Total substitution of soybean protein source with Hermetia illucens meal in Lohmann Brown Classic hens diet: effect on liver and visceral fat composition

At present, soybean is the main protein source in poultry feed but the need for alternative ingredients has been growing due to the continuous increase of prices, and for environmental aspects. In this context, insects are considered a viable attractive solution for animal feeding, especially for poultry since they are natural food sources for them. Despite the high attention of the international scientific community on the possible utilisation of insect meal, the information about the effect of the substitution of soybean with insect meal on the characteristics of tissues such as liver and visceral fat is scarcely investigated. The present study aims to fit this gap by evaluating the effects of a total replacement of soybean with Hermetia illucens defatted meal as protein source on physical characteristics, lipid content and composition of both liver and visceral fat. Twenty Lohmann Brown Classic laying hens were farmed from 24 to 45 weeks of age and divided into 2 groups fed two isoproteic and isoenergetic diets, differing in the main protein source: soybean meal based diet (SB group) or Hermetia illucens larvae defatted meal based diet (HI group). At the end of the trial, hens were sacrificed and both liver and visceral fat were collected. Physical characteristics, as weight, colour parameters (lightness - L*, redness index - a*, and yellowness index - b*), and pH were recorded, and Chrome, Hue, Colour difference (ΔE) were calculated from colour parameters. In addition, the lipid content and fatty acid composition of liver and fat were analysed by gas-chromatography in order to verify if and how they were affected by the diets. ANOVA analysis of data was conducted for detecting the statistical differences among the two experimental groups. From physical analyses emerged that livers from the two different experimental groups significantly differed in lightness (L*) and yellowness index (b*), as well as in the calculated values of Chrome and Hue. Specifically, HI group showed liver higher in L* values (37.17 vs 31.84) and more yellow (17.70 vs 12.09) with difference observable by the eyes of non expert people (∆E>5). Weight and pH were not significantly different. In parallel, colour parameters differed (p<0.05) in fat of HI and SB groups, HI group presenting fat with lower L* value (60.95 vs 64.55) and higher b* value (21.09 vs 15.23) than fat from SB group, thus resulting in a visible colour difference (∆E>5). Regarding lipid composition of liver (Table 1), diets affected both total lipid content and its fatty acid composition (p<0.05). HI hens presented liver higher in fat than SB group. As a consequence, total fatty acids increased in HI liver. The analysis of fatty acid composition revealed that C18:1-n9cis, C16:0, C18:2-n6cis, and C18:0 were the main fatty acids, amounting at 55% of the global fatty acid profile. HI liver presented lower contents of C18:1-n7 and C20:4-n6 than SB liver, however no significant differences in saturated (SFA), monounsaturated (MUFA), and polyunsaturated fatty acids (PUFA) of both n6 and n3 series were found. Concerning the visceral fat composition, C18:1-n9, C16:0, and C18:2-n6cis supplied the 65% of total fatty acids. HI visceral fat resulted in a lower content of C16:0, C16:1-n7, and C18:1n7 than SB group visceral fat. On the contrary, C18:0 and C18:2-n6 were found significantly (p<0.05) higher in HI visceral fat. Globally, these differences lead the significant lower MUFA and PUFA-n3 contents and higher PUFA-n6 values found for HI fat than for SB one. In conclusion, a total substitution of soybean with Hermetia illucens larvae meal as protein source of the diet for Lohmann Brown Classic hens significantly changed the colour of both liver and visceral fat. Moreover, diet affected liver lipid content without alteration of its fatty acid composition. On the contrary, total lipid content of visceral fat was not affected by the inclusion of insect meal in the diet whilst its fatty acid composition was deeply modified.