In animal feed, by-products are those materials left over after the processing of other materials in the agri-food industry.

They may be of no value to the human food industry, but due to their characteristics and/or nutrient content, they are of great value in animal feed.

For example, beet pulp, which is a by-product of the sugar industry, is of great value for feeding cows, horses or sows. Wheat and rice bran are by-products obtained from the processing of these cereals for human consumption, and soybean, rapeseed, and sunflower oilcakes are by-products obtained after the extraction of oil from these seeds.

Also, in the wine and olive oil production process, by-products that can be used in animal feed are generated.

By-products of the Wine Industry

Grape Pomace

Grape pomace is one of the most abundant solid by-products generated during winemaking.

Represents the residue from pressing process of fresh grapes, constitutes 20–25% of grape weight and contains skin, seeds and other solid parts.

Its characteristics vary considerably depending on the type of wine produced (red or white), the grape variety and the type of separation process used.

It has medium levels of easily assimilated crude protein. Although it has excellent levels of neutral detergent fiber (NDF), the presence of a high percentage of lignin (LAD) significantly increases the acid detergent fiber (ADF). In addition, it has good concentrations of polyphenols and fats.

It is mainly used in ruminant and rabbit feed.

Its content in polyphenolic compounds (anthocyanins and flavonols) that have an antioxidant capacity similar to vitamin E. (Brenes et al., 2008) and nutraceutical properties should be highlighted. Therefore, apart from its nutritional component, its inclusion in the diet of ruminants and monogastrics increases the stability of the products obtained from them (meat, milk, etc.). Furthermore, its antimicrobial activity allows the growth of beneficial bacteria that inhibit, by competition, certain pathogenic bacteria in the gastrointestinal tract and in the rumen (Ianni et al 2020), (Brenes et al., 2016).

Defatted grape seed

This is the by-product obtained from the extraction of oil from grape seeds.

It has a high fiber content (50%), composed mainly of lignin and cutin. The protein content is 10%, but its digestibility is low, both due to the high proportion of protein bound to the cell wall (greater than 50%), as well as due to the presence of tannins.

It is incorporated, basically as a source of fiber, in ruminant maintenance feeds and especially in rabbit feeds, in which it complies with part of their fiber and lignin requirements.

It is not used in poultry or pig feed, except in sows if there is no other more appropriate source of fiber.

By-products of the Olive Oil Industry

Olive Oil Pomace

The industrial process by which the olive oil is extracted generates a highly polluting raw residue. Olive oil pomace is the main solid by-product from the olive oil extraction standing for 35–40% of the total weight of olive processed in the mill, but it must be dehydrated and extracted to be used.

It is made up of the pulp, skin and pits of olives. It is a highly lignified fibrous product, low in protein and with variable fat content, depending on the process to which it has been subjected (sifting, pitting, defatting).

It is a product traditionally used in feeding goats and sheep, but due to its content in ethereal extract (oil), it is also indicated for maternity feed in prolific species, such as sows and rabbits, which need an extra energy supply.

Its fatty acid profile (very rich in oleic acid) makes it especially suitable for fattening animals, such as pigs, especially Iberian pigs, rabbits for its effect on the fatty acid profile of the meat and intensively fattened ruminants in which a significant proportion of the fatty acids in the pulp (mainly oleic) are deposited directly in the carcass, increasing its quality from the point of view of human nutrition.

In the case of dairy cattle, their interest would be more focused on milk quality and its fatty acid profile.

Studies with dairy goats (Molin-Alcaide et al 2005) and dairy sheep (Vargas-Bello et al 2013) observed a change in the fatty acid profile of milk towards a higher proportion of oleic, linoleic and conjugated linoleic acids and the ratio of unsaturated/saturated fatty acids, with the inclusion of olive pulp in the rations.

Its use in broilers has been studied, with positive results in animal performance (Papadomichelakis et al 2019), improvements in intestinal mucosa characteristics, and preservation of oxidation in meat (Tuffarelli et al 2022).

With the moderate inclusion of olive pomace in fish diets, an improvement in carcass composition has been observed, with no detrimental effects on fish performance. Furthermore, its antioxidant, antibacterial, antimicrobial and antifungal properties improve intestinal health and the immune response of animals (Hazreen-Nita et al 2022).

Bibliography:

• Brenes, A, Viveros, A., Goni, I., Centeno, C., Sáyago¬Ayerdy, S.G., Arija, I. and Saura¬ Calixto, F. (2008). “Effect of Grape Pomace Concentrate and Vitamin E on Digestibility of Polyphenols and Antioxidant Activity in Chickens.” Poultry Science, 87 (2): 307¬316.
• Brenes A., A. Viveros, S. Chamorro, I. Arija “Use of polyphenol-rich grape by-products in monogastric nutrition. A review.” Anim. Feed Sci. Technol., 211 (2016), pp. 1-17 https://www.sciencedirect.com/science/article/abs/pii/S0377840115300250
• Hazreen-Nita, M.K, Z. Abdul Kari, K. Mat, N.D. Rusli, S.A. Mohamad Sukri, H. Che Harun, et al. “Olive oil by-products in aquafeeds: opportunities and challenges” Aquac Rep, 22 (2022), p. 100998. https://www.sciencedirect.com/science/article/pii/S2352513421004154
• Ianni A, Martino G. “Dietary Grape Pomace Supplementation in Dairy Cows: Effect on Nutritional Quality of Milk and Its Derived Dairy Products”. Foods. 2020; 9(2):168. https://doi.org/10.3390/foods9020168
• Papadomichelakis G., A.C. Pappas, E. Tsiplakou, G.K. Symeon, K. Sotirakoglou, V. Mpekelis, K. Fegeros, G. Zervas “Effects of dietary dried olive pulp inclusion on growth performance and meat quality of broiler chickens” Livest. Sci., 221 (2019), pp. 115-122 https://www.sciencedirect.com/science/article/abs/pii/S1871141319301593?via%3Dihub
• Tufarelli V., L. Passantino, R. Zupa, P. Crupi, V. Laudadio“Suitability of dried olive pulp in slow-growing broilers: performance, meat quality, oxidation products, and intestinal mucosa features” Poultry Science Volume 101, Issue 12, December 2022, 102230. https://www.sciencedirect.com/science/article/pii/S0032579122005260?via%3Dihub