Effects of a low calcium diet on feed intake, milk production, and response to blood calcium challenge in lactating Holstein cows.

Twenty-four lactating cows were fed a normal-calcium (.75% of dry matter) diet plus free-choice dicalcium phosphate supplement for 8 wk, a low-calcium (.25% of dry matter) diet for 9 wk, and a low-calcium (.25% of dry matter) diet plus free-choice supplement for 4 wk. The low-calcium diet did not appear to affect adversely feed intake, milk production, or plasma ions. Depression of plasma calcium by sequestration with a chelating agent was less following low intake of calcium than following adequate calcium intake. Presumably, lower calcium intake increased parathyroid hormone which resulted in a larger and more responsive calcium pool immediately mobilizable. Changes in plasma phosphorus and magnesium were similar among treatments. Low calcium intake for short times apparently will not affect intake or production and may increase resistance to calcium stress such as hypocalcemia and parturient paresis.