Citation of this paper

Effect of replacing dietary protein with cassava leaf meal on performance and nutritional composition of two-spotted crickets (Gryllus bimaculatus)

Vo Lam, Nguyen Thi Bich Hanh and Bui Phan Thu Hang

An Giang University Vietnam National University Ho Chi Minh City, Vietnam
volam.agu@gmail.com

Abstract

This study aimed to evaluate growth performance and chemical composition of crickets fed diets containing increasing proportions of cassava leaf meal as partial replacement of dietary protein. Two-spotted crickets (Gryllus bimaculatus) (n=14,400) with a mean initial weight of 3.1±0.2 mg and seven days of age were housed in cages (300 per cage) and fed diets containing increasing proportions (15, 20, 25, 30, 35, 40 and 45%) of cassava leaf meal replacing soybean and fish meal. The design was a randomized block with 8 treatments and 6 replications (300 crickets per treatment/replicate).

There were curvilinear relationships between levels of cassava leaf meal in the diet and the responses in DM intake, liveweight gain and feed conversion. The feed intake continued to increase up to the highest level of intake of cassava leaf meal but at a reduced rate. In contrast, the response in weight gain and feed conversion showed a negative trend as the level of cassava leaf meal in the diet was increased beyond 20%. The composition of the crickets was affected by cassava leaf meal supplementation with curvilinear increases in protein and ash content but with a curvilinear decrease in lipid content as the level of cassava leaf meal in the diet was increased.

Key words: cassava leaf meal, insects, protein

Introduction

Two thousand and one hundred species of insects are consumed as food in over 110 countries (Jongema 2017). Crickets are the most consumed insects (Magara et al 2019, Orinda 2018, Oonincx et al 2015). Crickets have been consumed as food in Africa, Latin America and Asia (Ayieko et al 2016, Gelfand 1971, Séré et al 2018, Bani 1995, Bodenheimer 1951, Feng et al 2017) and are being appreciated in Australia, America and Europe with the appreciation of their role in food security and for their nutritional benefits (EFSA Scientific Committee 2015, Frigerio et al 2020, Instar Farming 2020, Angie 20197). Their potential is related to their nutritional quality and for being environmentally friendly (with low emission of greenhouse gases), the small land requirement for their production as compared to livestock, and as economically feasible alternatives for the food industry in the future (Van Huis et al 2013, Orinda 2018, Oonincx et al 2015, Halloran et al 2018). Crickets have lower feed conversion rates when compared to livestock (Van Huis et al 2013). Crickets also have the potential to use a wide variety of plant material such as food waste and byproducts from agriculture and the food industry. They are credited cleaning the environment (Magara et al 2019, Orinda 2018, Miech et al 2016, Van Huis and Losasso 2017).

Cassava leaves have potential as feed for crickets in Africa and Asia. Cassava leaf meal provides a high level of protein, is rich in minerals, carotene and vitamin C which can be used for feeding livestock (Anya et al 2019, Li et al 2019, Adedokun et al 2021). Fresh cassava leaves are suitable as feed crickets (Bui Phan Thu Hang et al 2020).

The research described in this paper was designed to evaluate the growth performance and chemical composition of crickets fed diets containing increasing levels of cassava leaf meal in partial substitution of soybean and fish meal. The hypothesis was that cassava leaf meal had potential to be to be a major source of protein in the diet of crickets.

Materials and Methods

Location and source of crickets

This study was carried out in a farm located in Long Xuyen city, An Giang province, Vietnam. The crickets (n = 14 400; 7 days old) were sourced from a rearing unit in An Giang University.

Experimental design

The crickets were fed one of the eight experimental diets. The allocation to treatments was according to a Randomized Block Design with 6 replications (each treatment/replicate had 300 crickets). The experiment lasted for 5 weeks.

Feeding and management

Rice bran, maize, soybean meal and fish meal were bought from the local market. Cassava leaves with petioles and stems (Photo1) were collected from sweet cassava plants cultivated in fields around Long Xuyen city. They were dried in an oven at 55-60^oC for 72 h . All ingredients used in the diets were previously ground fine (Photo 2).

Eight diets were formulated to contain a similar crude protein content (Table 1) replacing dietary protein by cassava leaf meal. The diets were offered ad libitum on plastic plates.

Table 1. Ingredients and chemical composition of diets (% as DM)
	0CM	15CM	20CM	25CM	30CM	35CM	40CM	45CM

Rice bran	34	30	27	23	16	17	15	15
Maize	28	20	19	18	20	15	13	9
Soybean meal	21	16	14	14	13	12	10	9
Fish meal	16	15	15	14	14	13	13	12
Cassava leaf meal	0	18	24	30	36	42	48	54
Premix mineral-vitamin	1	1	1	1	1	1	1	1
Chemical compositions , % of DM
Crude protein	22.0	22.0	22.0	22.0	22.0	22.1	22.1	22.1
Ether extract	12.1	11.0	10.5	10.1	9.3	9.3	8.8	8.7
Crude fiber	7.7	9.4	9.8	10.3	10.4	11.2	11.7	12.5

The crickets were confined in plastic mesh cages (Photo 4) with dimensions of 50 cm x 30 cm x 20 cm). Cardboard egg holders (Photo 3) provide hiding and mounting places for the crickets. The crickets in each cage were weighed together at the start of the experiment and then after every week, before feeding in the morning, using an electronic scale. The amounts of feed offered and refused were recorded. Feed conversion ratio was calculated by dividing the total DM consumption by the total weight gain.


Photo 1. Cassava leaves, petioles and fine stems	Photo 2. Cassava leaf meal

Photo 3. Arragement of egg trays	Photo 4. The cages housing the crickets

Chemical analysis

Samples of ingredients and of diets offered and refused were analysed for DM, CP, CF, EE and ash according to AOAC (1990).

Statistical analysis

The data from the experiment were subjected to analysis of variance using the General Linear Model (GLM) procedure of Minitab Software Release version 17 (2013). Sources of variation were treatments and error. Response curves, relating outputs (weight gain, feed conversion and body composition of the crickets) with inputs (percentage of cassava leaf meal in the diet) were determined by fitting polynomial functions (Microsoft Excel Version 10) to the data.

Results and discussion

There were curvilinear relationships between levels of cassava leaf meal in the diet and the responses in DM intake, liveweight gain and feed conversion (Table 2 and 3; Figures 1-3). The feed intake continued to increase up to the highest level of intake of cassava leaf meal, but at a reduced rate. In contrast, the response in weight gain and feet conversion showed negative trends as the level of costs cassava leaf meal in the diet was increased beyond 20%.

Table 2. Feed intake during the experiment, mg/cricket/d
Item	0CM	15CM	20CM	25CM	30CM	35CM	40CM	45CM	SEM	p

Dry matter	37.7^b	47.6^ab	48.2^ab	47.9^ab	49.8^a	51.0^a	49.9^a	53.8^a	2.58	0.007
Crude protein	8.30^b	10.5^ab	10.6^ab	10.6^ab	11.0^a	11.3^a	11.1^a	11.9^a	0.57	0.006
Organic matter	34.6^b	43.3^ab	43.7^ab	43.5^ab	45.3^a	46.2^a	45.1^ab	48.5^a	2.34	0.011
Ether extract	4.56	5.25	5.03	4.85	4.64	4.75	4.41	4.70	0.25	0.353
Crude fiber	2.90^d	4.52^c	4.77^bc	4.95^bc	5.17^bc	5.76^abc	5.88^ab	6.77^a	0.29	0.000
^abcd Means within columns with different superscripts are different at P<0.05

Table 3. Mean values for DM intake, live weight gain and feed conversion of crickets fed increasing proportions of cassava leaf meal
Item	0CM	15CM	20CM	25CM	30CM	35CM	40CM	45CM	SEM	p

DM intake, mg/d	37.7^b	47.6^ab	48.2^ab	47.9^ab	49.8^a	51.0^a	49.9^a	53.8^a	2.58	0.007
Initial weight, mg/cricket	3.1	3.1	3.1	3.0	3.2	3.1	3.2	3.2	0.08	0.75
Final weight, mg/cricket	802^b	1001^ab	1072^a	984^ab	969^ab	980^ab	932^ab	939^ab	44	0.01
ADG, mg/cricket/d	22.8^b	28.5^ab	30.5^a	28.0^ab	27.6^ab	27.9^ab	26.5^ab	26.7^ab	1.3	0.01
FCR, mgDM/mgADG	1.67^bc	1.68^bc	1.58^c	1.70^bc	1.80^abc	1.83^ab	1.88^ab	2.01^a	0.05	0.00
^abc Means within columns with different superscripts are different at p<0.05


Figure 1. Effect of proportion of cassava leaf meal in the diet on DM intake of crickets	Figure 2. Effect of proportion of cassava leaf meal in the diet on growth of crickets

Figure 3. Effect of proportion of cassava leaf meal in the diet on feed conversion ratio of crickets

The levels of crude protein and minerals in the crickets were increased with curvilinear tends as the content of cassava leaf meal in the diet was increased (Table 4, Figure 4 and 6). In contrast, the proportion of lipid on the cricket was reduced as the proportion of cassava leaf meals in the diet was increased (Table 4; Figure 5).

Table 4. Mean values for chemical composition of the cricket’s (% in DM)
Item	0CM	15CM	20CM	25CM	30CM	35CM	40CM	45CM	SEM	p

Dry matter	68.8	69.3	69.9	68.4	69.0	69.5	69.9	71.4	0.84	0.34
% in DM
Crude protein	54.2^g	55.0^f	59.5^cd	58.2^e	58.8^de	59.8^c	61.6^b	65.9^a	0.18	<0.01
Ether extract	30.9^a	29.9^b	30.1^b	28.1^c	28.1^c	26.3^d	23.4^e	21.8^f	0.10	<0.01
Ash	3.49^c	4.06^b	4.66^a	3.74^c	4.15^b	4.85^a	4.30^b	4.88^a	0.07	<0.01
^abcdefg Means within columns with different superscripts are different at p<0.05


Figure 4. Effect of level of cassava leaf meal in the diet on crude protein content of crickets	Figure 5. Effect of level of dietary cassava leaf meal on the ether extract content in the crickets

Figure 6. Effect of level of cassava leaf meal in the diet on the ash content of crickets

Conclusions

The protein and ash content of the crickets were increased with curvilinear trends as the of cassava leaf meal in the diet was increased. By contrast, the lipid content of the crickets was decreased by cassava leaf supplementation.

Acknowledgements

The authors are grateful for the financial for this research from Vietnam National University Ho Chi Minh City (VNU-HCM) under grand number C 2021-16-01/HĐ-KHCN.

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