Veterinarians use clinical chemistry and other laboratory tests to diagnose disease, to monitor disease progression or response to therapy, and to screen for the presence of underlying disease in apparently healthy animals. Clinical chemistry tests are offered by clinical pathology laboratories for this purpose and Metabiolab is keen to help them by in more specialized topics such as cellular metabolism and oxidative stress.
Notion of metabolic disorders in animals
They are of clinical significance because they affect energy production or damage tissues important for survival of the animal.
Inherited Metabolic Genetic Disorders do exist in many animals (most commonly dogs & cats) resulting in inborn errors in metabolism. These diseases occur due to absence of enzymes critical in intermediary metabolism. These are progressive in nature and usually are fatal. Examples are diseases associated with decreased RBC survival and anemia such as pyruvate kinase (PK) deficiency in Basenjis and Beagles, phosphofructokinase (PFK) deficiency in English Springer Spaniels. Glucose-6-phosphate dehydrogenase (G6PD) deficiency and hyperkalemic periodic paralysis in horses. α-Mannosidosis in cattle and goat.
Acquired metabolic disorders are primarily related to production or management and metabolism is a critical factor in the pathogenesis of each disease. For example hypoglycemia, promoted by management practices which are aimed at greater production, hence they are entitled production diseases. However, they are also metabolic diseases because the demand for greater production is beyond the capacity of the animal’s metabolic reserves to maintain the particular nutrient at physiologic concentrations.
Ketosis In Cattle and other ruminants
Bovine ketosis is a metabolic disease of lactating dairy cows and occurs worldwide whenever dairy cows are selected and fed for high milk production. Ketosis is basically the result of a negative energy balance in the 6 weeks after parturition. The cow is unable to eat or assimilate enough nutrients to meet her energy needs for maintenance and milk production. Therefore, blood glucose levels drop and body fat and limited protein stores are mobilized in the form of triglycerides and amino acids for gluconeogenesis. Ketone bodies (acetoacetate, β-hydroxybutyrate and acetone) are produced during the mobilization process. Ketone bodies are produced primarily in the liver and in smaller quantities in the mammary gland and rumen wall.
Subclinical ketosis: Post-calving dairy cows with increased BHB, but no clinical signs of are considered to be in a state of subclinical ketosis. Associations have been made between subclinical ketosis and an increased incidence of inflammatory (metritis, mastitis) and metabolic (displaced abomasum, clinical ketosis) diseases post-calving. (Ospina et al., 2013).
Clinical ketosis: Clinical ketosis typically occurs in cows during early lactation and is most frequently seen in dairy cows Cows with clinical ketosis in dairy herds fed concentrate rations are frequently concurrently hypoglycemic. Blood β-hydroxybutyrate values >27 mg/dL are considered compatible with clinical ketosis. Cows with underlying hepatic lipidosis may have concurrent elevations in liver leakage enzymes or cholestatic enzymes
Pregnancy toxemia in small ruminants: Clinical ketosis due to excess energy demands from the fetus (particularly with twins) also occurs in sheep and goats.
Diabetic ketoacidosis in small animals: Clinical ketosis is seen primarily in small animals as a consequence of diabetes mellitus with a stimulation of gluconeogenesis (which decreases oxaloacetate in hepatocyte mitochondria, facilitating ketogenesis). Affected animals usually have a metabolic acidosis (from accumulation of ketones) and ketonuria. β-hydroxybutyrate concentrations are markedly increased. Rarely, dogs in lactation can also suffer from ketosis. Note that horses have poorly developed ketogenic pathways, so ketosis is rare in this species.
Fatty Liver Disease Of Cattle
Fatty liver is most common in periparturient cattle. It occurs during periods when blood concentrations of non-esterified fatty acids (NEFA) are increased. Oxidation of NEFA leads to the formation of CO2 and ketones, primarily acetoacetate and β-hydroxybutyrate. Fatty liver is often associated with obese cows and downer cows.
Bovine liver diseases
Increase in glutathione peroxidase (GPX) and glucose 6-phosphate dehydrogenase (G6PD) in liver tissue from cattle suffering from liver disease, indicating increased oxidative stress in the liver tissues but not in the blood (Abd Ellah et al., 2007).
Decreased production of glucose by the liver can occur secondary to inherited defects such as deficiencies of α 1-4 glucosidase (GAA, Pompe disease) and glucose-6-phosphatase (G6PC, von Gierke’s disease). This results in hypoglycemia from defective glycogenolysis.
Juvenile hypoglycemia (usually affects toy and small breed dogs) is due to hepatic immaturity, low liver stores of glycogen and insufficient gluconeogenesis to meet demands. In horses, glucose notably decreases if they are fed a high grain diet, with little roughage.
Hypoglycemia of hunting dogs and endurance horses: A hypoglycemic state is reached from an imbalance in which glucose consumption (glycolysis) occurs at a much faster rate than glucose replenishment (gluconeogenesis and glycogenolysis).
Acidosis in Cattle
Acute and chronic acidosis, conditions that follow ingestion of excessive amounts of readily fermented carbohydrate, are prominent production problems for ruminants fed diets rich in concentrate (Owens et al., 1998).
- Glycolysis: Anaerobic microbes typically thrive when free glucose is available. Rate of glycolysis can be limited by inhibiting hexokinase (HK), phosphofructokinase (PFK), and pyruvate kinase (PK); lack of NAD⁺ also can limit glycolysis.
- Volatile Fatty Acid Production and Lactate Production: Bacteria in the rumen often are classified as “lactate producers” or “lactate users. Under anaerobic conditions, pyruvate is converted to lactate to regenerate the NAD used in glycolysis. Conversion of pyruvate to VFA involves multiple steps and generates approximately half the ATP for microbial growth in the rumen; the other half is derived from conversion of glucose to pyruvate.
- During sub-acute ruminal acidosis, it has been observed increased values on the concentrations of some acute phase proteins in dairy cows, such as SAA and Haptoglobin (Tothova et al., 2014)
In dogs, females are affected twice as often as males. Diabetes mellitus has been associated with bovine virus diarrhea infection in cattle and paramyxovirus infection in llamas, through destruction of pancreatic islets.
Acute phase proteins (APPs) are defined as proteins that change their serum concentration by >25% in response to inflammatory cytokines (IL-1, IL-6, TNFα). The acute-phase response is considered part of the innate immune system, and APPs play a role in mediating such systemic effects as fever, leukocytosis, increased cortisol, decreased thyroxine, decreased serum iron, and many others.
The rapidity and magnitude of the increase in each acute phase protein varies depending on the species. The following table list the acute phase proteins that are major and moderate responders in various animal species.
Serum amyloid A (SAA) is produced in the liver in response to inflammatory cytokines. It is considered a major acute phase protein in domestic species, except for the pig,
Systemic inflammation: High SAA concentrations are seen in horses, dogs (Christensen et al., 2014) and other species with induced or spontaneously occurring inflammation and concentrations decline with resolution.
Localized inflammation: High SAA concentrations have been detected in synovial fluid of horses with various inflammatory joint and tendon conditions. High concentrations of SAA were also seen in the peritoneal fluid and serum of horses with colic (Pihl et al., 2013).
Acute phase proteins and their use in the diagnosis of diseases in ruminants
The clinical application has been studied widely in human medicine (Tothova et al., 2014), but they are still relatively under-utilized in veterinary medicine, predominantly in farm animals. Acute phase protein concentrations are elevated in animals with many different diseases. Therefore, they have very poor diagnostic specificity. On the other hand, they have very high sensitivity in detecting many conditions that alter the health of the animal and in revealing subclinical inflammation or infections. The possible use of acute phase proteins in cattle has been investigated in various inflammatory and non-inflammatory conditions.
- Acute phase proteins in mastitis: Mastitis has remained economically the most important disease in dairy cattle. In all cows with mastitis, they found elevated concentrations of haptoglobin, ceruleoplasmin and α-1 antitrypsin in comparison to cows without mastitis. The presence of haptoglobin and SAA in milk was associated with lower total protein, casein, lactose content and higher proteolysis activity, which are signs of poor milk quality.
- In reproduction and peripartum reproductive disorders: The usefulness of acute phase protein analyses is predominantly in the detection and monitoring of metritis. Cows with acute puerperal metritis have significantly higher haptoglobin concentrations than healthy cows. The highest haptoglobin concentration was found in the period of three days after parturition, and for SAA concentrations four to seven days post partum.
- In abdominal and cardiac disorders : Evidence of usefulness of fibrinogen and haptoglobin in the diagnosis of traumatic reticuloperitonitis in dairy cows. Cases with pericarditis and endocarditis had higher haptogobin and SAA concentrations than cows with murmurs. In addition, the concentrations of both measured APPs were lower in cows with endocarditis than those measured in cows with pericarditis, which suggests that the measurement of APPs can be helpful in differentiating an acute inflammatory condition like pericarditis from other cardiac disorders.
- In hoof diseases and lameness: Study results showed higher concentrations of SAA in lame cows than in healthy animals.
- In calf diseases : In calves with clinical signs of omphalophlebitis concentrations of SAA were markedly higher than in healthy calves.
- Acute phase proteins and stress: With respect to transport stress on cattle, it has shown that after four to six hours of transport, the serum concentrations of haptoglobin and SAA were significantly increased indicating that they could serve as markers of stress in cattle
- In small ruminants: In ovine and caprine practice, haptoglobin and SAA are considered the major acute phase proteins.
Cystatine C (CST3)
It is generally considered superior to creatinine as a marker of Glomerular filtration rate GFR in all species (Ghys et al., 2014). In general, studies in dogs show that CST3 concentrations are higher in dogs and cats with CKD (Chronic kidney disease) than healthy dogs or cats.
Oxidative stress in animals
There is growing evidence that oxidative stress (OS) significantly impairs organic function and plays a major role in the etiology and pathogenesis of several metabolic diseases in veterinary medicine.
The measurement of hepatic oxidative status in liver biopsy, help in diagnosis of hepatic dysfunction and reflect the degree of deterioration in the liver tissues. On the other hand, an increasing body of evidence suggests that OS is involved in the pathogenesis of a wide range of cardiovascular diseases. The establishment of the specific role of OS in cardiovascular diseases will help to choose the antioxidant therapy that will prove beneficial in combating these problems.
In cardiac diseases in dog, supplementation can play a protective role, avoiding cell disorganization and cellular damages.
Proper anti-oxidant supplementation (coenzyme-Q10, polyphenols, or omega-3 fatty acids) increase the concentration of anti-oxidants in heart cells and make them less sensitive to free radicals.
A number of vitamins and trace minerals are involved in the anti-oxidant defense system and a deficiency of any of these nutrients may depress immunity. Some vitamins (such as Vitamin E or Vitamin C) are important anti-oxidants that have been shown to play an important role in immune-responsiveness and health. A number of trace minerals are required for the functioning of enzymes involved in the anti-oxidant defense system, and certain trace minerals may also affect immune cells via mechanisms distinct from antioxidant properties. Two reports analyze the protective effects of Zinc or Vitamin C in different species (chickens and mice) in different diseases (parasitic infections and hematological disturbances). Finally, OS has been implicated in the pathogenic mechanism of some heavy metals (such as lead or cadmium), causing many disease conditions and toxicities in animals. (Rodriguez et al., 2011)
Our understanding of the role of oxidants and antioxidants in physiological and pathological conditions is continuously increasing and some oxidant-associated or oxidant-mediated processes are now considered as future therapeutic targets. Interestingly, an important part of animal research in this field has been performed in horses, in particular with regard to exercise physiology.
In the page dedicated to “Oxidative Stress in Horses”, authors provide insight into the concept of the oxidant/anti-oxidant equilibrium in horses, by describing how the oxidant/anti-oxidant equilibrium or oxidative stress might be evaluated in the equine species and by presenting current knowledge about oxidative stress in equine medicine (Kirschvink et al., 2007)