Prasad Shinde, Akash Wadal, Jayant Kumar Kakwani, 1MVSc Scholar, Department of Animal Nutrition, College of Veterinary Science and Animal Husbandry
INTRODUCTION-
Photosensitization is a condition where an animal’s skin or tissues become hypersensitive to sunlight or other sources of ultraviolet radiation, leading to inflammation, skin lesions, and potential systemic complications. Th ephotodynamic compounds, when present in the animal’s body, can absorb specific wavelengths of light and undergo chemical reactions that generate reactive oxygen species (ROS). These ROS can cause damage to cell membranes, proteins, and DNA, leading to various clinical manifestations, including skin lesions, edema, and, in severe cases, organ dysfunction. Animal nutrition plays a crucial role in the prevention and management of photosensitization. The introduction of certain plants or feed sources containing photosensitizing compounds can increase the risk of this condition. Additionally, deficiencies in specific nutrients can compromise the animal’s ability to mitigate the effects of photosensitization.
Mechanism of photosensitization in animals’ body –
- Absorption of light by photosensitizer molecule leads to its excitation from ground state to excited singlet state.
- This excited singlet state molecule undergoes intersystem crossing and leads to transition of molecule into triplet state.
- The excited triplets state undergoes energy transfer by type-1 or type-2 reactions in which type-1 reaction photosensitizer molecule directly transfer electron or hydrogen atom to other molecules generating free radicals.
- The type-2 reaction involves excited triplet stage photosensitizer molecule transfer electron to molecular oxygen which produces highly reactive single oxygen.
- Reactive substrate produced by type 1 and type 2 will produce a wide range of chemical or biological effects such as oxidation of biomolecules, generation of reactive oxygen species (ROS), etc.
FACTORS INFLUENCING SUSCEPTIBILITY OF ANIMALS TO PHOTOSENSITIZATION-
Breed and genetic predisposition-
- Certain breeds of animals are more prone to developing photosensitivity reactions due to genetic factors.
- For example, Brahman and Santa Gertrudis breeds of cattle are considered more susceptible to photosensitization.
Age-
- Young animals, especially neonates, tend to be more sensitive to photosensitizing agents due to their immature liver function and inability to efficiently metabolize and excrete these compounds.
Skin pigmentation-
- Animals with lighter skin pigmentation or non-pigmented areas (e.g., white-faced animals) are more vulnerable to the effects of sunlight and tend to develop more severe photosensitivity reactions.
Dietary factors-
- Consumption of plants or feeds containing photosensitizing compounds (e.g., St. John’s Wort, buckwheat, certain clovers) can increase the risk of photosensitization. Deficiencies in certain nutrients, such as vitamin E, selenium, and carotenoids, can predispose animals to photosensitivity reactions.
Liver function-
- Impaired liver function can lead to the accumulation of photodynamic agents in the body, increasing the risk of photosensitization.
Environmental factors-
- Exposure to intense sunlight, particularly during the summer months or at high altitudes, can trigger photosensitivity reactions in susceptible animals.
Medications and chemicals-
- Certain medications (e.g., phenothiazine tranquilizers, antibiotics) and chemical substances can act as photosensitizing agents or potentiate photosensitivity reactions.
Stress and immune status-
- Stress and compromised immune function can make animals more susceptible to photosensitization by altering their ability to metabolize and eliminate photosensitizing compounds.
PHOTOSENSITIZATION TYPES –
Primary photosensitization-
- Primary photo sensitization occurs when a photo dynamic agent is ingested, injected or absorbed through skin.
- The agent enters systemic circulation which on contact with UV light reacts to develop skin lesions.
- Primary photo sense typing agents include hypericin from Hypericum perforatum, fagopyrin from fagopyrin esculentum(Buckwheat), psoralens in families like apiaceae, Rutaceae which include bishops weed, cymopteruswatsonii (spring parsley), phenylheptatriyne from certain legumes like clover & alfaalfa, furanocoumarins in plants like citrus fruits, umbelliferous vegetables (parsnips, celery). Also, other genera like Trifolium, Medicago, polygonum & brassica are included in primary photosensitization.
Secondary photosensitization-
- In secondary photo sensitization which occurs due to impaired biliary excretion of phylloerythrin which is a byproduct of chlorophyll metabolism. Secondary sensitization is sequela of any hepatocellular dysfunction or cholestasis is not related to photo toxin injection.
- Also, the metabolic disorders and nutritional imbalances plays significant role in photosensitization like due to vitamin A, vitamin E, selenium deficiency led to oxidative stress by photosensitizing agents. Accumulation of porphyries, impaired renal functions may also promote photosensitization reaction.
Observations in animals with photosensitization-
- Animal affected with photosensitization may show Skin lesions which range from reddening and swelling to blistering, peeling, and crusting.
- These lesions typically appear on areas of the body that are sparsely covered with hair or feathers, such as the ears, nose, muzzle, and areas around the eyes.
- Sunburn: Photosensitized animals can experience severe sunburn, characterized by reddened and inflamed skin, which can be painful and may lead to further complications.
- Photophobia: Some animals may exhibit photophobia, which is an increased sensitivity to light and a tendency to avoid bright light or seek shade.
- Restlessness and discomfort: Skin lesions and sunburn can cause significant discomfort and pain, leading to restlessness and behavioral changes in the affected animals.
- Eye damage: In severe cases, photosensitization can also affect the eyes, leading to symptoms such as excessive tearing, squinting, and potentially corneal damage or blindness if left untreated.
- Fever and lethargy due to the inflammatory response and potential systemic involvement. Decreased appetite and weight loss due to discomfort and pain
NUTRITIONALMANAGEMENT FOR PREVENTION OF PHOTOSENSITIZATION-
- Avoidance of plants containing photosensitizing agents-
Identify and avoid grazing animals on pastures or feeding them with plants known to contain photosensitizing compounds, such as St. John’s Wort, buckwheat, certain legumes, and umbelliferous vegetables. Proper pasture management and selective grazing practices can help minimize exposure to these plants. Practice rotational grazing, which involves dividing the pasture into smaller paddocks and rotating the animals through them regularly. This prevents overgrazing and reduces the likelihood of animals consuming large quantities of photosensitizing plants.
- Supplementation with antioxidant vitamins and minerals-
Provide adequate levels of antioxidant vitamins (vitamins A and E) and minerals (selenium and zinc) in the diet to enhance the body’s antioxidant defense mechanisms against photosensitization reactions & Reactive oxygen species (ROS). Supplementing animal diets with vitamin E, particularly during periods of high UV exposure or when animals are at risk of ingesting photosensitizing agents, can help reduce the severity of photosensitization reactions. Vitamin C is a water-soluble antioxidant that can scavenge ROS and regenerate other antioxidants, such as vitamin E.
Selenium is an essential mineral that plays a role in the activity of antioxidant enzymes, such as glutathione peroxidase. Carotenoids, such as beta-carotene and lutein, are potent antioxidants that can neutralize ROS and protect cells from oxidative damage. The addition of carotene rich supplements like green forages and hay, carrots, sweet potatoes in diet can help in prevention of photosensitization.
- Balanced protein and energy intake-
Protein ensures skin and tissue integration and also supports the immune system. Deficiency of protein intake will lead to compromised skin and tissue integrity make animals more susceptible to photosensitization.
Energy requirements vary among different animal species, ages, and production stages (e.g., growth, lactation, gestation). Insufficient energy intake can lead to metabolic imbalances, nutrient deficiencies, and compromised immune function, increasing the risk of photosensitization.
Maintaining a proper balance between protein and energy intake is crucial for optimal nutrient utilization and metabolism. Imbalances due to excess protein or energy deficiency can lead to metabolic disorders and increased oxidative stress, which can exacerbate photosensitization reactions.
Excessive protein intake or energy deficiency can contribute to the accumulation of photosensitizing agents in the body.
- Adequate fiber and roughage-
In ruminants’ fiber and roughages are important formaintaining properrumen function and pH by rumination and saliva production. The acidic condition in rumen can increase the absorption and accumulation of certain photosynthesizing agents leading to photosynthesizing reactions. Roughage and fiber components like lignin can bind to and help in elimination of toxins and photosynthesizing agents from digestive tract.
Provide sufficient dietary fiber and roughage to maintain healthy digestive function and prevent potential gastrointestinal disturbances that could lead to impaired liver function.
- Monitoring and correction of nutrient deficiencies-
Regularly monitor the levels of essential vitamins, minerals, and trace elements in the diet and supplement as needed to prevent deficiencies that can increase the risk of photosensitization. Pay particular attention to iron levels, as iron deficiency can contribute to the accumulation of porphyrins, which are photosensitizing agents.
- Liver support and protection-
Include dietary components that support liver health and function, such as choline, methionine, and antioxidants, to aid in the metabolism and excretion of potential photosensitizing agents. Avoid exposure to hepatotoxic substances that could compromise liver function.
- Consideration of species-specific nutritional requirements-
Tailor nutritional management strategies to the specific needs and dietary habits of different animal species, as their susceptibility to photosensitization and nutritional requirements may vary.
Conclusion-
Animal nutrition plays a vital role in the prevention and management of photosensitization. A well-balanced diet, appropriate supplementation, and careful management of pastures and feed sources can significantly reduce the risk of photosensitization in animals. By implementing the above nutritional management strategies, in conjunction with proper pasture management, veterinary care, and environmental controls, the risk of photosensitization in animals can be effectively reduced or prevented.
