Hypomagnesaemia in beef cows wintered in Ontario

Area of Science:

• Animal Science
• Nutritional Physiology
• Veterinary Medicine

Background:

• Assessing magnesium status is crucial for beef cattle health.
• Hypomagnesaemia (low magnesium) can impact livestock productivity.
• Understanding regional deficiencies is key for effective supplementation.

Purpose of the Study:

• To evaluate the magnesium status of beef cattle in Northern Ontario.
• To investigate the impact of different magnesium supplementation strategies.
• To identify factors influencing magnesium levels in beef cows.

Main Methods:

• Field experiment with pregnant Shorthorn beef cows.
• Three dietary magnesium treatments: no magnesium, magnesium oxide, sequestered magnesium.
• Monitoring blood and urine magnesium levels, and bone biopsies.
• Comparing indoor housing versus pasture access.

Main Results:

• No significant differences in serum magnesium due to supplementation treatments.
• All groups showed drastic drops in serum magnesium before pasture release, linked to yarding stress.
• Slower recovery from hypomagnesaemia in pasture-grazing cows.
• Lower bone magnesium levels in pasture-grazing animals compared to housed animals.

Conclusions:

• Magnesium supplementation strategy did not alter serum magnesium levels in this study.
• Yarding stress appears to be a primary trigger for hypomagnesaemia.
• Pasture access may exacerbate low magnesium status, indicated by urine and bone levels.
• Clinical signs of hypomagnesaemia were absent despite biochemical evidence.