Feed costs account for nearly 70-80% of the total costs in poultry production. In many cases, this may be out of reach for smallholder poultry farmers who lack economies of scale and access to credit. This makes the prospects of utilising insects as a source of protein feasible because they are much cheaper and available throughout the year. However, do these alternative sources offer the same efficacy?
Work has shown that the nutrient composition of insects compare favourably with major conventional protein sources such as fish meal and soybean meal, indicating that insect meals can partially or completely replace such expensive sources and hence contribute to the profitability of smallholder poultry production. In addition, harvesting insects for use as feed ingredients will reduce damage in the crop fields, minimise the use of pesticides for the management of pests and reduce environmental pollution.
This article intends to examine the use of insects and other vermin species as sources of proteins in poultry diets in comparison with the conventional protein sources, and the results of such feeding strategies obtained worldwide.
Biodegradation of poultry manure with pupae has a great potential for recycling of waste materials into protein-rich feeds for poultry and other animals. This aspect is particularly important in areas known to be protein-deficient, such as many tropical and sub-tropical regions.
Houseflies, Musca domestica, are best used for the biodegradation purpose, because of their tremendous reproductive capacity. It has been calculated that in a three-month time a pair of house files could produce enough flies, if all survived, to cover the earth 47 feet deep. Regardless of the usual focus on these particular insects as enemies of man, such insects can produce an impressive amount of pupae and hence provide a reliable source of animal protein for livestock and poultry.
The pupae are separated from the inoculated manure by floating, then dried at 65°C overnight, and removed from the bulk of the residual manure by a vibrating screen. The collected pupae, when properly processed, are highly nutritious having average values of 63% protein, 15.5% fat, 5.3% ash and 580 Kcal of energy/g. Amino acid composition (Table 1) indicates that the protein quality of the pupae is comparable with that of meat-and-bone meal or fishmeal, and superior to soybean oil meal. Pupae are also a good source of limiting amino acids, particularly lysine, methionine and arginine.
In a trial, fly pupae were included in a starter ration of white leghorn chicks either in a pure form or mixed with the residual manure. The diets were fed over a period of three weeks. Performance of chicks on both dietary treatments was compared with another group of chicks fed a control diet with a protein supplement containing fishmeal, soybean meal, and met-and-bone meal.
As shown in Table 2, weight gain and feed efficiency were similar for the chicks fed either the pupae or the control supplement. Performance was however, reduced when the mixture of pupae and the residual manure was fed. The decreased performance in that case may have resulted from the lower protein content and the lower digestibility value attributed by the residual manure.
Grasshoppers prevail mainly in Africa, Australia, Asia, and the Middle-East. A single swarm of grasshoppers can contain up to 10 billion insects weighing approximately 30,000 tonnes. They can thus cover an area of up to 40 square kilometres of arable land, thereby causing severe damage to the crops. Because of the swarming behaviour, this makes grasshoppers relatively easy to harvest. This is usually done in the wild, preferably at night (using artificial light) or in the morning when the temperature is cooler and the insects are less active and easier to catch. The harvesting of grasshoppers for food and feed is an effective means of biologically controlling them and reducing the application of chemical pesticides and hence alleviate environmental pollution.
Grasshoppers are generally rich in CP (50-65%), though some lower values (<30%) have also been reported. the dm is 23-35%, and fat content is quite variable and ranges from relatively low values (><5%) to high ones (>20%). Ca content is rather poor, as in other insect species. The fibre content may be significant and increases with age, i.e. adult insects contain up to 22% neutral detergent fibre (NDF) vs 12% for the nymphs.5%)>30%)>
In feeding terms, grasshopper meal was as palatable as fishmeal when fed to broilers. Attempts have therefore been made to replace a part of fishmeal with grasshopper meal, and as such, partial substitution was generally suitable. In Nigeria, broilers (1-28 days) fed on desert locust meal (Schistocerca gregaria) as a substitute for fishmeal, replacing 50% fishmeal protein with locust meal (1.7% in the diet), resulted in higher body weight gain, feed intake and feed conversion ratio. In China, meal from the grasshopper Acrida cinerea could replace 20% and 40% fishmeal in broiler diets with a similar growth rate and feed consumption as the control diet. In Nigeria, grasshopper meal (unspecified species) at the inclusion levels of 2.5 to 7.5% (weight basis) in broiler diets (1-49 days) depressed weight gain and feed efficiency, though it increased the protein content of the carcass. In a later study, grasshopper meal included at 2.5% in the diet was found to be a suitable and cheaper substitute for imported fishmeal (100% replacement on weight basis) though the overall diet contained slightly less protein (22.2% vs. 22.8%). The meat from free-range grasshopper-fed broilers had lower cholesterol but higher concentrations of total lipid and phospholipids. Higher anti-oxidative potential and longer storage life have also been observed.
Dried bee meal, produced from bees killed after the honey-producing season, has been assessed as a high protein feedstuff in diets of growing turkeys from 6 to 41 days of age. Although higher in crude protein and differing in amino acid composition, dried bee meal was similar to soybean meal in total amino acids and true metabolisable energy.
Live-weight gain and efficiency of feed conversion were improved when the diet contained 150 g bee meal/kg, but was depressed by 300 kg bee meal/kg. The adverse effects may be related to non-protein nitrogen in bee meal or to the toxicity of dried bee venom.
The Mormon cricket (Anabrus simplex) exists in populations of relatively low density throughout most of its range. At certain times and places, however, population explosions or infestations occur in which large numbers of the crickets form roving bands. These bands may include millions of individuals and be found with densities of up to 100 individuals per square meter. These infestations may last years or even decades, and are characterised by a gradual increase and then decrease in population. The factors that trigger these infestations are poorly understood, but are thought to be weather-related.
Several workers have studied the value of Mormon cricket as a feed source for broilers. Broiler chickens (1-21 days) fed a diet of 62% maize grain and 30% cricket meal had better growth than broilers fed a control diet based on maize and fishmeal. In a later experiment, maize-cricket diets in which soybean meal was totally replaced with cricket meal containing 28% (1-3 weeks), 22% (4-6 weeks) and 18% (7-8 weeks) crickets were compared with maize-soybean meal diets in broilers up to 8 weeks. There were no significant differences in weight gain and feed-to-gain ratio; and no adverse effect on the taste of the meat from birds fed the maize-cricket diet was observed.
In other studies, however, performance of chickens fed on Mormon crickets were lower compared to the performance obtained with fishmeal or soybean meal. This result has been attributed to the lower methionine, arginine, and lysine levels in Mormon crickets compared to the other protein sources. Although methionine supplementation may be practical, arginine and lysine supplementation is probably not economical. Mixing ground crickets with a complementary protein, perhaps sunflower, sesame, or peanut meal might lead to economical mixtures adequate in both arginine and lysine and only require methionine supplementation.
The first study on the use of field rats was conducted in 1987 in the Philippines, where millions of rats infest the crop fields throughout the country every year causing great damage, low production, and extreme poverty among farmers. One of the attempts made to solve this problem was to use at least part of the rat population in poultry feeding. Laboratory analyses have revealed that the rat meal contains about 59% CP which is comparable to fishmeal (60% CP) and shrimp meal (56% CP). For the feeding trial, rat meal was prepared from freshly collected dead rats in newly ploughed rice and corn fields. They were then boiled in cooking vats and dried under the sun for 3-4 days, and were finally ground in hummer mills.
A performance study was then conducted to compare weight gain, feed efficiency, and feed cost of broiler chickens fed on diets containing 10% rat meal, 10% fishmeal, and 10% shrimp meal over a 45-day period. Results are given in Table 3. The non-significant differences between the three treatments obviously indicate that the rat meal has comparable feeding value and can substitute shrimp or fishmeal in broiler diets. The use of rats in feeding also has an economic advantage due to the lower cost compared to the other protein sources, in addition to the advantage of reducing crop damage due to a minimised rat population.
Silk worm pupae
Silkworm pupae remnants after the removal of cocoons for silk manufacture are the major by-product of the silk industry of the Orient. Significant quantities of spent silkworm pupae are available in China, Japan and India. In China, the annual availability of silkworm pupae is estimated to be over 150,000 tonnes. The pupae contain about 48% crude protein and 27% crude fat, and require de-oiling to improve their keeping quality. De-oiling is also necessary to remove the highly unsaturated fats that affect the flavour of poultry meat. De-oiled silkworm pupae meal may contain as much as 80% crude protein.
Silkworm pupae meal has been successfully used to replace fish meal completely in layer diets and to replace up to 50% of the fish meal in chick diets. The presence of unidentified production factors which lead to improved feed efficiency, egg weight, fertility and hatchability have also been reported. It is suggested that ecdysteroids, a hormone involved in the metamorphosis of the pupae, may be responsible for these performance-stimulating effects. Another feature that may enhance the feed value of silkworm pupae meal is its high vitamin content.
Silk worm pupae have also been used in other countries as a top class unconventional protein and energy feed for poultry. In Bangladesh, for example, such a feed source has been used in place of fishmeal owing to the following reasons:
In one of the numerous feeding studies, silk worm pupae have been used in 2 dietary treatments, namely 0% fishmeal + 6% silk worm pupae, and 6% fishmeal + 0% silk worm pupae fed with basal diets to broiler chickens from day-1 through 42 days of age. Results are shown in Table 4. Here it is clearly shown that the use of silk worm pupae in place of fishmeal has resulted in higher performance and better economic returns without compromising health or survivability of the birds.
References available on request
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