Introduction
In the poultry sector, chicken rearing in alternative systems, such as free-range or organic, is a profitable alternative, in a market with a great number of consumers willing to pay higher prices for the obtainable food products. Furthermore, the free-range system has a positive effect on meat quality traits (Castellini et al., Reference Castellini, Mugnai and Dal Bosco2002; Fanatico et al., Reference Fanatico, Cavitt, Pillai, Emmert and Owens2005, Reference Fanatico, Pillai, Emmert and Owens2007). Castellini et al. (Reference Castellini, Mugnai and Dal Bosco2002) reported that the chicken meat quality enhancement in free-range birds is due to the higher total n-3 polyunsaturated fatty acid (PUFA) content in free-range birds, when compared with standard breeding. Regarding diet availability for free-range chickens, the birds roam freely through meadows and mimic their original foraging dietary habits, eating not only grass but also earthworms from the soil (Fanatico, Reference Fanatico2006; Sossidou et al., Reference Sossidou, Dal Bosco, Elson and Fontes2011). The search for alternative feeds which can make the production of free-range birds viable is a way to adequately and economically replace the traditionally used feedstuffs. The use of insects as an alternative and attractive natural protein source in animal feeding is becoming globally more appealing, especially due to its high sustainability (van Huis and Oonincx, Reference van Huis and Oonincx2017). Chickens with access to outdoor areas pick up insects at all life stages and eat them voluntarily, which indicates that they are evolutionarily adapted to eat insects as a natural part of their diet (Biasato et al., Reference Biasato, De Marco, Rotolo, Renna, Dabbou, Capucchio, Biasibetti, Tarantola, Costa, Gai, Pozzo, Dezzutto, Bergagna, Gasco and Schiavone2016). Current research has highlighted that insect-based protein meals could represent a valid alternative to conventional protein sources (fish or plant protein meals) or as a complementary feed source for poultry (Biasato et al., Reference Biasato, Gasco, De Marco, Renna, Rotolo, Dabbou, Capucchio, Biasibetti, Tarantola, Bianchi, Cavallarin, Gai, Pozzo, Dezzutto, Bergagna and Schiavone2017, Reference Biasato, Gasco, De Marco, Renna, Rotolo, Dabbou, Capucchio, Biasibetti, Tarantola, Sterpone, Cavallarin, Gai, Pozzo, Bergagna, Dezzutto, Zoccarato and Schiavone2018; Schiavone et al., Reference Schiavone, De Marco, Martínez, Dabbou, Renna, Madrid, Hernandez, Rotolo, Costa, Gai and Gasco2017a).
The use of insect meals in poultry feeds is not currently allowed in the European Community. Given, however, the potential ecological advantages and a good acceptance among producers and consumers (Verbeke et al., Reference Verbeke, Spranghers, De Clercq, De Smet, Sas and Eeckhout2015), it seems likely that the political legal frameworks may change in the near future, making the utilization of insect protein possible. This would imply a valuable potential also for organic systems (Leiber et al., Reference Leiber, Gelencsér, Stamer, Amsler, Wohlfahrt, Früh and Maurer2017). Among insect species, yellow mealworm (Tenebrio molitor L.; TM), belonging to the Tenebrionidae family, is currently considered one of the most promising insect species to be used as an innovative protein source for fishmeal and soybean meal (SBM) substitution in fish (Belforti et al., Reference Belforti, Gai, Lussiana, Renna, Malfatto, Rotolo, De Marco, Dabbou, Schiavone, Zoccarato and Gasco2015; Gasco et al., Reference Gasco, Henry, Piccolo, Marono, Gai, Renna, Lussiana, Antonopoulou, Mola and Chatzifotis2016; Iaconisi et al., Reference Iaconisi, Marono, Parisi, Gasco, Genovese, Maricchiolo, Bovera and Piccolo2017; Piccolo et al., Reference Piccolo, Iaconisi, Marono, Gasco, Loponte, Nizza, Bovera and Parisi2017) and poultry (Bovera et al., Reference Bovera, Piccolo, Gasco, Marono, Loponte, Vassalotti, Mastellone, Lombardi, Attia and Nizza2015, Reference Bovera, Loponte, Marono, Piccolo, Parisi, Iaconisi, Gasco and Nizza2016; Biasato et al., Reference Biasato, De Marco, Rotolo, Renna, Dabbou, Capucchio, Biasibetti, Tarantola, Costa, Gai, Pozzo, Dezzutto, Bergagna, Gasco and Schiavone2016, Reference Biasato, Gasco, De Marco, Renna, Rotolo, Dabbou, Capucchio, Biasibetti, Tarantola, Bianchi, Cavallarin, Gai, Pozzo, Dezzutto, Bergagna and Schiavone2017, Reference Biasato, Gasco, De Marco, Renna, Rotolo, Dabbou, Capucchio, Biasibetti, Tarantola, Sterpone, Cavallarin, Gai, Pozzo, Bergagna, Dezzutto, Zoccarato and Schiavone2018; Schiavone et al., Reference Schiavone, De Marco, Martínez, Dabbou, Renna, Madrid, Hernandez, Rotolo, Costa, Gai and Gasco2017a) feeds.
Gasco et al. (Reference Gasco, Gai, Maricchiolo, Genovese, Ragonese, Bottari, Caruso, Gasco, Gai, Maricchiolo, Genovese, Ragonese, Bottari and Caruso2018) mentioned that TM larvae and adults contain a high amount of crude protein (CP) (44.1–60.3% dry basis) even if it has recently been reported that insect protein content is slightly overestimated due to the use of a wrong nitrogen to protein conversion factor (Janssen et al., Reference Janssen, Vincken, van den Broek, Fogliano and Lakemond2017; Nery et al., Reference Nery, Gasco, Dabbou and Schiavone2018). Using the appropriate conversion factor, Janssen et al. (Reference Janssen, Vincken, van den Broek, Fogliano and Lakemond2017) reported that TM larvae contain about 45% of CP.
Bovera et al. (Reference Bovera, Piccolo, Gasco, Marono, Loponte, Vassalotti, Mastellone, Lombardi, Attia and Nizza2015) compared the amino acid (AA) profile of TM larvae with SBM and reported that the two protein sources had a different composition in essential AAs, and this was particularly manifested for methionine and cystein. The authors concluded that only methionine and lysine contents limit the use of TM in poultry feeds.
In addition, TM contains fat (16.6–43.1% dry basis), minerals and vitamins (Gasco et al., Reference Gasco, Gai, Maricchiolo, Genovese, Ragonese, Bottari, Caruso, Gasco, Gai, Maricchiolo, Genovese, Ragonese, Bottari and Caruso2018). It has been recently demonstrated that insect fat can successfully substitute conventional lipid sources in poultry diets, without affecting growth performance and gut histology (Schiavone et al., Reference Schiavone, Cullere, De Marco, Meneguz, Biasato, Bergagna, Dezzutto, Gai, Dabbou, Gasco and Dalle Zotte2017b, Reference Schiavone, Dabbou, De Marco, Cullere, Biasato, Biasibetti, Capucchio, Bergagna, Dezzutto, Meneguz, Gai, Dalle Zotte and Gasco2018). Owing to the reasons mentioned above, the potential of insect protein and lipid in poultry diets has attracted much attention. In addition, in the only available study on free-range chickens, TM provided satisfactory results in terms of growth performance and gut morphology (Biasato et al., Reference Biasato, De Marco, Rotolo, Renna, Dabbou, Capucchio, Biasibetti, Tarantola, Costa, Gai, Pozzo, Dezzutto, Bergagna, Gasco and Schiavone2016). However, there is still a lack of published data on the effects of dietary dried mealworm on meat quality of free-range chickens. Therefore, the aim of this study was to evaluate the effects of the inclusion of a full-fat TM larva meal in a diet for free-range chickens on their meat quality and fatty acid (FA) profile.
Materials and methods
Ethical approval
The study was performed by the Department of Veterinary Science (DVS) and the Department of Agricultural, Forest and Food Sciences of the University of Turin (Italy) in collaboration with a private farm called ‘Fattoria La Fornace’, located in Montechiaro d'Asti (Asti, Italy). The experimental protocol was designed according to the guidelines of the current European and Italian laws on the protection of animals used for scientific purposes (Directive 2010/63/EU, put into force in Italy with D.L. 2014/26). Furthermore, the experimental protocol was approved by the Ethical Committee of the DVS (protocol no. 1/2016).
Experimental design and feeds’ preparation
A detailed description of the experimental design is reported in Biasato et al. (Reference Biasato, De Marco, Rotolo, Renna, Dabbou, Capucchio, Biasibetti, Tarantola, Costa, Gai, Pozzo, Dezzutto, Bergagna, Gasco and Schiavone2016). Briefly, at the age of 43 days, 140 female Label Hubbard hybrid chickens (female: JA 57 × male: S77CN; average initial live weight (LW): 716.26 ± 22.54 g), a medium-growing genotype, were randomly allotted to two groups (each consisting of five pens as replicates, with 14 birds per pen). Each pen had an indoor area (2.5 m × 3.5 m) and an outdoor paddock of the same dimensions. The indoor floor was covered, to a height of 10 cm, with wood shaving litter. The birds were exposed to natural light only. A full-fat TM meal purchased from Gaobeidian Shannong Biology Co. Ltd. (Hebei, China) was used. Two diets were formulated: a control diet, widely used in commercial farms, and an experimental diet with 75 g kg−1 of TM meal in substitution of corn gluten meal (Table 1). The diets were designed to meet or exceed National Research Council (1994) requirements and were formulated to be isonitrogenous and isoenergetic using the apparent metabolizable energy values for TM calculated for broiler chickens (De Marco et al., Reference De Marco, Martínez, Hernandez, Madrid, Gai, Rotolo, Belforti, Bergero, Katz, Dabbou, Kovitvadhi, Zoccarato, Gasco and Schiavone2015). Chickens had ad libitum free access to water and feed throughout the whole trial. As reported in Biasato et al. (Reference Biasato, De Marco, Rotolo, Renna, Dabbou, Capucchio, Biasibetti, Tarantola, Costa, Gai, Pozzo, Dezzutto, Bergagna, Gasco and Schiavone2016), the average daily intake did not differ between groups (112.8 and 111.6 g for control and TM groups, respectively). All the birds were individually identified with a shank ring.
Table 1. Ingredients (g kg−1 as feed), chemical composition (g kg−1 DM, unless otherwise stated) and FA profile (g/100 g DM) of the experimental diets
SBM, soybean meal; TM, Tenebrio molitor; DM, dry matter; CP, crude protein; EE, ether extract; CF: crude fiber; FA, fatty acids; c, cis; Other FA = (C12:0 + C14:1 c9 + C18:3 n-6 + C20:1 c9 + C20:1 c11) – all <45 g/100 g DM in the diets; SFA, saturated fatty acids = (C12:0 + C14:0 + C16:0 + C18:0 + C20:0); MUFA, monounsaturated fatty acids = (C14:1 c9 + C16:1 c9 + C18:1 c9 + C18:1 c11 + C20:1 c9 + C20:1 c11); PUFA, polyunsaturated fatty acids = (C18:2 n-6 + C18:3 n-3 + C18:3 n-6); TFA, total fatty acids. All values are reported as mean of duplicate analyses.
a The vitamin–mineral premix (Trevit Volatili 3.5, Trei, Rio Saliceto (RE), Italy) given values are supplied per kg diet: 22,750 IU of vitamin A; 2275 IU of vitamin D3; 22.75 IU of vitamin E; 2.80 mg of vitamin K; 2.80 mg of vitamin B1; 5.25 mg of vitamin B2; 26.95 mg of vitamin B3; 2.80 mg of vitamin B6; 0.02 mg of vitamin B12; 8.40 mg of pantothenic acid; 164.50 mg of betaine; 61.25 mg of iron(II) carbonate; 64.22 mg of magnesium oxide; 56.42 mg of zinc oxide; 6.23 mg of copper(II) oxide; 0.64 mg of potassium iodide; 0.23 mg of sodium selenite; 143.50 mg of DL-methionine; 192.50 mg of L-lysine; 4.20 g calcium carbonate; 15.75 g calcium phosphate; 0.40 g of sodium chloride.
Chemical composition and FA profile of experimental diets
The diets were ground to pass through a 0.5-mm sieve. Samples were analyzed for dry matter (DM, #934.01), and CP (#984.13) according to AOAC International (2000); ether extract (EE, #2003.05) and crude fiber (CF, #962.09) were determined following the procedures of AOAC International (2003) and (2005), respectively. All chemical analyses were performed in duplicate.
A combined direct trans-esterification and solid-phase extraction (Alves et al., Reference Alves, Cabrita, Fonseca and Bessa2008) was used for the determination of the FA profile of the diets. Separation, identification and quantification of fatty acid methyl esters (FAME) were performed as reported by Renna et al. (Reference Renna, Gasmi-Boubaker, Lussiana, Battaglini, Belfayez and Fortina2014). The results are expressed as g/100 g DM. The proximate and FA compositions of experimental diets are reported in Table 1.
Slaughtering procedures and muscle sampling
At 97 days of age, ten birds (two birds/pen) from each feeding group (chosen on the basis of pen average final LW) were individually identified and weighed. The chickens were electrically stunned and then slaughtered at a commercial abattoir. The plucked and eviscerated carcasses were obtained, and the head, neck, feet and abdominal fat were removed to obtain the chilled carcass. The weight of the breasts, thighs, deboned thighs and abdominal fat were immediately recorded. The breast and thigh weights were expressed as percentage of LW. A total of ten breasts and ten thighs were collected in their right and left side, individually vacuum-sealed and refrigerated (4 ± 1 °C). Meat quality parameters (pH24, color and drip losses) were assessed on the Pectoralis major muscle on the right breast and on the Biceps femoris muscle on the right thigh, while the left breast and thigh meat were frozen at −20 °C until further chemical analysis (proximate composition and FA profile).
Meat quality parameters
pH24
The pH at 24 h postmortem was measured in duplicate using a Crison portable pH-meter (Crison Instruments, S.A., Alella, Spain) fitted with a spear-type electrode and an automatic temperature compensation probe.
Color
Meat color was measured at 24 h postmortem using a portable colorimeter Chroma Meter CR-400 Minolta (Minolta Sensing Inc., Osaka, Japan) with an 8 mm diameter measuring area, D65 illuminant and 2° standard observer. The results were expressed in terms of lightness (L*), redness (a*) and yellowness (b*) in the CIELAB color space (Commission Internationale de l’Éclairage, 1976). Chroma (C*) and hue (H*) indexes were calculated using the following equations: C* = (a*2 + b*2)0.5; H* = tan−1(b*/a*); H* = 180 + tan−1(b*/a*), when a* < 0.
Chroma refers to the vividness or dullness of a color. Hue is the name of the color and is that quality by which we distinguish color families (red, green, blue, etc.). The color values were obtained considering the average of three readings per sample.
Drip losses
Twenty-four hours after slaughtering, breast and thighs were weighed and placed within a container on a supporting mesh and sealed. The samples were blotted for the excess surface fluids and reweighed. Drip losses were determined as percentage of weight lost by the samples during the refrigerated storage period (Honikel, Reference Honikel1998).
Proximate composition and FA profile
Breast and thigh samples were cut, homogenized and divided into two parts. A portion was used to determine moisture (#950.46) and ash (#920.153) contents according to AOAC International (2000) procedures. The remaining part was freeze-dried and afterward analyzed for protein and EE contents, and FA composition. The total N content was determined according to the Dumas method, using a macro-N Nitrogen analyzer (Foss Heraeus Analysensysteme, Hanau, Germany). The content of CP was calculated by multiplying the measured nitrogen quantity by the appropriate nitrogen-to-protein conversion factor (6.25). The EE content was determined by Soxhlet extraction with petroleum ether according to method #991.36 of AOAC International (2000). Proximate composition results were expressed as g/100 g of fresh matter (FM).
The FA composition was assessed in detail as in Renna et al. (Reference Renna, Brugiapaglia, Zanardi, Destefanis, Prandini, Moschini, Sigolo and Lussiana2019). Peaks were identified by injecting pure FAME standards as detailed by Renna et al. (Reference Renna, Cornale, Lussiana, Malfatto, Fortina, Mimosi and Battaglini2012). Quantification was assessed using tridecanoic acid (C13:0) as an internal standard. The results were expressed as g/100 g of total detected FA.
The atherogenicity (AI) and thrombogenicity (TI) indexes were calculated according to Ulbricht and Southgate (Reference Ulbricht and Southgate1991) as follows:
$$\eqalign{& {\rm AI} = \displaystyle{{{\rm C}12:0 + 4 \times {\rm C}14:0 + {\rm C}16:0} \over {\Sigma {\rm MUFA} + \Sigma {\rm n}-6 + \Sigma {\rm n}-3}} \cr & {\rm TI} = \displaystyle{{{\rm C14}:0 + {\rm C16}:0 + {\rm C18}:0} \over {0.{\rm 5} \times \Sigma {\rm MUFA} + 0.{\rm 5} \times \Sigma {\rm n}-6 + {\rm 3} \times \Sigma {\rm n}-3 + \Sigma {\rm n}-3/\Sigma {\rm n}-6}}} $$where MUFAs are monounsaturated FA.
Statistical analysis
The statistical analysis was performed using IBM SPSS Statistics v.21.0 for Windows (IBM SPSS Statistics, Armonk, NY, USA). The effects of the diet on the carcass characteristics, as well as on quality parameters, proximate composition and FA profile of meat were analyzed using Student's t-tests for independent samples. The assumption of normality and homogeneity of variance was assessed using Shapiro–Wilk and Levene's tests, respectively. Results are reported as means and standard error of the mean (SEM). Significance was declared as P < 0.05. A statistical trend was considered for 0.05 < P ≤ 0.10.
Results and discussion
The current study provides new insights into the use of TM larva meal in the diet of medium-growing chickens reared under free-range conditions. All the experimental groups were kept on the same farm and were reared with the same free-range production system, allowing the birds to have access to outdoor paddocks. No mortality was recorded throughout the trial.
Carcass characteristics
The effect of TM larva meal on carcass traits is reported in Table 2. Dietary TM inclusion did not affect the carcass characteristics of the birds. These results confirm the possibility of using insect meals in the diets of medium-growing hybrid chickens as an interchangeable ingredient compared with the conventional ingredients used in chicken nutrition. This promising result reinforces the potential of this innovative feed ingredient for poultry. To the best of our knowledge, no studies are currently available in the literature on the use of TM larva meals in free-range chicken nutrition. For this reason, all the comparisons with literature data were performed with chickens or other farmed birds. The results of this study are in agreement with those reported by Bovera et al. (Reference Bovera, Loponte, Marono, Piccolo, Parisi, Iaconisi, Gasco and Nizza2016) and Biasato et al. (Reference Biasato, Gasco, De Marco, Renna, Rotolo, Dabbou, Capucchio, Biasibetti, Tarantola, Sterpone, Cavallarin, Gai, Pozzo, Bergagna, Dezzutto, Zoccarato and Schiavone2018) who did not find an influence of TM meal on slaughtering performance of broiler chickens. The results obtained in this trial do not always agree with those reported in other studies performed using TM. Indeed, Ballitoc and Sun (Reference Ballitoc and Sun2013), using increasing levels of TM larva meals (0.5, 1, 2 and 10% as feeds), found improved slaughter yield, dressed carcass and eviscerated weights in broiler chicken-fed TM diets with a 2% inclusion level. Biasato et al. (Reference Biasato, Gasco, De Marco, Renna, Rotolo, Dabbou, Capucchio, Biasibetti, Tarantola, Bianchi, Cavallarin, Gai, Pozzo, Dezzutto, Bergagna and Schiavone2017) evaluated the effects of a partial replacement of SBM, corn gluten meal and soybean oil with TM larva meal on carcass characteristics of female broiler chickens, finding an increase of the carcass weight, abdominal fat weight and abdominal fat percentage with increasing levels of TM meal utilization. Hussain et al. (Reference Hussain, Khan, Sultan, Chand, Khan, Alam and Ahmad2017), including different levels of TM meal (1, 2 and 3 g kg−1 of diet) in a broiler diet, showed an improvement of carcass yield in all mealworm-supplemented broiler groups compared with a control group. Loponte et al. (Reference Loponte, Nizza, Bovera, De Riu, Fliegerova, Lombardi, Vassalotti, Mastellone, Nizza and Moniello2017), in a trial with barbary partridge (Alectoris barbara), formulated five diets substituting 25 and 50% of the SBM protein with TM larva meal and a defatted Hermetia illucens (HI) larva meal, respectively. The authors found improvements of carcass weights. In contrast, Cullere et al. (Reference Cullere, Tasoniero, Giaccone, Miotti-Scapin, Claeys, De Smet and Dalle Zotte2016) in broiler quails and Schiavone et al. (Reference Schiavone, Cullere, De Marco, Meneguz, Biasato, Bergagna, Dezzutto, Gai, Dabbou, Gasco and Dalle Zotte2017b, Reference Schiavone, Dabbou, De Marco, Cullere, Biasato, Biasibetti, Capucchio, Bergagna, Dezzutto, Meneguz, Gai, Dalle Zotte and Gasco2018) in chicken-fed diets with HI meal and fat, respectively, did not find significant effects on carcass traits.
Table 2. Effect of TM larva meal on the carcass traits of the free-range chickens
TM, Tenebrio molitor; LW: live weight; SEM, standard error of the mean.
Meat quality parameters of breast and thigh muscles
The pH24, color and drip loss values of breast and thigh muscles of free-range chickens are reported in Table 3. All these meat quality traits were not affected by treatment. For both groups, breast pH24 fell in the range of standard poultry meat (5.77 and 5.73 for the control and TM groups, respectively), as for values lower than 5.7 and higher than 6.2, breast broiler can be classified as pale, soft and exudative or dark, firm and dry, respectively (Fletcher et al., Reference Fletcher, Qiao and Smith2000). Our results are in contrast with those reported by Bovera et al. (Reference Bovera, Loponte, Marono, Piccolo, Parisi, Iaconisi, Gasco and Nizza2016), who observed a higher pH value of breast muscle of broiler chicken-fed TM compared with a control group. On the contrary, Cullere et al. (Reference Cullere, Tasoniero, Giaccone, Miotti-Scapin, Claeys, De Smet and Dalle Zotte2016) in broiler quail-fed diets with increasing levels of HI larva meal reported a decrease in breast muscle pH and demonstrated that the differences could be ascribable to different muscle glycogen contents. The observed differences could be related to species, genotype and rearing system (Mir et al., Reference Mir, Rafiq, Kumar, Singh and Shukla2017).
Table 3. Effect of TM larva meal on the quality parameters of P. major (breast) and B. femoris (thigh) muscles of the free-range chickens
TM, Tenebrio molitor; SEM, standard error of the mean.
Meat color is a very important quality parameter since it is directly perceived by the consumer. In our trial, the use of TM did not influence color parameters (P > 0.05). To the best of our knowledge, no published data are currently available comparing muscle color of free-range chicken-fed TM meals and other diets. In broiler chickens, Bovera et al. (Reference Bovera, Loponte, Marono, Piccolo, Parisi, Iaconisi, Gasco and Nizza2016) did not find a significant effect on raw and cooked color meat, as well as on skin, and they showed that meat from broiler-fed TM meal could be easily accepted by consumers. A significant decrease for L* was reported by Pieterse et al. (Reference Pieterse, Pretorius, Hoffman and Drew2014) in breast muscle of broiler-fed diets containing Musca domestica larva meals compared with a fish meal-based diet. Using HI larva meal in broiler quails, Cullere et al. (Reference Cullere, Tasoniero, Giaccone, Miotti-Scapin, Claeys, De Smet and Dalle Zotte2016) observed that redness index (a*) in the cranial and caudal part of the P. major muscle of broiler quails was significantly affected by the treatment and showed its highest (1.13) and lowest (0.46) values for HI groups, corresponding to 10 and 15% HI inclusion levels, comparing with a control group (0.81).
Proximate composition of breast and thigh meat
The proximate composition (water, ash, CP and EE) of breast and thigh meat was not affected by the dietary treatment (Table 4). The absence of differences in the proximate composition of meat from the two groups of chickens is an important finding for the positive evaluation of this new ingredient as a novel alternative feed in poultry nutrition. Our results are in agreement with those reported by Bovera et al. (Reference Bovera, Loponte, Marono, Piccolo, Parisi, Iaconisi, Gasco and Nizza2016). These authors did not find a significant effect on the proximate composition of meat obtained from the breast of broiler-fed diets containing TM larva meal during the growing period. The same results were found by Cullere et al. (Reference Cullere, Tasoniero, Giaccone, Acuti, Marangon and Dalle Zotte2018) in broiler quails and Schiavone et al. (Reference Schiavone, Cullere, De Marco, Meneguz, Biasato, Bergagna, Dezzutto, Gai, Dabbou, Gasco and Dalle Zotte2017b) in chicken-fed diets with HI meal and fat, respectively. Ballitoc and Sun (Reference Ballitoc and Sun2013), including different levels of TM meal (0.5, 1, 2 and 10%) in a standard commercial broiler diet, reported that the inclusion level of 1% of TM showed the highest and lowest percentages of moisture in the thigh and breast portion, respectively, as compared with the other groups. These authors reported that, compared with a control group, the group fed with 1% TM meal had a higher percentage of protein in the breast portion of the meat. The higher TM inclusion level (10%) in the trial performed by Ballitoc and Sun (Reference Ballitoc and Sun2013) showed the highest percentage of fat for thigh and breast (6.30 and 1.25%, respectively); such values are comparable with those obtained in our experimental trial (5.64 and 0.50% of FM).
Table 4. Effect of TM larva meal on the proximate composition (g/100 g FM) of breast and thigh meat of the free-range chickens
TM, Tenebrio molitor; CP, crude protein; EE, ether extract; SEM, standard error of the mean.
FA profile of breast and thigh meat
The FA composition of the full-fat TM larva meal used in this trial was very similar to that recently reported for dietary TM oil by Kierończyk et al. (Reference Kierończyk, Rawski, Józefiak, Mazurkiewicz, Świątkiewicz, Siwek, Bednarczyk, Szumacher-Strabel, Cieślak, Benzertiha and Józefiak2018).
Table 5 shows the differences observed in terms of FA composition of breast and thigh meats between the control and TM groups. As expected, the predominant FA in the breast and thigh meat of the free-range chicken-fed both the control and TM diets was C18:1 c9 (breast: 32.00 and 34.67 g/100 g total FA, respectively; thigh: 38.21 and 39.41 g/100 g total FA) followed by C16:0 (breast: 32.67 and 30.40 g/100 g total FA; thigh: 26.67 and 26.44 g/100 g total FA) and C18:2 n-6 (breast: 14.99 and 14.93 g/100 g total FA; thigh: 15.89 and 15.43 g/100 g total FA).
Table 5. Effect of TM larva meal on the FA composition (g/100 g of total FA) of breast and thigh meat of the free-range chickens
TM, Tenebrio molitor; c, cis; nd, not detected; SEM, standard error of the mean; SFA, saturated fatty acids = (C12:0 + C14:0 + C16:0 + C18:0 + C20:0); MUFA, monounsaturated fatty acids = (C16:1 c9 + C18:1 c9 + C18:1 c11 + C20:1 c11); PUFA, polyunsaturated fatty acids = (C18:2 n-6 + C18:3 n-3 + C18:3 n-6 + C20:2 n-6 + C20:3 n-6 + C20:4 n-6); AI, atherogenicity index; TI, thrombogenicity index; TFA, total fatty acids; FM, fresh matter.
The TM group showed significantly higher C18:1 c9 and C18:3 n-3 (P < 0.05) percentages, a tendency (P < 0.10) toward higher ΣMUFA rates, and contemporarily lower C16:0 and Σsaturated fatty acid (SFA) rates in breast meat. Regarding thigh meat, only negligible differences were observed, with significantly higher rates of C14:0 and C20:0, in the TM group. Oleic acid is the predominant FA in TM larvae (Paul et al., Reference Paul, Frederich, Caparros Megido, Alabi, Malik, Uyttenbroeck, Francis, Blecker, Haubruge, Lognay and Danthine2017) and increased C18:1 c9 and ΣMUFA deposition in the breast muscle of chickens fed a diet containing TM oil when compared with a diet containing soybean oil has recently been reported by Kierończyk et al. (Reference Kierończyk, Rawski, Józefiak, Mazurkiewicz, Świątkiewicz, Siwek, Bednarczyk, Szumacher-Strabel, Cieślak, Benzertiha and Józefiak2018). These authors also showed a significant reduction in ΣSFA in breast muscle when using dietary TM oil.
Feeding broilers with a diet containing full fat TM meal resulted in an increased C12:0 and C14:0 percentages in breast meat (Loponte et al., Reference Loponte, Bovera, Piccolo, Gasco, Secci, Iaconisi and Parisi2019).
The ΣPUFA/ΣSFA ratio did not differ between groups and ranged in breast and thigh meat between 0.40 and 0.51. Turley and Thompson (Reference Turley and Thompson2015) reported that, in human diets, this ratio should be maintained close to 1 and more generally in the range 0.34 to 2.99 to avoid promotion of tumor formation and AI.
Indexes (AI, TI) correlating the different amounts of some specific SFA, MUFA and PUFA of both the n-3 and n-6 series were proposed to indicate the contribution of these FAs to the prevention or promotion of pathological phenomena in humans (Lands, Reference Lands2014). Our results showed that the TM group had significantly lower AI and TI in the breast meat when compared with the control group. It has to be pointed out that, in both groups, the AI and TI values were low, and could be considered healthy for human consumers (Lazzaroni et al., Reference Lazzaroni, Biagini and Lussiana2009). Loponte et al. (Reference Loponte, Bovera, Piccolo, Gasco, Secci, Iaconisi and Parisi2019) did not observe any difference between breast meat of broilers fed with TM larva meal and those fed with SBM in term of quality indexes (PUFA n6/n3 ratio, AI and TI).
The FA profile of poultry meat usually mirrors that of the administered diet (Schiavone et al., Reference Schiavone, Chiarini, Marzoni, Castillo, Tassone and Romboli2007, Reference Schiavone, Marzoni, Castillo, Nery and Romboli2010, Reference Schiavone, Cullere, De Marco, Meneguz, Biasato, Bergagna, Dezzutto, Gai, Dabbou, Gasco and Dalle Zotte2017b). In this study, the chickens were reared according to a free-range system, having access to outdoor paddocks. The observed little discrepancies in terms of meat FA responses to dietary variations of FAs could be attributed to green grass and wild invertebrate consumption of the free-ranged chickens when accessing outdoor areas (Dal Bosco et al., Reference Dal Bosco, Mugnai, Rosati, Paoletti, Caporali and Castellini2014).
Conclusion
This study provided new data and knowledge on the potential use of a sustainable feedstuff for the nutrition of free-range chickens. The substitution of 75 g kg−1 of corn gluten meal with TM larva meal in the diet did not affect the quality (pH24, color and drip losses) of P. major and B. femoris muscles, and the proximate composition of breast and thigh meat. Regarding the FA profile of meat, only negligible differences in the thighs between the control and TM-fed chickens were observed. However, the dietary inclusion of TM increased the deposition of C18:1 c9 and reduced the AI and TI indexes of breast meat. In conclusion, this study could help producers and farmers to make informed decisions on the use of TM meal in free-range chicken diets.
Author ORCIDs
S. Dabbou, 0000-0002-3525-1614; L. Gasco, 0000-0002-1829-7936; C. Lussiana, 0000-0002-0641-5966; A. Brugiapaglia, 0000-0002-0619-7137; I. Biasato, 0000-0002-8855-4248; M. Renna, 0000-0003-4296-7589; L. Cavallarin, 0000-0001-7006-1683; F. Gai, 0000-0003-1037-9483; A. Schiavone, 0000-0002-8011-6999.
Acknowledgements
The research was supported by the University of Turin (2014) and by the Regione Piemonte, Italy (PSR-PIAS no. 08000558869) and EIT Food (2019) (FROM WASTE TO FARM: insect larvae as tool for welfare improvement in poultry). The authors are grateful to Mr Alessandro Varesio, Mrs Roberta Lacopo – ‘Fattoria La Fornace’, Montechiaro d'Asti (At, Italy) and Dr Paolo Montersino, Mr Dario Sola and Mr Mario Colombano for their technical support.
Conflict of interest
We declare that there is no conflict of interest with any financial organization regarding the material discussed in the manuscript.
