By-products: Benefits and limitations in poultry nutrition

In a study published in the Journal ‘Sustainability’, the potential of agro-industrial by-products (AIBPs) (e.g., fruit juice industry leftovers, oilseed industrial by-products, distillers’ grain by-products, vinification by-products, olive oil industry by-products, pomegranate by-products, tomato processing by-products) as functional feeds for poultry is elaborated, highlighting the associated limitations on utilisation. AIBPs contain several bioactive compounds that act as antimicrobial agents, antioxidants, and immune modulators.

Agro-industrial by-products may be a cheap source of feed, but to the best of our knowledge, economic analyses of their use in poultry nutrition are scarce.

Fruit juice industry leftovers

A common product is apple pomace which is a by-product of apple processing and cider production. Apple pomace is high in polyphenols. Researchers highlighted that:

• In broilers – dietary inclusion of 3–6% dried apple pomace promotes growth performance, gut morphometry, and histopathology
• In laying hens – dietary inclusion levels up to 10% with the concomitant addition of a multi-enzyme additive at 0.05% improved laying hens’ performance, egg traits, and blood parameters without influencing other traits.

Limitation
The limitation of apple pomace is the common presence of heavy metals, and toxins (e.g., ochratoxin A, biogenic amines).

Similar products show beneficial results:

• In broilers – dried sweet orange peel up to 3%, and dried citrus pulp up to 10%,
• In laying hens – variable results are reported.

Citrus products are rich in flavonoids, vitamin C and carotenoids.

Non-conventional oilseed industrial by-products

Sunflower meal is an example; a by-product of oil extraction from sunflower seeds that can be used as a protein source for broilers. The key ingredients in sunflower are peptides. The researchers state that results of previous studies show sunflower meal:

• In broilers – diets at levels up to 15%, especially when an enzyme mixture is added, provides favourable results.
• In laying hens – the inclusion of sunflower meal at levels up to 25% does not show negative results.

Limitation
The main antinutritional factor found in sunflower meal is chlorogenic acid and the high fibre content. A drawback to the utilisation of sunflower meal is the presence of mycotoxins and heavy metals.

Dried distillers’ grain with solubles

Dried distillers’ grain with solubles (DDGS) is a co-product generated from the production of bioethanol by the extraction of starch from cereals during fermentation, with wheat and corn-based being the most used. Studies show maize DDGS to contain high levels of crude protein (30%), betaine and phenolic compounds, but low lysine content.

Researchers report DDGS levels up to 24% in broiler diets and up to 25% in laying hen diets could be used, but variable results are reported depending on the growing period.

Limitation
The main limitations of the wide use of DDGS in poultry nutrition include the high variability of nutrient composition and the occurrence of mycotoxins.

Vinification by-products

Grape pomace, which is the solid residue of grapes, constitutes around 20% of the total grape weight and results from the extraction of the juice for winemaking. Grape products are rich in polyphenols and flavonols.

Research shows that grape pomace can be included at levels:

• up to 10% in broiler diets,
• up to 6% in quails and
• up to 6% in laying hen diets

without affecting growth performance;

in broilers, this inclusion level enhanced intestinal morphology, the antioxidant capacity, and PUFA content of breast muscle.

Limitation
The use of grape pomace in poultry nutrition is limited by the high content of lignified cell wall fraction and anti-nutritional factors such as condensed tannins and phytic acid.

Olive oil industry by-products

Large quantities of olive by-products are generated during olive oil extraction, such as leaves, stones, olive mill wastewater, and the solid wastes’ pomace residues and olive cake. The main active ingredients in olive by-products are polyphenols, tocopherol, and gallic acid. It is reported that olive cake could be incorporated at levels up to 20% in broiler and hen diets, with the addition of citric acid, and olive pulp at levels up to 10%.

Pomegranate by-products

Pomegranate pulp is generated during pomegranate juice extraction and comprises outer peel, seeds, and residual pulp. It could be utilised as urea-treated pomegranate peel, fermented, or in oil form. The by-product is rich in poly- and monomeric phenols.

• In broilers – studies show that the incorporation of 1–2% pomegranate pulp results in beneficial effects on meat fatty acid levels, protein content in the breast, and reduced meat cholesterol and lipid oxidation values. In other studies, the inclusion of 7–10% in the diet of heat-stressed broilers enhanced growth performance, blood cholesterol, and antioxidant status.
• In laying hens – supplementation with 2–4% pomegranate peel powder improved blood antioxidant activity and reduced plasma cholesterol and triglyceride content.

Tomato processing by-products

Tomato pomace is a residue by-product of the paste production industry, which comprises the seeds, skin (or peel), and a small amount of pulp. Tomato pomace accounts for 3–5% of the raw material and can be used as a protein and energy source in poultry nutrition. Tomato pomace is rich in lycopene, β-carotene, sterols, tocopherols, terpenes, and glycoalkaloids.

• In broilers – studies show that inclusion levels of up to 15–20% in the diet improve economic efficiency without negatively affecting performance and carcass characteristics.
• In laying hens – dried tomato pomace up to 10% was demonstrated to improve egg quality traits without posing adverse effects on growth performance or other egg characteristics.

Sugar beet and brewery products

Sugar beet pulp, a by-product of the sugar cane industry, can be a valuable source of highly digestible fibres, pectins, and sugars. Another product is the brewery product “brewers’ dried yeast” commonly used in poultry diets due to its content of riboflavin, niacin, pantothenic acid, choline, and phosphorus.

Limitation
Heavy metals are a potential hazard in sugar beet pulp, while brewery by-products are affected by mycotoxins.

Conclusion

The researchers concluded that, given that the availability and price of the different by-products may vary greatly across the regions, the use of such by-products as functional feed ingredients in poultry rations should be adjusted according to the nutritional composition, availability, and cost of each by-product.

“Agro-industrial by-products may be a cheap source of feed, but to the best of our knowledge, economic analyses of their use in poultry nutrition are scarce. However, in practice, it is widely known that it may be cost-effective in comparison with using conventional feeds,” they said.

Limitation
They emphasised the importance of the control of potential hazards through proper legislation and knowledge of the different stakeholders involved. “However, modern processing methods, new types or classifications, and appropriate developmental strategies are expanding the applications of agro-industrial by-products as animal feeds for poultry production,” they said.