Methane production and diet digestibility by growing cattle fed high or low quality forage

Abstract Text:

Six non-cannulated crossbred steers (initial BW = 369 ± 17) were used in a three period switchback design growing study to evaluate the effects of forage quality on methane production and total tract digestibility.  Treatments consisted of either a high quality forage (HQ; 60:40 blend of alfalfa hay and sorghum silage plus 20% modified distillers grains) or low quality forage diet (LQ; ground cornstalks plus 20% modified distillers grains).  Twenty-one d periods consisted of 11 d adaptation and 4 d total fecal collection using fecal bags, followed by headbox methane (CH₄) and carbon dioxide (CO₂) data collection for two consecutive 23-h periods on d 20 and 21.  Steers were also esophageally tubed for analysis of VFA concentration and microbial community structure on d 20 prior to feeding.  Methane and CO₂ were determined using gas chromatography. Data were analyzed using a mixed model with period and treatment as fixed effects and steer as the random variable. Intake of DM was dramatically greater for HQ (9.8 kg/d) compared to LQ (6.6 kg/d). Based on feed refusal analysis, ration sorting occurred when steers were fed LQ forage.  Intake of OM, and ADF was greater (P < 0.01) and intake of NDF tended to be greater (P = 0.06) for cattle consuming HQ forage. Digestibility of DM was also greater for steers on HQ forage (P = 0.05).  Steers consuming LQ forage produced 132 L CH₄ and 1654 L CO₂ compared to 210 L CH₄ and 2404 L CO₂ produced by those consuming HQ forage. This resulted in production of 63 and 69% the daily volumes (L/d) of CH­₄ and CO₂ respectively, of those cattle consuming HQ diets (P < 0.01).  Steers fed LQ diets also had a lower CH₄:CO₂ (P = 0.03) compared to those consuming HQ forage; 0.082 and 0.090, respectively.  When methane emissions are expressed as a function of nutrients digested, production of CH₄ in L/kg of OM digested was not impacted by diet (P = 0.14), which may be related to dramatic intake differences in this study. 

Keywords: digestibility, forage quality, methane