Introduction: the liver and its functions

The liver is a multifunctional organ that is responsible for synthesizing proteins from the amino acids absorbed in the intestine. Genetic selection of high-productivity strains makes liver function more relevant since any factor altering its physiology could affect growth and lay and even the capacity for immunogenic response to vaccines and diseases.

Among the most important functions performed by the liver we can highlight:

• Biliary secretion, thanks to its exocrine function, it releases this compound into the duodenum to facilitate the digestion of feed. Bile carries type A immunoglobulins (IgA) to the digestive tract.
• Detoxification of toxic molecules or substances (e.g., drugs) that are metabolized, transforming them into non-toxic forms to be eliminated through the bile.
• Metabolism of carbohydrates, which intervenes in the maintenance of glucose concentrations in blood through processes of glycogen synthesis, glycogenolysis and gluconeogenesis.
• Lipid metabolism synthesizes of lipoproteins, cholesterol, and phospholipids, and transformation of carbohydrates and proteins into fats.
• Amino acid metabolism, synthesis of 90% of the plasma proteins, ammonia removal through the production of urea.
• In relation to the immune response, it has antigen-presenting cells and many lymphocytes. Part of the proteins it synthesizes are precisely immune effectors, hence its importance in the immune response and the close relationship that the liver has with immunosuppression.

High production performance makes animals prone to suffer from hepatic stress, making the organ more susceptible to different challenges, such as mycotoxins, free radicals, infectious agents, and diets with an inadequate protein-energy ratio that end up causing the fatty liver syndrome. All these challenges are linked to inadequate feed management and nutritional imbalances.

Liver challenges derived from the diet

Mycotoxins

Mycotoxins are among the most important hepatotoxic agents in poultry and a widespread problem worldwide. Mycotoxins are metabolites produced by fungi that are incorporated into the food chain.

There is a great variety of mycotoxins, and aflatoxins are the ones that have the greatest hepatotoxic effect. They are absorbed and transported to the liver where their metabolism will take place, during which peroxides are generated that damage liver tissue.

Fumonisin is another mycotoxin of interest in poultry production. Continuous exposure in birds causes alterations at the intestinal and hepatic level. Ochratoxin can indirectly cause alterations in the liver leading to excessive accumulation of glycogen.

Drugs

Excessive use of drugs (antibiotics, growth-promoting antibiotics, coccidiostats, etc.) is frequent in diets formulated for industrial poultry because they have a negative effect on the liver function, since most of these chemicals are metabolized in this organ, causing an increase in ¡energy expenditure that will deteriorate the productive parameters. Prolonged use of these potentially toxic substances will cause irreversible liver damage.

Free radicals

These can be generated in the animal when the liver is forced to increase the speed of the mitochondrial respiratory chain and some oxygen molecules cannot be completely reduced. This is a common situation in intensively produced birds in which the demand energy is very high. They are also present in feeds with oxidized ingredients with poorly preserved or poor-quality fats.

Free radicals oxidize other cellular components such as DNA, enzymes, or the cytoplasmic membrane.

Toxigenic bacteria

The microbiological quality of raw materials and balanced feed is a very important aspect, since an excessive bacterial count (E. coli, Salmonella, Clostridium etc.) will pose a greater risk of bacterial challenges that can affect the liver.

The liver is a defense barrier against infections due to its filtering function and because it produces immune precursors. The high presence of microorganisms, together with other factors, can lead to an infection in the organ itself or in the bile ducts, and bacterial toxins can cause damage that will permanently affect productivity.

Hemorrhagic fatty liver syndrome

It is a liver dysfunction that occurs in birds. It is related to lipid metabolism and is characterized by an excessive accumulation of fat in the liver. It causes liver degeneration or steatosis characterized by a yellow coloration and bleeding of varying degrees. Although it is more frequent in layers, broilers can also develop it.

energy balance, diet composition, hormonal balance and environmental temperature are among the factors that can cause or predispose to the development of hemorrhagic fatty liver syndrome.

• Energy balance: The prevalence of this syndrome in birds is directly related to a positive energy balance, which leads to an excessive accumulation of fat and obesity.

Excessive energy consumption for two or three weeks, regardless of the energy source used, will induce the birds to develop the syndrome.

• The diet: in addition to the correct energy balance, enough pronutrients and lipotropic factors such as choline, methionine and vitamin B₁₂ need to be supplied to prevent fat infiltration. Free radicals need to be considered, too, since these also influence fat deposition in the liver. Temperature: high environmental temperatures (25-30°C) commonly generate a positive energy balance, a situation that predisposes the syndrome to develop.
• Hormonal balance: lipid deposition in the liver is influenced by the level of estrogens, and bleeding increases when high levels of energy and estrogens are combined.

Strategies to preserve liver physiology

Among the main actions that will help preserve the liver and maintain productive rates, the following stand out:

• Avoid excess of fat and control the presence of hepatotoxic substances: mycotoxins, free radicals, bacterial toxins, drugs, etc.
• Increase levels of pyridoxine (vitamin B₆); pantothenic acid; biotin; mesoinositol, choline and some pronutrients in the diet.

Liver conditioner pronutrients

Pronutrients are active molecules that are found in different botanical extracts and that optimize the physiological functioning of the organs in a natural way.

They act at the metagenetic level, increasing the expression of genes that were silenced or under-expressed, thus increasing the synthesis of functional proteins in the target cells on which they act.

Liver conditioner pronutrients act by regulating the physiology of hepatocytes.
The hepatoprotective effect of this type of pronutrient is based on:

• Stimulation of the synthesis of proteins and non-essential amino acids.
• Enhancement of liver regeneration.
• Stimulation of toxin elimination (mycotoxins, drugs).
• Blocking free radicals.
• Regulation of lipid metabolism and absorption.

Biovet S.A has developed this natural technology called pronutrients through different in vitro and in vivo tests. Moreover, the effectiveness of this tool was proven to counteract the productive losses caused by liver challenges.

An interesting application of Liver conditioner pronutrients is to administer them after liver damage to accelerate recovery and production rates.

In the case of layers and breeders, pronutrients are recommended in the late stages of the laying cycle, and, in broilers produced under heat stress conditions, they need to be applied continuously, thus helping to prevent hemorrhagic fatty liver syndrome.

Conclusions

Strategies to protect the liver must consider the different challenges derived from nutrition; therefore, raw materials and balanced feed need to be assessed to decide if the application of mycotoxin binders, preservatives and antioxidants is necessary, as well as the importance of a correct formulation with adequate levels of pyridoxine (B₆); pantothenic acid; biotin; mesoinositol, choline, and pronutrients.

The liver is a multifunctional organ of great importance in protein synthesis and liver function acquires special relevance in high-productivity birds.

A damaged liver can affect:

• growth
• the productivity
• the ability of the immune system to respond to vaccination and diseases

Toxins are highly harmful in industrial production systems because the liver is under constant metabolic stress. This is due to the high productive levels of the birds that increase their lipid and protein requirements. This prolonged demand over time will alter protein synthesis, energy use, fatty acid metabolism; slowing the development of the bird and even causing death.

Liver conditioner pronutrients are effective hepatic regenerators capable of restoring the state of the liver after being damaged by hepatotoxic substances such as mycotoxins, bacterial toxins, free radicals; they are also a tool for the prevention of fatty liver hemorrhagic syndrome.

Liver conditioner pronutrients are developed and marketed by Biovet S.A under the name ALQUERNAT LIVOL.

Biovet S.A offers technical services through Global Vet’s Lab^®; formulation of rations, mycotoxin analysis, microbiological analysis, among others.

Bibliographic references:

• Squires, E.J. and S. Leeson, 1995. An etiology of fatty liver syndrome in laying hens. Br. Vet. J., 144:
• Dr. Jaime Borrell, BIOVET S.A. LABORATORIOS, 2008, Pronutrientes con efecto hepatoprotector.
• Borrell, Uso de pronutrientes de origen vegetal en veterinaria, Real Academia de ciencias veterinarias (RACVE), disponible en: http://www.racve.es/publicaciones/uso-de-pronutrientes-de-origen-natural-en-veterinaria/
• Antillón, R. A. y López, C.C. (1987). Enfermedades Nutricionales de las Aves. 1a ed. Universidad Nacional Autónoma de México. México.
• Pié, Julia (2020), El papel del hígado en la producción de huevos. Veterinaria Digital. Disponible en: https://www.veterinariadigital.com/articulos/el-papel-del-higado-en-la-produccion-de-huevos/