Grass Tetany (Hypomagnesemia) in Dairy Cows Flashcards
What role does magnesium (Mg) play in cows?
t is essential for enzymatic reactions and synaptic transmission in the central nervous system.
How is magnesium distributed in the cow’s body?
60-70% in the skeleton, 30% intracellular, and 1% extracellular (of which 50-70% is ionized).
What are the Mg requirements for adult cows and lactating cows?
0.3 g per 100 kg body weight for adults, with increased needs of 0.45 g/kg during lactation.
Where does magnesium absorption primarily occur in cows?
In the rumen and reticulum through passive and Na-mediated active transport.
How does the kidney regulate magnesium in dairy cows?
By excreting excess Mg through urine if levels exceed 0.75-0.9 mmol/L in serum.
What is the primary condition referred to as “Grass Tetany”?
A hypomagnesemia condition affecting older, lactating cows grazing on lush, fertilized spring pastures.
Which factors contribute to the occurrence of grass tetany?
Older age, lush nitrogen- and potassium-rich pastures, and spring season with rapid plant growth.
How do soil magnesium levels influence the risk of grass tetany?
Mg levels below 20 mg/kg in soil solution increase the risk, especially with high potassium fertilization.
How does nitrogen fertilization impact magnesium availability in plants?
It increases protein and fatty acids but reduces soluble carbohydrates, lowering Mg absorption in ruminants.
What effect does soil pH have on magnesium availability in dairy pastures?
Raising soil pH above 5.5 through liming reduces Mg antagonism and supports clover growth, increasing Mg content.
What are the optimal conditions for magnesium absorption in the rumen?
pH below 6.5; high pH due to potassium-rich forage reduces Mg solubility and absorption.
Why does high dietary potassium (K) increase the risk of grass tetany?
t disrupts Mg transport by altering cell membrane potential, decreasing Mg absorption.
How can the risk of grass tetany be assessed?
Through serum Mg analysis, pasture analysis (for CP, K, Ca, Mg levels), and calculating the K and CP to Mg ratio.
What fertilization practices help prevent grass tetany?
Applying Mg fertilizers when Mg falls below 5 mg/100 g in soil and limiting K and N applications before tetany season.
How can magnesium be supplemented directly to prevent grass tetany in cows?
By administering MgO or MgCO₃, with doses of 20-30 g Mg for dairy cows during critical periods.
