Grape pomace in pig diets: Benefits for growth, health & sustainability

Introduction

The winemaking process generates vast quantities of solid residue known as grape pomace (GP), which is composed of skins, seeds, pulp, and stalks (Rockenbach et al., 2011; Garcia-Cabezon et al., 2020). Grape pomace is produced yearly on a large scale and as a byproduct of the wine industry, it presents significant environmental and economic challenges if not managed properly due to its high-water content and bulkiness (Garcia-Cabezon et al., 2020). Valorizing agro-industrial byproducts like GP by incorporating them into animal feed is recognized as a sustainable agricultural practice that helps reduce environmental impact and can potentially lower feeding costs (Salami et al., 2019). Beyond its fiber and nutrient content, GP is particularly rich in bioactive compounds such as polyphenols and tannins (Yu & Ahmedna, 2013). These compounds possess beneficial properties, including natural antioxidant, antimicrobial, and anti-inflammatory effects (Rockenbach et al., 2011; Garcia-Cabezon et al., 2020).

The Role of Grape Pomace in Animal Feed

Numerous studies have investigated the inclusion of GP in the diets of ruminant animals, including dairy cows, beef cattle, and sheep (Ianni & Martino, 2020; Tayengwa et al., 2020). Research indicates that feeding GP can contribute to reducing enteric methane emissions (Moate et al., 2014; Akter et al., 2025), improve nutrient utilization efficiency, enhance antioxidant status (Molosse et al., 2021), and influence the fatty acid profile of milk or meat (Chikwanha et al., 2019; Ianni & Martino, 2020). However, research on pigs is crucial due to high pork demand and significant feed costs. Exploring sustainable, cost-effective by-products like grape pomace is key for the pig industry. Therefore, this article aims to review the documented effects of feeding grape pomace to pigs or swine, and it summarises key research findings on its impacts on growth, gut health, and oxidative stress, while contextualizing its role in sustainable farming practices. This aims to provide valuable insights for farmers and contribute to the understanding of sustainable livestock feeding practices.

Impact of Grape Pomace on Growth Performance and Nutrient Utilization of Pigs

Grape pomace inclusion in swine diets has shown mixed effects on growth metrics. Kafantaris et al. (2018) reported that piglets fed 9% grape pomace silage had a 23.6% increase in average daily gain compared to controls, likely due to improved gut health and nutrient absorption. Vojáčková et al. (2020) observed declines in feed efficiency at higher inclusion levels (10–15%), attributing this to the high fiber content reducing digestibility. These contrasting results highlight the importance of dosage optimization. Furthermore, Brenes et al. (2016) reported that Iberian pigs fed 1 g/kg of grape pomace extract for 60 days exhibited a 7% increase in daily weight gain compared to controls, alongside reduced serum cholesterol (-18%) and triglycerides (-22%). The authors attributed these improvements to enhanced nutrient absorption and gut microbiota diversity. In contrast, Wang et al. (2020) found that 5% dried grape pomace powder in weaned piglet diets did not alter growth metrics (body weight gain, feed intake) despite improving gut morphology and immunity. This discrepancy suggests that lower inclusion levels or processed forms (e.g., extracts) may optimize growth, whereas higher doses of raw pomace could dilute dietary energy density due to its high fiber content. While beneficial, grape pomace’s high tannin content may impair protein digestibility at elevated doses. For instance, Romero et al. (2022) observed reduced protein digestibility in laying hens fed 30–60 g/kg grape pomace, a finding that may extrapolate to swine. Additionally, fiber-rich pomace could reduce feed energy density, necessitating careful formulation to avoid growth trade-offs.

Impact of Grape Pomace on Gut Health and Immunity

Grape pomace’s polyphenols and fiber positively influence intestinal health. Wang et al. (2020) observed that 5% grape pomace supplementation increased jejunal villus height and the villus height-to-crypt depth ratio in piglets, indicating enhanced nutrient absorption. Additionally, pro-inflammatory cytokines (IL-1β, IL-6, TNF-α) were downregulated, while serum IgG levels rose, suggesting improved immune function. Similarly, Viveros et al. (2016) found that grape pomace extract increased beneficial gut bacteria, such as Lactobacillus, which compete against pathogens. These effects are likely mediated by polyphenols, which modulate microbial activity and strengthen intestinal barrier function (Brenes et al., 2016).

Grape Pomace for pigs.png

Antioxidant and Anti-Inflammatory Benefits

The antioxidant properties of grape pomace are well-documented. Grape pomace’s polyphenols, such as resveratrol and proanthocyanidins, enhance antioxidant capacity in swine. Chedea et al. (2018) found that 5% grape pomace in piglet diets reduced lipid peroxidation by 29–43% in intestinal tissues and boosted antioxidant enzymes (e.g., superoxide dismutase). Similarly, Kafantaris et al. (2018) observed elevated glutathione levels in the liver and spleen, critical for combating oxidative stress. Brenes et al. (2016) also highlighted improved immunity, with grape pomace reducing inflammatory markers in the gut and liver. Polyphenols like resveratrol and flavonoids reduce oxidative stress by scavenging free radicals and boosting endogenous antioxidant enzymes. Viveros et al. (2011) found that grape pomace extracts increased superoxide dismutase (SOD) and glutathione peroxidase (GPx) activity in pig livers, reducing lipid oxidation in meat. This aligns with studies in other species, such as lambs, where grape pomace improved meat shelf life by lowering thiobarbituric acid-reactive substances (TBARS) (Hassan et al., 2019). For swine, these properties could enhance the nutritional value and marketability of pork products.

Impact of Grape Pomace on Reproductive Health in Boars

Emerging research suggests that grape pomace improves reproductive outcomes. Quintero-Moreno et al. (2025) reported that boars fed 4% dried grape pomace produced two additional seminal doses per ejaculate without compromising sperm motility. Gloria et al. (2019) observed similar benefits with grape marc (2–4%), linking polyphenols to enhanced sperm membrane integrity. These findings position grape pomace as a natural alternative to conventional reproductive supplements.

Meat Quality and Shelf Life

In finishing pigs, grape pomace enhances meat quality. Tian et al. (2023) demonstrated that grape pomace extract increased intramuscular fat and improved water-holding capacity, resulting in juicier pork. Ospina-Romero et al. (2024) noted higher oxidative stability in meat, delaying spoilage during storage. However, Tayengwa et al. (2020) cautioned that over-supplementation (>10%) could increase meat toughness due to elevated shear force.

Economic and Environmental Considerations

Replacing conventional feed ingredients with grape pomace can lower costs. Chikwanha et al. (2018) found that 12.2% grape pomace inclusion in lamb diets maximized profit margins, a finding applicable to swine. Additionally, its use aligns with circular economy principles by repurposing winery waste (Kokkinomagoulos & Kandylis, 2023).

Conclusion

Grape pomace shows promise as a functional feed ingredient for swine, offering antioxidant, anti-inflammatory, and gut-health benefits, and growth, and meat quality at moderate doses. However, its efficacy depends on dosage, form, and basal diet composition. By valorizing this agro-industrial by-product, farmers can improve sustainability while enhancing animal health and product quality. Farmers can leverage grape pomace to reduce feed costs and improve sustainability, though careful formulation is critical to avoid digestive inefficiencies.

Future Research Directions

Future research directions should include determining species- and growth-stage-specific inclusion levels, assessing the long-term effects on swine longevity and reproductive consistency, and evaluating processing methods such as fermentation, ensiling, or extraction to enhance bioavailability.

Key Takeaway:

Studies on grape pomace supplementation in pigs reveal dose- and form-dependent effects on growth.
Moderate inclusion (5–9%) supports growth, while excessive amounts may impair nutrient absorption.
Grape pomace mitigates oxidative stress, potentially reducing reliance on synthetic antioxidants in feed.
Low-dose grape pomace may boost fertility in breeding stock.
Grape pomace improves meat quality but requires careful dosage to avoid texture issues.
Grape pomace offers economic and sustainability benefits without compromising productivity.

References

Akter, A., Li, X., Grey, E., Wang, S. C., & Kebreab, E. (2025). Grape pomace supplementation reduced methane emissions and improved milk quality in lactating dairy cows. Journal of Dairy Science, 108(3), 2468-2480.
Brenes, A., Viveros, A., Chamorro, S., & Arija, I. (2016). Use of polyphenol-rich grape by-products in monogastric nutrition: A review. Animal Feed Science and Technology, 211, 1–17.
Chedea, V. S., Pelmus, R. S., Lazar, C., Pistol, G. C., Calin, L. G., Toma, S. M., Dragomir, C., & Taranu, I. (2017). Effects of a diet containing dried grape pomace on blood metabolites and milk composition of dairy cows. Journal of the Science of Food and Agriculture, 97(8), 2516–2523.
Chikwanha, O. C., Moelich, E., Gouws, P., Muchenje, V., Nolte, J. V. E., Dugan, M. E. R., & Mapiye, C. (2019). Effects of feeding increasing levels of grape (Vitis vinifera cv. Pinotage) pomace on lamb shelf-life and eating quality. Meat Science, 157, 107887.
Chikwanha, O. C., Muchenje, V., Nolte, J. E., Dugan, M. E. R., & Mapiye, C. (2018). Grape pomace (Vitis vinifera L. cv. Pinotage) supplementation in lamb diets: Effects on growth performance, carcass and meat quality. Meat Science, 147, 6–12.
Garcia-Cabezon, C., Gobbi Teixeira, G., Dias, L. G., Salvo-Comino, C., García-Hernandez, C., Rodriguez-Mendez, M. L., & Martin-Pedrosa, F. (2020). Analysis of phenolic content in grape seeds and skins by means of a bio-electronic tongue. Sensors, 20(15), 4176.
Gloria, A., Contria, A., Grottab, L., et al. (2019). Effect of dietary grape marc on fresh and refrigerated boar semen. Animal Reproduction Science, 205, 18–26.
Hassan, Y. I., Kosir, V., Yin, X., Ross, K., & Diarra, M. S. (2019). Grape pomace as a promising antimicrobial alternative in feed: A critical review. Journal of Agricultural and Food Chemistry, 67(35), 9705-9718.
Ianni, A., & Martino, G. (2020). Dietary grape pomace supplementation in dairy cows: Effect on milk quality. Foods, 9(2), 168.
Kafantaris, I., Stagos, D., Kotsampasi, B., Hatzis, A., Kypriotakis, A., Gerasopoulos, K., ... & Kouretas, D. (2018). Grape pomace improves performance, antioxidant status, fecal microbiota and meat quality of piglets. Animal, 12(2), 246-255.
Kokkinomagoulos, E., & Kandylis, P. (2023). Grape pomace, an undervalued by-product: Industrial reutilization within a circular economy vision. Reviews in Environmental Science and Biotechnology, 22, 739–773.
Molosse, V. L., Deolindo, G. L., Cécere, B. G., Marcon, H., da Rosa, G., Vedovatto, M., ... & Da Silva, A. S. (2021). Effect of dietary supplementation with grape residue flour on weight gain, metabolic profile, leukogram, proteinogram and antioxidant response in suckling lambs. Research in Veterinary Science, 139, 112-120.
Moate, P. J., Williams, S. R. O., Torok, V. A., Hannah, M. C., Ribaux, B. E., Tavendale, M. H., Eckard, R. J., Jacobs, J. L., Auldist, M. J., & Wales, W. J. (2014). Grape marc reduces methane emissions when fed to dairy cows. Journal of Dairy Science, 97(8), 5073–5087.
Ospina-Romero, M. A., Medrano-Vázquez, L. S., Pinelli-Saavedra, A., Sánchez-Villalba, E., Valenzuela-Melendres, M., Martínez-Téllez, M. Á., Barrera-Silva, M. Á., & González-Ríos, H. (2023). Productive Performance, Physiological Variables, and Carcass Quality of Finishing Pigs Supplemented with Ferulic Acid and Grape Pomace under Heat Stress Conditions. Animals, 13(14), 2396.
Quintero-Moreno, A., Martínez-López, C., Luongo, C., García, M. L., Argente, M. J., Romero, G., Pérez-Patiño, C., Díaz, J. R., García-Vázquez, F. A., & Llamas-López, P. J. (2025). Wine grape pomace as a dietary supplement to improve semen quality in boars. Reproduction in Domestic Animals, 60(4), e70049.
Rockenbach, I. I., Rodrigues, E., Gonzaga, L. V., Caliari, V., Genovese, M. I., Gonçalves, A. E. D. S. S., & Fett, R. (2011). Phenolic compounds content and antioxidant activity in pomace from selected red grapes (Vitis vinifera L. and Vitis labrusca L.) widely produced in Brazil. Food Chemistry, 127(1), 174-179.
Romero, C., Arija, I., Viveros, A., & Chamorro, S. (2022). Productive performance, egg quality and yolk lipid oxidation in laying hens fed diets including grape pomace or grape extract. Animals, 12(9), 1076.
Salami, S. A., Luciano, G., O'Grady, M. N., Biondi, L., Newbold, C. J., Kerry, J. P., & Priolo, A. (2019). Sustainability of feeding plant by-products: A review of the implications for ruminant meat production. Animal Feed Science and Technology, 251, 37-55.
Tayengwa, T., Chikwanha, O. C., Raffrenato, E., Dugan, M. E. R., Mutsvangwa, T., & Mapiye, C. (2020). Comparative effects of feeding citrus pulp and grape pomace on nutrient digestibility and utilization in steers. Animal, 15(12), 100020.
Tian, X., Li, D., Zhao, X., Xiao, Z., Sun, J., Yuan, T., ... & Yu, T. (2023). Dietary grape pomace extract supplementation improved meat quality, antioxidant capacity, and immune performance in finishing pigs. Frontiers in Microbiology, 14, 1116022.
Viveros, A., Chamorro, S., Pizarro, M., Arija, I., Centeno, C., & Brenes, A. (2011). Effects of dietary polyphenol-rich grape products on intestinal microflora and gut morphology in broiler chicks. Poultry science, 90(3), 566-578.
Vojáčková, K., Mlček, J., Škrovánková, S., Adámková, A., Adámek, M., Orsavová, J., ... & Búran, M. (2020). Biologically active compounds contained in grape pomace. Potravinarstvo Slovak Journal of Food Sciences.
Wang, R., Yu, H., Fang, H., Jin, Y., Zhao, Y., Shen, J., Zhou, C., Li, R., Wang, J., Fu, Y., & Zhang, J. (2020). Effects of dietary grape pomace on the intestinal microbiota and growth performance of weaned piglets. Archives of Animal Nutrition, 74(4), 296–308.
Yu, J., & Ahmedna, M. (2013). Functional components of grape pomace: Their composition, biological properties and potential applications. International Journal of Food Science and Technology, 48(2), 221-237.