Can high-lipid concentrates offset the high enteric methane production caused by high-forage diets fed to lactating dairy cows?

It is well-known that feeding supplementary concentrates can boost milk production and lower CH4 (methane) intensity of dairy production. Also, dietary fats and oils are known for their potential to reduce enteric CH4 production while modifying the rumen microbiome. A further potential benefit is that the inclusion of plant oils or oilseeds can enhance feed efficiency and enrich the nutritional value of milk fatty acids. However, the feasibility thereof will depend on the relative costs associated with forage and concentrates, as well as profitability in terms of product prices. Therefore, the study cited from Finland aimed to find practical solutions for reducing enteric CH4 production in a high-forage diet through natural feed ingredients. The authors hypothesized that high-ether extract concentrates could offset increased CH4 production from high-forage diets in lactating dairy cows. Consequently, their objective in the study was to evaluate the effects of lipid inclusion to high-forage diets on enteric CH4 production, animal performance, ruminal fermentation, nutrient utilization, and ruminal and faecal microbial populations.

Four multiparous Nordic Red dairy cows at about 60 days in lactation were randomly assigned to a 4 × 4 Latin square design in a 2 × 2 factorial arrangement of dietary treatments. There were four 21-day experimental periods, each consisting of a 16-days adaptation and a 5-day sampling period in metabolic chambers. The diets comprised TMR based on grass silage with a forage-to-concentrate (FC) ratio of 70:30 (high-forage; HF) or 50:50 (low-forage; LF) mixed with either a low ether extract (lipid) concentrate (LEE) containing rapeseed meal and barley or a high-ether extract concentrate (HEE) containing rapeseed cake and oats. Ether extract concentrations were respectively 3.6, 4.8, 3.2, and 5.3% of DM for the treatments HF-LEE, HF-HEE, LF-LEE, and LF-HEE, respectively.

Dry matter intake (DMI) was 3.2 kg/day lower in cows fed HF compared with LF diets, with no effect of concentrate type. Digestibility of NDF and OM was significantly lower in the LF-HEE diet compared with the other diets. Additionally, HF diets reduced milk yield, which further declined with HEE supplementation. The LF and HF diets had similar daily CH4 production (g/day), and CH4 yield (g/kg of DMI) was greater for HF compared with LF diets. Ether extract supplementation was more effective in reducing CH4 yield in the HF than the LF diet (7.1 vs. 4.2 g CH4/kg of DMI per each kilogram added ether extract). Methane intensity was the lowest in the LF-HEE diet; however, the HF-HEE diet reduced CH4 intensity (g/kg of Energy Corrected Milk) by 5.5% compared with HF-LEE, matching that observed with the LF-LEE diet. Significant changes in rumen bacterial, archaeal, and fungal abundances were induced by the dietary forage-to-concentrate ratio, and rumen protozoa and faecal fungi abundances were affected more by concentrate type.

In summary: By adding lipid through natural feed ingredients, CH4 production in both low- and high forage diets was effectively reduced. However, when presented per kg of added lipid, the effect on reducing CH4 yield was greater in high forage versus low forage diets (7.1 vs. 4.2 g CH4/kg of DMI per each kg added lipid), resulting in similar CH4 yield and intensity between low forage, low-lipid and high forage, high- lipid diets. High-lipid concentrates enhanced milk production in the low forage diet but decreased it in the high forage diet, potentially due to lower starch intake. Rumen bacterial, archaeal, and fungal communities were more affected by dietary forage-to-concentrate ratio, and rumen protozoa and faecal fungi were more affected by concentrate type.