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In: Ruminant physiology
In: Ruminant physiology

Mineral and heavy metal accumulation in black soldier fly (Hermetia illucens) larvae (BSFL) is of growing interest. The bioaccumulation of elements in BSFL is usually assessed by a bioaccumulation factor (BAF), which is the ratio between the concentration of an element in the organism and in its feeding substrate. Recently, a new index, i.e. bioaccumulation index (BAI), which represents the relative increase in the concentration of a given element to its initial concentration has been proposed. The BAI is claimed to be a more valid alternative to the BAF, especially because it takes into account the initial element concentration of the larvae. This work assesses BAF and BAI in comparison with true element retention rate in BSFL. Using an experimental setup that included the element turnover of BSFL in two different feeding regimes (with and without a different substrate for neonatal larvae), we show that: (1) the initial element concentration in BSFL is only a tiny fraction (<0.1%) of the total element pool in the system, implying that the feeding substrate is the main source of elements to be accumulated by the growing larvae; (2) each element has a specific concentration pattern from the start to the end of feeding experiments. Furthermore, in cases where both neonatal diets and experimental feeding substrates are used during the larval growth period, BAI can be confounded by time/age with diet-related effects. From an agri-food perspective of rearing BSFL for element accumulation, the retention rate of elements from the feeding substrate to the larval body remains the most valid evaluation parameter. The results of input-output calculations and element-unspecific correlations suggest a higher agreement of true element retention rate with BAF than with BAI. Therefore, we propose to assess the element accumulation in BSFL by retention rate followed by BAF under laboratory conditions.

Open Access
In: Journal of Insects as Food and Feed

A feeding experiment was conducted to investigate the impact of feeding defrosted whole black soldier fly larvae (BSFL) to broilers in increasing levels in the ration on blood metabolites, carcass characteristics (CC) and on changes in fatty acid (FA) composition in plasma, muscle and abdominal fat. Day-old chicks (Ross-308; n=252) were assigned to one of four groups each with 6 replicate pens (10-11 birds/pen). The birds were fed either a demand-oriented age-specific control (CON) diet and had no access to BSFL, or fed CON plus BSFL at 10% (L10), 20% (L20) or 30% (L30) of CON feed intake. At weeks (wk) 4 and 6, birds (2 per pen) were slaughtered to collect blood, breast muscle, and abdominal fat samples and to determine CC. Plasma triglyceride concentrations increased in a dose dependent manner with increasing levels of whole BSFL compared with CON (P<0.05). The L30 and L20 had higher plasma non-esterified FA concentrations than CON (P<0.05). There were no differences in slaughter weight and CC between groups (P>0.05). Broilers fed 30% BSFL had the highest saturated FA proportion in plasma, muscle and abdominal fat and the lowest monounsaturated FA proportion in abdominal fat tissue (P<0.05). The levels of total polyunsaturated FA in plasma and abdominal fat were lower in L30 than in CON (P<0.05). In plasma, muscle and abdominal fat, the proportion of conjugated linoleic acid (isomerC18:2cis-9, trans-11) was highest in L30 followed by L20 and L10 compared with CON (P<0.05). Overall, whole BSFL could be included in broiler diets up to 20% to promote sustainability in broiler farming without adverse effects on slaughter weight, meat quality and FA compositions, whereas, the highest inclusion level (i.e. 30%) of whole BSFL in the daily ration was associated with altered FA composition in plasma, fat and meat.

Open Access
In: Journal of Insects as Food and Feed

Abstract

The recycling of minerals is crucial for the future circular agriculture. Black soldier fly larvae (BSFL) can accumulate minerals in their body. This study investigated the effects of adding mineral-enriched BSFL, grown on substrates containing sewage sludge recyclates (SSR), to broiler feed to reintroduce minerals from waste streams currently subject to regulatory restrictions back into the nutrient cycle. Feed, nutrient, mineral and heavy metal intake, growth, blood metabolites and immunoglobulins, bone characteristics and mineral status of broilers were studied in response to different mineral-enriched BSFL supplements. Eighty newly-hatched mixed-sex Ross 308 chicks were divided into four groups, with six replicate pens per group. BSFL used in the broiler experiment were grown either on a modified Gainesville fly diet (FD) (L-FD) or on FD supplemented with 4% of sewage sludge biochar (L-BCH), or on the FD supplemented with Single Superphosphate (SSP) SSR (L-SSP). All broilers were fed age-specific diets and either had no access to BSFL (CON) or received 15% of CON birds’ feed intake as defrosted BSFL from three different sources. Inclusion of 15% of mineral-enriched whole BSFL in broiler rations had no adverse effects on growth performance parameters, nutrient intakes, nutrient conversion efficiency, plasma metabolites and immunoglobulins ( P > 0.05 ). Birds in BSFL supply groups had higher serum Ca concentrations than CON birds ( P < 0.05 ). L-BCH supplied birds had a lower serum P than CON birds ( P < 0.05 ). Tibial characteristics and mineral status of birds were not affected by larvae supply ( P > 0.05 ). Heavy metal intake (manganese, iron, zinc, copper, arsenic, cadmium, lead, and mercury) of the birds was not affected by dietary treatments ( P > 0.05 ). In conclusion, 15% of mineral-enriched-BSFL reared on SSP can be included in broiler diets for 42 experimental days without adverse effects on nutrient intakes, growth performance parameters and bone condition.

In: Journal of Insects as Food and Feed

Previous studies showed that heavy milk-fed calves often develop problems with glucose homeostasis and do not utilise dietary carbohydrates for body fat deposition. This suggests that calves may lack the metabolic capacity for synthesizing fatty acids from glucose. Poor glucose utilisation for growth may also be explained by the large supply of dietary fatty acids, allowing synthesis of body fat exclusively from dietary fatty acids. The main objective of the current study was therefore to assess energy balance, body fat deposition and de novo fatty acid synthesis when exchanging fat for lactose in milk replacer for veal calves. Sixteen Holstein-Friesian calves (121±3 kg) were assigned to either a high-fat (HF; 30% fat) or a low-fat (LF; 10% fat) milk replacer for 12 weeks. This large, iso-energetic exchange between fat and lactose did not affect growth performance, protein and energy retention. The respiratory quotient exceeded unity during several hours per day in LF calves, but not in HF calves. The difference in isotope recovery in expired CO2 between two glucose isotopomers, as a proxy for de novo lipogenesis, was greater in LF calves (12.9%) than in HF calves (1.4%), indicating increased fatty acid synthesis from glucose in LF calves. Expression of genes involved in fatty acid synthesis, desaturation and elongation, and triacylglycerol synthesis was greater in LF calves than in HF calves, and this was most pronounced in retroperitoneal adipose tissue. In conclusion, these findings indicate that calves are able to synthesize fatty acids from glucose when a low-fat milk replacer is fed.

In: Energy and protein metabolism and nutrition

Abstract

There is a growing interest in the ability of black soldier fly (Hermetia illucens) larvae (BSFL) to convert low-value organic residues into high-value products. This leads to more publications with conversion data for various organic resources. However, these results are rarely comparable between laboratories due to differences in study protocols. This hinders comparisons among studies, the use of results in practice, and overall advancement in BSFL conversion research. Therefore, a standardised research protocol was developed for nursing, rearing and harvesting of BSFL for feed assessment. The utility of this protocol, was assessed via an international ring test with 9 partners. One batch of Gainesville diet (wheat bran (50%), alfa-alfa (30%) and maize (20%)) was produced and distributed among the partners to avoid dietary variations. Five-day-old BSFL larvae were used for the growth trial with six replicates per partner. Average larval weight was assessed after 3 days, 7 days, and harvest (>10% prepupae). Total yield and frass were recorded, and samples were chemically analysed to allow the quantification of the conversion efficiency. The results were used to calculate the within and between partner variability of the protocol. The results indicate that for the biological parameters (average weight, yield and density) the within partner variability was 24% and the between partner variability was 60%. For the assessed chemical parameters (N, fat, ash, P, K, pH), both the within and between variability was lower (respectively 9 and 28%). The results of this study give a first indication of the variability that can be expected within and between BSFL feeding experiments for different parameters and can therefore serve as guideline when developing a new experimental designs, assess standard operating procedures and other applications. The protocol can be used as first basis for future feed experiments, improving the comparability of results.

Open Access
In: Journal of Insects as Food and Feed