By Emeritus Professor Simon J Davies, Harper Adams University and John Hardy, UrticaPlus, UK
We have discussed many products in International Aquafeed magazine that are produced by companies around the world with biological and functional properties as feed additives and supplements. Their value as immunomodulators and anti-inflammatory agents for animals such as poultry, pigs and even pets in feed products is undeniable. These natural ingredients have been widely used in fish and shrimp feed with great success, revolutionizing the aquaculture industry with their ability to improve health and provide protection against disease and stress. One of the most interesting terrestrial plants to grow is the stinging nettle Urtica dioica. The stinging nettle belongs to the Urticaceae family, native to Europe, North Africa and the Americas. It is a perennial herbaceous plant with soft green leaves with serrated margins and covered with trichomes (stinging parts).
Properties of nettle
Nettle has received considerable attention in human health care as a medicine and is increasingly popular in animal feed applications. It is recommended for use in fish and other aquaculture species due to its properties that will be focused on in this article.
Urtica has unique properties in terms of comprehensive nutritional profile with a wide range of nutrients from macro to micronutrients (Bhusal et al., 2022; Devkota et al., 2022). Many publications have addressed the chemical composition and articles in the field of food science. A comprehensive review conducted by Jan et al. (2016) described nettle as a reserve of major nutritional and biological components with excellent functional properties. The biological substances include phenolic compounds such as p-hydroxybenzoic acid, gentisic acid, quinic acid, rutin, quercetin. It is also a rich source of aldehydes, alkenes, amines, amides and various halogenated and aromatic organic compounds.
Oxidative stress is a metabolic consequence of oxidative events in animal tissues during both normal life and pathological conditions. The antioxidant capacity of stinging nettle has been noted for its ability to reduce free radicals. The ability to scavenge hydrogen peroxide and reduce superoxide anion has been evaluated using in vitro and in vivo models with positive results confirmed. This is due to a combination of mechanisms, including prominent levels of ascorbic acid (Vitamin C) and other factors such as flavonoids.
Nettle also has strong antibacterial activity due to its characteristic phenolic groups. The phenolic compounds in the aqueous extract exhibited significant antibacterial activity against specific gram-positive bacteria and some yeast species. It has been shown to be effective against Streptococcus pneumoniae, Staphylococcus aureus and various strains of Enterobacter. This is relevant to many other pathogens found in fish and shrimp. The alcoholic extract of U. dioica has antifungal activity against various fungal strains found in animal systems. Nettle leaf or root extracts have been shown to modulate and inhibit the level of hyperplasia in tissues, which may be of interest in fish farming, especially to prevent the spread of pathogens in the industry.
Role in animal nutrition
As with humans, there have been numerous studies examining the potential of nettle and its products in animal feed, with a particular focus on species such as pigs and poultry for supplementation in commercial diets. Studies have provided excellent evidence of health promotion with a focus on improving nutritional status, metabolism, and immune responses. For example, nettle provides nutrients and bioactive components, stimulates growth and feed utilization, modulates metabolism, and supports the immune system in broilers (Milosevic et al., 2021).
Research on fish and potential in aquaculture
In aquaculture, the use of nettle appears to be promising from several studies to date. In fact, De Vico et al. (2018) stated that “nettle is a neglected plant with emerging growth-promoting and immunomodulating potential in farmed fish”. These authors provided compelling evidence for the use of nettle in commercial fish diets as a biological and functional ingredient. The scientific literature has mainly evaluated dietary nettle powder from a feed additive perspective. In this study, Awad and Austin (2010) evaluated Urtica dioica as a feed additive to prevent Aeromonas hydrophilia infection in rainbow trout, Oncorhynchus mykiss. After 14 days of pathogen challenge, they noted increased survival when nettle was added to the diet. In addition, there was an increase in serum bactericidal activity and respiratory burst responses associated with innate immune mechanisms (respiratory burst activity of leukocytes, neutrophils, monocytes, and macrophages) as combined strategies of the immune system in the process of killing pathogens. Nettle also gave higher hematocrit and red blood cell and white blood cell counts than the control salmon group without nettle.
Effects on the immune system
Most studies in fish have focused on the effects of nettle on the immune status of fish. A comprehensive review on the use of nettle additives for growth promotion and immune enhancement in fish was presented by Zare et al. (2023). Saeidi Asl (2017) reported that Urtica can be very effective in rainbow trout (Oncorhynchus mykiss). A trial of nettle supplementation in rainbow trout diets to examine growth performance, skin mucus, immune response and resistance to pathogens was conducted after two months of feeding trials. At a three percent supplementation level, improvements in weight gain, specific growth rate and feed conversion ratio were observed compared to other groups.
Improve liver function with nettle in your diet
Other studies in fish have focused on the modulatory effects to provide more detailed evidence of the effects of nettle as a functional feed additive. Overall, nettle has been reported to have positive effects on a variety of parameters related to blood biochemical markers, liver enzymes, antioxidant status, and immune system components.
Application for Atlantic salmon
In a recent investigation, Martin and Hardy (2023) were the first to pioneer the potential of Urtica in experimental diets for Atlantic salmon (Salmo salar). This trial examined the performance of salmon fed a diet supplemented with nettle from a stable, high-quality source (Urtica+plus®).
Conclude
In conclusion, Urtica dioica has been shown to possess numerous functional properties after being evaluated through rigorous research trials on many animal species and is gaining increasing interest in the aquaculture field.
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