Hawkey, Kerensa J.
(2022)
Tenebrio molitor (yellow mealworms) as potential ‘nutrient concentrators’ for sustainable animal feeds.
PhD thesis, University of Nottingham.
Abstract
Alternative protein sources are urgently needed to replace the traditional sources for animal feeds (e.g. soybean meal). Mealworms are being investigated as one such source, due to similar nutrient composition to soybean meal, but production methods and feed sources need to be sustainable for it to be an effective replacement feed ingredient. There is large variation in production methods and already available technologies in conventional livestock production, such as commercial enzymes have not been utilised in insect production.
The aim of this work was to investigate mealworm production methods such as water supply, feed sources and production environment, to manipulate mealworm growth and proximate composition using exogenous enzymes and finally, to utilise mealworms and potentially improve mealworms as a partial replacement for soybean meal in broiler feeds.
Results found that feeding mealworms rehydrated wheat bran significantly reduced growth compared to a control feed of wheat bran and carrot (P<0.001), water alone can replace vegetable sources, such as carrots, with no negative effects on growth (P>0.05) and increased crude protein (%DM) (P>0.05). Mealworms could be fed on either high quality chick crumb or low-quality wheat bran in either an uncontrolled room or a controlled incubator with no significant differences in initial or final group live weights, dry matter, crude protein, total fat or total energy content of mealworms (P>0.05). Total feed intake was significantly lower in the groups fed in the room (P<0.001), with those on wheat bran the lowest suggesting these were the most feed efficient.
There was no effect of phytase inclusion in the feed or water on mealworm growth or proximate composition (P>0.05). Pre-treatment of wheat bran with water (with or without exogenous phytase), decreased mealworm growth (P=0.02) and crude protein content (P=0.002) while increasing total fat content (P=0.044). This suggests that endogenous phytase within the wheat bran was activated by water soaking. Varying effects of high dose phytase were seen on mineral content of mealworms. Xylanase inclusion significantly reduced mealworm growth (P=0.033) and dry matter (P=0.004). In the absence of phytase, xylanase reduced crude protein (P=0.002) and increased total fat content (P=0.007).
Replacing 10% of soybean meal with mealworms had no effect on broiler growth or apparent ileal digestibility but did increase feed intake (P=0.01) resulting in a negative increase in feed conversion ratio (P=0.002). There was also a significant effect on the caecal microbiota at both a phyla and genus level, with increases in Romboutsia timonensis (P=0.006) and Sellimonas intestinalis (P<0.001) associated with healthy gut. Exogenous chitinase successfully hydrolysed chitin releasing D glucosamine in vitro (P<0.001) but was inconclusive with mealworms. Chitinase inclusion into broiler feeds resulted in improved feed conversion ratio in the last 5 days of the trial compared to the negative control (P=0.049). There was no effect of chitinase inclusion on broiler growth, feed intake, apparent ileal digestibility of crude protein or amino acids and overall caecal microbiota. There was a significant increase in Blautia hydrogenotrophica suggesting that chitooligosaccharides were being utilised by bacteria leading to increased production of hydrogen and carbon dioxide for cross feeding.
In conclusion, mealworms can be manipulated through changing production conditions, feed and water sources, but inclusion of exogenous enzymes had little overall effect. Partial replacement of soybean meal with mealworms decreased feed conversion ratio but had no other negative impacts on broiler production and addition of exogenous chitinase improved feed conversion ratio in older birds.
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