Influence of dry-rolled corn processing and distillers grain inclusion rate on rumen pH, VFA and NH3 concentration and in vitro methane production

Abstract Text:

Increased DDGS inclusion and decreased corn particle size have been shown to lower ruminal pH and reduce methanogenic bacteria and hydrogen production.  Objectives were to determine the effects of dry-rolled corn processing and DDGS inclusion rate on ruminal pH, VFA and NH₃ concentration, and in vitro methane production.  Eight ruminally cannulated Holstein steers (526 ± 3.6 kg) were assigned to treatments in a 2 × 2 factorial arrangement with factors including 1) Particle size (coarse-rolled corn (2.5 mm) or fine-rolled corn (1.7mm)) and; 2) DDGS inclusion level (20 or 40%).  Diets were formulated to meet or exceed NRC recommendations and were offered ad libitum.  The experiment was designed as a 4 × 4 Latin square with 7 d of diet adaptation and 7 d of sample collection.  Ruminal pH was measured using wireless pH sensors (Kahne Ltd.) with measurements taken every 5 min from d 3 to 5 of the collection period.  To determine VFA and NH₃ concentration, approximately 200 mL of ruminal fluid were sampled from d 3 to 5 in a manner to represent every other hour in a 24-h cycle. Gas production was examined on d 1 and 7 of the collection period using 4 replicates per treatment.  Approximately 0.375 g of each of the 4 dietary substrates was added to 250-mL flasks with 175 mL of McDougall’s buffer and 37.5 mL of ruminal fluid. The flasks were flushed with CO₂, fitted with pressure monitor caps and placed in an oscillating waterbath at 39°C for 24 h.  A gas pressure monitoring system (ANKOM) was used to measure the changes in pressure relative to atmospheric pressure as a consequence of gas produced during fermentation.  Data were analyzed using the Mixed procedure of SAS (SAS Inst. Inc., Cary, NC) with statistical significance declared at P ≤ 0.05.  Ruminal pH was not affected (P ≥ 0.07) by treatment while NH₃ concentration was greater (P = 0.02) in steers fed 20% DDGS.  Steers fed fine-rolled corn had greater (P = 0.02) concentrations of butryric acid.  Total gas production and methane concentration were not influenced (P ≥ 0.08) by particle size or DDGS inclusion level.  Urea was supplemented in diets containing 20% DDGS to meet DIP requirements which likely accounted for the increase in NH₃.  Despite a rise in ruminal butyric acid, acetate and propionate were not affected (P ≥ 0.20) possibly reducing the likelihood of hydrogen capture and subsequent methane mitigation.  

Keywords: bovine, corn, distillers, rumen