Insect meals as animal feed

By Harinder P.S. Makkar, FAO, Rome

Introduction

There has been a major shift to diets with increased consumption of animal products, and this change is likely to continue in the coming decade. The demand for meat and milk is expected to be 58% and 70% higher in 2050 than their levels in 2010 and a large part of this increase will originate from developing countries.

The livestock production is resource hungry: for example it occupies 30% of the world’s ice-free surface or 75% of all agricultural land (including crop and pasture land) and consume 8% of global human water use, mainly for the irrigation of feed crops. In addition, the livestock sector contributes approximately 14.5% of all anthropogenic greenhouse gas (GHG) emissions (7.1 Gigatonnes of CO₂-equivalent per year). As a result of huge demand for animal products, enormous need of resources including feeds to produce them will ensue. Fuel-feed-food competition is expected to further exacerbate the situation. A quest for novel feed resources is a must. 

Insect rearing could be one of the ways to enhance food and feed security. They grow and reproduce easily, have high feed conversion efficiency (since they are cold blooded) and can be reared on bio-waste streams.

Insects as animal feed

Protein and lipid contents

Table 1 compares the crude protein (CP) and lipid contents in insects meals with those in soymeal and fishmeal. The CP contents are high, varying from 42 to 63%, which are of the same order as is in soymeal but are slightly lower than that in fishmeal. After defatting, the CP content in insect meals is expected to be higher than those of both the conventional resources – soymeal and fishmeal – generally used in the preparation of livestock and fish diets respectively (Table 1). Some insect meals, for example (black soldier fly larvae, housefly maggot meal, mealworm, silkworm) contain as high as 36% oil, which can be isolated and used for the preparation of biodiesel; and the rest of the defatted meal, being rich in CP, could find a place as an invaluable protein-rich resource in the feed industry. Presence of high levels of lipids in the meals can also decrease fibre digestion in the rumen and is also not good for optimal rumen fermentation, and hence defatted insect meals would be an ideal choice for ruminants. Insect meals (e.g. black soldier fly larvae) contain high levels of ash and hence their higher levels of inclusion in the diet, especially of monogastrics, can decrease its intake and cause other adverse effects.

Amino acids

For growing pigs and broilers the major limiting amino acids are lysine and methionine. The deficiency of tryptophan and threonine could also decrease the performance of these animals. Amino acid compositions of various insect resources and other conventional feed resources are given in Table 2. Methionine levels in all insect meals are higher than that in soymeal, while the levels of sulphur-containing amino acids (methionine + cystine) are lower in black soldier fly larvae, mealworm, house cricket and mormon cricket than in soymeal. Lysine is lower in mealworm, locust meal, house cricket and mormon cricket than in soymeal. Lysine levels are adequate in black soldier fly larvae, housefly maggot and silkworm pupae meals. Overall levels of essential amino acids in insect meals are good; most essential amino acid levels in silkworm pupae meal and black soldier fly larvae being higher than in soymeal or the FAO Reference Protein. A 50:50 mixture of black soldier fly larvae and housefly maggot meals would provide a balanced amino acid composition for use in livestock feed as soymeal replacers. Arginine is also considered an essential amino acids for laying hens and the level of this amino acid in all insect meals was lower than in soymeal, suggesting its addition in the diets of laying hens containing these insect meals. Other insect meals having lower levels of essential amino acids could also be invaluable soymeal replacer in livestock diets when supplemented with synthetic amino acids. Synthetic amino acids are low-cost additives, which now-a-days are commonly used in the preparation of compound feeds by the feed industry.

For fish species, fishmeal could be considered as an ideal feed ingredient for optimal growth. The supplementation of synthetic lysine and tryptophan with almost all insect meals and of threonine and sulphur-containing amino acids with all insect meals except silkworm pupae meal would be required for the optimum growth.

Nutrient digestibility

The digestibility of insect proteins and their utilization in vivo have also been good. Apparent faecal digestibility of black soldier fly larvae and soymeal in male growing pigs has been reported to be similar (76 vs 77% respectively). Studies conducted using housefly meal in broilers have also shown variable results. Reports suggest that silkworm proteins have low rumen degradability and hence they could be a good feed resource for high yielding ruminant livestock. However a report suggests low intestinal protein digestibility of the ruminal undegradable fraction, while another report suggests higher digestibility of silkworm protein than groundnut cake proteins. More studies are required to evaluate the potential of silkworm proteins in the diets of, for example, high milk producing animals which respond to rumen bypass protein.

Minerals

Ca and P values are important for poultry and pig production as well as for milk production from large and small ruminants. Black soldier fly larvae are rich in Ca (7.56%) with highest Ca: P ratio of 8.4, while for other insect meals the Ca levels were very low and its supplementation would be required should these be used in animal feed. Ca fortification of the substrate on which the insects are raised also increases the Ca level in the larvae meals (Table 1). Ca: P ratio of 2 is generally considered to be optimum for most livestock feeds, which is far from the Ca:P ratios, varying from 0.19 to 1.18 in insect meals other than that in black soldier fly larvae. In some insects (e.g.housefly maggot meal and Mormon cricket) P levels are particularly high (1.0 to 1.6%).

Fatty acid composition

Polyunsaturated fatty acids have a hypocholesterolaemic effects. Increasing levels of polyunsaturated fatty acids in human diet reduce the risk of cardiovascular diseases and chronic pathologies (e.g. cancer, diabetes (Simopoulos, 1999). Deficiencies of essential fatty acids such as linoleic (18:2), linolenic (18:3) and arachidonic (20:4) elicit a number of adverse effects such as growth retardation, dermal symptoms, malabsorption and catabolic diseases. Unsaturated fatty acids (monosaturated plus polyunsaturated) concentrations are high in mealworm, house cricket and housefly maggot meals (60-70%), while this concentration is lowest in black soldier fly larvae (19-37%), suggesting the presence of higher levels of saturated fatty acids in black soldier fly larvae (Table 3). Unsaturated fatty acid levels in soybean oil and sunflower oil are respectively ca 85 and 89%. In the insect meals, as in the plant oils, linoleic acid concentration is higher than that of alpha-linolenic acid (18:3n–3) (e.g. soybean oil 54 % vs. 6% and sunflower oil 63% vs. 0.2%) (Table 3). Fatty acid composition in black soldier fly can be manipulated by changing the composition of the substrate. On changing the substrate from cow manure to 50:50 mix of cow manure and fish offal containing omega fatty acids increased the level of omega-3 fatty acid in the larvae from 0.226% to 1.99%. Omega-3 fatty acids are linked to lowering the coronary heart diseases. However, the use of fish offal also increased the levels of saturated fatty acids, from 46.1 to 61.9% which could possibly counteract the beneficial effects of omega-3 fatty acids. The use of fish offal might not be a good option for enhancing the quality of black soldier larvae from health benefitting point of view for humans or monogastric animals but evidence do exist that fatty acid composition in insect meals can be manipulated using wastes containing lipids of different fatty acid composition.

Animal studies

The feeding studies conducted so far have confirmed that the palatability of the insect meals containing diets is good and that these alternate feed resources can replace soybean and fishmeal in the diets of livestock and fish species. Most feeding studies with diets containing insect meals have been conducted on fish and poultry, followed by pigs and then ruminant animals. This is attributed to the limited availability of insect meals. The nutrient utilization and growth studies in pigs and ruminants require a substantial amount of insect meal, and their limited availability allows their evaluation and use in fish or poultry diets. Future higher availability of insect meals would provide impetus to the studies on evaluation of these alternate feed resources in ruminant livestock as well.

Studies conducted on including black soldier fly larvae in poultry, pig and fish diets suggest that it could replace soymeal in their diets; however more in-depth studies are required to optimize its levels of inclusion, and at its high levels of inclusion to also optimize the levels of deficient amino acids supplementation. Studies on fish also showed that the aroma and texture of fish do not change on feeding black soldier fly larvae. Processing of these larvae (e.g. cuticle removal, rendering or chopping) appears to increase nutrient availability from the larvae in fish. In shrimps the addition of black soldier fly larvae produced lighter coloured shrimp and also increased economic returns. Acceptability of diets containing these larvae by alligators has been limited.

Backyard chickens and fish can be fed live housefly maggots. Studies conducted in Africa have demonstrated that feeding of live housefly maggots increased growth rate, egg size and egg weight. In poultry a number of studies have been conducted on broilers. Studies on laying hens are limited. In laying hens maggots could replace up to 50% of fishmeal (maggots inclusion: 5% in diet) without any adverse effects; however 100% replacement produced negative effects on egg production. For broilers, the optimum level of their inclusion is generally lower than 10% and methionine supplementation is suggested. In fish species, 25% replacement of fishmeal does not affect growth performance; however higher levels of fishmeal replacement appear to produce adverse effects. Supplementation of amino acids in the diets that are deficient in maggots could increase their levels of inclusion in fish diets.

There is limited information on the use of mealworm in the diets of both broilers and laying hens. The information so far obtained suggest that it could be a valuable replacer of soymeal and fishmeal when supplemented with methionine. As with most other insect meals Ca supplementation would be required for growing chicks. A 10% level of mealworm in the diets of broiler starter diets could be used without any adverse effects. In catfish diet, mealworm can replace 40% of fishmeal. Information on the use of mealworm in the diets of other fish species needs to be generated.

Feeding of grasshopper-containing diets to free-range chickens increased protein and decreased cholesterol content in meat. Higher antioxidant potential and longer shelf life has also been observed. A number of other meat quality parameters were also affected on feeding grasshopper diets. In the Philippines people prefer taste of meat from free-range chickens fed grasshoppers and such chickens are sold at a higher price in the market. It appears that grasshopper meal could be added into the diets of broilers at a level of up to 2.5% (as a substitute for fishmeal). Studies suggest that the Mormon cricket can be incorporated into the broiler diets at a level of up to 30% without any adverse effects. Crickets are deficient in amino acids methionine and arginine and their addition in the diets containing crickets is expected to further enhance the nutritional value of these feed resources. In quail (Cotornix japonica) 50% of fishmeal could be replaced by grasshopper meal without affecting growth or fecundity. Evaluation of grasshopper meal and crickets containing diets in pigs is limited and to our knowledge does not exist in ruminants. In various fish species (African catfish, walking fish and Nile tilapia) the studies suggest that 25% of fishmeal can be replaced with grasshopper meal without any adverse effects.

In fattening diets of Jersey calves defatted silkworm meal can replace 33% of groundnut cake without affecting performance. In lambs and sheep as well the nutrient utilization results were encouraging. Also from experiments in growing and finishing pigs it can be concluded that defatted silkworm meal can replace 100% of soymeal or fishmeal. For common carp, full replacement of fishmeal with silkworm meal is possible. In comparison with plant protein sources (e.g. alfalfa or mulberry leaf meals) the silkworm meal is a better protein source for common carp. In fish species, silkworm meal has high protein digestibility (ca 85%). In silver barb fingerlings and Asian stinging catfish, 38% and 75% respectively of dietary protein can be replaced with silkworm protein without affecting the growth. For broilers, replacement of 50% fishmeal in the diets with silkworm meal is suggested. Limited studies on laying hens suggest that silkworm meal could be incorporated at 6% in the diets without any adverse effects. Caution is required in using silkworm meal in the diets of breeder males since detrimental effects on their breeding performance have been recorded. However, further studies on the evaluation of silkworm meal in laying hens and breeder males are required.

Table 1. Main chemical constituents in insect meals vis-à-vis fishmeal and soymeal

Values in parentheses are calculated values of the defatted meals

Table 2. Amino acid composition (g/16 g nitrogen) of insect meals versus FAO reference dietary protein requirement values, soymeal and fishmeal

Notes: (1) Reference for the 2-5 year old child; (2) Methionine plus cystine; (3) Phenylalanine plus tyrosine.

Table 3. Fatty acid composition of insect lipids

(1) Values using cow manure as substrate. Round parentheses are the values obtained on using 50% of cow manure and 50% of fish offal as substrate. Square parentheses are values obtained on swine manure as substrate.

Further reading and source

Harinder P.S. Makkar, Gilles Tran, Valérie Heuzé, Philippe Ankers (2014), State-of-the-art on use of insects as animal feed, Animal Feed Science and Technology, 10.1016/j.anifeedsci.2014.07.008.

Note: this article is available on ResearchGate

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