46 Feed Technology
Protein in aquafeeds, a major cost and strategies for its use Valuation of formulations for optimum cost savings with a feed additive in fish feeds By Pierre Fortin
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rotein is a major cost in aquafeed. Indeed, aquatic animals have high protein requirements compared to terrestrial animals (Figure 1). Furthermore, fishmeal is very often used in fish and shrimp diets. Its price increases faster than other ingredients. Over a 25-year period, fishmeal prices have increased by 350%, while soybean meal increased only by 150% (Source: Indexmundi). It is true especially in these days of raw material price uncertainty. Soybean meal price increased by 65% in the last half of 2020. Even if prices have lowered this year, they are still 25% higher than in 2019 or early 2020. In this situation, feed producers need to be careful when using protein sources to fulfil the needs of animals. First from an economic point of view, but also with regards to its quality. In fact, protein itself does not mean a lot. Protein could have low digestibility (because of the intrinsic composition of an ingredient, or for example, effects resulting from processing methods) and it could also be unbalanced. This could result in lower growth performance of the animal. This brief article will help you save some costs on your feed while safeguarding its quality.
Figure 1. Crude protein requirements for various aquatic species in comparison to that for poultry and swine (Source: Techna).
Feed quality depends on the quality of its ingredients “Quality inputs lead to quality outputs” - this saying is also true for feed. If one does not pay attention to the supply source or does not handle the product properly, even fishmeal could be lower in quality than plant ingredients. It will depend on the raw material quality and how it is processed, cooked and dried, extracted, protected and finally stored. These key points are similar for other ingredients. Therefore, analysis can give a good overview of the quality of ingredients. Specific analyses are needed for different types of raw material.
September/October 2021 AQUA Culture Asia Pacific
Figure 2. Some important analysis to ensure the quality of several ingredients (Source: Techna).
For example, fishmeal quality could be impacted before processing if the fish, or trimmings are not stored properly. This will be evaluated by the TVN (total volatile nitrogen) or biogenic amine values, which are the result of degradation of specific amino acids. Processing could also have an impact on the quality of the product by overcooking; this could be evaluated by oxidative parameters. Overall quality of the proteins of fishmeal is often evaluated by pepsin digestibility. Similar parameters could be analysed on animal meals such as poultry meal and meat and bone meal. For soybean meal, different tests exist such as the urease test and anti-trypsin factors. Analysis of the protein is important to determine whether it is well-cooked and digestible, but without overcooking it which may result in lower digestibility of certain sensitive amino acids such as lysine. Free lysine could also be an indicator of the quality of DDGS or distillers dried grain with solubles. The main risk with these products is overcooking which reduces the overall digestibility. Figure 2 summarises some important analyses to ensure the quality of several ingredients. It is important to analyse these parameters according to importance and risk.
Beyond protein: digestibility and amino acid profile to fulfil the needs of each species
Once the raw materials are sourced, analysed and validated, the second step is to know if they are digestible by the targeted animals. Digestibility of protein depends on several factors but mainly on the type of raw material. Indeed, the form of protein, amino acid chain, together with other compounds such as carbohydrates affect the way fish or shrimp enzymes can fully utilise the raw material. As an example, fishmeal digestibility is affected by ash content; the more ash there is, the less digestible it will be. But note that this is not the only parameter to take into consideration. Within the various plant protein sources available globally, some are more digestible than others. Some of the most digestible will be soybean, peas and beans whereas copra, alfalfa or linseed will be among the least digestible.
