Immediate Neonatal Period
Important physiologic adjustments to extrauterine life include cardiopulmonary function (lung expansion and circulatory dynamics), acid-base balance, and distribution of body fluids. Not surprisingly, therefore, causes of death from birth to day 4 of the neonatal period tend to be consequences of birth-related physiologic maladjustment, such as anoxia or hypoxia, metabolic acidosis, and dehydration. Similarly, an inadequate environment that promotes oxygen deficit (inadequate management of parturition or inattention by the dam) or dehydration (excessive ambient temperature, inattention by the dam, or induced hypothermia) can contribute either additively or independently to neonatal morbidity and mortality. During the nursing period (days 5–42), causes of morbidity and mortality in puppies and kittens shift toward environmental problems, such as accidents and infections.
Neonatal Supportive Measures
Several simple measures can minimize neonatal losses, but they require training and attendance during delivery. These include 1) early recognition of dystocia, with early veterinary intervention; 2) early recognition of the green-black vulvar discharge that signals placental separation and that will dictate veterinary intervention if not followed by delivery; 3) caution when administering drugs that stimulate uterine motility (ecbolics should never be used unless obstructive dystocia has been ruled out, and should never be used by untrained caretakers); 4) clearing oronasal passages and fetal membranes promptly if the dam does not act immediately after delivery (oronasal passages may be cleared mechanically, supported further by holding the neonate in a warm, dry cloth and gently swinging the neonate in a head-down arc); 5) stimulating respiration by external massage and gently extending fore- and hindlimbs in opposite directions with the neonate in lateral recumbency, holding extension for several seconds, and releasing; 6) stimulating respiration pharmacologically, usually by direct sublingual injection, remaining mindful that repeated administration of respiratory stimulants carries risk of aggravating metabolic acidosis; 7) maintaining age-specific body temperature; 8) avoiding dehydration through assisted suckling or by administration of isotonic fluid-electrolyte preparations (1 mL/30 g body wt SC or PO, in the presence of normothermia or near-normothermia, initial PO doses are lower); and 9) monitoring suckling and intervening early when necessary, recalling that hypothermia suppresses appetite and gut motility. Oral feeding or supplementation of hypothermic neonates (rectal temperature <94°F [34.4°C]) carries risk of regurgitation and aspiration.
Low birth weight is an important determinant of survival in mammals. Normal birth weight of puppies varies by breed but varies less among kittens. Newborn kittens weighing <70–80 g at birth are at high risk. Likewise, early weight loss (≥10% of birth weight in puppies) is associated with increased risk of death.
Ongoing monitoring of neonates should include the following: 1) Weigh high-risk neonates soon after birth, at 12 and 24 hr, and daily until consistent daily weight gain is observed. 2) Weigh high-risk neonates before and after suckling to assess adequacy of intake or the need for feeding intervention. 3) Provide for colostrum intake by assisted suckling, milking the dam and oral feeding of dam's milk to neonates, or if necessary provide passive antibodies by serum harvest and PO or SC administration. 4) Assess muscle tone and level of unstimulated activity daily to facilitate early recognition of failure. 5) Assess temperature and hydration daily.
Specific Physiologic Issues
Hypoxia and Acid-Base Balance
At birth, combined respiratory and metabolic acidemia is normal and should resolve spontaneously. However, severe or prolonged hypoxia at birth can lead to prolonged metabolic acidosis that may be fatal. The need for intervention is dictated by skin and rectal temperature, heart rate, rate and character of respiration, character and color of mucous membranes, activity, and response to handling.
Body temperature is lowest ~40 min after birth, with gradual recovery to 95–99°F (35–37.2°C). Rectal temperature should be 97–100°F (36.1–37.8°C) by age 14 days, reaching adult-like autoregulation by age 28 days. Warming of hypothermic neonates should be done slowly, over at least 3 hr, followed by subsequent administration of colostrum that can help prevent fatal secondary hypoxic enterocolitis. Protective measures include frequent monitoring of age-specific rectal temperature; monitoring (several times daily) of ambient temperature, especially when supplying a heat source; avoiding oral intake during significant hypothermia; and avoiding rapid warming of neonates.
Proper hydration is critical to normal development. Dehydration can occur in association with prematurity, fluid-wasting diseases (diarrhea, pneumonia), fever, high ambient temperature, poor suckling, and poor milk production by the dam. Short-term weight loss most often is due to fluid deficit that may be corrected using warmed isotonic solutions. Depending on the cause of dehydration, ongoing fluid requirements can be >6 mL/100 g body wt/day.
Hypoglycemia is common among moribund neonates and is especially likely to occur in association with prolonged prepartum maternal anorexia (>72 hr), placental insufficiency, early placental separation, hypoxia, dystocia, injudicious pharmacologic intervention, agalactia, or infection. These instances indicate oral (at normothermia) or IV glucose support as 5–10% solution, to effect.
Ambient Conditions and Feeding Support
Ambient temperature in the canine or feline neonatal environment should approximate 85–90°F (29.4–32.3°C) through age 7 days, followed by 80°F (26.6°C) from days 8–28, 70–75°F (21.1–23.9°C) from days 29–35, and 70°F (21.1°C) after day 35. Relative humidity should be ~55–65%. Noise, drafts, and dampness should be avoided.
Supplementary or total feeding support should not be delayed when poor suckling, lack of milk production, or other impediments to intake are recognized. General nutritional guidelines include 1) ensuring appropriate nutrient sources (in particular, cross-species administration of milk is nearly always tantamount to malnutrition and must be avoided); 2) individualizing feeding volumes and frequencies, based on partial support, full support, and clinical status; 3) avoiding overindulgence for natural suckling or feeding support, because it can lead to diarrhea, aspiration, and later to juvenile obesity and poor orthopedic development; 4) initiating support feeding with small volumes; and 5) establishing specific diagnoses when possible.
During feeding support, caretakers should look for signs of gastric overload (regurgitation, diarrhea, bloating, abdominal discomfort, and nasal discharge of milk). Digestive disturbances can occur after several common errors, including injudicious feeding intervention and volume overload, altered gut microbial colonization or microfloral balance, and improperly timed pharmacologic intervention, such as overuse of antibiotics. For feeding support, tube-feeding is more rapid and therefore less stressful but requires training and experience.
The time from day 21 to day 28 is a critical period of maturation for both puppies and kittens. The key features of this period are related to 3 main areas. First, appendicular neuromuscular changes include muscular normotonia (ie, maturation beyond flexor dominance through day 4 and extensor dominance over days 5–21) by age 21 days, transition to coordinated walking by age 28 days, and development of the peripheral nervous system toward adult-like reflexes. Second, sensory and thermoregulatory changes include temperature autoregulation; extinction of rooting, suckling, and anogenital eliminatory reflexes; sound orientation; and visual depth perception. Last, psychosocial maturation includes peak lactation, ability and inclination to prehend first moistened and then progressively more solid non-milk food as the first stage of weaning, early transition to more adult-like independence, environmental exploration, and social contacts.
Abnormal maturation through day 28 has undesirable results that include the need for delayed weaning (or unpreparedness for weaning), the risk of injury in the postweaning environment, susceptibility to secondary or opportunistic infections, separation anxiety and anorexia, social maladjustment, small adult size and behavioral disorders, and termination in wasting.
Weaning is characterized by permanent cessation of suckling and separation from dam and often siblings. Puppies and kittens that have not successfully transitioned from parturition through physiologic adjustment after birth, the 0- to 4-day neonatal period, and the 21- to 28-day maturation, likely will be unprepared for weaning. Secondary infections, anorexia, separation anxiety, and behavioral disorders commonly follow weaning of unprepared individuals.
During weaning and the postweaning period, puppies and kittens should be monitored for adequate food intake and weight gain; social behavior with siblings or toward people, including feeding behaviors; alertness and activity; hydration and normothermia; digestive disturbances; evidence of depression and separation anxiety; visual and auditory responses; rate and character of respiration; cough; condition of oral membranes; abdominal discomfort; parasites; evidence of viral or bacterial infection; and excessive crowding, noise, dampness, and ambient hyperthermia or hypothermia.
Wasting is a relatively common complication of weaning. Wasting is characterized by progressive anorexia and growth impairment, often accompanied by separation anxiety. Secondary infections that are the common causes for clinical presentation may mask the underlying problem. Wasting often begins with delayed growth during the second or third week of lactation, before the time that veterinary attention ordinarily is sought by caretakers who may not suspect abnormal development. The 21- to 28-day maturation does not occur normally, and weaning occurs at undesirably low body weight. Extended poor intake of milk, often resulting from inadequate lactation or inadequate mothering, can be recognized by reduced serum alkaline phosphatase and phosphorus levels (reflecting slowed growth) and elevated serum cholesterol and triglycerides (reflecting alternate energy metabolism).
The basis of nutritional management of wasting is recognition as early as circumstances permit, which necessitates maintaining an index of suspicion for any undersized nursing or postweaning puppy or kitten. Nutritional support can be provided by tube-feeding, bottle-feeding, pan-feeding of species-specific milk replacer, or warm gruel prepared from good-quality commercial formulations, depending on age and clinical status of the patient. Parasite control and management of secondary infections should be done simultaneously with nutritional support.
Additional protective steps for support of wasting puppies and kittens include the following: 1) Avoid temperature extremes and rapid changes; maintain a warm environment (see Ambient Conditions and Feeding Support). 2) Maintain relative humidity at 40–70% and avoid drafts. 3) Handle puppies and kittens frequently and gently, allowing adequate sleep time. 4) Avoid coincident stressful events. 5) Avoid multiple diet transition. 6) Monitor feeding competition among siblings. 7) Provide parasite control and vaccination according to geographic requirements and individual needs. Using relatively safe therapeutic agents such as pyrantel, oral deworming of high-risk puppies and kittens can begin as early as age 14 days, and may be continued at 14-day intervals until the parasite burden has been cleared satisfactorily.
Last full review/revision July 2011 by Dennis F. Lawler, DVM