Causes of fading puppy and kitten syndrome
Chances are that you have been presented with puppies or kittens that have failed to thrive, some of which have eventually died. The causes of neonatal illness, commonly referred to as fading puppy and kitten syndrome, are many. Overall neonatal mortality in puppies varies from 12% to 36% in both closed breeding colonies and in breeders' homes, while in kittens in purebred catteries it is 15% to 27%.1,2
Various maternal and litter factors affect mortality in neonates. For example, in laboratory beagle breeding colonies, as a bitch ages the neonatal mortality rate of her offspring increases.3 And in queens in a large domestic shorthaired breeding colony, the smallest neonatal loss was at the fifth parity, with the greatest loss at the seventh parity.4 While other factors likely play a role, the dam's age is an important element in neonatal mortality, although the precise reasons for this have not been defined.
Causes of fading puppy and kitten syndrome can be divided into three groups: environmental, genetic, and infectious.ENVIRONMENTAL CAUSES
Environmental causes include factors affecting the dam as well as those due to poor mothering.
Hypothermia and hyperthermia
Hypothermia is a primary or contributing cause of many neonatal deaths. In their first week of life, puppies and kittens are essentially poikilothermic (their body temperatures vary with environmental temperature). The ability to shiver develops after Day 6. In the first week of life, normal body temperature in neonates is 95 to 98 F (35 to 36.7 C).5 In the second and third week, normal body temperature rises to 97 to 100 F (36.1 to 37.8 C), and by the fourth week neonate body temperatures are the same as those in adults.6 Hypothermia results in a decreased heart rate and circulatory collapse. In addition, hypothermic neonates do not nurse, are unable to digest food, and develop ileus. Hypothermia quickly results in a deterioration of cardiovascular, respiratory, and gastrointestinal function, which can rapidly cause death.7
In hot climates or with inappropriate supplemental heat, hyperthermia can occur. While hyperthermia is less common than hypothermia, a body temperature higher than normal for the neonate's age should alert you to this possibility. Neonates in the first week of life can pant in response to overheating and may cry relentlessly.
Maternal factors can affect neonatal survival. Overweight queens have increased neonatal mortality compared with normal-weight queens.4 Maternal obesity is also a contributing factor to neonatal loss in bitches.8
In bitches, the dam's age has a significant effect on neonatal mortality. Beagle colony bitches from puberty to 4 years of age had a neonatal mortality rate of 18.5%.3 This rate increased to 38.9% in bitches at 7 years of age and to 79.3% at 9 years of age.3
Maternal neglect is another common environmental cause of fading puppy and kitten syndrome. Primigravida dams and dams that deliver by caesarean section are at increased risk for poor mothering. In one study, bitches with normal vaginal delivery had a 2.2% neonatal mortality rate at birth and an 8% mortality rate at Day 1, while bitches that delivered by caesarean section had an 8% neonatal mortality rate at birth and a 13% neonatal mortality rate two hours postpartum.2 While causes for this difference were not delineated in this study, possibilities include the effect of anesthetic drugs on pups, postoperative pain in the dam, and inadequate mothering due to lack of exposure to dog attachment pheromone in the amniotic fluid.
In my clinical experience, mothering ability has a genetic aspect, so breeding bitches and queens should be selected with this in mind. Clinical reports indicate that poor mothering may sometimes be associated with hypocalcemia.9,10 Maternal neglect can be exhibited by a dam's reluctance to lie with and warm the neonates, refusal to permit nursing, or lack of sufficient milk production or letdown. Large-breed or barrel-bodied bitches may also step on or clumsily crush puppies. Trauma is a common cause of neonatal death during the first week of life—16.7% in one study.5 Queens may exhibit cannibalism, especially inexperienced dams or dams in a stressful or crowded environment.