Methane emission, nutrient digestibility, and rumen microbiota in Holstein heifers fed 14 different grass or clover silages as the sole feed

This experiment investigated the variation in enteric methane production and associated gas exchange parameters, nutrient digestibility, rumen fermentation, and rumen microbiome when a range of silages based on different forage types (grass or clover), and different species within the 2 types, were fed as the sole feed to heifers. Three grass species (perennial ryegrass, festulolium, and tall fescue) and 2 clover species (red clover and white clover) were included. Perennial ryegrass was harvested at 2 maturity stages in the primary growth, white clover was harvested once in the primary growth, and 4 cuts of festulolium and tall fescue and 3 cuts of red clover were harvested during the growing season, giving 14 different silage batches in total. Sixteen Holstein heifers 16 to 21 mo old and 2 to 5 mo in pregnancy were fed the silages ad libitum as the sole feed in an incomplete crossover design. Each silage was fed to 4 heifers, except for the 2 perennial ryegrass silages, which were fed to 8 heifers; in total 64 observations. The CH₄ production was measured for 3 d in respiration chambers. Heifers fed clover silages had higher dry matter intake (DMI) compared with heifers fed grass silages, and heifers fed tall fescue silages had the numerically the lowest DMI. Compared with grass silages, feeding clover silages led to higher crude protein digestibility but lower neutral detergent fiber (NDF) digestibility. Rumen pH was higher in heifers fed clover silages compared with those fed grass silages. Based on composition analysis, the rumen microbiota of the heifers clustered clearly according to forage type and species. More specifically, 7 of the 34 dominating rumen bacterial genus-level groups showed higher relative abundances for the clover silages, whereas 7 genus-level groups showed higher abundances for the grass silages. Methane yield was higher for heifers fed grass silages than for those fed clover silages when methane production was related to dry matter and digestible organic matter intake, whereas the opposite was seen when related to NDF digestion. The gross energy lost as methane (CH₄ conversion factor, %) reduced from 7.5% to 6.7%, equivalent to an 11% reduction. The present study gives the outlines for choosing the optimal forage type and forage species with respect to nutrient digestibility and enteric methane emission in ruminants.

Effect of dried oregano (Origanum vulgare L.) plant material in feed on methane production, rumen fermentation, nutrient digestibility, and milk fatty acid composition in dairy cows

Essential oils (EO) from oregano may have antimicrobial properties, potentially representing a methane mitigation strategy suitable for organic production. This study aimed to (1) examine the potential of oregano in lowering enteric methane production of dairy cows fed differing levels of dried oregano (Origanum vulgare ssp. hirtum) plant material containing high levels of EO; (2) determine whether differing levels of dried oregano plant material of another subspecies (Origanum vulgare ssp. vulgare) with naturally low levels of EO in feed affected enteric methane production; and (3) evaluate the effect of various levels of the 2 oregano subspecies (containing high or low levels of EO) in feed on rumen fermentation, nutrient digestibility, and milk fatty acids. Each experiment had a 4 × 4 Latin square design using 4 lactating Danish Holstein dairy cows that had rumen, duodenal, and ileal cannulas and were fed 4 different levels of oregano. Experiment 1 used low EO oregano [0.12% EO of oregano dry matter (DM)] and evaluated a control (C) diet with no oregano and 3 oregano diets with 18 (low; L), 36 (medium; M), and 53 g of oregano DM/kg of dietary DM (high; H). Experiment 2 used high EO oregano (4.21% EO of oregano DM) with 0, 7, 14, and 21 g of oregano DM/kg of dietary DM for C, L, M, and H, respectively. Oregano was added to the diets by substituting grass/clover silage on a DM basis. Low or high EO oregano in feed did not affect dry matter intake (DMI) or methane production (grams per day, grams per kilogram of DMI, grams per kilogram of energy-corrected milk, and percentage of gross energy intake). Rumen fermentation was slightly affected by diet in experiment 1, but was not affected by diet in experiment 2. In both experiments, the apparent total-tract digestibility of DM, organic matter, and neutral detergent fiber decreased linearly and cubically (a cubic response was not observed for neutral detergent fiber) with increasing dietary oregano content, while milk fatty acids were slightly affected. In conclusion, dried oregano plant material with either high or low levels of EO did not lower the methane production of dairy cows over 4 consecutive days, and no substantial effects were observed on rumen fermentation or nutrient digestibility. This conclusion regarding methane production is in contrast with literature and requires further study.