Minimal Erythema Dose Determination in Holstein Friesian Cattle

Cattle on pasture are continuously exposed to solar UV radiation, which has been associated with biological effects such as sunburn, photosensitization, squamous cell carcinoma, and cutaneous vitamin D3 production. The minimal erythema dose (MED) required to produce first-degree sunburn (erythema) is poorly researched in cattle. Since cattle are naturally covered with dense hair coats, the MED is influenced by the UV protection offered by the hair. The objective of this study was to determine the MED on intact-hair-covered (MED-H) and shaved white skin (MED-S) of Holstein Friesian cattle. Twenty-one Holstein Friesian cows and heifers were MED tested using a narrowband UV-B LED light (peak irradiance at 292 nm) on eight hair-covered and eight shaved areas over white skin previously unexposed to direct sunlight. Erythema was visually assessed after 24 h. The mean MED-H and MED-S were 5,595 and 329 J/m2, respectively. Heifers had a higher MED-H compared to cows, 7,600 and 4,969 J/m2, respectively. The mean UV transmittance of white cattle hair was 6.7%. MED-H was correlated with hair length (Spearman's rho = 0.76). A linear regression model showed that each millimeter of hair coat length increased the MED-H by 316 J/m2. In conclusion, this study provides a MED testing protocol for cattle and reports standardized values of MED for cattle on intact-hair-covered and shaved areas.

Modern Approaches for the Objective Assessment of Minimal Erythema Dose

At present, the assessment of the degree of ultraviolet (UV) exposure is based on the calculation of the minimal erythema dose (MED). The concept of MED is inextricably linked to the process of acute UV skin damage, which is accompanied by damage to the structures of the epidermis and dermis, dermal vasodilation, and it manifests clinically in erythema formation. The knowing of the MED value is necessary to choose the starting dose for UV-phototherapy of various dermatoses and to evaluate individual photosensitivity. Meanwhile, the determination of MED in clinical practice is most often performed visually by naked eye. The traditional assessment of MED is a subjective, inaccurate, poorly reproducible and not quantifiable method. In addition, preliminary UV irradiation is necessary for the estimation of MED and waiting for the results takes 24 hours. Inaccurate determination of MED may lead to the wrong dosing of UV-exposure, which leads to various complications. Today, there are a number of non-invasive methods that allow making the calculation of the MED more objective and accurate. However, these techniques have a number of limitations: the difficulty in mastering the methods, the lack of standardization of the data recording process and the evaluation of results. The majority of methods are based on the assessment of the subjective parameters of UV erythema, but not its objective pathophysiological criteria. In addition, available technologies still do not allow to estimate the MED in the first hours after UV exposure (on-site) or predict MED without UV exposure.

Phototherapy in Dermatology

Phototherapy is a therapeutic procedure in dermatology. Phototherapy uses certain ultraviolet wavelengths classified into 3 types,broadband UVB (BBUVB), narrowband UVB (NBUVB), and psoralen UVA (PUVA). The most widely used is NBUVB for treating psoriasis, atopic dermatitis and vitiligo. The mechanism of action of phototherapy is to reduce epidermal proliferation, suppress the immune system, reduce the inflammatory process, and induce repigmentation. Before starting phototherapy, the dose adjustment depends on skin type and minimal erythema dose (MED). Frequency of use is recommended based on the severity of the disease, continuously administered needed. Besides of this therapeutic effect, some contraindications and side effects that need to be considered in the use of phototherapy such as drug interactions, photoallergic and risk of skin malignancy.