INTRODUCTION

One of the most important facets in animal production is the care of neonatal individuals. Unfortunately, little attention has been given on the recognition of disease processes in these individuals, such that the student clinician is left on extrapolating the information gained on disease processes of mature animals applying them to the neonates. The same observation may be applied to therapy of neonates, with dosages for mature animals given to these animals. While disease processes affecting neonatal individuals defy compilation, this lecture will deal with the important considerations in the diagnosis of diseases involving neonates.
 

DEFINITION OF TERMS

Several classification schemes have been proposed in the categorization of neonatal diseases. The most widely used classification scheme categorizes diseases of the foetus and newborn as follows:

1. Fetal diseases - refers to disease processes involving the foetus during intra-uterine life. Examples include prolonged gestation, congenital defects, abortion, fetal death and maceration and/or mummification;

2. Parturient diseases - refers to disease processes associated with dystocia and include cerebral anoxia, and injury to the skeleton or soft tissues.

3. Postnatal diseases - refers to disease processes occurring within the first month of neonatal life. These are further classified as:

a) Early postnatal disease - those  occurring within 48 hours after  birth. These include  malnutrition due to poor  mothering, hypothermia, and  navel infection.

b) Delayed postnatal disease - those  occurring within the first week  after birth. These include  starvation following desertion  by mother and mammary  incompetence, infections  resulting from  hypogammaglobulinaemia.

c) Late postnatal disease - those  occurring from 1-4 weeks of  age. Examples include non- specific diarrhoea,  enterotoxaemia, and  malnutrition states.
 

DETERMINANTS OF MORTALITY IN NEONATES

Immunocompetence

Neonates are considered immunocompetent. This may be due to the fact that most immune cells are still actively being programmed and maturing. The transfer of maternal immunoglobulin is limited by placental cyto-architecture and occurs only in kittens and pups. Piglets, foals, calves, kids and lambs depend largely on colostrum as the source of maternal immunoglobulin. Failure of these animals from receiving colostrum thus results to an immunodeficiency syndrome predisposing to a host of postnatal diseases.

The transfer of maternal immunoglobulin through the colostrum is not without apparent problems. Intestinal absorption of maternal immunoglobulin terminates within 24-48 hours after birth in piglets, foals, calves and pups. In kids and lambs, this intestinal absorptive capability is present up to 4 days after birth. Hypogammaglobulinaemia is considered to be the most important predisposing factor in postnatal diarrhoea and respiratory disorders.
 

Thermosensitivity

Neonatal animals are particularly susceptible to upward or downward alterations in environmental temperature. In pigs, the thermoregulatory mechanism remains inefficient up to the first 9 days of life and is not fully functional until the 20th day. Although knowledge of this fact is important, ironically, little information is available in other domestic animal species. What is apparently important to consider is the effect of hypothermia in neonates. Although hyperthermia could result to fatal consequences, current husbandry practices, overruling negligence on the part of the animal owner, seems to curb this condition to happen. Neonatal individuals are very susceptible to overheating such that sever tissue damage due to burning may occur when the animals are artificially warmed.

The major causes of hypothermia in neonates include excessive heat loss as influenced by environmental factors, and depressed heat production as a result of starvation. The major effect of hypothermia on neonate is the demand for an increase in metabolic activity and subsequent development of acidosis. Death follows due to metabolic disturbance and development of shock.
 

High energy demands

The nutritional requirement of neonates differs greatly from that of adult animals for obvious reasons, and yet their only source of nutrition is through the milk. Thus, one of the most critical factor is the nursing behaviour of the dam to which the neonates are at their mercy. Newborn lambs, calves and foals are much more capable of maintaining blood glucose levels when starved than piglets. It is for this reason that hypoglycaemia occur much more frequent in piglets.

The effect of hypoglycaemia has been well-studied in piglets. Following this condition, liver reserves of glycogen are rapidly depleted, and since there is but little amount of stored lipid and the animal body's capacity for gluconeogenesis converting protein and lipid into glucose is largely underdeveloped, the animal succumb to severe hypoglycaemia. The effects of low blood glucose levels result to a breakdown of metabolic activity in the animal body, ATP's being of insufficient amount. This result to widespread parenchymatous degeneration of organs particularly the brain,  coma and death.
 

Digestive capabilities

Newborn individuals are endowed at birth with digestive enzyme capacities to digest lactose, milk fat and milk proteins. In neonatal ruminants, their digestive capability occur in a similar fashion to that of its non-ruminant counterpart; the rumen being non-functional at this stage. With increasing age and as the neonate become less dependent on milk, the digestive enzyme capacity also include other substances apart from those found on milk.

The relative importance of this fact is that while milk replacers are commercially available, most contain relatively indigestible non-milk carbohydrates, non-milk proteins or heat denatured skim-milk powder. These materials, obviously would result to indigestion, and diarrhoea.
 

Intestinal microflora
 

Right after birth, the neonatal intestinal tract is considered to be sterile. Colonisation of bacteria commences as the animal is exposed to the environment and takes in milk. At the level of intestines, bacterial "settlers" compete for space and nutrient in order to establish a niche that would later on form the complex bacterial ecology in the gut. It is at this stage where normal control mechanisms for overgrowth of bacteria are at its lowest ebb, for mucosal immune defense mechanisms are still not fully operational. The possibilities of pathogenic strains taking part in establishing most part in the bacterial population are great. This may be aggravated by failure of passive transfer of immunity.

It is evident that at this stage, oral administration of antibiotics could wreck havoc and alter bacterial population, and even favor fungal overgrowth. It may even favor overgrowth of a specific bacterial population over other particularly if a narrow spectrum antibiotic is used.
 

Dependence to the dam

The neonate is at the mercy of the dam for obvious reasons. Thus, poor mothering ability of the dam frequently result to death of neonates. A poor mother-young bond is most likely on the side of the dam, but contributing factors include husbandry practices and environmental influences.

The causes of neonatal mortality associated to poor mother-young bond are varied and ranges from trauma to the neonate as a result of crushing, desertion, and even irregular feeding resulting to starvation of neonate. Contributory factors are husbandry practices and environmental influences. Harassment of the dam and other interference during nursing (particularly when forced), frequent handling of the neonate, sudden shift in diet and/or poor nutrition of the dam, inclement weather, unregulated access of predators such as stray dogs and even rats, all contribute to neonatal mortality.
 

INVESTIGATING NEONATAL DEATHS

In investigating neonatal deaths, several information should be sought during history taking. This include the husbandry practices being done such as feeding and nutrition of the dam (types and frequency of feeding, sources of feeds, supplementation given to the neonates, sanitation and quarantine practices, provision to limit access of predators). Inquiries should be made on the prevailing weather condition when the mortality was noted, the rapidity by which the disease take its toll, how many neonates are there in the litter, how many are affected and their clinical symptomatology, surveillance by owner, and all other factors which could influence the survival rate.

It is best to perform necropsy on the dead neonate whenever feasible. During necropsy, take particular attention to the condition of the carcass, if it has breathed (by taking portion of the lung and allowing it to float on water to detect presence of air, especially for newly born individuals), if the animal has walked (by examining the presence of dirt in the feet/hooves), if the animal was able to suckle milk (examine the content of the stomach), and its state of hydration. For routine microbiological examination, it is best to obtain the stomach content and a segment of the gastrointestinal tract, and the liver. For newly born individuals, samples of placenta if available should also be included. These samples should be submitted for microbiological examination requesting in particular examination for common pathogen of neonate as Leptospira spp., Escherichia coli, Salmonella spp., and Brucella spp.

Make a thorough physical examination of the dam, and ensure that there is milk supply. Observe or inquire on the maternal behaviour of the dam. Determine the duration of pregnancy to ensure that the neonates were delivered at full term. Check the drugs used or given on the dam, and other medications or surgical interventions performed.
 

GENERAL PRINCIPLES IN THE TREATMENT OF INFECTIOUS DISEASES IN NEONATES

Similar to their mature counterpart, the first principle in the treatment of infectious diseases in neonates is to obtain an aetiological diagnosis as soon as possible. "Shotgun" type of medication and symptomatic treatment are of little use since neonates most often succumb rapidly to infection such that the intervening time before they show the typical signs and symptoms is often of short duration. However, since process by which an aetiologic diagnosis is obtain require some time, the choice of a therapeutic regimen may be based on a tentative diagnosis and previous experience with treatment of similar cases.

In the choice for antibacterial preparations, the drug preparations being used in adult animals may be used. Ironically, however, while exact dose rates are established for mature animals, little information or very few drugs whose dose rate are known for neonatal individuals. In most cases, what is being used is the adult dose and frequency of administration is applied to neonates, although this should be evaluated. Neonates present peculiar characteristics as follows:

1. The drug metabolising enzymes are  low in neonates than in adult  individuals, such that the  margin of safety may be less  than their adult counterparts;  Hepatic microsomal oxidative  reactions are deficient for  varying period of time, usually  up to 6 weeks after birth;

2. There is slower elimination of  drug in the kidneys due to  immaturity of the nephrons.  Renal function reach maturity  is reached from 2-4 weeks in  most domestic animals;

3. There is greater absorption of  drug from the gastrointestinal  tract, but lower extent of  plasma protein binding, such  that plasma peak levels may be  attained in a short time, but  plasma half-life of drugs may  be longer;

4. There is increased permeability of  blood-brain barrier, such that  drugs that normally do not  reach the brain may affect its  functions;

5. There are increased avenues for  distribution of drugs (in the  extracellular fluid or body  water) such that in some cases,  the dose required may be higher  to elicit the same response to  that of mature animals.

In the therapy of neonates, the provision of rehydrating fluid is essential. Dehydration affect young animals much faster than adults. The use of whole blood transfusions or hyperimmune serum may also be employed and the principles required prior to their application are the same as those described for adults (i.e. screening for lack of anti-red blood cell antibodies from donors).