What does a calcium deficient diet primarily affect in dairy cows?

A calcium deficient diet primarily affects the function of the parathyroid gland in dairy cows. This gland plays a crucial role in regulating calcium levels in the bloodstream. When the diet lacks sufficient calcium, the parathyroid glands become more active in an attempt to maintain adequate calcium levels, releasing parathyroid hormone (PTH). This hormone stimulates the release of calcium from bone and increases calcium absorption from the intestines, as well as influencing kidney function to retain calcium.

When calcium is insufficient, the cows can experience conditions such as milk fever, where the demand for calcium, particularly during lactation, exceeds the dietary supply. This condition results not only in acute health issues but also in long-term metabolic challenges, further compromising parathyroid function if deficiencies are consistent.

While bone density, milk production, and fertility rates can also be impacted by calcium deficiency, the most direct and immediate physiological effect is on the parathyroid gland's function, striving to rectify calcium balance in the body.