The Effect of Increasing Inclusion Level of Different Rumen Buffers or Alkalizing Agents on in vitro Fermentation Outcomes When Added to a Low-roughage Diet for Finishing Beef Cattle.

Abstract

Reducing the beef industry’s contribution to methane (CH4) emissions represents an opportunity to mitigate environmental impacts while enhancing production efficiency. Buffers and alkalinizing compounds alter ruminal conditions, which influences hydrogen availability and may inhibit methanogenesis. Four independent completely randomized design experiments were conducted to evaluate the effects of increasing dietary inclusion of limestone, sodium bicarbonate (NaHCO3), potassium carbonate (K2CO3), or urea on in vitro fermentation outcomes when replacing steam-flaked corn in a low-roughage [8% of diet dry matter (DM)] finishing diet. Treatments included (DM basis) either 0, 1, or 2% NaHCO3, K2CO3, or urea while limestone inclusions were 0, 1.5, and 3%. Duplicated ground diet samples were weighed into fiber filter bags and randomly assigned to 1 of 36 incubation jars fitted with a gas collection bag (n = 12/treatment). Jars contained buffered rumen fluid and were incubated at 39 °C for 48 h. Gas samples were analyzed for CH4 concentration. Rumen fluid samples were analyzed for volatile fatty acid (VFA) and ammonia concentrations. Data were analyzed using a general linear model [jar = experimental unit; treatment = fixed effect; 0-h gas production (GP) and total sample weight = covariates]. Orthogonal contrasts were used to evaluate linear and quadratic treatment effects. Significance was declared at P ≤ 0.05 and tendencies declared when 0.05 < P ≤ 0.15. Gas production at 48 h was unaffected by limestone, NaHCO3, or urea (P ≥ 0.29), but increasing K2CO3 tended to affect 48-h GP (positive quadratic; P = 0.06). Limestone, NaHCO3, or urea did not affect CH4 measurements (P ≥ 0.17). Increasing K2CO3 affected %CH4 and CH4 yield (positive quadratic; P ≤ 0.01). Digestibility was unaffected by NaHCO3 (P ≥ 0.43) Increasing K2CO3 linearly decreased in vitro DM digestibility (IVDMD) and true DM digestibility (TDMD; P ≤ 0.01). Increasing urea affected IVDMD and TDMD (negative quadratic; P = 0.05). Limestone did not affect IVDMD (P = 1.00), but linearly increased TDMD (P < 0.01). Final pH linearly increased with increasing limestone, NaHCO3, K2CO3, or urea (P ≤ 0.02). Limestone, NaHCO3, or K2CO3 did not affect total or individual VFA concentrations (P ≥ 0.18). Increasing urea linearly increased butyrate (P = 0.02) and linearly decreased valerate (P < 0.01), but no other VFA concentrations (P ≥ 0.16). Ammonia concentration was linearly decreased by increasing NaHCO3 (P < 0.01), linearly increased by increasing urea (P < 0.01), affected by increasing limestone (positive quadratic; P = 0.02), and tended to be affected by increasing K2CO3 (positive quadratic; P = 0.10). Results indicate addition of buffers or alkalizing compounds to finishing beef cattle diets have little effect on in vitro CH4 production but may alter rumen fermentation outcomes related to live animal performance or rumen health.