Introduction
Calf milk replacers (CMR) are manufactured from many different ingredients – proteins, fats, vitamins, minerals, amino acids, and additives. Depending on where the CMR is produced, the fat portion will contain different ingredients – in the United States, most CMR contain animal fats such as lard and tallow, whereas in other areas (e.g., Europe, Asia) most CMR contain combinations of plant fats such as coconut and palm oils.
There is a trend to reduce the use of tropical oils such as palm and coconut in many parts of animal agriculture. The use and sustainability of palm oil is controversial (Oosterveer, 2020). Concerns regarding use of palm oil, particularly in the European Union, include deforestation and rainforest destruction, reduction of biodiversity and habitat for endangered species in palm growing regions, use of fires for deforestation, and societal problems associated with displacement of local communities in palm growing regions (Oosterveer, 2020). So, alternatives to tropical oils is a topic of significant research at laboratories around the world.
The black soldier fly (Hermetia illucens) is a promising source of protein and fat because the larvae decompose organic waste to material suitable for animal feed (Surendra et al., 2016; Shumo et al., 2019) by accreting protein and fat from organic waste decomposition. Black soldier fly larvae (BSFL) contain approximately 42% and 35% protein and fat (DM basis), respectively (Raman et al., 2022). A comprehensive Wikipedia page describes their lifecycle and use in agriculture.
Industrial use of BSFL to produce oil and protein by compositing waste such as food waste, manure, feed by-products (which are the substrate for BSFL used for animal feed) are becoming established. Black soldier fly larvae are highly efficient at converting biomass into lipids and protein. Oil from BSFL is commercially produced world-wide for many industrial uses. Protein and oil from BSFL have been evaluated as feed sources in poultry (Kim et al., 2020, 2021), fish (Fawole et al., 2021; Maldonado-Othón et al., 2022), and other species (Lu et al., 2022). Oil from BSFL contain high amount of lauric acid, which some authors suggest may provide immune benefits.
Both the protein and oil from BSFL are highly processed, so there is no resemblance to the original black soldier flies or the larvae in neither the protein nor the oil.
With the interest in replacing tropical oils with other, more sustainable oils in CMR, we organized a research trial to test the value of BSFL oil in CMR formulated with palm and coconut oil (Quigley et al., 2025). Since palm / coconut oil blends are most common in Europe, we conducted at a dairy farm in Italy.
The Research
The study was conducted on a dairy farm outside of Rome, Italy from September 2023 to January 2024 We used 100 Holstein heifer calves (birth BW = 37.2 kg) that were assigned at birth to one of four experimental CMR formulas. He four CMR were formulated to contain an 80/20 ratio of palm/coconut oil (B0, negative control), 80/20 ratio of palm/BSFL oil (B20), 70/30 ratio of palm BSFL (B30), or 60/40 ratio of BSFL.
Calves were initially fed colostrum, then assigned to their experimental treatments at 2 d of age. Calves were initially offered 680 g of CMR powder from d 1 of the study, increasing to 900 g of CMR powder per day from d 7 to 55, split evenly into 2 meals at approximately 0600 h and 1600 h. From d 56 to 63, amount of CMR offered was reduced to 600 g/d in 2 meals and from 64 to 70 d, amount was reduced to 300 g/d in one meal. All 4 experimental CMR were mixed to 15% solids and fed by bucket.
The CMR contained 25% crude protein based on all milk sources and 19% fat (DM basis) based on the experimental lipid sources. The BSFL oil was prepared as a fat-filled whey powder and dry-blended in various proportions with palm/coconut FFWP to create the experimental CMR.
Commercial pelleted calf starter (FORTIS ONE, Raggio di Sole, Milan, Italy) containing 18% CP, 3.5% fat, and 36% NDF (as fed basis) was offered once daily at the morning feeding for ad libitum consumption. Amounts of CMR, calf starter (CS) offered and refused were measured daily. Chopped straw was available throughout the study; however, straw consumption was not recorded. Water was offered twice daily and provided for ad libitum consumption. Farm staff monitored calf height and BW (weekly), fecal scores (daily), and measured feed efficiency.
The Results
There were no consistent effects of increasing amounts of BSFL oil on intake or BW gain. Weekly BW and average daily gain (ADG) of calves (Figures 1 and 2) shows the consistent increase of BW with increasing age without effect of BSFL oil.
In Figure 3, we see the probability of a “non-normal” fecal event (fecal score ≥ 1, feces was scored on a scale of 0 = normal fecal consistency; 1 = pasty fecal consistency; 2 = liquid consistency; 3 = severe scours). During the first 3 weeks of the study, calves fed B20 had lower risk of a “non-normal” event – i.e., a lower risk of diarrhea. This is consistent with the idea that lauric acid in BSFL oil might assuage moderate maldigestion, though the limited effect on probability of diarrhea events suggests that BSFL oil may not reduce effects of early life pathogens such as rotavirus or Cryptosporidium parvum.
Alternatively, BSFL oil may be more digestible than the palm/coconut oil blend, thereby changing fecal consistency while digestibility of fat increases early in life (Quigley et al., 2021).
There were no effects of BSFL oil on feed efficiency, wither height growth or other measure of whole animal performance, suggesting that BSFL at the quantities tested can substitute for combinations of palm/coconut oils under commercial conditions.
Will manufacturers suddenly switch to this new source of oil for CMR? It’s unlikely that, in the short term, manufacturers will use BSFL oil. In most regions of the world, regulations need to be updated to allow the use of BSFL oil calf diets. Safety and efficacy studies need to be done. And, finally, the cost of the product must be competitive with other oils, if there is no “added value” to the oil. Our data points to some improvement in fecal consistency early in life as do other data from different species, but this needs to be confirmed with a larger number of animals and the ROI calculated. Until then, the oil needs to be competitive on a nutritional basis, unless there is an incentive to remove tropical oils from CMR formulas and consumers are willing to pay the additional cost.
Summary
Oil from BSFL successfully replaced palm/coconut in CMR to a ratio of 60/40 with palm/BSFL oil. While this production indicated no major changes in intake or growth, it seems prudent to conduct other research to monitor digestion and tissue composition of calves fed CMR containing BSFL oil.
References
Fawole, F. J., S. N. Labh, S. Hossain, K. Overturf, B. C. Small, T. L. Welker, R. W. Hardy, and V. Kumar. 2021. Insect (black soldier fly larvae) oil as a potential substitute for fish or soy oil in the fish meal-based diet of juvenile rainbow trout (Oncorhynchus mykiss). Animal Nutrition. 7:1360e1370. https://doi.org/10.1016/j.aninu .2021.07.008.
Kim, B., H. T. Bang, J. Y. Jeong, M. Kim, K. H. Kim, J. L. Chun, and S. Y. Ji. 2021. Effects of dietary supplementation of Black Soldier Fly (Hermetia illucens) larvae oil on broiler health. J. Poult. Sci. 58:222–229. https://doi.org/10.2141/jpsa.0200070.
Kim, B., M. Kim, J. Y. Jeong, H. Kim, S. Y. Ji, H. Jung, and S. H. Park. 2022. Black soldier fly (Hermetia illucens) larvae oil as an alternative fat ingredient to soybean oil in laying hen diets. Anim. Biosci. 35:1408–1417. https://doi.org/10.5713/ab.22.0052.
Lu, S., N. Taethaisong, W. Meethip, J. Surakhunthod, B. Sinpru, T. Sroichak, P. Archa, S. Thongpea, S. Paengkoum, R. Aprilia, P. Purba, and P. Paengkoum. 2020. Nutritional Composition of Black Soldier Fly larvae (Hermetia illucens L.) and its potential uses as alternative protein sources in animal diets: A review. Insects 13:831. https://doi.org/10.3390/insects13090831.
Maldonado-Othón, C. A., E. De La Re-Vega, M. Perez-Velazquez, and M. L. González-Félix. 2022. Replacement of fish oil by camelina and black soldier fly larvae oils in diets for juvenile Totoaba macdonaldi and their effect on growth, fatty acid profile, and gene expression of pancreatic lipases. Aquaculture 552:737985. https://doi.org/10.1016/j.aquaculture.2022.737985.
Oosterveer, P. J. M. 2020. Sustainability of palm oil and its acceptance in the EU. J. Oil Palm Res. 32:365–376. https://doi.org/10.21894/jopr.2020.0039.
Quigley, J. D., T. S. Dennis, F. X. Suarez-Mena, T. M. Hill, and M. Aragona. 2021. Meta-analysis of effects of age on intestinal digestibility of liquid feeds in young calves. JDS Commun. 2:114–117. https://doi.org/10.3168/jdsc.2020-0057.
Quigley, J. D., A. Zontini, G.F. Schroeder, Y. Roman-Garcia, L. Houbiers, and A. Bach. 2025. Nutritional value of black soldier fly Larvae oil in calf milk replacers. J. Dairy Sci. (In press).
Raman, S. S., L. C. Stringer, N. C. Bruce, and C. S. Chang. 2022. Opportunities, challenges and solutions for black soldier fly larvae-based animal feed production. J. Clean. Prod. 373:133802. https://doi.org/10.1016/j.jclepro.2022.133802.
Shumo, M., I. M. Osuga, F. M. Khamis, C. M. Tanga, K. K. M. Fiaboe, S. Subramanian, S. Ekesi, A. van Huis, and C. Borgemeister. 2019. The nutritive value of black soldier fly larvae reared on common organic waste streams in Kenya. Sci. Rep. 9:10110. https://doi.org/10.1038/s41598-019-46603-z.
Surendra, K., R. Olivier, J. K. Tomberlin, R. Jha, and S. K. Khanal. 2016. Bioconversion of organic wastes into biodiesel and animal feed via insect farming. Renew. Energy 98:197–202. https://doi.org/10.1016/j.renene.2016.03.022.