The north-western part of South Africa, in particular, is well known for mineral imbalances. Aphosphorosis, resulting in rickets and osteomalacia, received a lot of attention at the turn of the nineteenth century (1882–1912). This was followed in 1997 by research on Vryburg hepatosis, another area-specific mineral imbalance–related disease in young calves reared on manganese-rich soil derived from the weathering of dolomitic (carbonate) rock formations. In 1982, a totally new syndrome (osteochondrosis) manifested in, amongst others, areas in South Africa where aphosphorosis was rife. Osteochondrosis was also identified in the south-western parts of Namibia as well as southern Botswana and other areas in South Africa. Osteochondrosis has a multifactorial aetiology and this study focused on the role of minerals, particularly phosphorus, in the development of the disease. A significant improvement in the clinical signs in experimental animals and a reduction of osteochondrosis occurred on farms where animals received bioavailable trace minerals and phosphorus as part of a balanced lick. An increase in the occurrence of the disease on farms during severe drought conditions in 2012–2013 prompted researchers to investigate the possible role of chronic metabolic acidosis in the pathogenesis of the disease.
Since the 1800s, the north-western parts of South Africa, particularly the North West and Northern Cape Provinces, have been known as an area characterised by aphosphorosis (‘stiff sickness’) in cattle (Theiler
Initially, the lameness seemed to affect only a small number of show animals and it was also seen in Phase D tested bulls, but the incidence steadily increased, and in 2004, farmers reported an incidence that ranged from 2% to 20%. In some instances up to 40% of animals were affected. The syndrome was found to be present in cattle of all age groups and classes (both commercial and non-commercial), and apparently in most breeds of cattle farmed in that area. Afrikaner cattle seemed to be more resistant to this condition. The only factor in common amongst affected animals was the geographical area in which they lived.
Necropsies performed on 21 severely affected cattle revealed chronic lesions that enabled a diagnosis of osteochondrosis to be made. Osteochondrosis is a common and important joint disorder that occurs in humans and many animal species, particularly pigs, horses and dogs (Bradley & Dandy
As early as 1978, it was suggested that the pathophysiology of osteochondrosis is essentially the same in all species, including humans (Olsson
Osteochondrosis in cattle is found in all types of husbandry systems, including feedlots (Davies & Munro
Cattle affected with this disorder develop effusions in the weight-bearing joints, in particular the femoro-tibial (stifle) joint, associated with inflammation and pain, causing lameness of varying degrees. As a result, animals are unable to walk long distances for grazing, have decreased feed intake, have decreased milk production and a loss in body condition, and bulls have decreased mating ability (Persson, Soderquist & Ekman
Because, in the North West Province, outbreak cattle of multiple breeds were affected, and the area is characterised by mineral imbalances, samples of liver and rib were subjected to mineral analysis together with samples taken from healthy control cattle and water samples from the affected area. A limited feeding trial on seven cattle of the same group as the necropsied cattle was undertaken. Based on the results obtained, various studies were subsequently undertaken to examine the possible role of mineral imbalances in the syndrome, the details of which will be published elsewhere. The study describes the pathology of the lesions observed at necropsy on which the diagnosis of osteochondrosis is based. The other important syndromes caused by mineral imbalances in the same area are discussed, and the results of the mineral analysis and pilot feeding trial are briefly summarised.
During June 2004, 28 clinically affected female adult animals (2–7 years old), representing various breeds, were donated by farmers from the North West Province to the University of Pretoria for research purposes. The animals showed lameness and articular swelling that was most prominent in the stifle joint. From the time of arrival, animals were fed only good quality
Necropsies were conducted on 21 animals (5 animals 2–3 years old and 16 animals 4–6 years old). All the joints of the limbs were opened and examined, as well as multiple vertebral joints, and lesions were described and photographed. Bone samples were taken for histopathological examination, and bone and liver samples were taken for mineral analysis (to be described in detail elsewhere).
The remaining seven animals (three 2–3 years old and four 4–6 years old) with less severe lameness and swelling of the stifle joints were fed on a commercial production supplement (Maxitech, AFGRI) at a recommended daily intake of 1.5 kg per animal per day for a period of 3 months, from August to October 2004.
An additional supply of a commercial 6% phosphorus supplement (Sukrafos) containing macro- and micro-minerals was also fed for the first month at a daily intake of 80 g per animal per day.
Lesions involving the articular cartilage were present in all the animals in various joints (including the atlanto-axial, tibio-tarsal, scapular-humeral and femoral-pelvic joints), but were consistently most prominent in the femoro-tibial joints, often evident clinically as a joint effusion (
Joint effusion of the femoro-tibial joint in a clinically affected animal with osteochondrosis.
There was notable variation in the extent of the lesions. The opposing articular cartilage surfaces lacked the normal lustre and had a mildly eroded appearance. In the stifle joints, lesions on the medial and lateral condyles ranged from shallow clefts to several converging fissures, to multifocal to coalescing ulcerations forming grooves and irregular craters in the thickened cartilage (
Irregular crater in the right femur condyle.
Subchondral cysts containing necrotic material and surrounded by well-vascularised fibrous connective tissue.
Severe degenerative chondral lesions extending to the menisci.
Ulceration of the articular cartilage often resulted in an exposed, irregular connective tissue base. Abnormal trabecular pattern of the growth plate was noted in young animals, whereas in some older animals, lesions in the growth plate indicative of endochondral failure were characterised by the presence of a cyst approximately 10 mm – 15 mm in diameter at the level of the growth plate (
Abnormal trabecular pattern of the growth plate was noted in young animals.
Cyst at the level of the growth plate (older animal).
Representative lesions on the distal femur were selected to demonstrate the histopathological lesions. Lesions were noted in the entire articular–epiphyseal cartilage complex, involving both the avascular articular cartilage and the vascular epiphyseal cartilage, and extended into the underlying subchondral bone (
Extensive necrosis of the articular–epiphyseal cartilage complex extending to the subchondral bone.
After a period of 3 months it was agreed by several observers, including two experienced farmers from the North West Province, that a significant improvement in the degree of external swelling of the most severely affected stifle joints had occurred and that this was accompanied clinically by a reduction in the degree of lameness, particularly in the younger animals. All the animals also showed an increase in body condition score; at the start of the trial, they had a score of 2 and all improved to a score of 3. Body mass also increased by an average of approximately 43 kg per animal. At necropsy, joint fluid samples were collected and tested negative for bacteria and mycoplasmas. Lesions in the joints and bones were similar to those described in the slaughtered animals, except that in the younger animals, the degenerative hyaline cartilage was replaced by irregular fibrous cartilage (
Note irregular fibrous articular cartilage covering the femur condyle.
The pathological lesions confirmed a diagnosis of osteochondrosis. The current study confirmed that failure of endochondral ossification resulting in necrosis of either the physis or the articular–epiphyseal cartilage was central in the pathogenesis of the lesions, as proposed by Ytrehus
Even though the clinical signs and macro- and microscopic lesions associated with osteochondrosis are well documented, to a large extent the aetiology remains controversial. Problems associated with the study of osteochondrosis include, amongst others, the multifactorial aetiology proposed for the condition, a lack of parameters to measure the improvement in affected animals (e.g. following a change in the diet because of the relatively slow regenerative capacity of cartilage and bone, which are the main tissues affected) and the difficulty in producing clinical cases experimentally. Whilst strong evidence has been adduced for breed and conformation being influential in the development of osteochondrosis (Ytrehus
From a geological point of view, the north-western parts of South Africa, the south-western parts of Namibia, as well as southern Botswana where osteochondrosis was reported are characterised by the presence of superficial dolomitic (carbonate) rock formations. The area also has a history of well-documented syndromes in cattle that are demonstrably because of mineral deficiencies or imbalance. The best known of these is osteomalacia resulting from aphosphorosis, described by Theiler (
Stiff sickness and botulism (
Osteomalacia is essentially defective mineralisation of osteoid in adult animals. Its pathogenesis is very similar to that of rickets in young animals. In rickets, there is abnormal endochondral ossification of the cartilage growth plates as well as defective bone formation at sites of bone remodelling. In osteomalacia, because the growth plates have closed, only sites of bone remodelling are affected. The essential lesion is defective mineralisation of the cartilage matrix of growth plates (rickets) and defective mineralisation of osteoid (both diseases). Osteomalacia and rickets are manifestations of one of a number of possible nutritional abnormalities, viz. aphosphorosis, vitamin D deficiency, calcium deficiency or calcium:phosphorus imbalance (Thompson
The lesions are variable, and a diagnosis may therefore be difficult. In rickets, the forelimbs are often bowed and the ends of the long bones at the growth plates are enlarged, as are the costochondral junctions. In severe cases of rickets, pathological fractures are common. In osteomalacia, the bones are weaker than normal, resulting in excessive bone matrix deposition where stresses and strains on the bones are greatest. As in rickets, the bones fracture easily. Macroscopically, the cortices of the bones are thin, spongy and soft. Kyphosis or lordosis is often noted. The thorax is often narrowed and flattened, and the sternum may be prominent (Thompson
Historically, osteomalacia occurred only on certain farms, where it was endemic every year at more or less the same time. Affected animals had a severe craving for bones. Young growing, pregnant animals or cows with calves at foot were most commonly affected, and the condition was most prevalent when the grazing was poor, for example, during times of drought. Clinically affected animals appeared to experience severe pain and showed signs of arthritis and laminitis, and in young animals, signs of rickets were noted. Animals showed a shifting lameness, lying down frequently. They walked with their backs arched and their hind legs tucked up underneath the abdomen and placed their weight on their heels, which resulted in abnormal hoof growth (Theiler
Pica noted in animals with stiff sickness was proven experimentally to be associated directly with aphosphorosis. The main stimulus attracting phosphorus-deficient cattle to bones is olfactory, with old bones being their first choice. Phosphorus-deficient cattle are not attracted to other animal products such as fat, meat or blood. An intravenous injection of sodium phosphate was found to abolish the cravings for bones within minutes (McDowell
Vryburg hepatosis is an area-specific mineral imbalance–related disease. The name is derived from the district in the North West Province in South Africa where most of the cases originated and the characteristic histopathological changes were observed in the livers of affected animals (Neser
The diagnosis of osteochondrosis indicated that the current outbreak likely had a different aetiology from osteomalacia. A survey of affected farms revealed that factors associated with the current outbreak included the following: geographical area, breed (fast-growing breeds were more severely affected than slow-growing breeds), sex (male animals were more severely affected than female animals), age (weaner’s were more affected than adult animals), conformation of the animals (cattle with structural bone deformities, e.g. straight hocks were more at risk), nutritional status of the animals, management systems (calving throughout the year compared to fixed calving seasons) and ongoing selection pressures on animals (shorter calving intervals and heavier weaning weights). It was, however, unclear whether any of these were the primary cause of the condition or whether they merely exacerbated it. That the conditions were linked to the area was strengthened when enquiries further afield revealed that the condition was also present in certain geologically similar parts of Namibia and Botswana.
Given the apparent geological link and the fact that an association between nutrition and cattle diseases has been demonstrated in the area, possible involvement of mineral imbalances warranted further investigation, although the involvement of dietary factors was not supported by evidence presented in a recent review (Ytrehus
Davies and Munro (
Calcium deficiency, with a distorted calcium-to-phosphate ratio, was associated with an outbreak of osteoarthritis in fattening bulls that was probably osteochondrosis. Calcium deficiency caused more serious lesions in the age group 5–8 months than in the age group 12–18 months. Osteoarthritis lesions occurred in more than 80% of the animals with a calcium-deficient diet (Heinola
The results of the preliminary investigation using samples of liver and rib from affected cattle as well as from cattle from an unaffected herd within the area of the outbreak and an unaffected herd outside the outbreak area revealed that the cattle had low magnesium levels and some of the cattle had low manganese and/or phosphorus levels at the time of testing. Water samples collected from 27 affected farms revealed high levels of bromine in all samples, with nickel, lead and selenium often in elevated concentrations. The very high water hardness values suggest that scaling and poor palatability may pose some problems, whilst contributions to acid–base balance aspects may also be relevant. It is, however, realised that mineral analysis of liver, bone and water samples from farms where osteochondrosis is rife must be analysed on an ongoing basis to compare results during different times of the year, and particularly during periods of drought, which has a significant influence on the composition of the water. However, preliminary observations including the feeding trial indicate that the primary cause of osteochondrosis in southern Africa may be a deficiency or imbalance in mineral intake.
Extensive on-farm trials after the completion of this study have confirmed that supplementation with balanced minerals, bioavailable phosphorus and vitamins has a significant impact on preventing and curing the condition in the field. Commercial mineral supplements have been formulated for use in affected areas. An upsurge of the condition during a drought in 2012/2013 has implicated metabolic acidosis as a possible complicating factor, as described in previous studies (Barzel & Jowsey
The authors declare that they have no financial or personal relationships which may have inappropriately influenced them in writing this article.
L.P. was the project leader. J.N. performed some of the experiments. H.M. assisted with the project design. K.B., C.S. and G.v.d.V. were postgraduate students at the University of Pretoria and performed most of the experiments. H.V., H.K., C.d.B. and L.J. assisted with the experimental design. J.v.Z. Farmer, Vryburg, made his cattle available for the trial and assisted with the experiments.