Which component is essential to check if a beef heifer shows signs of downness close to parturition?

When assessing a beef heifer that shows signs of downness close to parturition, checking calcium and phosphorus levels is particularly essential. This is due to the significant metabolic demands placed on the heifer as she approaches calving. During this period, her body requires increased calcium for muscle function and milk production. A deficiency in calcium can lead to hypocalcemia, often referred to as milk fever, which can cause weakness and immobility, manifesting as downness.

Phosphorus is also crucial as it plays an important role in energy metabolism and muscle function. Both minerals' imbalances can lead to severe health issues in the heifer and impact the overall outcome of the calving process.

In contrast, while blood glucose levels, hormonal levels, and magnesium levels can influence a heifer’s health, they are not as directly correlated with the specific signs of downness due to the imminent calving process. Nutritional deficiencies related specifically to calcium and phosphorus are more commonly associated with the observed clinical signs in recreational scenarios typical of beef cattle during late gestation.