Better Pork - April 2004

U.S. research gives guidance on controlling PCV2-associated disease

With diagnosis of PCV2-associated disease on the rise, control measures are still related primarily to good management and production practices
by S. ERNEST SANFORD
Although porcine multisystemic wasting syndrome (PMWS) caused by porcine circovirus type 2 (PCV2) was first described in Western Canada a decade ago, over the last few years its greatest impact and severity has been in Europe, where the disease has assumed near epidemic proportions.

As a result, most of the activity and research directed against PCV2 have been coming out of Europe since the turn of the century. It was therefore enlightening to have Dr. Pat Halbur, researcher at the veterinary college, Iowa State University (ISU), present a comprehensive report last November on research being conducted at ISU on PCV2-related diseases.

Pigs with PMWS are usually between eight and 12 weeks of age, stop eating, experience varying degrees of weight loss and waste away. They often develop secondary diseases and mortality increases. Porcine dermatitis and nephropathy syndrome (PDNS) is another disease believed to be caused by PCV2 infection. Pigs with PDNS (see Figure 1) develop skin and kidney lesions and have high mortality.

My intent here is to concentrate on the treatment and control measures suggested by Dr. Halbur. First, however, I shall introduce a chart presented by Dr. Halbur on PCV2 cases submitted to the diagnostic laboratory at ISU and then highlight three of the dozen or so PCV2 research activities that Dr. Halbur updated, namely:

  • Production of PCV2-negative pigs from PCV2-positive sow herds.

  • PCV2 and Mycoplasma hyopneumoniae (Mhyo) coinfection.

  • Effect of timing of immune stimulation/ vaccination on development of PCV2-associated lesions.

Figure 1 below shows the number of PCV2-associated disease cases identified at the ISU-Veterinary Diagnostic Laboratory (ISU-VDL) in submissions from 1994 to 2002).

Herd Health graph

In 2002, the bulk of these cases were pneumonia-related (557 of 1,116) with actual PMWS being a distant second (346 of 1,116). Dr. Halbur indicated that PCV2-associated enteritis, though uncommon (25 of 1116 cases), occurred in grow-finish pigs and resembled subacute or chronic ileitis clinically and on gross postmortem. PCV-2-associated abortion/ reproductive failure (nine cases out of 1,116) was rare.

In this study, the researchers selected early-weaned pigs (10-14 days old) from sows with low PCV2 antibodies (Abs) and reared them offsite. The pigs lost their maternal Abs (ED: OK?) between three and seven weeks of age, remained free of PCV2 Abs and were negative for PCV2 virus. Several batches (50-80 pigs per batch) of PCV2-free pigs were reared this way by the researchers.

Take Home: SEW Isowean might be a means of producing PCV2-free pigs from PCV2-positive breeding herds.

PCV2 and Mycoplasma hyopneumoniae coinfection
In this study, weaned pigs were coinfected with PCV2 virus and Mhyo and the severity of lesions was compared against pigs infected with only single PCV2 or single Mhyo inoculations respectively. Results showed that the PCV2/Mhyo coinfected SEW pigs had more severe clinical respiratory disease, significantly reduced average daily weight gain, significantly higher PCV2 virus in serum, longer viremia, more severe gross lung lesions, significantly higher incidence and higher amount of PCV2 Ag in lymphoid and lung tissues. There was also a higher incidence and more severe microscopic lung and lymphoid lesions compared to single Mhyo- or single PCV2-inoculated groups.

Take Home: Mhyo infection increases the severity and duration of PCV2-induced lung and lymphoid lesions, PCV2 replication in tissues and clinical incidence of PMWS disease. Mhyo-induced lymphoid hyperplasia around lung airway passages may provide a welcome focus for PCV2 replication in lung.

Effect of timing of immune stimulation/vaccination on development of PCV2-associated lesions
This study was designed to determine if the timing of Mhyo vaccination had an effect on PCV2 proliferation and PCV2-associated lesion severity. The results showed no or minimal PCV2-associated lesions in pigs given routine Mhyo vaccinations two to four weeks prior to expected PCV2 exposure.

Take Home: Pigs vaccinated with routine Mhyo vaccines two to four weeks prior to PCV2 exposure are unlikely to develop PCV2-associated disease.

Control of PCV2-associated diseases
Successful treatment and control of PCV2-associated diseases focus primarily on good production practices that minimize stress, eliminate coinfections or minimize their effect and eliminate potential triggering factors that induce immune stimulation. Serotherapy has had some success in parts of Europe but has not been widely used elsewhere. Serotherapy involves the collection of serum (blood) from pigs that have recovered from PCV2 disease and injecting it back into young weaned pigs which have not yet been infected by the virus. This serum, called convalescent serum, contains antibodies that will protect the pig if it does become infected by the PCV2 virus later in life. Until a PCV2 vaccine is available, Dr. Halbur's recommendations for control of PCV2-associated diseases include:

  • First confirm the PCV2-associated problem by necropsy, histology and other relevant diagnostic tests.

  • Identify farm-, site- or system-specific concurrent infections through good quality diagnostic submissions.

  • Eliminate or minimize the effects of PRRSV coinfection, if present, by breeding herd stabilization, pig flow changes, and/or vaccination.

  • Eliminate or minimize the effects of SIV coinfection with breeding herd and possibly pig vaccination.

  • Determine if PPV is present in tissues of affected pigs and in the population by demonstration of seroconversion to PPV during the time when PCV2-associated disease occurs. Consider implementing PPV vaccination of growing pigs if PPV and PCV2 coinfection is confirmed.

  • Minimize the effect of mycoplasmal pneumonia with vaccination and strategic pulse medication.

  • If herd evidence suggests an association between vaccination practices and PCV2-associated disease, re-evaluate the necessity and timing of the vaccines in use. It may be beneficial to change the brand of vaccine used and/or the timing of administration of the vaccine.

  • Treat specific bacterial coinfections with appropriate antimicrobials.

  • Consider the use of anti-inflammatory drugs and enhanced diets on pigs that are slow to respond.

  • Remove pigs that do not respond to treatment.

  • Adhere to all-in/all-out pig flow rules.

  • Minimize mixing and moving of pigs whenever possible.

  • Decrease pig density.

  • Use disinfectants in buildings and transport vehicles that have been demonstrated to be efficacious against PCV2.

  • If it is an option, consider changing pig sources if the problem occurs repeatedly.

To sum up, diagnoses of PCV2-associated diseases continue to increase annually at ISU-VDL. PMWS is second to pneumonia in frequency of PCV2-infected cases submitted. Control measures at this time are still related primarily to good management and production practices. BP

S. Ernest Sanford, DVM, Dip. Path., Diplomate ACVP, is a swine specialist with Boehringer Ingelheim Vetmedica (Canada) Ltd. in Burlington.

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Better Pork - April 2004

Enzyme supplementation and feed processing provides solutions for low quality grains

Low quality wheat, concludes this study, has a higher fibre content and lower energy digestibility than high quality wheat in grower pigs. The reduction in energy digestibility can be partially overcome by enzyme supplementation or particle size reduction
by RUURD T. ZIJLSTRA
The nutritional quality of wheat or barley can vary substantially Ignoring an existing variation may cause lower finished feed quality and thereby hurt the swine producer economically through reduced growth performance.

For wheat and barley, reduced nutritional quality usually means a reduced digestible energy (DE) content. The reduction in DE content is almost completely caused by a reduction in energy digestibility, not by a reduction in the total amount of energy in the ingredient sample. The reduction in energy digestibility is usually related to an increase in fibre content of the grain.

Solutions for the use of low quality grains in diet formulations, while maintaining growth performance, should focus on two aspects: first, correcting diet formulations to achieve the formulated diet DE content or, second, enzyme supplementation or feed processing to overcome to the reduction in energy digestibility of the grain. For either solution, correct prediction of DE content of individual wheat and barley samples may be critical, but the impact of correct prediction of DE content on further decision making regarding enzyme supplementation or feed processing to improve energy digestibility is poorly understood. Equations to predict DE content of wheat and barley are presently being evaluated, using the 2002-harvest.

To study whether a specific wheat sample would affect the beneficial effects of enzyme supplementation or feed processing, three samples of wheat were collected from the 2002-harvest. The three wheat samples (W1, W2, and W3) had a similar content of crude protein of 18.8 to 19.7 per cent dry matter (DM) but had a wide range in neutral detergent fibre (NDF) content (W1, 20.1; W2, 29.3; and W3, 35.7 per cent DM).

Results of a digestibility study with grower pigs indicate that the increased fibre content for samples W1 to W3 did indeed result in decreased energy digestibility and reduced DE content from 3,680 to 3,320 kcal/kg DM. This confirmed the importance of ingredient evaluation and demonstrated that an increase in fibre (NDF) coincides with a decrease in energy digestibility and DE content. The range in wheat DE content also reflects a range in economic value of more than $15 per tonne of wheat used for swine feed.

Wheat diets were supplemented with a carbohydrase enzyme (xylanase). The enzyme should help the pig to digest energy, because negative effects of fibre fractions (or arabinoxylans) on energy digestibility will be alleviated. Indeed, enzyme supplementation improved energy digestibility for wheat samples W2 and W3, but not for W1, indicating that the beneficial effect of enzymes is dependent on the wheat sample in the diet.

This result further underlines the importance of ingredient evaluation, or the importance of enzyme supplementation to alleviated expected differences in energy digestibility. The reason for the positive response for W2 and W3 to enzyme supplementation and the lack thereof for W1 will be related to the content of fibre fractions in the wheat, specifically the fraction called xylan. Therefore, the wheat samples are presently being analysed for these fractions to further compare related wheat characteristics to prediction of an enzyme response.

Wheat samples were ground across three hammer mill screens to achieve a predicted particle size of 900, 650 and 400 microns. Particle size reduction should help the pig to digest energy, because a finer particle size means that the ratio of surface area to volume of the particles is increased. In other words, digestive enzymes of the pig or microbes of the pig have better access to the nutrients with a finer particle size.

Indeed, enzyme supplementation improved energy digestibility for wheat samples W2 and W3, but not for wheat sample W1, indicating that the beneficial effect of particle size reduction is dependent on the wheat sample in the diet.

The bottom line is that low quality wheat has a higher fibre content and lower energy digestibility than high quality wheat in grower pigs. The reduction in energy digestibility can be partially overcome by enzyme supplementation or particle size reduction. Ingredient evaluation is important to maximize the benefits of enzyme supplementation or ingredient processing. BP


Ruurd T. Zijlstra, Ph.D., is a research scientist in nutrition at the Prairie Swine Centre, Saskatoon.


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Better Pork - April 2004

Germany: "Starting blocks" give piglets a good beginning

by NORMAN DUNN
Giving piglets improved grip for their hind feet during suckling led to a six per cent reduction in mortality in trials at the Centre for Livestock Production and Technology in (CLPT) in Iden, Germany.

Big sows often mean that young piglets, especially underweight ones, have difficulty reaching the top row of teats when suckling, and attempts to get up there can lead to piglets struggling and slipping with the additional risk of scraping their legs on the flooring of the farrowing pen.

This problem has encouraged the French company Galvelpor to devise what it calls "starting blocks." These are plastic plates with a non-slip surface designed to be attached to the flooring on each side of the farrowing crate.

These plates seemed to give the hind feet of the suckling piglets a better grip and the CLPT researchers checked to see if this made any difference to overall performance.

Over 70 Pietrain-sired litters were involved in the review with half using starting blocks. The German researchers reported significant advantages for very young pigs up to three days old where the starting blocks were used. The better grip allowed the young animals, especially the weaker litter members, to drink much more milk compared with control litters on conventional slatted concrete flooring. This showed itself in an average daily liveweight gain (dlwg) that was 18 per cent higher over the first three days, at 127 grams.

While this early advantage does not persist through to weaning at 27 days (when average dlwg was about the same for the two groups), the improved weight gain early-on significantly reduced pre-weaning mortality from 19 per cent in the conventionally floored farrowing pens to 13 per cent for the litters with starting blocks, which returned an average weaned piglet per litter figure of 10.45. BP



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Better Pork - April 2004

A quiz to test your swine nutrition vocabulary

Some of the terms used in swine nutrition might as well be Greek. Here's a chance to test your knowledge and expand your lexicon of terms
by JANICE MURPHY
Reading through research reports and attending meetings to listen to experts in a field like swine nutrition is a fascinating and eye-opening experience. But, let's face it, sometimes you encounter terms and phrases that might as well be Greek, making you wish you had a volume on your bookshelf entitled "The Swine Nutrition Dictionary" or, in the current trend for books, "Swine Nutrition for Idiots."

Here are some questions about swine nutrition to test your vocabulary. See how you do with these, and let me know if you come across that book. I would love to borrow it sometime.

1. Which of the following are mycotoxins?

  1. aflatoxin
  2. ergot
  3. zearalenone
  4. all of the above
2. Pigs have a requirement for crude protein.
  1. true
  2. false
3. There are 21 primary amino acids that make up protein. How many are essential in swine nutrition?
  1. 10
  2. 13
  3. 17
  4. 21
4. Choline, pyridoxine and pantothenic acid are...
  1. amino acids
  2. fatty acids
  3. minerals
  4. vitamins
5. Phytase is...
  1. an enzyme
  2. a mineral
  3. a vitamin
  4. an antimicrobial agent
6. What are probiotics?
  1. natural substances produced by a microorganism that, at low concentrations, inhibit the growth of or kill another microorganism;
  2. non-digestible feed ingredients that improve the gut environment to support the growth of beneficial bacteria and/or deter the growth of pathogenic bacteria;
  3. organisms that help stimulate the growth of desirable organisms
  4. none of the above.

Answers:

 1. (d) All of the compounds listed are mycotoxins. Mycotoxins are compounds produced by moulds the can cause toxicity in pigs when they are consumed, depending on the type or amount of mycotoxin present. The two most commonly detected mycotoxins in corn, barley and wheat in Ontario are vomitoxin and zearalenone. Other types of mycotoxins include aflatoxin, ochratoxin, citrinin, tricothecenes such as T-2 toxin and HT-2 toxin, ergot and fumonisins.

2. (b) Pigs do NOT have a specific requirement for crude protein, but rather for the individual amino acids that make up protein. As a result, a ration's crude protein content is not a good measure of the adequacy of a particular ration. Protein sources differ widely in amino acid content. The content of essential amino acids, specifically lysine, is a much better indication of nutritional quality than percent crude protein. Lysine is the most limiting amino acid in typical corn-soybean meal diets. The pig is only able to support lean tissue growth to the point where it runs out of lysine for protein deposition.

3. (a) Proteins are made up of 21 primary amino acids, but not all are essential in swine nutrition. Essential amino acids cannot be synthesized, at least not at a rate sufficient to allow optimal growth. The 10 essential amino acids are arginine, histidine, isoleucine, leucine, lysine, methionine, phenyalanine, threonine, tryptophan, and valine. Non-essential amino acids can be synthesized as long as an adequate amount of nitrogen is present in the diet. The 11 nonessential amino acids are alanine, aspartic acid, asparagine, cystine, glutamic acid, glutamine, glycine, proline, hydroxyproline, serine and tyrosine.

4. (d) Choline, pyridoxine and pantothenic acid are water-soluble B-vitamins. In swine nutrition, we usually talk about four fat-soluble vitamins (A, D, E and K) and 10 water-soluble vitamins: thiamine, riboflavin, pyridoxine, vitamin B12, biotin, folic acid, niacin, pantothenic acid, choline and vitamin C. To ensure that requirements are met, nutritionists recommend that all vitamins be added at or above requirement levels when formulating swine rations.

5. (a) Phytase is an enzyme that releases the inorganic phosphorus (P) from phytate so that it can be used by pigs. The excretion of P can be reduced by 25 to 50 per cent with the addition of phytase. Since 60 to 80 per cent of P in traditional feed ingredients is present in the form of phytate, a compound that pigs do not use well, phytase can play a vital role in increasing the efficiency of P utilization and decreasing excretion of P into the environment. In addition, feeds supplemented with phytase for grower-finisher pigs and pregnant sows may need little or no supplementary feed phosphate.

6. (c) Probiotics, which means "in favour of life," have the opposite effect to antibiotics on the digestive tract. Answer (a) is the definition of an antibiotic. Answer (b) is the definition of a prebiotic. Probiotics are thought to increase the population of desirable microorganisms, instead of killing or inhibiting undesirable organisms. The most common microorganisms included in probiotic products are Lactobacillus, Streptococus, Saccharomyces and Bacillus species, which are normal inhabitants of the digestive tract of healthy animals. By encouraging the proliferation of these bacteria in the intestinal tract, it is possible to improve animal performance. BP


Janice Murphy is Swine Nutritionist with the Ontario Ministry of Agriculture and Food in Fergus. E-mail janice.murphy@omaf.gov.on.ca


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