South Africa Wine Technical Yearbook 2025

The trade-off – sustainability versus milk production The findings of this study highlight the trade-off between reducing methane emissions and maintaining milk production. While grape marc effectively cuts methane output, the lower energy content of this agricultural by-product leads to decreased milk yields, which may present a challenge for dairy farmers. From a sustainability standpoint, the use of grape marc aligns with efforts to reduce the dairy industry’s carbon footprint. However, for dairy farmers, maintaining milk production is equally important, as it directly affects their income. Challenges and considerations While the study results are promising, there are some challenges to consider before grape marc becomes a staple in dairy cow diets. One issue is the variability in the nutritional composition of grape marc, which can depend on factors such as grape variety, winemaking processes and regional differences. Ensuring consistent quality and nutritional content will be essential for widespread adoption. Another consideration is the potential for grape marc to introduce residues from pesticides or other chemicals used in grape cultivation. Strict monitoring and regulation would be necessary to ensure that grape marc is safe for animal consumption and does not pose any risks to food safety. A step toward sustainability in future dairy farming As the dairy industry faces increasing pressure to reduce its environmental impact, agricultural by-products like grape marc offer a promising solution. The Ellinbank experiment demonstrated that feeding grape marc to dairy cows can significantly reduce methane emissions, contributing to a more sustainable farming model. It can also be hugely beneficial during periods of drought. Additionally, the ability of grape marc to enrich milk with beneficial fatty acids presents an added health benefit for consumers. However, it may not be a one-size-fits-all solution. The trade-off between methane reduction and milk production must be strategically managed to ensure farmers can maintain their livelihoods while adopting more environmentally friendly practices. Grape marc could play a crucial role in helping the dairy industry transition to a more sustainable future. By integrating this waste product into animal feed, the industry can reduce reliance on traditional feed sources, lower its carbon footprint, and contribute to the global effort to combat climate change. Further research is needed to optimise the use of grape marc and explore ways to improve its nutritional value. 

white grape marc on milk production and methane emissions in dairy cows. The composition of red and white grape marc differs, because of the difference in the winemaking processes, which is why both were tested. The experiment was carried out following strict animal welfare guidelines. Thirty-two Holstein dairy cows in early lactation were divided into three groups. All cows had a baseline diet of 15.0 kg of dry matter (DM) from freshly harvested perennial ryegrass and 5.2 kg of a concentrate mix. • The control group was fed the baseline diet. • In the second group, 5 kg of ryegrass DM was replaced with 5 kg DM of red grape marc (RGM). • In the third group, 5 kg of ryegrass DM was replaced with 5 kg DM of white grape marc (WGM). Both red and white grape marc used in the experiment contained the skins and seeds of the grapes and had undergone a crimping process. Crimping involves crushing the seeds and removing the stalks to improve digestibility and energy availability for the cows. The grape marc was stored in airtight bags to prevent spoilage. The impact on milk production The experiment showed that substituting part of the cows’ ryegrass intake with grape marc – whether red or white – had a negative effect on milk production. Milk yields decreased by approximately 10% for cows fed RGM and WGM diets compared to those on the control diet. This reduction in milk output can be attributed to the lower metabolisable energy content in grape marc compared to perennial ryegrass. Despite the drop in milk yield, there were some notable differences between the effects of red versus white grape marc. Cows fed the RGM diet had a lower milk fat concentration than those on the control and WGM diets. However, red grape marc also resulted in higher concentrations of beneficial fatty acids in the milk, suggesting that it may offer superior nutritional While milk production suffered, the study found that grape marc positively affected methane emissions. Both RGM and WGM diets led to a 15% reduction in methane emissions compared to the control group. This reduction is primarily due to the high fat and lignin content in grape marc, which alters the fermentation process in the cow’s rumen. Grape marc contains high levels of lignin, a fibrous component poorly fermented in the cow’s rumen. In addition, lignin can bind to carbohydrates, making them less accessible to the digestive enzymes, resulting in reduced fermentation of carbohydrates and, hence, a reduction in ruminal methane production. benefits compared to white grape marc. The impact on methane emissions

For more information, contact Anel Andrag at anel@sawine.co.za. Reference https://www.wineland.co.za/grape-marc-a-game-changer-for-greener-dairies/

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TECHNICAL YEARBOOK 2025