Scientifically Speaking …
By Matthew Wedzerai
AA DIGESTIBILITY IN PIGS: COMPARING HOUSEFLY AND BLACK SOLDIER FLY When insects are considered as potential protein sources, black soldier fly appears to have been studied more often than most insects. But is black soldier fly more potent in delivering protein (amino acids) to the animal? A recent study published in the journal of Animal Feed Science and Technology (2020) compared the amino acid digestibility of housefly and black soldier fly in growing pigs – the results of this study are presented herein. Several studies have shown that, among other insects, housefly
(Musaca domestica) and black soldier fly (Hermetia illucens) can effectively be used as an alternative protein source for different livestock. The black soldier fly larva has the advantage of effectively growing and transforming organic wastes into valuable biomass. Protein is a costly nutrient in animal feed, and more attention
should be given to effectively formulate the diet to minimize nitrogen excretion and feed cost. The digestibility of AA is important for accurate formulation to meet AA requirement of pigs. We all know that formulating pig diets using digestible AA is more efficient than total AA. In general, the AA digestibility is measured by the ileal digestibility assay, of which the standardized ileal digestibility (SID) assay is the frequently used way to determine AA availability in pig diets. However, some models use the apparent ileal digestibility (AID). From several studies, the major concern with the use of AID
is that values for AID obtained in individual feed ingredients are not always additive in mixed diets due to a non-linear relationship between dietary AA level and observed AID, for example when varying the inclusion level of a test feed ingredient in an N-free basal diet. This lack of additivity can be overcome by using SID where the ileal AA outflow is corrected for basal ileal endogenous AA losses. The basal ileal endogenous AA losses represent the quantities of AA that will be lost from the animal (in ileal) regardless of the diet fed, i.e. these animal induced losses are not influenced by the feed ingredient composition. Another drawback of AID is that, for feedstuffs with low protein content, the apparent digestibility values are underestimated relative to feedstuffs with high protein content because of the relatively greater proportion of endogenous amino acids in the digesta or excreta.
The study The objective of their study was to determine and compare the apparent ileal digestibility (AID) and standardized ileal digestibility
PAGE 20 NOVEMBER/DECEMBER 2020 FEED COMPOUNDER
(SID) of amino acids in housefly (HF) and black soldier fly (BSF) prepupae meal in growing pigs. Grower pigs (initial body weight of 25.05 kg) were randomly assigned to one of two diets formulated to contain 976.7 g/kg of HF or BSF as the sole source of nitrogen.
Amino acid digestibility: HF vs BSF The present study provides indispensable AA digestibility values for HF and BSF. Both the AID and the SID of all AA is greater in HF than in BSF (Table 1). A similar trend was also observed with dispensable AA (although not reported here). The researchers attributed this result to the differences in crude fat and CP (AA) concentration of the two diets. This is because a previous study reported that the ileal digestibility of most of the AA increased linearly with increasing dietary fat levels (Li and Sauer, 1994), while another research showed an increase in ileal AA digestibility as the dietary CP or AA content increased (Fan et al., 1994; Htoo et al., 2007). In the present study, although the BSF had greater content of crude fat than HF, the contents of CP and most of the AA in HF were greater than BSF. It was then derived that the effect of CP or AA contents on digestibility may be greater than crude fat content. On the other hand, different concentration of chitin in insect meal may also have an influence on AA digestibility of insect meals (Marono et al., 2015). However, the current study did not analyze the chitin contents in the insect meals.
Table 1. Apparent ileal digestibility (AID) (%) and standardized ileal digestibility (SID) (%) of amino acids in housefly (HF) and black soldier fly (BSF) fed to growing pigs
Amino acid
Arginine Histidine Isoleucine Leucine Lysine
Methionine
Phenylalanine Threonine Valine
92.6 87.6 84.4 88.4 90.4 91.5 89.4 87.3 87.3
Source: Tan et al., 2020.
COMPARISON WITH SOYBEAN MEAL Soybean meal and other soy products contribute high-quality protein to diets fed to pigs because soy protein is rich in the limiting amino acids lysine, threonine, and tryptophan that are present in relatively low concentrations in most fed cereal grains. Research also show that amino acids in soy protein have a higher digestibility by pigs than amino acids in most fed protein sources. As HF and BSF are potential alternatives to commonly used protein sources such as soybean meal, it would be worthwhile comparing their AA digestibility to soybean.
Comment section is sponsored by Compound Feed Engineering Ltd
www.cfegroup.com
AID (%) Housefly Black
soldier fly 82.1 75.5 73.5 77.4 75.7 81.2 74.5 73.9 77.3
97.3 89.6 87.8 91.8 91.8 98.8 90.6 91.9 97.3
SID (%) Housefly Black
soldier fly 86.2 77.8 77.5 81.0 77.6 91.8 76.7 79.8 86.2
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