EFFECTS OF A LOW CALCIUM DIET ON FEED-INTAKE, MILK-PRODUCTION, AND RESPONSE TO BLOOD CALCIUM CHALLENGE IN LACTATING HOLSTEIN COWS

Lactating cows (24) were fed a normal Ca (.75% of dry matter) diet plus free-choice dicalcium phosphate supplement for 8 wk, a low-Ca (.25% of dry matter) diet for 9 wk and a low-Ca (.25% of dry matter) diet plus free-choice supplement for 4 wk. he low-Ca diet did not appear to affect adversely feed intake, milk production, or plasma ions. Depression of plasma Ca by sequestration with a chelating agent was less following low intake of Ca than following adequate Ca intake. Presumably, lower Ca intake increased parathyroid hormone which resulted in a larger and more responsive Ca pool immediately mobilizable. Changes in plasma P and Mg were similar among treatments. Low Ca intake for short times apparently will not affect intake or production and may increase resistance to Ca stress such as hypocalcemia and parturient paresis.