Energy is generated from the utilization of proteins, fats, and carbohydrates. The most readily usable material, the carbohydrate glycogen, is utilized first. This is derived from glycogen stored in the liver and is exhausted within a few hours. This is followed by stored fat from the various subcutaneous deposits, around the kidney, and in the mesentery and omentum tissue. Fat deposits in the parenchymatous organs are utilized next. The last area of the body to lose its fat deposits is the marrow of the bones. The final source of energy available is the protein comprising the cytoplasm of the cells. It is at this time that ketosis and an increase in nitrogen excretion may occur.
Ketosis (a condition in which ketone substances appear in the blood and urine) is commonly seen in malnourished animals. This is because it is necessary for the animal to derive its energy from the stored fat and protein. After all the fat reserves have been exhausted, nitrogen excretion rises due to the protein catabolism which occurs just prior to death. The animal will eventually reach a point where the cells of the body are unable to perform the functions necessary for life. Death results from lack of sufficient blood glucose to provide the energy needs of the brain and hypoglycemic shock occurs.
At the microbial level, inadequate food intake, especially in a ruminant species, results in a rapid decrease in the number of bacteria and protozoa present and in the volatile fatty acid concentration in the stomach. The ruminant obtains approximately 70% of its energy from these fatty acids, so a reduction in the level has a significant impact on the animal. The pH of the rumen becomes more alkaline because of the lack of these fatty acids. Decreasing the microbial populations probably diminishes the animal’s ability to digest cellulose (fibrous material). At the individual level, weight loss of 25 to 30% can occur and the animal may survive, but death is often the result.
Wild ruminant physiology has developed to allow them to withstand dietary deficiencies and obtain energy from the consumption of poor quality forage. Adult ruminants are able to store large amounts of nutrients and fat within their body tissues. They are also able to store minerals and nitrogen in their tissues for secretion into the rumen during the winter months. These fatter, older animals are thereby able to utilize more fat than protein, especially in the early stages of malnutrition and starvation. Young animals, which have smaller fat reserves because of their higher nutritional demands for growth, smaller body size, and position in the social hierarchy, utilize more protein than fat under starvation conditions.
Clinical Signs and Pathology Clinically, mammals suffering from malnutrition or starvation are lethargic, unsteady, listless, and unafraid of humans. The skin may appear loose, the hair coat erect, dull, and rough and the body more angular. The animal may have a humped or sagged back, a swollen appearing face, sunken eyes, and a small tucked up abdomen. Due to atrophy (shrinkage) of the muscles, there is usually an increased prominence of the bones of the shoulders, ribs, vertebrate, and pelvis. The muscles appear more prominent, but usually do not appear full, and consequently a definite demarcation may be seen between the neck and shoulders and the upper forelegs and chest.
Clinical signs of an avian species dying from malnutrition or starvation are listlessness, unsteady locomotion, ruffed feathers, and a lack of fear of humans. Pathological changes which occur in a starved animal are many and varied. The most striking gross change is a lack of fat in the subcutaneous, visceral, and bone marrow locations, and atrophic changes which occur in the musculature. Serous atrophy, a reddish gelatinous appearance to the fat tissue, is commonly seen in starving animals. The organs of the body decrease in size and weight.
The digestive tract of most species is empty and/or shrunken with dark green bile staining of the lining and contents. The stomachs of ruminant species usually contain food, but the contents are often dry and of poor quality. The rumen lining may be ulcerated, have erosions present, and shrunken villi. The femur marrow, due to a lack of fat present, will be red or yellow in color, transparent, and gelatinous in a starved animal. Severe weight loss (up to 50%) is a common occurrence in malnourished and starved avian species.
Gross lesions seen are an absence of fat deposits and atrophy of the musculature, with breast muscle atrophy being the most noticeable. The digestive tract is shrunken and/or empty with dark green stained linings, and there is a marked increase in the size (possibly 2 to 3 times normal) of the gall bladder due to an accumulation of bile. In avian species, malnutrition may increase the susceptibility of the bird to parasitic infection (lice and other endoparasites are more common), and may result in the drawing of contaminants from the fat deposits being used, thereby resulting in the circulating and redistribution of these compounds.
Diseases which could cause a malnourished condition, such as chronic infections of aspergillosis and lead poisoning must be ruled out when a definitive diagnosis is made. Diagnosis Starvation can be diagnosed either by field techniques through gross examination, or by laboratory analyses. To grossly diagnose starvation, the overall physical condition of the animal must be determined by examining for the presence or lack of adipose tissue (fat deposits) in the various subcutaneous and visceral locations.
In ruminants, the femoral or mandibular bone marrow fat can be examined and the percentage of fat present estimated visually. Some care must be taken when examining the femur marrow as it is used for fat storage in adult animals but serves as a production area for red blood cells rather than fat storage in young animals. Laboratory methods that are used nationwide are varied. There is a femur marrow compression method, ether-extract method, kidney fat index, and wet weight-dry weight method. We have used the latter 3 methods for determining physical condition of the various mammals we examine.