Abstract
This study examined the effects of altering ruminal fermentable carbohydrate (RFC) supply by feeding different amounts of corn and wheat in finishing cattle diets containing 15% corn dried distillers grains [DDGS; dry matter (DM) basis] on ruminal fermentation characteristics and nitrogen (N) utilization. Six ruminally-cannulated crossbred heifers were used in a replicated 3 × 3 Latin square design with 28 d periods. Dietary treatments were either corn (73% of diet DM; CON), 53:20 corn:wheat blend (20W) or 33:40 corn:wheat blend (40W) as the major fermentable carbohydrate source. Diets were isonitrogenous (12% CP; DM basis). Feed intake was measured daily. Indwelling pH logger were used to measure ruminal pH (d 22 to 28) and ruminal fluid was collected from d 26 to 28 to determine fermentation characteristics, as were feces and urine to measure N excretion. Data was analyzed using PROC MIXED in SAS. Dry matter and N intake tended to be lower (P ≤ 0.07) for heifers fed the 40W compared to the CON and 20W diets. There was no diet effect (P = 0.15) on total VFA concentration; however, the duration and area for pH < 5.5 tended to be longer (P = 0.07) and greater (P = 0.096), respectively, for heifers fed the 20W and 40W compared to the CON diet. There was no diet effect (P ≥ 0.44) on ruminal ammonia concentration and total urine N excretion (g and % of N intake). However, urine urea N (UUN) excretion as a percentage of total urine N tended to be lower (P = 0.05) in heifers fed the 20W and 40W compared to the CON diet. In summary, although altering RFC supply by feeding increasing amounts of wheat resulted in a decrease in UUN excretion, it also caused a decrease in ruminal pH that possibly compromised DM intake.
Effect of feeding condensed tannins in high protein finishing diets containing corn distillers grains on ruminal fermentation, nutrient digestibility, and route of nitrogen excretion in beef cattle1
