Effect of Level of Calcium and Rate of Reactivity of Calcitic Limestones on Utilization of High Concentrate Diets by Beef Steers

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Abstract
Feeding and digestion trials were conducted to evaluate the influence of level of Ca and(or) rate of reactivity of calcitic limestones on feedlot performance, nutrient utilization, carcass merit and gastrointestinal tract characteristics of finishing beef steers fed complete mixed diets consisting of 25% corn silage and 75% concentrate (dry matter basis). Limestones A, B and C were obtained from the same quarry and were classified by particle size (percentage passing through a 53-/μm sieve) and rate of reactivity (T50, seconds) as: (A) 4, 4110, (B) 32, 1230 and (C) 86, 60. Complete diets were formulated to contain, on a dry matter basis, 12.0% crude protein, .35% P and .35, .70 or 1.05% Ca. Average daily gains (kilograms) and average daily dry matter intakes (kilograms) for steers fed each limestone type and level of Ca during the 168-day feeding trial were; respectively: (A) .77, 7.4; .92, 7.7; 1.10, 7.8; (B) .85, 7.8; 1.08, 8.3; 1.29, 8.5, and (C) 1.10, 8.5; 1.31, 9.1; 1.24, 8.5. At each rate of reactivity of limestone, steers fed diets containing .35% Ca had the lowest average daily gains and poorest feed efficiencies. For steers fed diets containing limestone A or B, a level of 1.05% Ca in the diet increased average daily gains and improved feed efficiencies over those of steers fed diets containing .70% Ca. Improvements in digestibilities of dry matter, organic matter, cell walls and starch were observed at ad libitum intakes due to level of Ca and rate of reactivity of limestone. Furthermore, Ca balance data indicated that cattle may not effectively eliminate excess Ca from the body at Ca intakes above 67 mg/kg body weight. Results from these feeding and digestion trials indicate that the response of finishing beef steers to calcitic limestones varies, depending on both level of Ca and rate of reactivity. Moreover, rate of reactivity of limestone is influenced in part by particle size. Copyright © 1981. American Society of Animal Science . Copyright 1981 by American Society of Animal Science.