White muscle disease in foals: focus on selenium soil content. A case series

Abstract

Background: White muscle disease (WMD) is a nutritional myopathy caused by selenium (Se) deficiency. In most soils, Se is present in low concentrations, sometimes even below 0.2 mg/kg, a trend which is seen in many countries. Apart from total soil Se concentrations, soil conditions may be such that the bio-availability of Se is so low that it causes very low uptake in plants which can ultimately lead to deficiency problems in animals. This is the first case series to report clinical WMD in foals in areas deficient in Se, in the Netherlands. The aim of the current report is to provide an overview of the clinical history, symptoms and (clinical) pathology of 8 newborn foals living at 4 different premises and suffering from WMD together with the effectiveness of Se and vitamin E (Vit E) supplementation in the affected foals, their dams and herd members. Hands on practical information is provided to apply a correct and effective Se supplementation management in horses and which pitfalls need to be avoided for a successful approach.

Case presentation: Case features and history were mapped out for all foals. Se and Vit E status were assessed for the foals, their dams and herd members, at admission and after 3 months of Vit E/Se supplementation. Common symptoms were muscle weakness, inability to rise, lethargy and inadequate suckle reflex together with increased serum muscle enzymes and low glutathione peroxidase (GSH-Px) and low to normal serum vit E levels. Necropsy revealed necrosis of skeletal muscles consistent with nutritional myopathy. Se status of the dams and herd members correlated well with the Se status of the foals. All surviving foals (n = 6) showed normal Vit E and GSH-Px levels after supplementation, likewise, all horses tested at premises 1, 3 and 4. However, dams and herd members in premises 2 showed no normalization. Horses of that premises were diagnosed with pyrrolizidine intoxication one year prior to the study.

Conclusions: Certain regions in the Netherlands are sufficiently Se deficient to predispose newborn foals to develop WMD, especially when they are being fed a diet that mainly consists of locally harvested roughage.

Keywords: Liver disease; Nutritional myopathy; Selenium; Soil analysis; Vitamin E.

Fig. 1

Geographical overview of Se content in the Netherlands. Notice that all four premises with affected foals are indeed located in Se deficient areas. Panel a: Results on top soil (0–20 cm) on 358 locations in forests, agricultural and natural areas, representing total Se content. Panel b: representing “maximum available Se content” (analysis with ICP-MS after 0.43 HNO₃ extraction). Mark the important difference between “total” and “maximum available” Se content. The grey circles indicate the locations with Se concentrations exceeding the 95 percentile. Reprinted from Mol et al. [34]

Fig. 2

Geographical overview of Se content in top soil in Belgium (panel a) and top soil features of importance with respect to Se availability (panels b, c & d). Panel a: Geographical overview of Se content in Flanders. Results on top soil (0–6 cm) of 117 pastures between 2007 and 2015. Analyses with ICP-MS after HNO₃-HCl (1:3) extraction. The number in the circles is the number of samples in the municipality. Results of the Soil Service of Belgium. Panels b, c & d: Geographical overview of soil fertility (0–6 cm) of 117 pastures between 2007 and 2015 in Flanders. Analyses of pH-KCl, O.M. with modified Walkley and Black, P-AL with ICP-MS after ammoniumlactaat extraction. Results of the Soil Service of Belgium. The size of the diagram corresponding with 10 samples per municipality is given in the legend

Fig. 3

Histological image of a cross section of an affected skeletal muscle showing. Panel a: multifocal mineralization of muscle fibres (arrows). H&E stain. Panel b: Longitudinal section of a severely affected skeletal muscle revealing hyalinization and fragmentation of muscle fibres (arrows) and influx om macrophages phagocytizing myofibre remnants (arrowhead). H&E stain

Fig. 4

Schematic overview illustrating the influence of specific soil features such as pH on chemical behaviour and bio-availability of Se. Notice that the highly bio-available selenate is also most soluble and will therefore easily leach from well-drained soils. (Adapted from Fordyce [26])