Metabolic Diseases in Food Animals - 4

Metabolic Diseases in Food Animals
Hypocalcemia: Treatment

  • Definitions:

    • Hypocalcemia: A condition marked by low levels of calcium in the blood, significant in dairy cows, especially around parturition.

  • Subclinical Hypocalcemia:

    • Focus is on the presenting disease; treatment involves calcium supplementation.

  • Treatment Approach:

    • Stage 1 Hypocalcemia:

    • No intravenous (IV) calcium treatment is necessary.

    • Cows are still standing, indicating they can manage oral calcium supplementation.

    • An oral calcium supplement is recommended, as it is rapidly absorbed with little risk of subsequent hypercalcemia and rebound hypocalcemia.

    • Use an acidogenic source of calcium (calcium chloride or calcium sulfate) in a bolus formulation, enhancing the cow's calcium homeostasis by increasing parathyroid hormone (PTH) receptor responsiveness.

  • Risks Associated with Treatments:

    • Bradyarrhythmia

    • Relapse rate approximately 1/3 of cases for hypocalcemia after treatment.

  • Stages 2 and 3 Hypocalcemia:

    • For cows that are recumbent, immediate correction of hypocalcemia is essential through intravenous calcium infusion.

    • Recommended dose: 500 mL of a 23% calcium borogluconate solution provides 10.7 g of elemental calcium, which is sufficient for normocalcemia in even the heaviest cows with severe hypocalcemia.

    • Many marketed hypocalcemia treatments also include phosphorus, magnesium, glucose, or potassium; however, these additional electrolytes are unnecessary and potentially harmful for parturient paresis.

    • Calcium gluconate alone is the best treatment option for intravenous administration during parturient paresis.

Treatment Composition for Hypocalcemia

  • Calcium (as calcium borogluconate, equivalent to calcium gluconate 23.2%): 10.8 g

  • Potassium (as potassium chloride): 8.0 g

  • Phosphorus (as sodium hypophosphite • H2O): 2.5 g

  • Magnesium (as magnesium borogluconate): 1.6 g

  • Dextrose • H2O: 75.0 g

  • Total Composition: Each 500 mL of sterile aqueous solution contains the above listed elements.

Severe, Acute Hypophosphatemia (Downer Cow)

  • Causes:

    • Often seen in lactating cows following milk fever; caused by excessive PTH leading to phosphorus loss through urine/saliva.

    • Clinical signs include weakness resulting from Adenosine Triphosphate (ATP) depletion.

    • Phosphorus plasma levels can remain critically low (<1 mg/dL) even after calcium is treated, affecting the cow's ability to rise due to prolonged hypophosphatemia.

  • Treatment Options:

    • Same treatment as for milk fever.

    • Intravenous Treatment: Use 6 g of phosphorus dissolved in 1 liter of saline, typically using 23 g of monosodium phosphate for a rapid increase in plasma P levels.

    • Oral Treatment: Administer 50 g of phosphorus via 200 g monosodium phosphate drench for slower but longer-lasting results.

    • Key Note: Hypophosphite-based solutions are ineffective for restoring physiological function.

  • Primary Prevention Strategy:

    • Hypophosphatemia is not usually linked to dietary phosphorus deficiency since affected cows often receive sufficient dietary phosphorus (0.4% typically).

    • Primary prevention involves avoiding hypocalcemia to reduce potential for hypophosphatemia development.

Magnesium's Role in Metabolic Function

  • Body Distribution:

    • 70% of total body magnesium is in the skeleton; a small amount is released upon calcium release.

    • 30% is found intracellularly.

  • Functions:

    • Acts as a cofactor for various enzymes (including kinases and ATP), critical for the release of parathyroid hormone (PTH).

    • Magnesium plays a regulatory role in calcium homeostasis, influencing neuromuscular function.

Effect of Magnesium on Neuromuscular Function

  • Magnesium as a Cofactor:

    • Mg2+ is required for acetylcholinesterase (AchE) activity.

    • It competes with Ca2+ to inhibit the release of Ach into the neuromuscular junction (NMJ).

  • Effects of Imbalanced Magnesium Levels:

    • Low Mg2+ levels lead to increased Ach accumulation at NMJ, resulting in hyperexcitability and potential tetany.

    • Conversely, high Mg2+ can lead to Ach blockade, resulting in paresis.

Hypomagnesemia and Grass Tetany

  • At Risk Cows:

    • Cattle on fertilized, lush pastures, especially young grasses that are low in Sodium (Na) and Magnesium (Mg) but high in Potassium (K) and Nitrogen (N).

    • Dairy cattle in their first 2 months of lactation, and young growing calves on a milk diet.

    • Stress-induced cases (transport tetany) affecting cattle/sheep.

Clinical Signs of Hypomagnesemia

  • Early Signs:

    • Muscle fasciculations, aggressive behavior, bellowing, staggering, and a nervous attitude.

  • Later Signs:

    • Heart sounds audible without a stethoscope, significant recumbency, repetitive muscle contractions, and convulsions/seizures.

Diagnosis of Hypomagnesemia

  • Approach:

    • Evaluating signalment and clinical signs, performing dietary assessments, blood chemistry panels indicating decreased Mg levels.

    • Diagnosis can be complicated due to variability in magnesium intake, and outputs post-milking.

    • Post-mortem Assessments:

    • Cerebrospinal Fluid (CSF) testing is reliable up to 12 hours post-mortem. Vitreous humor is viable for 24-48 hours.

Treatment of Hypomagnesemia

  • Acute Treatment Options:

    • Administer 200-300 mL of 20% IV magnesium sulfate (MgSO4); this gives 8g -12g of Mg.

    • Alternatively, use 200 mL of 50% MgSO4 subcutaneously (SC).

    • If concurrent hypocalcemia is present, a Ca/Mg combination is most effective: 500 mL of 23% calcium borogluconate solution is recommended.

  • CSF Levels:

    • It takes approximately an hour for CSF levels to normalize; during this time, avoid stimulating the cow to rise for at least 30 minutes and refrain from oral treatment before recovery.

Prevention and Treatment of Hypomagnesemia

  • Relapse Management:

    • Oral supplementation within 12 hours is crucial; must verify swallowing reflexes.

    • Supplementation Options:

    • Mg salts can be administered, with 50g Mg and Mg oxide (100 g) being effective. Better absorption occurs with Mg sulfate (200-400 mL of a 50% solution).

    • Preventative Strategies:

    • Effective pasture management and supplementation protocols to maintain adequate magnesium levels.

Potassium: Internal and External Balance

  • Body Distribution:

    • Intracellular potassium normal levels around 150 mmol/L and extracellular around 5 mmol/L.

  • Sources of Potassium:

    • Primarily obtained through diet.

    • Elimination occurs mainly via renal excretion, with minor losses through saliva, gastrointestinal (GI) fluid, and milk.

Hypokalemia: Clinical Signs

  • Symptoms:

    • Absent feces, decreased rumen motility, paretic gait (weakness), kyphosis (abnormal curvature of the spine), tachycardia (increased heart rate), arrhythmias, recumbency, S-shaped neck posture.

Diagnosis of Hypokalemia

  • Clinical Pathology:

    • Potassium levels below <2.5 mEq/L indicate severe deficiency.

    • Muscle enzymes (creatine kinase (CK), aspartate aminotransferase (AST)) can be elevated, necessitating checks for other electrolyte imbalances.

Treatment of Hypokalemia

  • Supplementation Options:

    • Potassium supplementation typically involves intravenous (IV) and oral methods. IV is effective only for severely hypokalemic cattle that are recumbent with rumen atony.

    • Maximum administration rate for IV potassium is 0.5 mEq/kg/hr.

  • Oral Supplementation:

    • Administer KCl salts via orogastric intubation at dosages of 125-240g up to twice daily for adult cattle, ensuring that the daily maximum does not exceed 240 g to avoid adverse effects such as diarrhea, excessive salivation, muscular tremors, and excitability.

5 Ms of Down Cows

  • Mastitis ✓

  • Metritis

  • Metabolic Disorders

    • Hypocalcemia, Mg, K, P, hypoglycemia.

  • Musculoskeletal/neurological disorders ✔

  • Massive Sepsis.

  • Peritonitis, pneumonia…

Clinical Approach

  • Different management strategies for beef vs. dairy cows, both prepartum and postpartum.

  • Factors including days in milk (DIM) and physical examination should be considered.

Vicious Cycle

  • Transition Period:

    • Lastting 8 weeks prior to calving begins 3 weeks before calving.

    • Key periods: Fresh cow, lactation preparation, dry-off periods.

    • After calving, transition to fresh cow management before necessary to ensure healthy lactation.

  • Monitoring Factors:

    • Blood parameters management and overall cow-side management; ensuring proper mineral and vitamin supply is vital.

  • Risks of Neglecting Management:

    • Reduced dry matter intake (DMI), negative energy balance (NEB), lipid mobilization leading to fatty liver issues.

DAMNIT-VP Framework

  • A diagnostic mnemonic used in veterinary medicine for identifying potential causes of down cows:

    • D: Degenerative

    • A: Anomalous

    • M: Metabolic

    • N: Neoplasia

    • I: Infectious, Inflammatory, Immune, Iatrogenic

    • T: Traumatic, Toxin

    • V: Vascular

    • P: Parasitic

Prognosis and Treatment Plans for Downer Cows

  • Determining prognosis is essential for outlining treatment plans based on cost, time, and expected return to productivity.

  • Prompt treatment with appropriate veterinary drugs and care is critical. Identify the cause of recumbency to decide treatment efficacy.

  • Nursing should be reserved for cows with a reasonable chance of recovery; otherwise, euthanasia may be necessary for those with poor prognoses.

Conclusion

  • Veterinary students, practitioners, and farmers must remain vigilant during the transition period of dairy cows to avoid metabolic diseases that can lead to severe outcomes in animal welfare and productivity.