EFFECTS OF DIETARY CALCIUM, CORN PARTICLE SIZE, FORAGE SOURCE AND CATTLE TYPE ON SITE AND EXTENT OF DIGESTION IN STEERS

Abstract

Effects of dietary Ca on site and extent of digestion were evaluated using four Holstein (dairy) and four Angus × Hereford (beef) steers fitted with T-type cannulas at both the proximal duodenum and distal ileum of the small intestine. In trial 1, steers were fed diets based on corn (85% of diet dry matter (DM) and corn silage (15% of diet DM) at 2.1% of body weight. Treatments were dairy or beef type cattle, cracked (2.4 mm) or whole (6.0 mm) corn grain and 0.31 or 0.62% of diet DM as Ca from CaCO3 in a 2 × 2 × 2 factorial design. Cattle type and dietary Ca did not affect (P > 0.05) site or extent of organic matter (OM) or starch digestion. Steers fed cracked corn digested more (P < 0.05) OM and starch in the rumen than steers fed whole corn. Fecal pH was higher (P < 0.05) in steers fed high Ca diets. In trial 2, steers were fed diets based on ground corn (80% of diet DM) and chopped hay (20% of diet DM) at 1.8% of body weight. Treatments were dairy or beef type, alfalfa or smooth bromegrass hay and 0.34 or 0.61% of diet DM as Ca from CaCO3 in a 2 × 2 × 2 factorial design. Cattle type and dietary Ca levels did not affect (P > 0.05) site or extent of OM or starch digestion. Steers fed alfalfa digested more (P < 0.05) dietary starch in the rumen than those fed smooth bromegrass. Digesta collected from the distal ileum of steers fed alfalfa had a higher pH than that from steers fed smooth bromegrass. The higher dietary Ca resulted in higher (P < 0.05) fecal pH. Key words: Calcium, particle size, starch, forage source, cattle