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 the Verax™ and its role in providing valuable insights for poultry producers.
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 seeing 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.
Blood is always maintained in a state of electroneutrality, where the sum of cations (positively charged ions) equals the 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.
Blood is maintained at electroneutrality, with the molar sum of cations equal to the molar sum of anions. 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.
Figure 1. The anion gap in poultry | Source: dsm-firmenich
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.
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.
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.
| NAGMA | HAGMA | |
| Definition | Elevated blood chloride (>113 mmol/l) and reduced blood bicarbonate (<21 mmol/l) concentrations. | Low blood pH and an anion gap >17 mmol/l. Blood chloride concentration is usually normal, but blood bicarbonate may be slightly reduced. |
| Common Causes | Excess chloride ingestion via feed or drinking water, excessive bicarbonate excretion via the renal system. | Lactate accumulation, renal failure, iron toxicity, excessive ketone production. |
| Symptoms | Panting, wet litter, strong smell of ammonia in the barn, above-average water intake, poor bodyweight uniformity, unusual behavior, dermatitis, wing flapping, reduced feed intake. | Elevated blood uric acid and phosphate levels, symptoms related to underlying causes such as lactate overproduction or renal failure. |
| Blood Chloride Concentration | Elevated (>113 mmol/l) | Normal |
| Blood Bicarbonate Concentration | Reduced (<21 mmol/l) | Slightly reduced |
| Anion Gap | Normal | High (>17 mmol/l) |
Poultry producers can take a number of steps to reduce the risk of metabolic acidosis, including:
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.
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