Abstract
BackgroundThe hypothesis was tested that insect meal (IM) as protein source influences intermediary metabolism of growing pigs. To test this, 30 male, 5-week-old crossbred pigs were randomly assigned to 3 groups of 10 pigs each with similar body weights (BW) and fed isonitrogenous diets either without (CON) or with 5% IM (IM5) or 10% IM (IM10) from Tenebrio molitor L. for 4 weeks and key metabolic tissues (liver, muscle, plasma) were analyzed using omics-techniques.Results Most performance parameters did not differ across the groups, whereas ileal digestibilities of most amino acids were 6.7 to 15.6%-units lower in IM10 than in CON (P < 0.05). Transcriptomics of liver and skeletal muscle revealed a total of 166 and 198, respectively, transcripts differentially expressed between IM10 and CON (P < 0.05). Plasma metabolomics revealed higher concentrations of alanine, citrulline, glutamate, proline, serine, tyrosine and valine and a lower concentration of asparagine in IM10 than in CON (P < 0.05). Only one out of fourteen quantifiable amino acid metabolites, namely methionine sulfoxide (MetS), in plasma was elevated by 45% and 71% in IM5 and IM10, respectively, compared to CON (P < 0.05). Plasma concentrations of both, major carnitine/acylcarnitine species and bile acids were not different across groups. Lipidomics of liver and plasma demonstrated no differences in the concentrations of triacylglycerols, cholesterol and the main phospholipids, lysophospholipids and sphingolipids between groups. The percentages of all individual phosphatidylcholine (PC) and phosphatidylethanolamine (PE) species in the liver showed no differences between groups, except those with 6 double bonds (PC 38:6, PC 40:6, PE 38:6, PE 40:6), which were markedly lower in IM10 than in CON (P < 0.05). In line with this, the percentage of C22:6n-3 in hepatic total lipids was lower in IM10 than in the other groups (P < 0.05).ConclusionsComprehensive analyzes of the transcriptome, lipidome and metabolome of key metabolic tissues indicate that partial or complete replacement of a conventional protein source by IM in the diet has only a weak impact on the intermediary metabolism of growing pigs. Thus, it is concluded that IM from Tenebrio molitor L. can be used as a dietary source of protein in pigs without causing adverse effects on metabolism.
Highlights
The hypothesis was tested that insect meal (IM) as protein source influences intermediary metabolism of growing pigs
We have recently demonstrated for the first time in two studies with genetically obese rats that IM produced from larvae of the yellow mealworm (Tenebrio molitor L.) has remarkable effects on lipid metabolism, such as attenuation of liver steatosis and decrease of hyperlipidemia, − effects which are likely explained by the profound inhibition of hepatic lipid synthesis observed in these studies [15, 16]
Characterization of the experimental diets The concentrations of crude protein and gross energy did not differ across the three diets indicating that partial (IM5 diet) and complete (IM10 diet) replacement of soybean extraction meal (SEM) by IM was isonitrogenous and isocaloric
Summary
The hypothesis was tested that insect meal (IM) as protein source influences intermediary metabolism of growing pigs. There is an urgent need for alternative protein sources which can be efficiently produced with lower environmental impact [1] In this regard, protein-rich insect meal (IM) may offer great potential, because it can be produced from industrialized mass-rearing of edible insects (e.g. Tenebrio molitor L., Hermetia illucens) with higher feed conversion ratios and lower utilization of natural resources than conventional protein sources, at least in theory [2, 3]. Several studies in birds (broilers, ducks) [4,5,6,7,8,9] and a few studies in pigs [10,11,12] already demonstrated that IM as dietary protein source can partially or completely replace soybean extraction meal (SEM) – the major protein source used in diets for monogastric farm animals – without impairing animals' performance. There are only some largely descriptive studies, in which the effect of a partially defatted IM produced from Hermetia illucens has been studied on selected blood parameters (e.g. blood lipids and minerals) and/or histological traits (e.g. histopathological scores) in broilers [7, 8, 13], ducks [14], and pigs [12]
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