PSLBII-8 - Evaluation of the in vitro ruminal methane production in heifers fed high-forage or high-concentrate diets during entire pregnancy

Abstract: Ruminal methane (CH₄) emission from cattle represents about 2-12% gross energy loss and is considered as one of the main contributors to the greenhouse gas emissions by the livestock industry. Recent multiple lines of research indicated that maternal gut microbiome may influence offspring ruminal CH₄ emission phenotype via potential influence on fetal programming and transmission of methanogens from the dam to calf perinatally. Our objective was to evaluate the effects of altering maternal microbiota via feeding high forage (HF) and high concentrate (HC) diets during the entire gestation on the maternal ruminal CH₄ emissions in beef heifers. For this, 61 Crossbred replacement beef heifers bred with male sexed semen were randomly assigned into two groups and were fed either a high forage (75% forage:25% concentrate; HF, n=29) or high concentrate (25% forage:75% concentrate; HC, n=32) diet with limited feed intake to gain 0.45 kg/day during the gestation. Individual feed intake was monitored, and body weights were measured bi-weekly and diet deliveries were adjusted to ensure the target gain. A subset of pregnant heifers (n = 10 per treatment group) was harvested at 180 d of gestation. Ruminal fluid was collected by stomach tubing on days (d) 180 (20 heifers slaughtered), d238 of gestation, and at the postpartum (within 3 h of calving). The ruminal fluid was placed in 15-ml falcon tube, kept in a warm thermos and immediate processing for the in vitro CH₄ production assay. About 12.5 ml of ruminal fluid was placed into separate 120-ml serum bottles each containing 0.62g of feed (HC or HF diet) and 50 ml of McDougall buffer under CO² infusion before the bottle sealed with stoppers. The cultures were incubated at 39 ^oC for 24h. Immediately after incubation, total biogas production, headspace CH₄ concentration (using Gas chromatography), and pH of the 24h culture was measured. Overall, the mean total volume of gas produced over 24h was not statistically different (P > 0.05) between HF and HC heifers at any of the days measured, although it was numerically greater on d238 (219 vs. 197 ml) and at postpartum (246 vs. 219 ml) in HC than HF heifers. Methane concentration in per ml gas was ranged between 13.3 and 16.3% but was not different between HF and HC heifers on any of the days evaluated (P > 0.05). Total volume of CH₄ gas produced over 24h was tended (P = 0.067) to be higher in HC heifers on d238 (37.5 vs. 25. 7 ml). The culture pH from the ruminal fluid of HC heifers was lower on d238 (6.08 vs. 6.57) and at postpartum (P < 0.05). Overall, in vitro ruminal CH₄ was not different in the ruminal fluid of HF and HC pregnant heifers.