The anion gap: a key biomarker for poultry health

Summary

The anion gap is a crucial biomarker in poultry health, helping to diagnose and differentiate between various types of metabolic acidosis. This article explains what the anion gap is, how it is calculated, and its significance in poultry production. It also discusses Verax™ and its role in providing valuable insights for poultry producers.

Introduction

The body has a unique way of keeping itself in balance, and positive and negative charged ions are a great example of that balance. The anion gap, a key biomarker in the Verax™ blood panel, offers the potential to diagnose and differentiate between various types of metabolic acidosis by evaluating the difference between positive and negative charged ions in broilers. Understanding and leveraging this biomarker can significantly enhance your ability to manage and improve poultry health..

What is the anion gap?

Blood is always maintained in a state of electroneutrality, where the molar sum of cations (positively charged ions) equals the molar sum of anions (negatively charged ions). For example, if a bird has a blood cation concentration (sodium (Na) and potassium (K)) of 148 mmol/l, the sum of anions (bicarbonate (HCO3) and chloride (Cl)) should also be 148 mmol/l.

However, the sum of measured anions is typically less than the sum of measured cations by around 12-18 mmol/l. This difference is termed the ‘unmeasured anion gap’ and consists of a complex mixture of anionic compounds such as lactate, sulphate, albumin, phosphate, urate, and keto acids.

Definitions and calculations

The mean cation and anion concentration in avian blood is approximately 148.5 mmol/l, with extreme values ranging from 142 to 157 mmol/l. The cation profile is dominated by sodium (Na), which accounts for around 95-96% of the total cation load, with potassium (K) making up most of the remainder. Other cations, such as calcium (Ca) and magnesium (Mg), contribute minimally.

The anion profile is more complex, dominated by bicarbonate (HCO3) and chloride (Cl). Chloride accounts for around 75% of the anion concentration, with bicarbonate making up about 15%. The remaining 10% is the anion gap, composed of albumin, sulphate, phosphate, urate, organic acids, and other negatively charged molecules.

Clinical diagnosis and implications

The anion gap plays a fundamental role in diagnosing and differentiating between two major types of metabolic acidosis: normal anion gap metabolic acidosis (NAGMA) and high anion gap metabolic acidosis (HAGMA). These conditions share a low pH phenotype but have different underlying causes, making the anion gap crucial for accurate diagnosis and treatment recommendations.

Normal anion gap metabolic acidosis (NAGMA)

NAGMA is typically associated with elevated blood chloride (>113 mmol/l) and reduced blood bicarbonate (<21 mmol/l) concentrations. Common causes include excess chloride ingestion via feed or drinking water and excessive bicarbonate excretion via the renal system. Symptoms may include panting, wet litter, a strong smell of ammonia in the barn, above-average water intake, poor bodyweight uniformity, unusual behavior, dermatitis, wing flapping, and reduced feed intake.

High anion gap metabolic acidosis (HAGMA)

HAGMA is defined by a combination of low blood pH and an anion gap >17 mmol/l. Blood chloride concentration is usually normal, but blood bicarbonate may be slightly reduced. Causes of HAGMA in poultry include lactate accumulation, renal failure, iron toxicity, and excessive ketone production. Lactate-induced HAGMA can result from overproduction of lactate by the enteric microbiome or hypoxic conditions. Renal failure can also cause HAGMA, often presenting with elevated blood uric acid and phosphate levels.

Practical tips for producers

Poultry producers can take a number of steps to reduce the risk of metabolic acidosis, including:

• Regular Monitoring: Keep an eye on both total and ionized calcium levels to ensure your birds are healthy.
• Minimize Stress: Reduce stress during handling to maintain normal calcium levels.
• Balanced Diet: Ensure your birds get a balanced diet with the right amount of calcium and other nutrients.

Conclusion

The anion gap is a key biomarker analyzed by Verax™ and can separate the two major types of metabolic acidosis and assisting with the classification of various acid/base pathologies.

When a high anion gap is encountered (>16-17 mmol/l), it is worth exploring the possibility of lactate accumulation, iron toxicity, renal failure, or hypoglycemia and carbohydrate metabolism problems.

Understanding and leveraging this biomarker can significantly enhance your ability to manage and improve poultry health.