Neonatal mortality (Proceedings)

Questions regarding neonatal mortality are common in general practice. Most serious breeders are well aware of the extent of neonatal losses and have a compelling economic incentive minimized those losses. Generally, clients with neonatal losses fall into one of the following categories the novice with their first or second litter and the dam being the house pet; hobby breeders having a couple litters yearly with a few of dogs; then the commercial breeders with a kennel of multiple animals. In the latter two instances neonatal deaths should be viewed in a "herd" health perspective which implies that extensive diagnostics and necropsies should be employed, and if necessary a very ill puppy or kitten may need to be sacrificed for necropsy in an attempt to obtain a diagnosis.

Key time benchmarks for survival in our practice are birth then the first 24 hours, once that is achieved the first week is the most worrisome. Puppy and kitten losses in those who survive the first week are much more infrequent through weaning.

Mortality Bench Marks: (various studies)

The Primary causes of death in neonates are hypothermia, trauma, and malnutrition (starvation). Puppies do not have the ability to control their body temperature as adults. Neonates can become hypothermic for a variety of reasons either lost from mother (often trapped in bedding), pushed away from mother, low environmental temperature, poor mothering, the neonate gets wet, and illness. Puppies and kittens rely upon brown fat to maintain body temperature for the first week until they can shiver. Hypothermic neonates are incapable of digesting milk.

Normal Neonatal Body Temperature

Traumatic injuries are responsible for up to 37% of mortalities. Traumatic injuries include birthing injuries, crushed, overzealous cleaning by dam, suckling by litter mates, and thermal burns from heat source errors among others.

Malnutrition or starvation can occur as a result of a weak neonate unable to hang on to teat, poor competitor with litter mates, structural issues like cleft palate, and hypothermia. Additionally, the dam may produce an insufficient milk supply, have mastitis, or won't lay down for babies to nurse. Neonates have minimal body fat reserves and limited metabolic capacity to generate glucose. Glycogen stores are depleted shortly after birth, making adequate nourishment from nursing vital. Even minimal fasting can result in hypoglycemia. Care should be taken when supplementing glucose to a neonate as they can easily become hyperglycemic since they have immature metabolic regulatory mechanisms.

Neonatal Indicators of Illness

• Crying more than 20 minutes

• Decreased activity

• Separated from mother

• Decreased muscle tone

• Diarrhea

• Rough hair coat

• Panting or labored breathing

• Decreased bowel sounds

• Pale or cyanotic mucus membranes

Environmental:

Incorrect environmental temperature can cause several problems. Low environmental temperature forces the dam and puppy to use energy to maintain body temperature and places more stress on the babies. Elevated environmental temperatures cause the dam to be uncomfortable, she may be panting and refuse to lie with the neonates. Mom and puppies or kittens are spread out in the birthing area, which makes it more difficult for the offspring to find mom and nurse.

Incorrect selection of bedding materials allows for puppies and kittens to be trapped in the bedding, bedding which fails to absorb waste, does not wick moisture away from the offspring, and bedding which conducts heat away from neonates.

Correct husbandry techniques also involve proper hygiene to prevent infection, usually umbilical, leading to septicemia. Daily changing of the bedding is required at a minimum. Wet bedding allows for bacterial growth, becomes a heat sink causing hypothermia, and various dermatologic conditions.

Several internal parasites can be passed from the dam to the offspring in utero or shortly thereafter. Proper prenatal care includes parasite control. Flea bite anemia in puppies and kittens is most likely to occur around eight weeks of age when the neonate is shifting from a near adult packed cell volume at birth to making its own red cells as the initial RBC need to be replaced. At 8 weeks their packed cell volume is lowest in the low 20% it is then they are most susceptible to flea bite anemia.

Causes of neonatal mortality related to the environment

• Temperature (including drafts)

• Poor Bedding

• Poor Hygiene

• Parasitic

Maternal:

Obese mothers have decreased litter sizes, increased risk of dystocia and increased neonatal mortality. Older bitches have smaller litter sizes and increased neonatal mortality although recent data does not support this conclusion in queens.

All mothers should be checked for proper milk production for problems such as agalactia and mastitis which otherwise may not be recognized before neonates start dying. Nervous mothers often will not stay in a nursing position long enough for the neonates to suckle sufficient qualities of milk, additionally; stressed dams may not let their milk down as easily.

Poor mothering, extreme nervousness, savaging neonates may be due to border line hypocalcaemia, in the authors experience post whelping/queening supplementation with calcium will correct these problems. This is particularly true for smaller breeds and terriers.

Mothers should be monitored for post birthing infectious conditions; sick mothers make poor volume and quality milk. They should also be monitored for maternal diabetes mellitus caused by inhibition of insulin by progesterone.

Maternal hypothyroidism has been shown to cause increased neonatal mortality (34%). The exact mechanisms are unknown at this time.

Maternal causes of neonatal mortality

• Agalactia

• Mastitis

• Nervous (crazy) bitch

• Poor mothering

• Hypothyroidism

• Eclampsia

• Obesity

• Dystocia

• Uterine inflammation

• Maternal Diabetes Mellitus

Neonatal:

Low birth weight indicates poor intrauterine nutrition or congenital abnormalities, and is related to a poor prognosis with upwards of 60% mortality by weaning age in kittens with low birth weight.

Poor growth rates are a cause for concern. Neonates may lose weight in first 24 hours, and then steadily gain so they double their birth weight by 7 to 10 days. Weight loss of more than 10% in first 24 hours has poor prognosis for survival. Usually poor growth rates are due to decreased nursing where a newborn is excluded by siblings, mom has hyperkeratoic nipples, mastitis, or the new born has a congenital problem.

Common causes of poor growth

• poor body condition: shunts, renal, megaesophagus, cardiac, exocrine pancreas

• normal body condition: decreased thyroid, diabetes mellitus, adrenal disease

Moderate neonatal anoxia, particularly at birth is generally not associated with negative outcomes in neonates.

Failure of passive immunity does occur and intestinal absorption of IgG generally ceases at 24 hours post parturition.

Neonatal isoerythrolysis occurs acutely in kittens. Kittens with blood type A born to queens with blood type B develop illness rapidly after ingesting colostrum with anti type A antibodies. Kittens exhibit anemia, icterus, weakness, tachycardia hemoglobinuria, and sudden death.

Neonatal dehydration is usually due to feeding errors. The degree of dehydration is often difficult to assess. Neonates require more water per body mass than adults and have greater surface losses. Normal fluid requirement is about 200ml/kg day.

Meconium aspiration syndrome can occur if the fetus is stressed and expels meconium into the amniotic fluid. The meconium mixes with time and becomes less particulate in nature. In humans 2% of newborns with meconium stained amniotic fluid aspirate sufficient material to develop meconium aspiration syndrome developing an inflammatory response from bile salts and other irritating chemicals in the meconium.

Atelectasis of lung lobes can prevent proper ventilation causing a cardiovascular pulmonary mismatch and subsequent tissue hypoxia. Decreased surfactant production may be involved. Diffuse atelectasis is commonly caused by lack of surfactant, respiratory distress syndrome, transient tachypnea of the newborn, and pneumonia.

Bleeding disorders can occur because of congenital problems and neonates less than 48 hours old have reduced thrombin levels.

Respiratory distress may occur for a variety of reasons including debris blocking the trachea, air leaks, atelectasis, and aspiration of food among others.

Hypocalcemia occurs in the first 24-48 hours then stabilizes usually to adult levels by the end of the first week of life. Before birth fetal calcium concentrations are higher than maternal levels through a constant uptake of calcium across the umbilical circulation from the placenta; this causes the fetal levels of parathyroid hormone and 1,25-dihydroxycholecalciferol concentrations to be low and fetal serum calcitonin to be high. Once born the high rate of calcium from the mother is stopped and since there is no initial source of exogenous mineral the neonate is without adequate supplies of calcium for several days. This problem is particularly enhanced in puppies which have significant perinatal depression causing an increased stress response and therefore increased calcitonin production.

Neonatal causes of mortality

• Low birth weight

• Poor growth rate

• Anoxia

• Feeding aspiration

• Failure of passive immunity

• Hypoglycemia

• Neonatal isoerythrolysis

• Dehydration

• Meconium aspiration syndrome

• Persistent pulmonary hypertension of newborn

• Atelectasis

• Hypocalcemia

• Air leaks

• Bleeding disorders

• Congenital abnormalities

• Infections

Congenital abnormalities can affect any organ system commonly affected systems are hepatic, cardiac, and neurologic. Cleft palates, open fontanels, and inborn metabolic errors also occur. A thorough physical exam of all neonates should be performed and their weight gain and general health closely monitored daily by the owners.

Infectious causes of neonatal mortality are not uncommon frequently through umbilical infections secondary to poor hygiene issues in the husbandry of the dam and offspring.

Common Infections of Neonates

Fading puppies and kittens can occur from a variety of causes numerous infectious, toxic, metabolic and nutritional factors could play a role. One suspected etiology is thymic dysfunction syndrome due to either a hypoplastic thymus from a congenital or genetic origin or secondary to another cause of fading neonate syndrome. Neonatal thymectomy results in wasting and death. If a thorough history, physical examination, and/or necropsy do not indicate a cause for the fading syndrome, then defective thymus function should be considered. The clinician should request both gross and histological examination of the thymus gland be included in the post mortem examination report.