Canis ISSN: 2398-2942

Fading puppy syndrome

Contributor(s): Autumn P Davidson, Prof Gary England

Introduction

  • Puppies that die soon after birth are frequently termed fading puppies.
  • There are two distinct categories:
    • True fading puppies where the cause of the demise is unknown.
    • Fading puppies where there is a known cause of neonatal mortality.
  • True fading puppy syndrome:
    • Approximately 55% of pups which die have no identifiable cause.
    • Birth weight usually normal; develop depression and show poor sucking with persistent crying.
    • Condition progresses to generalised weakness and death usually 3-5 days after birth.
    • Pups usually have no macroscopic lesions, no identifiable congenital defects, no histological lesions but may have an absence of contents within stomach and small intestine.
    • Etiology may involve inadequate surfactant production or other complications from unrecognized dystocia.
  • Known causes of neonatal mortality:
    • Known causes account for approximately 45% of all cases of neonatal mortality.
    • Include:
      • Poor husbandry.
      • Maternal factors (including illness and poor nutrition resulting in low birth weight pups).
      • Congenital defects.
      • Problems at parturition (usually dystocia resulting in anoxia or hypoxia)
      • Poor mothering behavior.
      • Trauma.
      • Immune insufficiency.
      • Infection with viruses, bacteria or parasites.

Pathogenesis

Etiology

True fading puppy syndrome

  • Pups usually have:
    • No macroscopic lesions (except often a small liver without obvious morphological lesions).
    • No identifiable congenital defects.
    • No histological lesions.
    • Absence of contents within stomach and small intestine.
    • Some have evidence of aspiration of amniotic fluid during parturition.
  • True fading puppies have significantly lower phosphatidylcholine components of lung surfactant than pups that died from known causes.
  • Lung surfactant required for normal respiratory adaptation and maintenance following birth.
  • In normal animal, increased respiratory effort tends to stimulate surfactant production and it may be that pups with true fading puppy syndrome are born marginally hypoxic, do not breathe deeply and therefore enter a fatal cycle of low surfactant → hypoxia → failure to thrive → failure to suck → hypothermia → ultimately death.
  • May also be impacted by subclinical dystocia Dystocia.

Known causes of neonatal mortality

  • Etiology can include:
    • Poor husbandry.
    • Maternal factors (including illness, poor nutrition etc which usually result in low birth weight pups).
    • Congenital defects.
    • Problems at parturition (usually dystocia resulting in anoxia or hypoxia).
    • Poor mothering behaviour.
    • Trauma.
    • Immune insufficiency.
    • Infection with viruses, bacteria or parasites.
  • Infectious causes account for up to 20% of all cases depending upon country.
  • Some infectious agents are specific pathogens, whilst others are opportunistic organisms which colonize a compromised neonate.
  • Number of bacteria have been isolated from dead pups with:
  • Bacteria include:
  • Most are part of commensal flora of genital tract and only cause disease when neonate is additionally challenged. Inherent vulnerability of neonate puts it at risk for colonization by these organisms.
  • Transplacental infection with Toxoplasma gondii Toxoplasma gondii is uncommon although experimental infection may result in neonatal death.
  • Incidence of natural transplacental transmission of Neospora caninum Neospora caninum is unknown; experimental infection results in stillbirth with evidence of myocarditis Heart: myocarditis.
  • Toxocara canis Toxocara canis infection usually causes disease in pups over 2 weeks when worms are large and cause gastrointestinal obstruction or migrate up biliary tract and cause hepatitis. Migrating larvae in prepatent period can also cause disease.

Consequences of neonatal illness

  • Whatever initial challenge, inherent susceptibility of newborn results in ultimate demise.
  • Neonates have poor mechanisms of thermoregulation, are unable to shiver and have poor reserves of brown adipose tissue; therefore susceptible to hypothermia Hypothermia.
  • Puppies are susceptible to dehydration and have immature liver enzyme systems and an immature ability to regulate glucose (relying almost entirely on hepatic glycogen reserves over first 24 hours). Prolonged parturition or a prolonged interval to feeding means that reserves may be exhausted; hypoglycemia Hypoglycemia may complicate hypothermia. When there is a neonatal challenge, common for pup to enter a fatal cycle hypoxia → failure to thrive → failure to suck → dehydration → hypothermia → ultimately death.

Predisposing factors

General

  • Predisposing factors include:
    • Subclinical dystocia Dystocia.
    • Persistent hypoxia due to delay in removal of fetal membranes or fluid by dam.
    • Persistence of hypothermia associated with delay in drying neonate or a cold or draughty environment.
    • Poor mothering behaviour by inexperienced bitch may be primary cause of both hypoxia and hypothermia.
  • Inadequate intake of fluid is a significant problem, not only because of requirement to absorb colostrum, but since adequate fluid maintenance is important for recovery from acidosis Acid base imbalance. Neonates have high percentage of fluid within extracellular space and relatively poor renal function. When combined with ability to lose fluid because of high surface area: body ratio and undeveloped urine concentrating ability, results in increased susceptibility to changes in fluid balance compared to adults.
  • Neonates have incompletely developed immune system until at least 10 days after birth and are therefore susceptible to bacterial and viral infection. 80% antibodies must be absorbed across intestine 24-48 hours after birth. Failure to consume sufficient colostrum during time when intestinal wall is open to absorption of protein will seriously compromise neonate.
  • Neonates have limited fat reserves and poor ability to generate energy from precursors. Glycogen reserves are depleted shortly after birth, leaving neonate requiring early intake of energy. Short period of time without food can result in significant hypoglycemia Hypoglycemia , particularly in neonates that have been hypoxic or hypothermic.

Pathophysiology

  • Whilst initial cause may differ, namely unknown etiology (possibly due to inadequate production of surfactant for true fading puppy syndrome) or a known etiology, ultimate issue is:
    • Dehydration and hypoxia.
    • Resultant failure to thrive.
    • Failure to suck.
    • Hypothermia and ultimately death.

Timecourse

  • Most pups die 3-5 days after onset of clinical signs.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Blunden A S (1988) Diagnosis and treatment of common disorders of newborn puppies. In Practice 10 (5), 175-184 VetMedResource.
  • Blunden A S, Hill C M, Brown B D and Morley C J (1987) Lung surfactant composition in puppies dying of fading puppy complex. Res in Vet Sci 42, 113-118 PubMed.
  • Blunden A S (1983) The 'fading puppy complex': an assessment of a paraimmunity inducer as a means of control. Vet Rec 113 (9), 201 PubMed.

Other sources of information

  • Davidson A P (2003) Approaches to reducing neonatal mortality in dogs. In: Recent Advances in Small Animal Reproduction. Eds. P W Concannon, G England, J Verstegen and C Linde-Forsberg. International Veterinary Information Service, Ithaca NY (www.ivis.org), 2003; A1226.0303.
  • Blunden A S (1998) The neonate: congenital defects and fading puppies. In: Manual of Small Animal Reproduction and Neonatology.BSAVA, Cheltenham pp 143-152.


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