Is vitamin D deficiency a factor in PFTS?

Monday, April 2, 2012

Research and observations on several fronts are helping our understanding of Peri-weaning Failure to Thrive Syndrome (PFTS), in particular the suspicion that vitamin D deficiency may play a part  

by ERNEST SANFORD

I have written previously about Peri-weaning Failure to Thrive Syndrome (PFTS), but under the name Post-weaning Catabolic Syndrome (April 2009).  Over the summer and fall of 2011, several things have emerged to create a better understanding of PFTS, including the following:

•    Development of clinical case definition of PFTS (more on this below);
•    Creation of a most compelling video, narrated by University of Guelph post-doctoral fellow Dr. Terri O'Sullivan, depicting the prominent features of PFTS;
•    A barrage of presentations at key swine veterinary conferences and industry meetings last fall;
•    On-line survey of veterinarians around the world seeking input from those seeing PFTS.

The clinical case definition of PFTS consists of a pig that is afebrile (no fever) with normal behaviour and body condition at weaning (around three weeks of age) and lacking evidence of respiratory, enteric and systemic diseases, and that within seven days of weaning is not eating, becomes depressed, may "chomp" and becomes progressively debilitated within two to three weeks of weaning. Pigs infected with PRRS virus do not qualify to be included in this case definition.

PFTS presents as newly weaned pigs in good or above average body condition which refuse to eat, lose weight, remain alert, maintain normal vital signs, but become weak, debilitated and demonstrate a mouth "chomping" behavior, usually within seven days of weaning.

Aggressive management techniques to stimulate and encourage eating are usually futile and these pigs go on to become emaciated and die, or have to be euthanized two to three weeks post-weaning. The number of affected pigs per litter (morbidity) in affected herds is highly variable but, for affected pigs, mortality approaches 100 per cent even with aggressive management and medical interventions. There is an apparent increase in cases between November and May.

Recent findings. With practitioners, diagnosticians and researchers paying closer attention to this evolving syndrome, several new findings related to PFTS have surfaced over the last year. These include:

•    Gastritis observed by diagnosticians at the University of Guelph;
•    University of Minnesota's observations of Hemagglutinating Encephalomyocarditis Virus (HEV)/ Vomiting & Wasting Disease virus;
•    And, most persuasive of all, Kansas State University and Steve Henry's Vitamin E deficiency work.

PFTS associated with gastritis. Diagnosticians at the Animal Health Laboratory, University of Guelph, have observed a severe, diffuse non-suppurative gastritis in cases submitted to the laboratory fitting the definition of PFTS. No cause has been determined for the gastritis to date.

PFTS is associated with HEV. The HEV virus is a coronavirus similar to TGE virus that was first reported in Ontario in 1962 and associated with encephalomyelitis in suckling pigs. Later, the same virus was isolated in Britain from suckling pigs that were vomiting and wasting.

HEV was subsequently determined to be a ubiquitous virus present in the swine population worldwide with maternal immunity usually protecting suckling pigs until they acquire their own immunity by the time of weaning. Diagnosticians at the University of Minnesota have identified HEV in tonsils of pigs with and without clinical signs of PFTS but, more importantly, they are diagnosing an increasing number of pigs with systemic HEV infections – that is, HEV in many tissues throughout the body, including tonsils, stomach, lungs, salivary glands and nasal turbinates – nearly all of these in pigs with signs of PFTS.

PFTS associated with vitamin D deficiency. Perhaps the most compelling of all, or at least the most passionately presented case for an etiology of PFTS, is the evidence of vitamin D deficiency advocated by Dr. Steve Henry of the Abilene Animal Hospital and his colleagues at Kansas State University.  

Dr. Henry observed abnormally "rubbery" rib bones in PFTS pigs. When he submitted bones to the university's diagnostic laboratory, the pathologists reported micro-fractures and suggested that Vitamin D deficiency might be the reason for the bone pathology. On checking, the Vitamin D levels in clinically affected PFTS pigs were at less than five ng/mL (normal range for baby pigs is 25-30 ng/mL).

Even more revealing, when pigs in PFTS herds were supplemented with Vitamin D3 at processing to bring their levels up into the normal range, they responded clinically by showing increased activity and vigour, became bright, alert, frisky and playful. Furthermore, no pigs developed PFTS after weaning. This in herds that would have been expected to have a certain percentage of their weaned pigs develop PFTS.

What does vitamin D do? Vitamin D (25 hydroxycholecalceferol) or 25(OH)D calceferol is needed for the absorption of calcium from feed in the intestines. Lack of Vitamin D results in reduced calcium absorption, leading to reduced mineralization of bones and hence "rubbery" bones (rickets) in the young and "brittle" bones (osteoporosis) in the old. Both conditions can lead to fractures.

Animals can synthesize Vitamin D by exposure of the skin to sunlight, hence the name "the sunshine vitamin." Pigs can synthesize Vitamin D from birth if exposed to sunlight, which is how wild pigs get most of their Vitamin D and how domesticated pigs got Vitamin D before we moved to total indoor rearing of pigs. Now the major source of Vitamin D is via supplementation in the diet.

Vitamin D also affects neuromuscular function, deficiency of which might just explain some of the very characteristic mouth "chomping" activity seen in PFTS pigs.

Supplementing vitamin D at processing. A nationwide (U.S.) project involving a large number of collaborators (nicknamed "Ubiquitous Collaborators") was launched in summer of 2011 whereby pigs are supplemented with Vitamin D orally from a specially prepared product called "Wean-D."

Wean-D is delivered orally via a syringe to pigs at processing. At the time of writing, Wean-D was not available in Canada. Data are being collected by the Ubiquitous Collaborators and results will be presented at upcoming conferences.

A survey is being conducted by Dr. O'Sullivan of the University of Guelph to get feedback from veterinarians worldwide on how widespread and recognized the PFTS syndrome is. So far, replies indicate PFTS is being recognized in at least 10 countries, including Argentina, Australia, Italy, Japan, Mexico, New Zealand and the United Kingdom among others. BP

S. Ernest Sanford, DVM, Dip. Path., Diplomate ACVP, is a swine specialist with Boehringer Ingelheim Vetmedica (Canada) in Burlington. Email: ernest.sanford@boehringer-ingelheim.com