Agro-industrial by-products and crop residues to reduce dependency on cereals for feed

Spain is a European leader and one of the top ten world producers of animal feed. In 2020, 37.69 million tons of feed were produced, 48% for pigs, 27% for ruminants and the remaining 25% for other animal species.

Animal feed is based on the use of large amounts of cereals, mainly corn and barley. Currently, there is the problem of the scarcity of cereals, due, among other reasons, to the cessation of imports from the Ukraine, the second largest supplier of corn to Spain (behind Brazil), with an average volume of 2.7 million tons imported per year.

Alternatives to alleviate the crisis

The reduction in the supply of cereals has caused an increase in its price, which has been added to the increase in the cost of raw materials already registered in recent months.

Measures such as the increase of land dedicated to the cultivation of cereals and the authorization of their importation from different countries can contribute to resolving this crisis, but other measures such as the use of non-conventional raw materials can also be useful.

The substitution of conventional raw materials for agro-industrial by-products or crop residues can reduce production costs, environmental pollution, the carbon footprint of animal products and the competition between animal and human food, contributes to the sustainability of farms livestock, enhances the circular economy in the producing sectors and can improve the green image of livestock.

In addition, it can have beneficial effects on animal health and the quality of animal products. Consequently, it benefits the health of the consumer.

However, the practical use of these resources requires knowing their nutritional value and the ideal conditions for their inclusion in the diet of animals.

In Spain, numerous investigations have been carried out that support the potential of different agro-industrial by-products and vegetable waste to feed animals.

By-products of the olive grove and the vineyard

Spain is the world’s leading producer of olive oil. In its manufacture, different types of olive pomace are generated, formed by pulp, skins and bones of the olives and water.

Olive pomace is a fibrous material poor in protein that has been used fundamentally in the feeding of ruminants in times of food scarcity and to feed animals in maintenance or low production level.

However, this by-product has also been included in the feed of pregnant and lactating sheep and calves, replacing cereals without reducing productive performance. The use of olive pomace in pig feed can modify the fatty acid content of the meat towards a more unsaturated and healthier profile for human consumption.

Viticulture and wine production have great social and economic importance in Spain, one of the world’s leading producers. This industry generates a large number of by-products, among which grape pomace is the majority.

Grape pomace is a fibrous material with low nutritional value, but its inclusion in lamb feed can improve the shelf life of meat without reducing animal production. This improvement in the oxidative stability of meat has also been observed when small amounts of grape pomace are included in chicken feed.

By-products of horticultural crops

Spain is the first European country and second in the world in terms of area dedicated to greenhouse crops. Large amounts of plant remains are generated in them, such as leaves, branches and fruit debris that are available throughout the year. These plant materials have a high water content and can be mixed with other raw materials to form multi-nutrient building blocks.

The administration of multinutrient blocks with tomato and cucumber waste to dairy goats modified the fat of the milk towards a healthier profile and reduced the emissions of methane, a gas with a powerful greenhouse effect.

The tomato’s potential to reduce methane emissions has also been noted in other studies. Tomato processing to produce juices and paste generates tomato pulp, a very abundant by-product in Spain. Ensiled or dried tomato pulp can improve the quality of ruminant meat and milk.

Tomato pulp has also been used in diets for pigs, poultry and rabbits, improving the fatty acid profile of meat, and in feed for aquaculture and pets.

Another very abundant by-product in Spain is citrus pulp, which is generated in the industrial production of juices and can be used fresh, ensiled or dehydrated.

Dehydrated pulp has a high energy content and can replace cereals, as has been shown in cattle, sheep, goats and pigs. In pigs, orange pulp can also reduce polluting emissions from manure.

Another by-product of citrus cultivation is the leaves of the trees. Lemon and orange leaves have been shown to reduce methane emissions from dairy goats and improve the fatty acid profile of milk.

In dairy goats, silage with artichoke and broccoli by-products and avocado and mango by-products have been used. Avocado by-products can also improve the quality of pork meat by reducing its fat content, decreasing its oxidation and increasing the content of polyunsaturated fatty acids.

beer by-products

Beer is one of the most consumed beverages in Spain, the third largest producer in the EU. Beer production generates several by-products, but the main one is bagasse, a material rich in protein and fiber that is highly degradable, but also has a high water content and rots easily.

Fresh bagasse is used in dairy ruminant farms (mainly cows) close to breweries and has beneficial effects on milk production and quality by improving the lipid profile, although it can also be ensiled. Bagasse can also be dehydrated and used in poultry and pig diets, although its nutritional value for these animals is less well known.

What if several by-products are mixed in the feed?

The nutritional composition of by-products is often unbalanced, so mixing several in feed can be a good practical option. The inclusion of 44% of a mixture of by-products (citrus pulp, distillers grains and olive pomace) in the feed of fattening lambs improved the quality of the meat by increasing its proportion of polyunsaturated fatty acids and reducing lipid oxidation .

When the same concentrate was fed to dairy goats it also improved milk fat towards a healthier profile without altering production.

In fattening calves, the inclusion of 73.5% of a mixture of distillers grains, malt culms and grape seeds in the feed maintained the same production levels and the same quality of the meat as when administering a feed rich in cereals.

The inclusion of a mixture of tomatoes, citrus pulp and bagasse, and brewer’s yeast in goat feed reduced methane emissions and increased the proportion of polyunsaturated fatty acids in milk.

These studies show that the combination of by-products and plant remains in the feed can replace conventional raw materials. Thanks to the numerous works carried out by different Spanish research groups, the nutritional value of many by-products and local plant remains is known. Some have already been included in nutritional value tables.

However, it is essential to continue characterizing the by-products generated in different industries, analyze their variability and develop effective and low-cost systems for their conservation, such as silage, solar drying or the production of multinutrient blocks.

In this sense, there are many companies that generate by-products and are making a great effort to develop sustainable procedures that allow their storage.

Although by-products are only included in low proportions in animal rations, they can play a particularly relevant role in the current raw material crisis and reduce the livestock sector’s dependence on imports and its exposure to market volatility.

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