Insect Meal (Tenebrio molitor) Has High Nutrient Digestibility for Newly Weaned Piglets
Funding: This work was supported by Coordenation for the Improvement of Higher Education Personnel (CAPES) and São Paulo Research Foundation (FAPESP) (PIPE Process 2019/16802/5).
ABSTRACT
This study aimed to evaluate the inclusion of insect larvae meal (Tenebrio molitor) on the apparent total digestibility of dry matter (DM), gross energy (GE), ether extract (EE), crude protein (CP), neutral and acid detergent fiber (NDF and FDA), and the apparent and standardized ileal digestibility of amino acids (Exp.1) and to evaluate the inclusion of insect meal with iron and manganese supplementation on growth performance and serum hemoglobin concentration by collecting blood (day zero), on the 14th and 32nd days of the experiment (Exp.2). The standardized ileal digestibility values for amino acids and crude protein of insect meal were similar to those found for soybean meal, with high metabolizable energy values (Exp.1), and there was no difference in performance for any of the variables analyzed (p ≥ 0.05) in any of the periods (Exp.2). For serum hemoglobin values, there was no interaction (p ≥ 0.05) between the treatments used and the collection days; however, hemoglobin values increased (p < 0.05) at each collection time. It can therefore be concluded that insect meal for pigs can be considered an alternative ingredient to soybean meal as a source of protein in piglet nutrition due to high digestibility of amino acids without deleterious effect on productive performance.
1 Introduction
The fluctuating price of ingredients used in animal feed, such as wheat bran, soybean meal, and corn, is driving the use of alternative ingredients (Khan et al. 2016). Soybean meal is a source of protein for pigs and has an average of 89.6% dry matter (DM) and 45% crude protein (CP) (Rostagno et al. 2017). Although it is the main source of protein used in pig feed because it is rich in lysine, it contains some anti-nutritional factors such as hemagglutinins, saponins, lectins, and trypsin inhibitors, which inhibit the animal's utilization of proteins and other nutrients (Araba and Dale 1990; Hancock et al. 1990). Animal product meal can therefore be used as an alternative ingredient to plant-based protein meals such as soybean meal, due to the absence of many anti-nutritional factors commonly found in plant-based ingredients (Li et al. 1990).
Several studies have shown that piglets perform better when fed animal products such as plasma (Coffey and Cromwell 2001), fish meal (Kim and Easter 2001), or offal meal (Udedibie and Esonu 1987). In turn, insect meal can be used as a protein and amino acid source to replace soybean meal, as it contains amino acids equal to or greater than soybean meal, making it a sustainable and high-quality source (Sánchez-Muros, Barroso, and Manzano-Agugliaro 2014). Among insect meals, Tenebrio molitor meal has around 52.8% CP and 36.1% ether extract (EE) and soybean meal 45.85% CP and 1.40% EE (Makkar et al. 2014). In addition to the protein fraction, insect meal can be used as an energy source due to its high concentration of lipids, with concentrations ranging from 25% (Siemianowska et al. 2013), 32.95% (Jin et al. 2016), or 35% lipids (Makkar et al. 2014).
Iron is an important mineral that directly participates in the constitution of hemoglobin, myoglobin, oxygen transport in the blood and in the mineralization of bone tissue (Spencer and Palmer 2012) and when supplemented in the diet improves the performance of newly weaned piglets (Rincker et al. 2004). Industrial production of insect meal could be developed with iron enrichment to help pig performance, because feeds with iron sources of animal origin have better iron absorption due to the higher proportion of heme radicals (Morris 1987).
Manganese is involved in bone growth, the maintenance of connective tissue, and the metabolism of carbohydrates and lipids, and a deficiency of this mineral is detrimental to the growth and development of piglets (Apple et al. 2005; Kiefer 2005). Its supplementation in piglet diets has been shown to improve production performance (Kerkaert et al. 2021). The inclusion of bran ingredients used in formulations can increase the manganese present in the diet, as its concentration is higher in the outer layer of grains; however, in the most commonly used grains such as corn, soy, wheat, and fishmeal, manganese is considered unavailable to pigs (Baker 2001; Suttle 2010). Due to its low bioavailability in food, manganese has low absorption and high excretion in feces (Leeson and Summers 2001).
However, due to processing and the large number of species used to make the meal, there may be variations in the chemical composition and digestibility of these ingredients. In addition, enriching insect meal with iron and manganese can be advantageous for supplementing these minerals in a more available way. However, little is known about the digestibility of insect meal and its effects on replacing soybean meal in piglet diets enriched with minerals.
The aim of this study was to evaluate the nutrient and energy digestibility of T. molitor insect larvae meal and its use as a mineral-enriched protein source to replace soybean meal in the diet of newly weaned piglets on performance and serum hemoglobin concentration.
2 Materials and Methods
Two experiments were carried out (Exp. 1—digestibility assay and Exp. 2—performance) at the Swine Teaching, Research and Extension Laboratory of the School of Veterinary Medicine and Animal Science (FMVZ - UNESP - Botucatu/SP). All experimental procedures were previously approved by the Animal Use Ethics Committee (CEUA) of FMVZ/UNESP/Botucatu, protocol number 0176/2022.
2.1 Experiment 1—Digestibility
2.1.1 Installation, Animals and Experimental Diets
In Experiment 1, were used 12 castrated male piglets with an initial live weight of 14.58 kg ± 1.23, with an average age of 45 days. They were housed in metabolism cages similar to those described by Pekas (1968), with a width of 0.55 m, a length of 1.30 m, and a height of 1.60 m, with only one compartment for a feeder and a drinker, and before being fed, the water was removed, and after feeding, it was replaced ad libitum. The animals were individually housed (experimental unit) in a randomized block design (by weight), with six replications and two treatments: NF = semi-purified diet, with no inclusion of nitrogen, based on starch, sugar, oil, lignocellulose, as well as sources of minerals and vitamins, with the aim of calculating endogenous nitrogen losses; FI = test diet formulated with the same proportions as NF, but with the inclusion of 30% insect meal as the only source of protein and amino acids (Tables 1 and 2). The experimental period lasted 12 days, with 5 days for the animals to adapt to the cages and to the experimental diets and 7 days for samples collection, with drinking water ad libitum. One group of animals was fed NF diet to measure the AA losses, and another group of pigs was fed test diet with a known proportion of the component from basal diet replacing the test ingredient (Adeola et al. 2016).
| Composition (%) | Starch | Insect meal |
|---|---|---|
| Dry matter | 86.700 | 94.520 |
| Total crude protein | 0.3500 | 49.07 |
| Crude energy (kcal/kg) | 3530 | 6315 |
| Neutral detergent fiber (NDF) | — | 9.59 |
| Acid detergent fiber (FDA) | — | 6.36 |
| Total fat (g/100 g) | — | 35.48 |
| Iron (μg/g) | — | 33.5 |
| Manganese (μg/g) | — | 8.10 |
| Aspartic acid | — | 4.15 |
| Glutamic acid | — | 5.72 |
| Serine | — | 2.28 |
| Glycine | — | 3.13 |
| Histidine | — | 1.50 |
| Arginine | — | 2.81 |
| Threonine | — | 2.04 |
| Alanine | — | 3.59 |
| Proline | — | 2.85 |
| Tyrosine | — | 3.79 |
| Valine | — | 3.24 |
| Methionine | — | 0.80 |
| Cystine | — | 0.29 |
| Isoleucine | — | 2.20 |
| Leucine | — | 3.68 |
| Phenylalanine | — | 1.93 |
| Lysine | — | 2.71 |
| Tryptophan | — | 0.22 |
| Sum of total amino acids | — | 46.93 |
| Ingredients (%) | NF | IM |
|---|---|---|
| Starch | 57.610 | 39.365 |
| Insect meal | 30.000 | |
| Sugar | 30.000 | 20.465 |
| Soybean oil | 3.000 | 2.050 |
| Lignocellulose | 4.000 | 2.730 |
| Lime | 0.450 | 0.450 |
| Bi-calcium phosphate | 2.600 | 2.600 |
| Salt | 0.700 | 0.700 |
| Potassium chloride | 0.520 | 0.520 |
| Choline chloride | 0.070 | 0.070 |
| Magnesium oxide | 0.070 | 0.070 |
| Mineral mixture | 0.100 | 0.100 |
| Vitamin blend | 0.150 | 0.150 |
| Palatability enhancer | 0.030 | 0.030 |
| Zinc oxide | 0.200 | 0.200 |
| Titanium dioxide | 0.500 | 0.500 |
| Total | 100.000 | 100.000 |
| Nutritional values analyzed (natural matter) | ||
| Dry matter (%) | 92.44 | 93.30 |
| Total protein (%) | 0.56 | 15.69 |
| Crude energy (kcal/kg) | 3386 | 4307 |
| Neutral detergent fiber (NDF) (%) | 3.47 | 10.35 |
| Acid detergent fiber (FDA) (%) | 3.26 | 4.11 |
| Total fats (g/100 g) | 2.69 | 10.45 |
| Aspartic acid (%) | — | 1.23 |
| Glutamic acid (%) | — | 1.80 |
| Serine (%) | — | 0.69 |
| Glycine (%) | — | 0.85 |
| Histidine (%) | — | 0.47 |
| Arginine (%) | — | 0.81 |
| Threonine (%) | — | 0.66 |
| Alanine (%) | — | 1.21 |
| Proline (%) | — | 0.82 |
| Tyrosine (%) | — | 1.16 |
| Valine (%) | — | 0.99 |
| Methionine (%) | — | 0.20 |
| Cystine (%) | — | 0.13 |
| Isoleucine (%) | — | 0.68 |
| Leucine (%) | — | 1.15 |
| Phenylalanine (%) | — | 0.59 |
| Lysine (%) | — | 0.85 |
| Tryptophan (%) | — | 0.26 |
| Sum of total amino acids (%) | — | 14.54 |
- Note: NF (basal diet, without nitrogen); IM (test diet with insect meal). Mineral premix providing per kg of feed: 100 mg Fe, 10 mg Cu, 0.45 mg Se, 40 mg Mn, 80 mg Zn, 1 mg Co, 1.5 mg I, 79.70 mg S, 0.30 mg. Vitamin premix providing per kg of feed: 9000 UI vit. A, 2700 UI vit. D3, 48 UI vit. E, 2.5 mg vit. K, 2.03 mg vit. B1, 6 mg vit. B2, 3 mg vit. B6, 30 mg vit. B12, 0.9 mg folic acid, 14.03 mg pantothenic acid, 30 mg niacin, 0.12 mg biotin.
2.1.2 Sample Collection
To determine the start and end of the feces and urine collection period, the feed was marked with 2% ferric oxide (Fe2O3). Also, from the start of the experiment, 0.5% titanium dioxide (TiO2) was added to the experimental diets as an indigestible marker for determining the standardized ileal digestibility of amino acids.
The estimated daily feed intake was calculated as 3% of the live weight (BW) and fed twice a day (07:00 and 17:00 h). Feces and urine samples were collected twice a day, weighed, individually identified and immediately frozen in a freezer at −20 °C. The urine samples were collected in plastic containers containing 20 mL of HCl to prevent NH3 losses and an aliquot of 10% of the total urine was stored.
At the end of the collection phase, on the 12th day of the experiment, 6 h after the last meal, the animals were stunned by electronarcosis with subsequent bleeding and immediately after slaughter, a portion of approximately 1 m of the terminal portion of the ileum was isolated and ileal digesta samples were collected in plastic containers containing formic acid, which were identified and stored in a freezer at −20 °C.
2.1.3 Chemical Analysis
At the end of the collection period, the feces samples were homogenized and dried in a forced circulation oven at 55 °C for 72 h. The dried feces, diets, and test ingredient were ground on a 1 mm sieve and analyzed for DM (Method 930.15, AOAC 2005), ether extract (EE; 2003.06, AOAC 2005), nitrogen (N) to estimate CP (Nx6.25; Method 990.03, AOAC 2006), neutral detergent fiber (NDF), acid detergent fiber (FDA) (Van Soest, Robertson, and Lewis 1991), gross energy (G, IKA Calorimetric Pump model 5000), and titanium (feces and diets, Myers et al. 2004).
The ileal digesta samples were thawed and freeze-dried for analysis of amino acids (AA, method 994.12, AOAC 2005), DM, CP, and titanium. Urine samples were thawed and dried for analysis of DM (Method 930.15, AOAC 2005), nitrogen (N) for estimation of CP (Nx6.25; Method 990.03, AOAC 2006), and crude energy (GE; IKA Calorimetric Pump model 5000).
2.1.4 Digestibility Calculations
The apparent and standardized ileal digestibilities of CP and AA were calculated using the indigestible marker method (Kong and Adeola 2014) and the apparent fecal digestibility of DM, CP, GE, and digestible energy (DE) and metabolizable energy (ME) values of the test ingredient was calculated using the total collection method, according to the method proposed by Zhang and Adeola (2017), considering the contribution of the test ingredient in the test diet, according to the following formula:
Apparent ileal digestibility (AID) = 100–100 × (% diet marker × % ileal digesta nutrient/% ileal digesta marker × % diet nutrient).
Standardized ileal digestibility (SID) = AID + [% digesta nutrient × (% NF diet marker/% NF digesta marker)/% nutrient (DM) test feed] × 100.
2.1.5 Statistical Analysis
As only one food was tested, there was no need for statistical analysis of the data, since the results are not comparative between the basal diet (NF) and the test diet (FI) and the diets were only used for the digestibility calculations.
2.2 Experiment 2—Performance
2.2.1 Installation, Animals and Experimental Diets
The animals were housed in a nursery facility (3.5 ceiling height) with 1.80 m side walls, curtains, and fan with a nebulizer. Each pen was partially slotted with ¼ concrete-solid and ¾ slatted floor (1.70 m2), equipped with drinking nipples, feeder trough type and an electric heat-resistant (radiation heat source).
Thirty-two crossbred 21-day-old piglets (castrated males and females) were used, with an average initial weight of 7.878 ± 0.974, in a randomized block design, housed individually (experimental unit) in the nursery pens up to an average age of 53 days (experimental period of 32 days), eight replications and four treatments, as follows: DB—basal diet based on corn and soybean meal; FI—DB with the inclusion of 6.00% insect meal in the diet; FIFe—DB with the inclusion of 6.00% insect meal enriched with iron in the diet (371 mg Fe/kg insect meal); FIMn—DB with the inclusion of 6.00% insect meal enriched with manganese in the diet (579 mg Mn/kg insect meal).
During the experiment, the piglets were fed three types of feed, according to the phase feeding system: phase 1—pre-starter 1 diet during 14 days (0 to 14 days); phase 2—pre-starter 2 diet for the following 14 days (15 to 28 days); and phase 3—initial diet (29 to 32 days). In each phase, all the feeds were formulated to meet nutritional requirements in essential amino acids, according to the Nutrient Requirements of Swine (NRC 2012) (Tables 3 and 4). All the animals were allowed ad libitum access to feed and water. The diets were formulated based on the amino acid digestibility and metabolizable energy values found in Experiment 1.
| Pre-initial 1 | Pre-initial 2 | Initial | ||||
|---|---|---|---|---|---|---|
| Ingredients | BD | IM | BD | IM | BD | IM |
| Corn, grain | 51.310 | 53.588 | 57.516 | 59.783 | 55.490 | 57.643 |
| Soybean meal | 19.500 | 13.500 | 24.000 | 18.000 | 32.000 | 26.000 |
| Blood plasma | 5.000 | 5.000 | 2.500 | 2.500 | — | — |
| Insect meal | — | 6.000 | — | 6.000 | — | 6.000 |
| Dried whey | 10.500 | 10.500 | 3.500 | 3.500 | — | — |
| Sugar | 5.000 | 5.000 | 5.000 | 5.000 | 5.000 | 5.000 |
| Soybean oil | 3.610 | 1.310 | 2.780 | 0.500 | 3.050 | 0.800 |
| Limestone | 0.220 | 0.220 | 0.105 | 0.120 | 0.040 | 0.050 |
| Bi-calcium phosphate | 2.050 | 2.140 | 2.200 | 2.250 | 2.310 | 2.400 |
| Salt | 0.130 | 0.130 | 0.470 | 0.470 | 0.680 | 0.680 |
| l-Lysine HCl | 0.690 | 0.690 | 0.540 | 0.550 | 0.465 | 0.472 |
| dl-Methionine | 0.195 | 0.185 | 0.140 | 0.130 | 0.120 | 0.110 |
| l-Threonine | 0.225 | 0.207 | 0.155 | 0.132 | 0.130 | 0.110 |
| l-Tryptophan | 0.030 | 0.055 | 0.009 | 0.040 | — | 0.020 |
| l-Valine | 0.135 | 0.070 | 0.060 | — | — | — |
| Zinc oxide | 0.330 | 0.330 | 0.200 | 0.200 | 0.140 | 0.140 |
| Choline chloride (60%) | 0.090 | 0.090 | 0.090 | 0.090 | 0.090 | 0.090 |
| Micotoxin binder | 0.200 | 0.200 | 0.200 | 0.200 | 0.200 | 0.200 |
| Silica | 0.500 | 0.500 | 0.250 | 0.250 | — | — |
| Flavor | 0.015 | 0.015 | 0.015 | 0.015 | 0.015 | 0.015 |
| Mineral premixa | 0.100 | 0.100 | 0.100 | 0.100 | 0.100 | 0.100 |
| Vitamin premixb | 0.150 | 0.150 | 0.150 | 0.150 | 0.150 | 0.150 |
| Halquinol | 0.020 | 0.020 | 0.020 | 0.020 | 0.020 | 0.020 |
| Total | 100.000 | 100.000 | 100.000 | 100.000 | 100.000 | 100.000 |
- Note: DB: basal diet (control treatment, without the inclusion of insect meal); IM: treatment with the inclusion of 6.00 of insect meal (insect meal containing manganese or iron was included in the respective treatments).
- a Mineral premix providing per kg of feed: 100 mg Fe, 10 mg Cu, 0.45 mg Se, 40 mg Mn, 80 mg Zn, 1 mg Co, 1.5 mg I, 79.70 mg S, 0.30 mg.
- b Vitamin premix providing per kg of feed: 9000 IU vit. A, 2700 UI vit. D3, 48 UI vit. E, 2.5 mg vit. K, 2.03 mg vit. B1, 6 mg vit. B2, 3 mg vit. B6, 30 mg vit. B12, 0.9 mg folic acid, 14.03 mg pantothenic acid, 30 mg niacin, 0.12 mg biotin.
| Pre-initial 1 | Pre-initial 2 | Initial | ||||
|---|---|---|---|---|---|---|
| Nutrients | DB | FI | DB | FI | DB | FI |
| ME (kcal/kg) | 3357 | 3376 | 3307 | 3328 | 3305 | 3324 |
| Crude protein (%) | 17.28 | 17.66 | 17.10 | 17.48 | 18.37 | 18.74 |
| Calcium (%) | 0.749 | 0.750 | 0.700 | 0.700 | 0.700 | 0.710 |
| Available phosphorus (%) | 0.450 | 0.460 | 0.426 | 0.430 | 0.422 | 0.430 |
| Lysine SID (%) | 1.510 | 1.514 | 1.300 | 1.310 | 1.260 | 1.265 |
| Methionine SID (%) | 0.430 | 0.460 | 0.370 | 0.307 | 0.365 | 0.370 |
| Threonine SID (%) | 0.890 | 0.900 | 0.760 | 0.777 | 0.733 | 0.744 |
| Tryptophan SID (%) | 0.237 | 0.240 | 0.214 | 0.204 | 0.205 | 0.204 |
| Lactose (%) | 12.060 | 12.060 | 7.020 | 7.020 | 4.500 | 4.500 |
| Sodium (%) | 0.300 | 0.299 | 0.302 | 0.302 | 0.280 | 0.280 |
- Note: DB: basal diet (control treatment, without the inclusion of insect meal); FI: treatment with the inclusion of 6.00 of insect meal (insect meal containing manganese or iron was included in the respective treatments).
- Abbreviations: ME, metabolizable energy; SID, standardized ileal digestibility.
2.2.2 Performance Evaluation and Serum Hemoglobin Concentration
For the performance evaluation, the animals, the feed provided, and the leftovers were weighed every 7 days to determine daily weight gain, daily feed consumption, and feed conversion. The final weighing was carried out on the 32nd day of the experiment, when the animals had reached an average weight of approximately 25 kg. For serum hemoglobin analysis, blood was collected from the animals at the beginning (day 0), on the 14th and 32nd days of the experiment, in appropriate collection tubes containing EDTA as an anticoagulant solution, by puncturing the vena cava using 25 × 8 mm needles through a vacuum system. The samples were kept under refrigeration, without stirring and immediately sent to the laboratory for hemoglobin determination by impedance volumetry (sft), carried out on an automatic analyzer using the hematoclin 2.8 vet kit (Bioclin).
2.2.3 Statistical Analysis
Discrepant data, homogeneity of variance, and normality of residuals were checked using the SAS univariate procedure. The performance data was submitted to analysis of variance using the GLM procedure in SAS. For hemoglobin analysis, the SAS MIXED procedure (SAS Inst. Inc., Cary, NC, USA) was used, with multivariate analysis of variance for the repeated measures model in independent groups and the means compared using the Tukey test and considered significant when p < 0.05.
3 Results
3.1 Digestibility (Exp.1)
The apparent and standardized ileal digestibility coefficients (Tables 5 and 6) and apparent total digestibility values of DM, CP, digestible and metabolizable energy values (Table 7) found for the insect meal used in this experiment showed higher values than those observed in the literature compared to soybean meal.
| Item | Digestibility coefficient (%) | Digestible values (%) | SEM |
|---|---|---|---|
| Crude protein (%) | 91.00 | 44.65 | 1.176 |
| Essential amino acids (%) | |||
| Arginine | 95.70 | 2.69 | 0.337 |
| Histidine | 89.81 | 1.35 | 1.063 |
| Isoleucine | 94.72 | 2.08 | 0.540 |
| Leucine | 94.69 | 3.48 | 0.516 |
| Lysine | 93.88 | 2.54 | 0.674 |
| Methionine | 96.10 | 0.77 | 0.437 |
| Phenylalanine | 94.17 | 1.82 | 0.616 |
| Threonine | 92.70 | 1.89 | 0.672 |
| Tryptophan | 91.89 | 0.20 | 0.938 |
| Valine | 94.47 | 3.06 | 0.563 |
| Non-essential amino acids (%) | |||
| Alanine | 95.00 | 3.41 | 0.463 |
| Aspartic acid | 95.47 | 3.96 | 0.338 |
| Cysteine | 91.88 | 0.27 | 0.714 |
| Glutamine | 95.06 | 5.4 | 0.435 |
| Glycine | 83.70 | 2.68 | 1.564 |
| Proline | 85.67 | 2.44 | 2.303 |
| Serine | 91.43 | 2.08 | 0.769 |
| Tyrosine | 96.33 | 3.65 | 0.394 |
- Abbreviation: SEM, standard error of the mean.
| Item | Digestibility coefficient (%) | Digestible values (%) | SEM |
|---|---|---|---|
| Crude protein (%) | 91.40 | 44.85 | 1.682 |
| Essential amino acids (%) | |||
| Arginine | 98.81 | 2.78 | 0.483 |
| Histidine | 91.78 | 1.38 | 1.830 |
| Isoleucine | 96.63 | 2.13 | 0.719 |
| Leucine | 96.91 | 3.57 | 0.691 |
| Lysine | 96.25 | 2.61 | 1.004 |
| Methionine | 97.96 | 0.78 | 0.538 |
| Phenylalanine | 96.67 | 1.87 | 0.745 |
| Threonine | 96.61 | 1.97 | 1.121 |
| Tryptophan | 97.02 | 0.21 | 1.472 |
| Valine | 96.34 | 3.12 | 0.805 |
| Non-essential amino acids (%) | |||
| Alanine | 97.08 | 3.48 | 0.672 |
| Aspartic acid | 96.64 | 4.01 | 0.648 |
| Cysteine | 96.49 | 0.28 | 1.190 |
| Glutamine | 96.79 | 5.54 | 0.631 |
| Glycine | 92.84 | 2.91 | 2.911 |
| Proline | — | — | 1.332 |
| Serine | 96.09 | 2.19 | 0.471 |
| Tyrosine | 97.32 | 3.69 | 0.788 |
- Abbreviation: SEM, standard error of the mean.
| Item | Inset meal |
|---|---|
| Total apparent digestibility | |
| Dry matter (%) | 84.02 |
| Crude protein (%) | 85.55 |
| Ether extract (%) | |
| Energy values | 5707 |
| Digestible energy (kcal/kg) | 5415 |
3.2 Performance and Hemoglobin Concentration (Exp.2)
There was no difference in performance for any of the variables analyzed (p ≥ 0.05) in any of the periods (p ≥ 0.05) (Table 8). Regarding to serum hemoglobin values, there was no interaction (p ≥ 0.05) between treatments and collection times and no difference between treatments (p ≥ 0.05). However, the hemoglobin values increased (p < 0.05) among the collection times (Table 9).
| BD | IM | IMFe | IMMn | CV (%) | p value | |
|---|---|---|---|---|---|---|
| 0–7 days | ||||||
| Wfinal 7d | 8.989 | 9.133 | 9.170 | 8.877 | 5.4312 | 0.6381 |
| DFC (g) | 0.257 | 0.299 | 0.298 | 0.253 | 35.6520 | 0.3427 |
| DWG (g) | 0.147 | 0.189 | 0.185 | 0.148 | 25.9023 | 0.4325 |
| FD | 1.748 | 1.580 | 1.610 | 1.710 | 28.9734 | 0.9657 |
| 0–14 days | ||||||
| DFC (g) | 0.387 | 0.426 | 0.421 | 0.369 | 18.7440 | 0.0805 |
| DWG (g) | 0.295 | 0.329 | 0.358 | 0.280 | 21.6951 | 0.5243 |
| FD | 1.311 | 1.295 | 1.176 | 1.318 | 11.6711 | 0.1184 |
| 0–28 days | ||||||
| DFC (g) | 0.632 | 0.659 | 0.699 | 0.590 | 14.8479 | 0.0722 |
| DWG (g) | 0.471 | 0.488 | 0.522 | 0.422 | 18.0948 | 0.3566 |
| FD | 1.342 | 1.350 | 1.339 | 1.398 | 8.6396 | 0.4591 |
| 0–32 days | ||||||
| DFC (g) | 1.470 | 1.415 | 1.614 | 1.427 | 14.6939 | 0.7726 |
| DWG (g) | 1.006 | 0.944 | 1.004 | 0.959 | 13.3100 | 0.2395 |
| FD | 1.462 | 1.499 | 1.607 | 1.488 | 10.0413 | 0.2359 |
- Note: BD—basal diet based on corn and soybean meal; IM—BD with the inclusion of 6% insect meal in the diet; IMFe—BD with the inclusion of 6% insect meal enriched with iron in the diet; IMMn—BD with the inclusion of 6% insect meal enriched with manganese in the diet.
- Abbreviation: CV, coefficient of variation.
| Treatmentsa | |||||||
|---|---|---|---|---|---|---|---|
| Variable | Moment | BD | IM | IMFe | IMMn | Averageb | p value interaction |
| Hemoglobin, g/dL* | Start (Day 0) | 11.80 | 9.95 | 10.68 | 11.82 | 11.06a | |
| Middle (Day 14) | 12.02 | 11.97 | 11.71 | 12.02 | 11.93a | 0.1135 | |
| End (32nd day) | 11.86 | 12.21 | 12.48 | 12.18 | 12.18b | ||
| Average | 11.89 | 11.38 | 11.62 | 12.01 | |||
- a BD—basal diet based on corn and soybean meal; IM—BD with the substitution of 6% insect meal in place of soybean meal; IMFe—BD with the substitution of 6% iron-enriched insect meal in place of soybean meal; IMMn—DB with the substitution of 6% manganese-enriched insect meal in place of soybean meal.
- b Differences between collection times (p = 0.0015); different letters in the row differ by Tukey's test (p < 0.05).
4 Discussion
4.1 Digestibility (Exp.1)
The digestibility values of amino acids and crude protein were similar to those found in other ingredients of animal origin, such as fish meal (Kim and Easter 2001), plasma (Coffey and Cromwell 2001), and offal meal (Udedibie and Esonu 1987).
Spranghers et al. (2018), using different levels of Hermetia illucens larvae meal in piglet diets, did not observe negative effects on the amino acids digestibility and its absorption, similar to what was observed in our work. The amino acid and protein digestibility values of insect meal found in our study were higher than the average values found for soybean meal (Rojas and Stein 2013), indicating the high biological value of this ingredient for pigs. The concentrations of NDF and FDA found by Biasato et al. (2019) in black soldier fly (H. illucens) meal were 192.3 g/kg and 87.0 g/kg, respectively, while our data were 95.9 g/kg of NDF and 63.6 g/kg of FDA, showing that the fiber fractions present in insect meal depend on the species used and its chemical components, which can influence digestibility.
Jin et al. (2016) found a linear increase in the digestibility of DM and CP in piglets fed increasing levels of T. molitor meal, which can be explained by the greater availability of the amino acids present in the meal compared to protein sources of plant origin. Tan et al. (2020) observed that the digestibility of all amino acids in Musca domestica meal was higher than in H. illucens meal, showing that the two insects differ in the amount of crude fat and in the concentration of crude protein and amino acids, resulting in greater digestibility in M. domestica meal.
The superior nutritional value of insect meal may be related to the fact that products of animal origin do not have anti-nutritional factors commonly found in products of plant origin Li et al. (1990). The metabolizable energy value found in this study was higher than that suggested by Jin et al. (2016), which was 5258 kcal/kg, for piglets at the same stage. Comparing the digestibility data found by Crosbie et al. (2020) in growing piglets, as data for piglets are not yet available, lower values of digestible (4927 kcal/kg) and metabolizable (4569 kcal/kg) energy were found for H. illucens larvae meal. However, considering the relationship between gross energy and its digestible fractions, the present experiment found values of 90% for digestible energy (5707/6315) and 94% for metabolizable energy (5415/5707), values very close to those found by Crosbie et al. (2020), which was 86% and 93% for digestible energy and metabolizable energy, respectively.
The values found in our work and in the literature for insect meal mentioned above were higher than those described by Rostagno et al. (2017) for soybean meal, which was 3484 kcal/kg for digestible energy and 3240 kcal/kg for metabolizable energy.
4.2 Performance and Hemoglobin Concentration (Exp.2)
Other studies, replacing fish meal with meal from house fly larvae (M. domestica) and soybean meal with meal from soldier fly larvae (H. illucens), respectively, found no difference in the animals' performance (Dankwa, Oddoye, and Mzamo 2000; Neumann, Velten, and Liebert 2018). According to Jin et al. (2016), the use of 6% insect meal to replace soybean meal, similar to our work, improved growth performance and nutrient absorption without any detrimental effect on the animals' immune responses. According to the author, this was due to the good palatability of the meal leading to increased feed consumption and the greater availability of nutrients found in animal protein sources compared to plant sources. Chen (2012), using up to 6% inclusion ofT. molitor larvae meal in the diet of weaned piglets, attributed the better weight gain of animals fed insect meal to the palatability of the meal; however, in our work, no effect on weight gain was observed, which can be explained by the fact that feed consumption was similar between treatments due to our diet being complex and with other highly palatable ingredients. Yoo et al. (2019) also obtained positive effects on the ileal digestibility of amino acids in growing pigs when fed 10% T. molitor meal in the diet, concluding that insect meal has high protein digestibility and can be used as an alternative protein source for growing pigs. In our study, the insect meal had no deleterious effect on pig performance, maybe because the inclusion of 6% of T. molitor larvae meal provides a high amount of amino acids, increasing the digestibility of nutrients.
Newton et al. (1977) observed no differences in average daily feed intake of diets containing H. illucens larvae meal compared to diets containing soybean meal, concluding that the two diets are palatable. The NDF and FDA values found for T. molitor larvae meal in our study were 95.9 g/kg NDF and 63.6 g/kg FDA, while the average described by Rostagno et al. (2017) for soybean meal is 136 g/kg NDF and 78 g/kg FDA, concluding that the lower amount of NDF and FDA present in insect meal improves the digestibility of nutrients and consequently the did not damage the performance of piglets. Biasato et al. (2019) using H. illucens larvae meal in the diet of piglets observed that the final weight of the animals was similar to the weight of pigs using commercial diets, not affecting growth performance and nutrient digestibility, which is similar to the results obtained in this work, showing that the inclusion of flours of animal origin can bring benefits to the feeding of pigs, improving digestibility, similar to soybean meal, without causing damage to the performance of the animals.
Braude et al. (1962) estimated that the iron requirement of piglets in the first week of life is 21 mg of iron for every kilogram of weight. Rincker et al. (2004) supplemented increasing levels of iron in the diet of weaned piglets (0, 25, 50, 100, and 150 mg Fe/kg) to determine the piglets' performance and blood parameters and resulted in a linear increase in the hematological variables for hemoglobin, hematocrit, and transferrin, without reducing the animals' performance. According to Nutrient Requirements of Swine (NRC 2012), the average daily manganese recommendation for pigs from 35 to 135 kg is 4.11 mg/kg, which is considered a low requirement. Kerkaert et al. (2021) tested different levels of manganese (8, 16, and 32 mg Mn/kg) on the performance of pigs and observed an improvement in the growth performance of animals supplemented with 8 mg Mn/kg. Iron in excess of 200 mg (Kadis et al. 1984) and manganese in excess of 400 mg (Jenkins and Hidiroglou 1991) can be toxic to piglets. If we correlate the amounts used in this study, which for each kilogram of feed contained 22,600 μg/g of iron and 34,200 μg/g of manganese, with the amount of feed consumed daily by the piglets, the amounts ingested are within the desirable standards, with no effect on performance or blood parameters.
As for serum hemoglobin, the value of this protein in piglets' blood should be equal to or greater than 10 g/dL (Jain 1993) similar to the data found in our research. Yu et al. (2020) used H. illucens larvae meal for weaned piglets and observed an improvement in the immune response of serum biochemical parameters, which may be similar to the results found, as the amount of hemoglobin present in the blood increased with age. In this study, insect meal was not able to modify the hemoglobin profile in the piglets' blood, which is similar to the results found by Rincker et al. (2004), which may be related to the bioavailability of iron present in insect meal.
In general, insect meal can be considered an alternative protein source in the nutrition of newly weaned piglets due to its excellent nutritional value, high digestibility of amino acids and high metabolizable energy value, without affecting animal performance. In addition, it can be considered a major expansion in animal feed, and in the near future, it will be an alternative feed increasingly present in the nutrition of livestock animals, adding value, viability, and sustainability.
Acknowledgments
To the Coordination for the Improvement of Higher Education Personnel (CAPES) for scholarship supplying. To São Paulo Research Foundation (FAPESP) for financial support (PIPE Process 2019/16802-5).
Conflicts of Interest
The authors declare no conflicts of interest.
