Feedlot performance, blood metabolic profile and calcium status of steers fed high concentrate diets containing several levels of calcium.

Two feeding trials with Hereford X Angus steers were conducted to evaluate effects of dietary Ca level in high concentrate diets on feedlot performance, carcass traits, blood metabolic profile and Ca status. Dietary treatments of .3, .6, .9 and 1.2% Ca (10 steers treatment-1 X trial-1) were fed for 90 (Trial 1) and 114 d (Trial 2). Ground limestone was the source of supplemental Ca. Blood samples were collected weekly throughout Trial 1 and for the first 7 wk of Trial 2. In both trials .3% Ca resulted in lighter weight (P less than .10) carcasses and lower (P less than .05) blood pH and HCO-3 than the rest of the Ca levels during the first 7 wk of feeding the high concentrate diets. Average daily gain increased linearly (P less than .10) in response to increased dietary Ca level in Trial 1, but not in Trial 2. There were no significant differences among treatments in feed intake, carcass quality traits, bone ash, bone Ca, or overall characteristics in the blood metabolic profile including total serum or plasma Ca and plasma ionizable Ca. Increasing dietary Ca to .6% or more resulted in improved blood acid-base status during the initial weeks of feeding high concentrate diets, which is associated with heavier carcasses and a trend towards more rapid weight gain. I interpret these data to suggest that the Ca requirement for steers fed high concentrate diets is greater than .3%, but no greater than .6% for maximal feedlot performance.