vitamins +Bio-Mos + PRRS Vac. H-5 7-12 4-8 6,231 253 4.1
PCVAD = porcine circovirus-associated disease
Table 3. Vitamin C, Vitamin E and Bio-Mos in Feed (Cost Estimates, Use Rates)
Item Amount,
Level of Nutrient Estimated Consumption/
Pig Per Day
Cost/Unit ($/lb.)
Vitamin C (pure ascorbic acid) 0.25 125 ppm 227 mg/day $3.25/lb.
Vitamin C, Stay-C for pelleted feeds 0.71 125 ppm 227 mg/day $4.54/lb.
Bio-Mos 2 454 mg/day $1.75/lb.
Vitamin E Dependent on source 60,000 International Units(IU)/ton 120 IU/day $0.50/ton for additional 40,000 IU/ton
Table 4. Water-Soluble Vitamin C (Cost Estimates, Use Rates)
Item lb./gal. stock
Level of Nutrient
in Water, ppm
Estimated Consumption/
Pig Per Day
Cost/Unit ($)
Initial treatment (First 6-12 hrs) .77 500 1,800 mg/day 3.30/lb.
Treatment — 3-4 weeks .385 250 900 mg/day 3.30/lb.