Rapeseed cake: A dietary strategy to reduce methane emissions in dairy cattle

Although CH4 is a more potent greenhouse gas than CO2, it has a shorter half-life than CO2, which makes it an attractive target to instate faster global warming mitigation efforts.

Current approaches to sustainable ruminant production seek to optimize animal feeding as well as establishing efficient management practices. Various nutritional and management strategies have been reported to be effective in mitigating greenhouse gas emissions associated with ruminant production (Knapp et al., 2014; Beauchemin et al., 2020). Amongst which lipid supplementation is one of the most promising tools used to reduce CH4 production (Beauchemin et al., 2009; Bayat et al., 2018). while increasing feed efficiency (NRC, 2001) and the proportion of nutritionally desirable milk fatty acids (FA; Kliem and Shingfield, 2016; Kliem et al., 2019).

Increasing attention has been given to the potential of chemical additives, such as3-nitrooxypropanol and nitrate, or plant extracts. However, many of these strategies are not feasible solutions in practice, due to availability, transient effects, or high implementation costs.

The replacement of rapeseed meal with rapeseed cake has been shown to reduce CH4 emissions, improves milk FA composition, and also may increase milk yield by providing additional oil to the diet. For such purpose researchers set a group of researchers set out to evaluate the potential benefits of fully replacing rapeseed meal with high-oil rapeseed cake. Assessing its effects on:  nutrient utilisation, enteric methane emissions, and milk production in dairy cattle.They hypothesized that the inclusion of high-oil rapeseed cake and that of dietary natural additives could reduce enteric methane emissions without impacting animal performance and nutrient utilization.

Materials and Methods

The experiment was conducted under regional State Administrative Agency approval (Hämeenlinnan, Finland; ESAVI/34265/2019).

The study was carried out with 8 multiparous Nordic Red dairy cows were randomly assigned to treatment sequences in a replicated 4 × 4 Latin square design.

Dietary treatments were formulated on yield at a 45:55 ratio of grass silage to concentrate. The composition of such treatments was:

1.  Control, containing 19.3% rapeseed meal on DM basis (CON).
2.  CON with full replacement of rapeseed meal with rapeseed cake (RSC; 19.3% DM).
3. CON supplemented with 20 g/d of yeast hydrolysate product plus 30 g/d of resin acid-based compound.
4. CON supplemented with 20 g/d of a combination of garlic-citrus extract and essential oils.

Results

• Results revealed that regardless although rapeseed meal and rapeseed cake diets had similar fermentation patterns, total rapeseed meal replacement with rapeseed cake was able to reduce CH₄ emissions (g/d) by 7%.  Rapeseed cake diet helped to reduce CH₄ emissions expressed per unit of feed intake (as dry matter intake, DMI). CO2 emissions were also reduced per unit of milk with the inclusion of rapeseed cake in comparison to rapeseed meal.
• The replacement of rapeseed meal for rapeseed cake did not have significant impacts on gross energy (GE) intake. Nonetheless, ME intake was greater for rapeseed cake compared to rapeseed meal.Gross energy, protein, and fat digestibility improved with the dietary replacement. Energy balance and N-balance values as well as feed efficiency (Milk/DMI and ECM/DMI) were higher in the rapeseed cake diet.
• Replacing rapeseed meal with rapeseed cake resulted in greater yields of milk and energy-corrected milk, and feed efficiency. Relative to the meal diet, the cake decreased saturated fatty acids (FA) by 10% in milk fat by increasing cis-monounsaturated FA but also increased the proportion of trans FA.
• In the present study, conducted with dairy cows in mid-lactation, the researchers suggested that the greater GE concentration (+0.4 MJ/kg DM) in rapeseed cake may have induced the improved milk yield without changing DMI. In addition, the increased milk yield with rapeseed cake was also attributed to increased milk lactose, as lactose is the main factor determining milk volume.
• Relative to rapeseed meal, the rapeseed cake diet reduced short chain fatty acids (SFA) by 10% in milk fat by replacing them with cis MUFA, especially cis-9 18:1. It not only reduced SFAs but also changed the composition of milk SFAs by reducing 12:0, 14:0, and 16:0, while  increasing 18:0. This implies a health benefit for consumers, as dairy products make up a great part of the fat and SFA contents found in human diets. The reduction in short chain fatty acid concentrations was attributed to an increase in the amount of long-chain unsaturated FA available for absorption. Which suppressed in novo synthesis of short- and medium-chain FA within the mammary gland.

Conclusions

• From the obtained results, researchers concluded that the replacement of rapeseed meal with rapeseed cake reduced methane production per kilogram of DMI while improving milk production and feed efficiency of lactating dairy cows.
• Therefore, researchers suggest that the dietary inclusion of rapeseed cake represents a viable alternative for reducing enteric methane emissions without negatively impacting milk yield and its composition.

Source: Abstract taken and modified from “Evaluating the effects of high-oil rapeseed cake or natural additives
on methane emissions and performance of dairy cows.”