WHITE MUSCLE DISEASE OF SHEEP AND ASSOCIATED TISSUE SELENIUM LEVELS IN WESTERN AUSTRALIA
B. J. GABBEDY*, H. MASTERS? AND E. B. BODDINGTONS SUMMARY: White Muscle Disease of s h e e p occurs in Western Australia as distinct syndromes in lambs and weaner sheep. Mean liver selenium concentrations of lambs and weaners with WMD and unaffected by WMD were 0.19 and 0.46 ppm, and 0.20 and 0.41 ppm (dry weight) respectively. There was considerable overlap between levels suggesting that selenium status was not the only factor involved in the development of WMD.
Introduction
White Muscle Disease (WMD) was first recognised in Western Australia (WA) in 1960 (Gardiner 1962). Since that time, the disease has occurred commonly. The pattern of disease outbreaks has been described by Gardiner (1962, 1969), Gardiner e,t ul (1962) as falling into 2 distinct age and seasonal groupings. Firstly, those occurring in young suckling lambs in winter and spring and secondly, those occurring in weaner sheep (6-12 months) in the summer and autumn. Field evidence in WA indicated that selenium prevented both forms of WMD and Gabbedy (197 1) demonstrated that selenium supplementation resulted in reduced mortality of weaner sheep during the summer and autumn. This paper briefly outlines epidemiological aspects of WMD in sheep in WA, additional to those described by Gardiner (1969), and records liver selenium levels in normal and affected sheep. Materials and Methods Data was collected from the records of the Animal Health Laboratories, South Perth, until December 1973 and includes the 78 outbreaks of W M D reported by Gardiner (1969). Tissues for histological examination and selenium estimation were submitted by field officers in the course of their normal investigational activities. A diagnosis of W M D was considered only when confirmed histologically and selenium levels considered only from flocks which had not received a selenium supplement. Liver selenium levels were selected for comparison from sheep unaffected with WMD, of similar age and during the same period of the year when the condition was known to occur. T h e lambs were tested in the period June to October and weaner sheep from January to April. To obtain normal selenium concentrations the livers were analysed from neonatal lambs born in 1970 to control ewes in the trials reported by Gabbedy (1971). On 15 properties, livers were collected from lambs born dead or which died within 3 days of birth and whose cardiac and skeletal musculature showed no indication of W M D when examined histologically. ~~
~
*Department of ?Animal Health Perth. Western XDepartment of
482
Histological diagnosis of W M D was based on segmental hyaline degeneration of striated muscle, characterised by swelling of the muscle fibre with loss of striation and cytoplasmic fragmentation. Later the area became infiltrated with macrophages and proliferation of the sarcolemmal nuclei occurred. Mineralization was often present. Selenium was analysed by the method of Watkinson (1966). Dried tissues were brought into solution by nitricperchloric acid digestion and selenium determined fluorometrically after reaction with purified 2,8diaminonaphthalene, with which the element forms a fluorescing piazselenol. Interferences were suppressed by masking with diammonium EDTA and hydroxylamine. The complex formed was extracted with cyclohexane and the fluorescence measured at 530 nm after excitation at 380 nm. The significance of differences in liver selenium 'levels between sheep affected and not affected with W M D were examined using the t test.
Results
Epidemiological Aspects Of 167 outbreaks of WMD recorded, 58 occurred in lambs ( 3 days to 16 weeks of age), 105 in weaners (6 to 12 months of age), and 4 in adult sheep. The monthly distribution of outbreaks of WMD in lambs and weaner sheep is shown in Figure 1. In sheep 6 to 12 months of
J
F
H
~~~~~
Agriculture, Bunbury. Western Australia 6230 Laboratory, Department of Agriculture, South Australis 6151 Agriculture, Albany, Western Australia 6330
Figure 1. Monthly distribution of White Muscle Disease outbreaks in Western Australia from March 1960 until December 1973.
Australian Veterinary Journal,
Vol. 5 3 , October, 1977
TABLE 1 Mean Liver Selenium Levels (ppm dry weight) of Sheep in Western Australia in Relation to Rainfall Observation White Muscle Disease Selenium concentration No. of flocks Negative WMD Selenium concentration No. of flocks
760
0.89 1
0.28 15
0.17 21
0.18
6
0.20 5
1.8 5
0.72 21
0.5 1 18
0.37
0.45
age the prevalence was highest from January to April whereas in sheep less than 3 months of age, the prevalence was highest from July to September The site of the lesion was specifically recorded in lambs from 14 outbreaks (6 skeletal, 8 skeletal and cardiac) and weaners from 50 outbreaks (36 cardiac, 15 skeletal, 9 skeletal and cardiac). Liver Selenium Levels Liver selenium concentrations, from normal sheep and those affected with WMD, are shown in Table 1 in relation to average annual rainfall. Where more than one value for a flock was known the average value was used. The liver selenium levels of lambs and weaners, affected and unaffected with WMD, are shown in Table 2. Each lamb value represents an individual animal from a different property except for the neonatal lamb values which were obtained from 15 properties. The weaner values represent individual animals but in some cases several values were from the same flock. In areas receiving < 410 mm of average annual rainfall WMD is uncommon and liver selenium levels are high (Table l), and therefore data from the area was not included in Table 2. Liver selenium levels of lambs and weaner sheep with WMD were significantly lower than those unaffected with WMD (P < 0.001). Discussion
White Muscle Disease of lambs in WA corresponds to the condition described in New Zealand by Andrews et a1 (1968) as Delayed WMD. This is the common form of nutritional myopathy of sheep throughout the world and has been diagnosed in New South Wales (Walker el a1 1961; Setchell et a1 1962), South Australia (M. F. Pulsford, personal communication) and Tasmania (D. Roche, personal communication). White muscle disease of weaner sheep, occurring during the summer and autumn (January to April) and involving primarily the cardiac musculature has been reported only in WA Australian Velerinary lournal, Vol. 53, October, 1977
8
7
(Gardiner 1962; Gardiner 1969), although it has occurred in South Australia @ F. lPulsford, . personal communication) and Tasmania @. Roche, personal communication). This condition does not correspond to myopathy in hoggets described by Andrews et nl (1968) in New Zealand which affects sheep of similar age (912 months) but involves skeletal musculature only and follows overwintering on turnips or swedes. Gardiner and Gorman (1963) found a correlation between plant selenium levels and annual rainfall in WA, the lower selenium levels occurring in higher rainfall areas. The figures for a liver selenium concentration presented in Table 1 are consistent with this finding in the lower rainfall areas (< 410mm to 635 mm) but do not decrease further in the higher rainfall areas. The mean liver selenium levels of lambs and weaners were significantly lower in those animals with WMD compared with normal animals. The range of levels, however, indicates that selenium levels per se do not govern the occurrence of WMD as some levels from normal lambs were extremely low whereas some levels from affected animals were in the accepted normal range. This TABLE 2 Liver Selenium Levels ( p p m Dry Weight) from Sheep in Western Australia Observations
Lambs Weaners 0.19 (A) 0.20 (D) Mean Confirmed WMD Range 0.08-0.39 0.09-0.67 No. of 13 65 Sheep 0.47 (B) 0.41 (E) Mean Negative WMD Range 0.07-1.3 0.06-15 5 No. of 14 44 Sheer, 0.46 (C) Mean Neonatal lambs Range 0.20-0.77 (Negative WMD) No. of 36 Sheep A differs from B and C (P
B. J. GABBEDY*, H. MASTERS? AND E. B. BODDINGTONS SUMMARY: White Muscle Disease of s h e e p occurs in Western Australia as distinct syndromes in lambs and weaner sheep. Mean liver selenium concentrations of lambs and weaners with WMD and unaffected by WMD were 0.19 and 0.46 ppm, and 0.20 and 0.41 ppm (dry weight) respectively. There was considerable overlap between levels suggesting that selenium status was not the only factor involved in the development of WMD.
Introduction
White Muscle Disease (WMD) was first recognised in Western Australia (WA) in 1960 (Gardiner 1962). Since that time, the disease has occurred commonly. The pattern of disease outbreaks has been described by Gardiner (1962, 1969), Gardiner e,t ul (1962) as falling into 2 distinct age and seasonal groupings. Firstly, those occurring in young suckling lambs in winter and spring and secondly, those occurring in weaner sheep (6-12 months) in the summer and autumn. Field evidence in WA indicated that selenium prevented both forms of WMD and Gabbedy (197 1) demonstrated that selenium supplementation resulted in reduced mortality of weaner sheep during the summer and autumn. This paper briefly outlines epidemiological aspects of WMD in sheep in WA, additional to those described by Gardiner (1969), and records liver selenium levels in normal and affected sheep. Materials and Methods Data was collected from the records of the Animal Health Laboratories, South Perth, until December 1973 and includes the 78 outbreaks of W M D reported by Gardiner (1969). Tissues for histological examination and selenium estimation were submitted by field officers in the course of their normal investigational activities. A diagnosis of W M D was considered only when confirmed histologically and selenium levels considered only from flocks which had not received a selenium supplement. Liver selenium levels were selected for comparison from sheep unaffected with WMD, of similar age and during the same period of the year when the condition was known to occur. T h e lambs were tested in the period June to October and weaner sheep from January to April. To obtain normal selenium concentrations the livers were analysed from neonatal lambs born in 1970 to control ewes in the trials reported by Gabbedy (1971). On 15 properties, livers were collected from lambs born dead or which died within 3 days of birth and whose cardiac and skeletal musculature showed no indication of W M D when examined histologically. ~~
~
*Department of ?Animal Health Perth. Western XDepartment of
482
Histological diagnosis of W M D was based on segmental hyaline degeneration of striated muscle, characterised by swelling of the muscle fibre with loss of striation and cytoplasmic fragmentation. Later the area became infiltrated with macrophages and proliferation of the sarcolemmal nuclei occurred. Mineralization was often present. Selenium was analysed by the method of Watkinson (1966). Dried tissues were brought into solution by nitricperchloric acid digestion and selenium determined fluorometrically after reaction with purified 2,8diaminonaphthalene, with which the element forms a fluorescing piazselenol. Interferences were suppressed by masking with diammonium EDTA and hydroxylamine. The complex formed was extracted with cyclohexane and the fluorescence measured at 530 nm after excitation at 380 nm. The significance of differences in liver selenium 'levels between sheep affected and not affected with W M D were examined using the t test.
Results
Epidemiological Aspects Of 167 outbreaks of WMD recorded, 58 occurred in lambs ( 3 days to 16 weeks of age), 105 in weaners (6 to 12 months of age), and 4 in adult sheep. The monthly distribution of outbreaks of WMD in lambs and weaner sheep is shown in Figure 1. In sheep 6 to 12 months of
J
F
H
~~~~~
Agriculture, Bunbury. Western Australia 6230 Laboratory, Department of Agriculture, South Australis 6151 Agriculture, Albany, Western Australia 6330
Figure 1. Monthly distribution of White Muscle Disease outbreaks in Western Australia from March 1960 until December 1973.
Australian Veterinary Journal,
Vol. 5 3 , October, 1977
TABLE 1 Mean Liver Selenium Levels (ppm dry weight) of Sheep in Western Australia in Relation to Rainfall Observation White Muscle Disease Selenium concentration No. of flocks Negative WMD Selenium concentration No. of flocks
760
0.89 1
0.28 15
0.17 21
0.18
6
0.20 5
1.8 5
0.72 21
0.5 1 18
0.37
0.45
age the prevalence was highest from January to April whereas in sheep less than 3 months of age, the prevalence was highest from July to September The site of the lesion was specifically recorded in lambs from 14 outbreaks (6 skeletal, 8 skeletal and cardiac) and weaners from 50 outbreaks (36 cardiac, 15 skeletal, 9 skeletal and cardiac). Liver Selenium Levels Liver selenium concentrations, from normal sheep and those affected with WMD, are shown in Table 1 in relation to average annual rainfall. Where more than one value for a flock was known the average value was used. The liver selenium levels of lambs and weaners, affected and unaffected with WMD, are shown in Table 2. Each lamb value represents an individual animal from a different property except for the neonatal lamb values which were obtained from 15 properties. The weaner values represent individual animals but in some cases several values were from the same flock. In areas receiving < 410 mm of average annual rainfall WMD is uncommon and liver selenium levels are high (Table l), and therefore data from the area was not included in Table 2. Liver selenium levels of lambs and weaner sheep with WMD were significantly lower than those unaffected with WMD (P < 0.001). Discussion
White Muscle Disease of lambs in WA corresponds to the condition described in New Zealand by Andrews et a1 (1968) as Delayed WMD. This is the common form of nutritional myopathy of sheep throughout the world and has been diagnosed in New South Wales (Walker el a1 1961; Setchell et a1 1962), South Australia (M. F. Pulsford, personal communication) and Tasmania (D. Roche, personal communication). White muscle disease of weaner sheep, occurring during the summer and autumn (January to April) and involving primarily the cardiac musculature has been reported only in WA Australian Velerinary lournal, Vol. 53, October, 1977
8
7
(Gardiner 1962; Gardiner 1969), although it has occurred in South Australia @ F. lPulsford, . personal communication) and Tasmania @. Roche, personal communication). This condition does not correspond to myopathy in hoggets described by Andrews et nl (1968) in New Zealand which affects sheep of similar age (912 months) but involves skeletal musculature only and follows overwintering on turnips or swedes. Gardiner and Gorman (1963) found a correlation between plant selenium levels and annual rainfall in WA, the lower selenium levels occurring in higher rainfall areas. The figures for a liver selenium concentration presented in Table 1 are consistent with this finding in the lower rainfall areas (< 410mm to 635 mm) but do not decrease further in the higher rainfall areas. The mean liver selenium levels of lambs and weaners were significantly lower in those animals with WMD compared with normal animals. The range of levels, however, indicates that selenium levels per se do not govern the occurrence of WMD as some levels from normal lambs were extremely low whereas some levels from affected animals were in the accepted normal range. This TABLE 2 Liver Selenium Levels ( p p m Dry Weight) from Sheep in Western Australia Observations
Lambs Weaners 0.19 (A) 0.20 (D) Mean Confirmed WMD Range 0.08-0.39 0.09-0.67 No. of 13 65 Sheep 0.47 (B) 0.41 (E) Mean Negative WMD Range 0.07-1.3 0.06-15 5 No. of 14 44 Sheer, 0.46 (C) Mean Neonatal lambs Range 0.20-0.77 (Negative WMD) No. of 36 Sheep A differs from B and C (P
