Osteodystrophic diseases of sheep

J.

COMPo PATH.

1962.

VOL. 72.

OSTEODYSTROPHIC DISEASES OF SHEEP

I. AN OSTEOPOROTIC CONDITION OF HOGGS KNOWN AS DOUBLE SCALP OR CAP PI By

D. I. NISBET and E.

J.

BUTLER

Moredun Institute, Edinburgh and

C. C. BANNATYNE and

J.

M. ROBERTSON

Veterinary Investigation Department, West of Scotland Agricultural College

INTRODUCTION This is the first of a series of papers describing the clinical, pathological and biochemical findings of a survey of osteodystrophic diseases affecting sheep on Scottish farms. These conditions are known only by popular or local names, and the object of this survey was to discover their nature and to classify them according to their pathological and biochemical characteristics, this being the initial step towards elucidating their etiology. Diseases of this kind are particularly prevalent in young growing sheep, 5 to 12 months of age, known as hoggs (or hoggets), due to the fact that their immature skeletons are particularly susceptible to metabolic disturbances, such as those caused by partial starvation, by a simple or conditioned deficiency of one or more of the nutrients required for bone formation, or by an imbalance of these substances. Consequently our survey mainly concerned sheep of this age group. Osteodystrophic disease is also of greater economic importance in hoggs than in older sheep since it affects the animal at a vital stage in its development, causing retarded or arrested growth, and may also render it more susceptible to intercurrent disease. This paper concerns an osteoporotic condition of young sheep known as 'double scalp' or 'cappi' (sometimes known as 'cappie', 'scappie', 'double scaup' or 'double skulp') which occurs in the autumn and winter on both hill and lowland pasture in many parts of Britain, but is particularly prevalent on the poor hill pastures in the North of England and South of Scotland. Its exact distribution and general incidence have not been determined. The characteristic lesion occurs in the frontal bone of the skull; the outer plate of bone overlying the frontal sinus becomes very thin and flexible and yields easily to pressure with the thumb. In this way it is possible to feel the inner layer of bone; hence the name 'double scalp'. It is now known that this lesion is simply a manifestation of a generalised osteoporosis. The occurrence and the clinical and pathological features of the disease were described by Bowes (1932) and Bosworth and Stewart (1932). Cresswell (1958) recently investigated the therapeutic value

D. I. NISBET

et al

27 1

of mineral supplements, vitamin D2 and phenothiazine, and discussed theories of the etiology of the disease. The only histological studies that have been reported hitherto were those of Bosworth and Stewart, who were reluctant to draw conclusions about the nature of the initial lesions since all the six cases they studied were of long standing and were in a very debilitated condition. This paper extends their observations on the histological changes and provides additional information on the biochemistry of the disease. MATERIALS AND METHODS

Veterinary investigation officers, practitioners and agricultural advisers were asked to report outbreaks of suspected osteodystrophic disease. The farms were then visited to examine affected sheep clinically, to take blood samples for analysis and also to select cases for post-mortem examination. Information was obtained from the flockmaster about the management of both stock and pasture and the disease history of the flock. Faecal samples were taken for worm egg counts when it was considered that helminth infestation might be associated with the disease. Pathological investigations. Eight cases of double scalp or cappi were obtained for post mortem examination as soon as possible after the disease had been recognized. They came from 5 farms and their age varied from 9 months to 2 years. Six were Blackfaces, one was a South Country Cheviot and the other a Halfbred (Border Leicester X Cheviot). Material for histological examination was taken from all the body organs, and from the skull, lumbar vertebrae, ribs, costochondral junctions and limb bones. All tissues were fixed in 10 per cent formol saline neutralised by saturation with MgCO a. Bone blocks were decalcified in 5 per cent nitric acid by the method described by Clayden (1952). The contents of the abomasum and intestine were sampled for estimation of the helminth burden. Chemical investigations. Blood samples were collected for chemical analysis from 57 cases of double scalp or cappi aged from 6 months to 2 years. These occurred on 7 farms at various times of the year from September to July. The analyses carried out and the methods used were as follows: serum magnesium-modification of Green and Allcroft (1937), serum calcium-Powell (1953), serum proteins-Phillips, van Slyke, Dole, Emerson, Hamilton and Archibald (1950), serum alkaline phosphatase-King (1951), inorganic phosphate in whole blood-Fiske and Subbarow (1925), haemoglobin-modification of Cohen and Smith ( 19 19). Bones from 6 of the 8 cases which were examined post mortem were analysed for calcium, phosphorus, magnesium and ash. The entire 4th rib and tibia were removed from the right hand side and scraped free of flesh. The density and volume of the tibia were then determined as soon as possible by displacement in water. After these bones had been broken into small pieces with a hammer they were defatted with a I: I mixture of petroleum ether (B.P. 60 to 80°C) and acetone, and dried to constant weight at 105°C. They were then ground to a powder in a Christy Norris mill. For the calcium, phosphorus and magnesium estimations about 0·5 g. of the powder was wet ashed with a mixture of 60 per cent (w/w) perchloric and concentrated nitric acids, and the final solution was transferred to a 100 m!. volumetric flask and made up to this volume. Aliquots

OSTEODYSTROPHY IN SHEEP

of this solution were taken for analysis by modifications of the methods used for serum and blood and the results were expressed in terms of both weight and volume of bone. For the determination of the ash content the dry, fat-free bone powder was heated in silica crucibles in a muffle furnace at 600°C until the weight became constant (72 hrs.). RESULTS

Occurrence if Double Scalp or Cappi The disease was diagnosed clinically on 7 farms (referred to below as farms A to G), in the counties of Argyll, Roxburgh and Selkirk. With the exception of farms D and G it occurred in ewe hoggs on hill pasture at altitudes of 800 to 2,000 ft. and had been recognised by the shepherds for many years. Farm D, situated on the island of Islay, differed in that the disease occurred for the first time in I959 among ewe hoggs which were being wintered on low ground ley pasture and did not appear in hoggs on hill grazing up to 1,300 ft. on this farm. On farm G the disease occurred in gimmers on hill pasture. Supplementary food was not normally provided on any of these farms during the winter. There was a considerable difference between the farms in the time of year when the disease was first recognised. On some it was seen as early as September while 0';; others it did not appear until February. There was little variation in the incidence among hoggs from year to year on hill pasture, the usual figure being close to 100 per cent. Both Blackfaces and Cheviots were kept on farm C and the farmer believed that the latter were more severely affected. Clinical Features Our observations on the clinical features of the disease were very similar to those of Bowes (1932) and Bosworth and Stewart (1932). Scouring was not a prominent feature except on farm D and here the faecal worm egg counts were lowest (Table I), 21 out of 34 counts being nil. Anaemia was present in a few cases but was not a general finding. A surprising observation in view of the generalised and often severe osteoporosis was that bone fractures do not appear to be particularly common in affected sheep. This was also commented on by Bosworth and Stewart (1932). Anatomical Findings In all cases the general condition of the animals was poor, with a complete lack of subcutaneous, omental and perirenal fat and marked atrophy of skeletal muscle. Excessive amounts of clear serous fluid were present in the peritoneal cavities. In one case the heart was extremely flabby, and the great vessels entering and emerging from it were surrounded by gelatinous oedema, while the kidney pelves showed periureteral oedema. The general impression gained from macroscopic observation was that of malnutrition ..

D. I. NISBET ct TABLE

at

273

I

FAECAL WORM EGG COUNTS OF 77 SHEEP ON AFFECTED FARMS

Farm

Date

No. qf sheep sampled

Breed

----

No. oj worm eggs per g·faeces Range

Mean

C

7.1.58

4

Cheviot

150 -

55 0

29 0

C

7.1.58

8

Blackface

100 -

750

4 00

C

3.3.58

4

Cheviot

0 - 1100

52 5

C

3.3.58

7

Blackface

0 - 2300

728

D

19·3·59

6

Blackface

0 - 100

17

D

2.2.60

12

Blackface

0-700

142

D

3.3. 60

16

Blackface

0-

1000

140

F

11.11.58

20

Cheviot

0-1200

345

With the exception of the sheep on farm F all were clinical cases of double scalp or cappi .

The bones were lighter and smaller than normal (Figs. 1 and 2). Longitudinal section of bones such as the humerus and femur, particularly the latter, showed a marked reduction in thickness of the cortical is which was especially obvious in the proximal metaphysis, and an expansion of the marrow cavity which in most cases extended close to the epiphyseal lines due to reduction in the amount of spongiosa. The trabeculae of cancellous bone present were therefore associated in the metaphyses with the peripheral zone of the epiphyseal plates, the central area being commonly quite unsup~ ported. The epiphyseal lines in long bones such as the tibia and radius were often reduced in thickness to approximately half that of a normal hogg, but fractures, even of the ribs, were nevertheless very uncommon. The atrophy of cancellous bone could be demonstrated most readily in transverse sections of the lumbar vertebrae. Sections made through the frontal bone of the skull showed the outer plate to be extremely thin and parchment-like, the rarefaction being so marked in one case that a circular area I·S cm. in diameter between the eyes and to one side of the midline had no bone at all, only periosteum and fascia separating the sinus cavity from the overlying skin. In the skulls of two Blackface sheep, fractures were found at the base of the horns as a result of similar rarefaction. Macerated specimens demonstrated clearly that these atrophic changes affected to the same degree the other bones of the skull and also the mandible. Areas of the calvarium were so thin as to be translucent, while the posterior borders of the mandible were wafer-like and sharp.

274

OSTEODYSTROPHY IN SHEEP

Histopathology Bone. The skeletal lesions were those of generalised osteoporosis, (Figs. 3-9) and closely resembled those of a similar condition in young lambs described by Butler, Nisbet and Robertson (1957). Endochondral bone growth was either retarded or arrested, the latter state being shown in many bones by lack of proliferation in the epiphyseal cartilage accounting for its thinness when seen by the naked eye, and by the deposition on its metaphyseal aspect of a transverse layer of bone. This had occurred in such sites as the proximal and distal ends of the humerus, the lumbar vertebrae, the costochondral junctions and the proximal end of the tibia. Osteoblasts were variable in appearance and in numbers. In some bones they were seen as flattened hyperchromatic nuclei with little or no cytoplasm and closely applied to the bone surface, while in others they were plump with normal amounts of basophilic cytoplasm. There was no evidence of any marked increase in bone resorption. The numbers of osteoclasts present were not excessive, and neither the periosteal nor the endosteal surfaces of the shafts of the long bones showed signs of erosion. On two farms (F and G) where the clinical symptoms of affected sheep were characteristic of cappi, histological examination of the bones showed, in addition to osteoporosis, lesions of rickets. These were slight in the sheep from farm G, consisting only of osteoid margins on the cancellous bone of the ribs, but were more extensive in the sheep from farm F where defective provisional calcification could be seen in the epiphyseal cartilages of the long bones as well as osteoid margins on the cancellous bone (Figs. 10 and I I) . Biochemical Results The results obtained for blood samples from 57 affected sheep are summarised in Table 2. They show that when rachitic lesions were absent there was no consistent abnormality in the levels of calcium, phosphate, alkaline phosphatase, magnesium, haemoglobin and protein, but when these lesions were present (on farms F and G) there were low levels of inorganic phosphate which were associated with elevated alkaline phosphatase values. The latter must, however, be interpreted with caution, in view of the great variability of the concentration of this enzyme in the serum of sheep (Allcroft and Folley, 1941; Duckworth, Godden and Thomson, 1943). This variability also obscures the significance of the fall in alkaline phosphatase values observed on farm C from January to March. Unusually low calcium values were also obtained for the affected sheep on farm F and these are significantly lower than those for osteoporotic sheep on farms A, Band C in September, January and March (P < .05). On the other hand the serum magnesium values for the farm F cases are significantly higher than the latter (P < ·01). Samples collected from clinically normal sheep on farm

I

Gr

July

II

2

±

±

± 1'06

0,65

0 ,87

2'gO

1'46

5"05

4 '98

0' 96

I

1

--I

I

49

II

22

26

-

±

±

±

±

-

22

3'4

9'5 t

6'0 *

Alkaline phosphatase Kirlg-Armstrong units/ I 00 mi. serum

r

The results are expressed as mean values with their standard deviations, Mild rachitic lesions were found in sheep from these flocks on histological examination. * Values for farm Conly, t Values for farm D only. tt Single value for farm B.

9'97

0 ,87

±

7'99

Fr

May

1'04

±

9'23

C

Mar.

1'49

±

8 '40

B, D & E

Feb,

5"'4

±

0 '92

±

9 '50

B&C

Jan.

0'3 2

±

5"77

1.58

±

9 '45

A&B

Farm

Inorg. P mg./lOo mi. blood

Calei/lm mg./loo mt. serum

Sept.

Month

TABLE

l

I

BLOOD ANALYSES FROM 57 SHEEP

3'15

2'55

2,84

2'33

2·67

0'5 1

0'30

0 '54

0'21

0'48

2,28

±

±

±

±

±

serum

lvfagnesium mg./lOo mi.

I

±

±

1'7

1'1

11'0

12'6

0,6

± -

"5

±

'4' 2tt

11 '5

8'5

Haemoglobin g. /lOO mi. blood

I

6'6

6'7

6'6

7'0

-

±

±

±

±

-

0'7

0'7

o '9t

0 '6*

Protein g./lOO mi. serum

~

~

(.;1

-...J

~

~

-l

z ~ t'l

!"'

OSTEODYSTROPHY IN SHEEP TABLE 3 BIOCHEMICAL AND PATHOLOGICAL DATA FOR BLOOD AND BONES OF EIGHT SHEEP

Sheep number

------------------2/58

Whole blood

Serum

Rib

6/60

2I/60

I2/60

78/59

I6I/60

C

C

C

D

D

E

F

G

Month

Jan.

Mar.

April

Feb.

Feb.

Feb.

May

July

Breed

BF

BF

BF

BF

BF

HB

Chev.

BF

Age, yrs.

9/ 12

10/12

10/12

10/12

13/ 12

2

Inorg. P (mg./wo mI.) Haemoglobin (g./wo mI.)

5"2

1'9

2'9

12'0

Calcium (mg./wo mI.) 8'94 Alkaline phosphatase (King-Armstrong Units/wo mI.) 23 Magnesium (mg.flOo mI.) 2'22 Protein (g./wo mI.) 7'1 Calcium (%,w/w) Phosphorus (%,w/w) Magnesium (%,w/w)

Density (g./ml.) Calcium (%,w/w) Calcium (%, w/v) Phosphorus (%,w/w) Phosphorus (%,w/v) Magnesium (%,w/w) Ash (%, w/w)

Histological findings

9 0 /5 8

Farm

Ash (%, w/w)

Tibia

37/58

------ --- --- --- --- --

11/12

I

--- --- --- --- --- --- ---

3.6

4.6

-

-

II '5 --- --- --- --- --- --- ---

-

-

-

-

-

-

-

-

-

2'13

-

3'53

2'28

-

-

-

5"0

-

7'0

-

25"1

24'7

25"8

-

-

-

21'2

10'3

9.8

10'5

-

-

-

8·6

-

-

-

-

0'45

-

7.69

16

-

-

7.89

52

9'97

-

--- ------ ------ --- --- ---

0'49 58 '0 1'29

0'44

0'5 0

48 '2 54'4 58 .6 --- --- --- ------ --- ---

1'34

1'27

27.6

28'0

25'4

17'9

18·6

16'3

II·6

11'4

11'9

7'5

7.6

7"7

0'57

0'5 6

0'53

63'0

Osteoporosis

+

Rickets

-

--

62·6

---

+

-

-

1'18

-

1'28

-

-

29'1

-

1'2

-

16'0

-

10·6

-

10'7

--

-

4'3

-

5"9

-

0'50

0'4 1

-

0'49

-

29'4* 27'4 -

II ·8*

I

62'5 60'5 59'2 --- --------- --- ---

+

+

+

+

-

-

-

-

+ +

+ +

The values for the calcium and phosphorus content of ribs and tibia are expressed as g./wo g. dry, fat-free bone (%, w/w), and g./wo ml. fresh bone (%, w/v). BF indicates Blackface, HB-Border Leicester X North Country Cheviot and Chev. -South Country Cheviot. * These values were obtained filr a radius.

D. 1. NISBET

et al

F at the same time gave similar results and it is therefore probable that they were also affected with rickets. The analytical data obtained for bones, recorded in Table 3, show the same general features as the results for blood, but are insufficient to provide more detailed information on the biochemistry of the disease. In the cases with no rachitic lesions there is no indication of any gross abnormality in the chemical composition of the skeleton and the results are therefore consistent with the histological findings. Bones were analysed from only one case with rachitic lesions and the ash, calcium and phosphate content of the rib is lower than that of the other cases.

Helminthological Findings Table 1 gives the results of faecal worm egg counts from sheep on affected farms, the majority of which were clinical cases of cappi. These figures suggest that the sheep were not carrying excessively heavy worm burdens. TABLE 4 WORM BURDENS IN THREE SHEEP

Total no. rif worms present in abomasum and intestines

Faecal worm egg count

Blackface

17,200 (8,300 of these were young stages)

650 e.p.g.

12.3.58

Blackface

16,000 (10,000 of these were young stages)

15·5·59

Cheviot

Date

Breed

C

10.1.58

C

F

Farm

356

-

1500 e.p.g.

Table 4 shows the worm population in three typical cases of cappi. The two cases from farm C are of considerable interest, since although the total number of worms present was high, at least half of these were young stages, indicating a recently acquired heavy infestation or the recent emergence of a latent infestation. In any case it is unlikely that the young stages played any part in the production of the disease. In the sheep from farm F the worm burden was low. DISCUSSION

The results of our investigations confirm the statement of Bosworth and Stewart (1932) that the pathological changes in double scalp or cappi are those of a generalised osteoporosis. This disease process causes no detectable alteration in the concentration of calcium and phosphorus in the blood and bones. Rachitic lesions may be co-existent without altering the clinical features of the disease, and they are accompanied by changes in the levels of the

OSTEODYSTROPHY IN SHEEP

mineral elements in the blood, the most marked being a reduction in the level of inorganic phosphate. This may explain the low blood phosphate values found by Bosworth and Stewart (1932) in some of their cases, which led to the mistaken but widespread belief that cap pi is a manifestation of phosphorus deficiency (Greig, 1943 ; Anon. 1955; Greig, 1956). Various opinions have been expressed concerning the part played by gastro-intestinal helminthiasis in this disease. Bowes (1932) stated that the bone atrophy resulted from the helminthiasis, and Bosworth and Stewart (1932) felt that helminthiasis was an important contributory cause. Greig (1943) considered that it was not an essential factor in the causation of the disease but rather that it followed a primary osteodystrophy, while Cresswell (1958), on the evidence of faecal worm egg counts and the absence of beneficial effects following dosage with anthelminthic drugs, suggested that helminthiasis played no part in the production of cappi. Our experience has certainly been similar to that of Greig in that while severe helminthiasis can occur in cappi, it is not an essential etiological factor. Gibson (1954), and others quoted by him, has stated that poorly nourished sheep carry more parasites than do those which are adequately fed, and has supported this statement by experimental evidence. There can be no doubt that young sheep affected with cappi are in a poor nutritional state. If the opportunities for acquiring helminth infestation are present, it is thus not surprising that many of them carry a heavy burden of worms. Two opposing views have been put forward concerning the pathogenesis of osteoporosis. The earlier view, suggested originally by Pommer (1885) and later by Albright, Smith and Richardson (1941), is that osteoporosis is brought about by decreased osteoblastic activity resulting in diminished formation of bone matrix. Con trary to this theory, Nordin (1960, 196 I) and Harrison and Fraser (1960) have stated that r apid bone formation occurs in osteoporosis accompanied by increased bone resorption. It appears from the experiments of Harrison and Fraser (1960) with rats that this increased resorption is not detectable histologically. Albright considered that one of the most important causal factors was a defect in the processes of protein synthesis, while Nordin and Harrison and Fraser have demonstrated that a negative calcium balance in the presence of adequate vitamin D will result in osteoporosis. Histological examination is of limited assistance in the investigation of the etiology of cappi, since the generalised osteoporosis which it reveals is non-specific and could be produced by deficiency of one or more essential dietary constituents. The cause and pathogenesis of the osteoporosis in cappi are still obscure, and are likely to remain so until attempts are made to investigate experimentally the many dietary deficiencies which can affect young growing sheep, particularly those grazing hill pasture

D. 1. NISBET

et

at

279

in wintertime. Cresswell (1958) reported that supplements of minerals and trace elements had no effect in reducing the incidence of the disease and it is therefore possible that deficiencies of dietary nitrogen and energy play a more important role in its etiology, particularly when it is realised that on most farms where cappi occurs· the hoggs subsist entirely on the available herbage and receive no supplementary food throughout the winter. Copper may merit a more detailed investigation in view of the claim made by Bowes (1932) that copper sulphate administered as an anthelminthic has curative effects, and the fact that osteoporosis is one of the principal features of copper deficiency in puppies (Baxter and van Wyk, 1953; Baxter, van Wyk and Follis, 1953) and pigs (Follis, Bush, Cartwright and Wintrobe, 1955). Cresswell (1958), quoting work carried out at the Rowett Research Institute, has suggested that the initial changes of cappi may be found in the foetus, indicating that maternal nutrition may be of primary importance. On some farms the disease has been observed to disappear following improvement of the pasture, and hence the general nutrition of the flock. This finding is however at variance with the sudden appearance of cappi, sometimes in high incidence, on improved pasture on other farms (as on farm D). It seems possible, therefore, that cappi is not a specific disease with a single basic causal factor, but may result from a number of widely different nutritional deficiencies acting either singly or in combination. CONCLUSIONS

The primary disease process in cappi (double scalp) of young sheep is a generalised osteoporosis. Rachitic lesions may also be present without altering the clinical picture, but are accompanied by low levels of phosphate in the blood. While helminthiasis is commonly associated with this condition it does not appear to be an essential etiological factor. Cappi occurs on both hill and lowground pasture. Consideration of the etiology of cappi suggests that it is not a specific disease with a simple cause, such as deficiency of phosphate, but rather that it could result from a number of widely differing nutritional deficiencies, either singly or in combination. Further investigation is required to confirm this theory. ACKNOWLEDGMENTS

We wish to thank Dr. J. T. Stamp, Director of Moredun Institute, for his continued interest in this work. Our thanks are also due to Mr. J. B. Dow for preparation of histological specimens, to Dr. J. Allan Campbell and Mr. J. Patterson for advice and assistance in the helminthological aspects of this investigation, and Drs. Jennie W. McCallum and B. S. W. Smith for help with analytical work. We are also grateful to Dr. H. H. Corner and Mr. H. J. Usher of the Edinburgh and East of Scotland College of Agriculture for bringing cases of the disease to our notice. D

280

OSTEODYSTROPHY IN SHEEP REFERENCES

- - (1955). Diseases of Sheep, p. 100. Brit. Vet. Assoc; London. Albright, F., Smith, P. H., and Richardson, A. M. (1941). J. Amer. med. Ass., 116, 2465. Allcroft, W. M., and Folley, S. J. (1941). Biochem. J., 35,254. Baxter,J. H., and van Wyk,J.J. (1953). Bull. Johns Hopkins Hosp., 93, I. Baxter,J. H., van Wyk,J.J., and Follis, R. H. (1953). Ibid., 25. Bosworth, T. J., and Stewart, J. (1932/3). Rep. Dir. Inst. animo Path., Camb., 3, 33. Bowes, H. G. (1932). Vet. J., 88,209. Butler, E. J., Nisbet, D. 1., and Robertson, J. M. (1957)· J. compo Path., 67, 378. Clayden, E. C. (1952). J. med. Lab. Technol.,10, 103. Cohen, B., and Smith, A. H. (1919). J. biol. Chem., 39, 489. Cresswell, E. (1958). J. agric. Sci., 50, 1I5. Duckworth, J., Godden, W., and Thomson, W. (1943). Ibid., 33, 190. Fiske, C. H., and Subba Row, Y. (1925). J. bioi. Chem.,66, 375. Follis, R. H., Bush,J. A., Cartwright, G. E., and Wintrobe, M. M. (1955). Bull. Johns Hopkins Hosp., 97,405. , Gibson, T. E. (1954). J. compo Path., 64,360. Green, H. H., and Allcroft, W. M. (1937). Methodsfor the Chemical Ana(ysis of Biological Material in Nutrition Investigations, Imperial Bureau of Animal Nutrition. Technical Communication NO.9. Edited by Godden, W. • Greig, J. R. (1943). Trans. High!. and agric. Soc., Scotland, 55, 30; (1956). The Shepherd's Guide, 2nd Ed., H.M.S.O.; Edinburgh. Harrison, M., and Fraser, R. (1960). J. Endocrinol., 21, 197. King, E. J. (1951). Micro-Anaylsis in Medical Biochemistry, p. 73. J. & A. Churchill Ltd.; London. Nordin, B. E. C. (1960). Proc. Nutr. Soc., 19,129; (1961). Lancet, i, 101 I. Phillips, R. A., van Slyke, D. D., Dole, V. P., Emerson, K., Hamilton, P. B., and Archibald, R. M. (1950). J. biol. Chem., 183,305. Pommer, G. (1885). Untersuchungen uber Osteomalacie und Rachitis. Leipzig. Powell, F. J. N. (1953). J. clin. Path., 6,286. [Received for publication, January 22nd, 1962]

D. I. NISBET

Fig.

I.

Fig.

2.

Fig. 3. Fig. 4.

et

at

Skull of Cheviot hogg affected with cappi viewed by transmitted light, illustrating the delicac)' of the bone structure especially in the calvarium. Femur and humerus of the same hogg, again viewed by transmitted light. The shafts, especially at their extremities, are particularly thin. Head of tibia, Blackface hogg, showing marked atrophy of cancellous bone throughout. Below the central part of the epiphyseal plate this allows the marrow cavitv to extend to the cartilage. Hand E X 3. Higher magnification of a portion of Fig. ::I showing thc narrowness of the eninhvseal cartila"e and slender trabeculae of cancellous bone. Hand E x aO.

OSTEODYSTROPHY IN SHEEP

Fig. 7. Fig. 8. Fig. g. Fig.

10.

Fig.

I I.

Frontal bone of Blackface hogg, transverse section. Hand E x 3. Transverse section of lumbar vertebra of Blackface hogg. Hand E X 3. Higher magnification of part of Fig. 8. Osteoblasts cover the atrophied trabecular bone in normal numbers. Hand E x 40. Distal radial epiphysis from a case of cappi associated with rickets. There is great thickening due to delayed removal of the mature cartilage cells. Hand E X 40. Rib shaft from the same case as Fig. 10. Osteoid borders can be dearly seen. Hand E X go.