Last update: November 22, 2010 04:02:30 PM E-mail Print

 

Investigation into the probable cause, predisposing factors and effective treatment

of swelling disease in Angora goats

 

Dr Gretha Snyman & Tino Herselman


Grootfontein Agricultural Development Institute, P/Bag X529, Middelburg (EC), 5900

email : Gretha Snyman

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Background

The first cases of swelling disease in South African Angora goats have been reported during the early 1970’s. At that time, veterinarians at the Regional Veterinary Laboratory at Middelburg EC were already busy investigating this condition. Numerous trials were conducted to investigate the cause of this disease. However, no conclusive evidence had been found as far as the cause of the disease is concerned. At the 1984 Mohair Growers’ Congress, the mohair industry also requested the Department of Agriculture to do research on swelling disease and to develop a vaccine in collaboration with Onderstepoort.  A survey of swelling disease was also done among Angora producers in 1985.

Outbreaks of swelling disease are still occurring periodically and some losses are still experienced by Angora producers. No definite cure is known; various farmers are practicing different treatments, all of which are not always successful. As a result of this, delegates at the 60th Annual General Congress of the Mohair Growers’ Association of South Africa unanimously accepted the following resolution in 2003:

“Congress requests Mohair SA to investigate and have purposeful research done on the cause, treatment and prevention of swelling disease in various areas among all age groups of Angora goats in South Africa, and also to investigate the genetics in this investigation” Consequently, Grootfontein Agricultural Development Institute was requested by Mohair SA to submit a project proposal to address the issues described in the above-mentioned resolution. The objectives of this research study are:

An intensive literature study was done on all available information regarding swelling disease. These findings are summarised below:

 

Description of the disease

Swelling disease in Angora goats is characterized by the sudden onset of severe subcutaneous oedema (fluid) of the lower body parts, viz. ventral neck, chest and abdomen, front and hind legs, especially over the joints and sometimes the lower jaw. However, the scrotum and udder are never affected.  The swelling is cold, pitted, painless and variable in intensity in different parts of the body. Fluid flows freely if the skin is cut or punctured. The fluid is clear, copious and non-clotting. There are no fever, heart or pulse irregularities or respiratory distress. Other symptoms include swollen lymph nodes, diarrhoea, slight depression and loss of appetite with consequent weight loss. No other clinical signs are apparent.

Swelling disease occurs most often in kids from after weaning (4 months) to 18 months of age and usually lasts between 2 and 14 days. Older animals could, however, also be affected. The percentage of animals affected varies from less than 1% to more than 50%, but is usually fairly low (below 10%). Mortality in uncomplicated cases is usually less than 1%. If pneumonia or severe verminosis accompany the disease, heavy mortalities could be expected.

According to Bath (1983), Bath & Vermeulen (1988) and De Wet & Bath (1994), there is strong evidence that swelling disease is a complex condition, which can be correlated to the following:

  1. Species and breed: Only Angora goats are known to suffer from the disease. (Van Tonder (1976), however, mentioned that a similar condition was observed in Merino and Dorper sheep).
  2. Genetic makeup: Swelling disease is most common in stud animals.
  3. Age: Almost unknown in kids prior to weaning, with a peak incidence between weaning and 18 months. Sometimes older animals could also be affected.
  4. Stress: There is nearly always a history of non‑specific stress (dipping, dosing, shearing, transportation, etc.) prior to an outbreak.

There is also some evidence that the following factors may affect the incidence of swelling disease:

  1. Pastures: Usually animals have been grazing lush, irrigated pastures.
  2. Open water: Outbreaks are often associated with open water (ditches, ponds, streams, wet lands).
  3. Crowding: Usually animals kept in crowded circumstances are affected.
  4. Shearing and dosing: Outbreaks frequently follow these procedures.
  5. Internal parasites: Variable numbers of Ostertagia and/or coccidia may be present in the abomasum and small intestine of affected goats.

There are no indications that swelling disease is correlated to the following:  sex, origin of animals, season, climate, weather, topography, veld type, specific plants, licks or external parasites. (It should be noted that many young goats are affected in late summer or winter mainly because they are then at the most susceptible age).

 

Profile of goats with swelling disease

From: Bath (1983), Vermeulen (1984), Vermeulen (1986), Bath & Vermeulen (1988) and De Wet & Bath (1994).

 

Post mortem findings

Mild to severe subcutaneous oedema (fluid), as well as oedema between the mucles, mesentery, abomasum and small intestine are found. Fluid in the abdominal cavity, the heart sac and in the thoracic cavity may be present to a moderate degree. Unlike subcutaneous fluid, these fluids clot on standing. Lymph nodes are swollen and oedematous, the spleen may be slightly enlarged and both liver and kidney may show mild degenerative changes. The lungs are normal. Variable numbers of gastro‑intestinal parasites may be present in the abomasum and small intestine.

 

Blood profile

The red blood cells and number of red blood celss are normal. Several blood parasites have been found in blood smears, but they do not appear to be significant. Total white cell counts are usually elevated.

 

Biochemistry

Urine analysis, as well as most blood constituents, including cortisol, are normal. The plasma of oedematous goats shows a lower total protein concentration, a lower colloid osmotic pressure, lower plasma albumin levels and a lower albumin : globulin ratio than that of normal goats.

An important constraint is the lack of reliable normal reference values for blood parameters of Angora goats. Even in the study of Mitchell et al. (1983), the plasma and interstitial fluid obtained from the normal goats were from Boer goats and not Angora goats. Work done by Herselman (1995), indicated that there are inherent differences between Angora and Boer goats with regard to blood parameters.

 

Parasitology

Full helminth counts of affected goats shows a variable picture of low to moderate parasite burdens. Most commonly brown stomach worm (Ostertagia circumcincta) is found, either alone or with bankrupt worm (Trichostrongylus colubriformis) and/or long necked bankrupt worm (Nematodirus spathiger). In some cases, no parasites are found even in undosed animals. This does not preclude the possibility that animals have carried high parasite burdens prior to this. Other worm species have been recorded and in general no clear pattern has emerged.

Faecal egg counts are generally low (<1000 e.p.g.), but can occasionally be very high (> 10 000 e.p.g.). Coccidial oocyst counts are low (< 10 000 o.p.g.). Coccidial lesions in the intestines are minimal.

Results of trials conducted at Grootfontein and the Regional Veterinary Laboratory at Middelburg EC

 

Parasite experiments

Three experiments were conducted during 1980 to 1984, in which 64 goats (4-tooth and older – trial 1), 54 goats (majority 12 months old, some were 4- to 6-tooth – trial 2) and 20 goats (4- to 6-tooth – trial 3) respectively, were infected with Ostertagia circumcincta larvae at varying doses (Vermeulen, 1986). No goats developed swelling symptoms in trial 1, while 2 goats from trial 2 and 1 from trial 3 developed distinct oedema. A further 10 goats from trial 2 developed mild oedema on the chest area. In all trials, all goats infected with Ostertagia circumcincta had reduced plasma protein levels. From these it seems as if Ostertagia circumcincta could be an underlying cause for the development of swelling disease. However, some or other trigger mechanism (any stress inducing condition – see predisposing factors) is necessary for the goat to develop full-blown swelling disease.

Possible explanations as to why only one and two goats developed swelling disease during these trials could be that the animals were too old and that no additional stress factor or trigger was present. According to Vermeulen (1986), the goats that indeed developed swelling disease were also the smallest in their respective groups. Stress caused during competition for food could most probably explain them developing oedema symptoms.

 

Other experiments

These experiments were conducted during 1977 and 1978. Eleven trials in laboratory animals and 45 trials in goats, using different organs inoculated by various routes, have failed to give any indication that the disease can be transmitted. Various attempts to culture bacteria and mycoplasmas from affected goats have yielded no significant results. Other experiments involving the role of various hormones also yielded negative results.

 

Predisposing factors

From the results of various trials discussed above, it can be deduced that the reduced blood albumin levels is the underlying mechanism responsible for accumulation of subcutaneous oedema in goats with swelling disease. It therefore follows that any condition / factor that contributes to a lowered blood albumin level, could be a predisposing factor for swelling disease. The following factors could all contribute to a lowered blood albumin level, and indirectly to the development of swelling disease:

1.   Protein deficiency – reduced production of plasma proteins

2.   Increased protein loss

                Loss through intestinal tract

                Loss through urine

                Pregnancy

                Hair worm (Haemonchus contortus)

                Other roundworms

                Coccidiosis

                Conical fluke (Paramphistomum)

                 Blue lice

3.  Any stress inducing condition

 

Other hypothesis

Wiese (1990) aimed to investigate the following hypothesis regarding swelling disease: Angora goats either have too low fat reserves, or they are unable to mobilize their fat reserves quickly enough to maintain their blood glucose levels during stress conditions. Thus gluconeogenesis is started, but with the poor muscular development of Angora goats, the source for gluconeogenesis would primarily be the albumins in the blood plasma.

However, Herselman (1995) reported results that suggest the opposite to the above-mentioned hypothesis. Trials relating to hardiness of different small stock breeds were conducted in which blood parameters of mature Angora goat, Boer goat, Dorper sheep, Merino sheep and Namaqua Afrikaner sheep were monitored over a period of five weeks, including a seven day fasting period. Blood levels of glucose, non-esterified fatty acids, ketones, total plasma proteins, plasma albumins and albumin : globulin were measured for a five week experimental period. All breeds, including the Angora goat, had mobilized fat reserves during the fasting period. Furthermore, total plasma proteins, plasma albumins and albumin : globulin remained virtually constant throughout the seven day fasting period. These results therefore proofed that Angora goats do not use blood albumin as source for gluconeogenesis during feeding stress conditions. As fasting is a drastic stress condition, it can be deduced that Angora goats would also be able to mobilize their fat reserves, instead of blood albumins under other types of stress conditions. This would obviously not held true for goats which have very little or no fat reserves, such as kids some months after weaning.

 

Research approach

Taking into account all factors discussed above, as well as the lack of any scientific proof for or against any of the possible contributing factors, the following approach will be followed with the intended research project:

 

The project will be carried out in four parts.

The first will dealt with identifying the causative agent/s responsible for swelling disease. This part in turn, will consists of three phases:

        Phase 1 – Profile of goats affected with swelling disease

        Phase 2 – Infection of animals with various bacterial strains obtained from post mortem animals

        Phase 3 – Induction of swelling disease through application of various predisposing factors

The second part of the study will focus on the evaluation of different treatments of the disease.

In the third part, data on all swelling disease cases available at the Middelburg Provincial Veterinary Laboratory for the past 20 years will be analysed.

The fourth part of the study will comprise literature studies into related diseases / conditions in other animal species, to determine any similarities with swelling disease in Angora goats.

With regard to investigating the genetics of the disease, as stated in the resolution accepted at the mohair congress, this would not be possible before the exact cause and mechanisms involved in the disease have been clarified.

The project will run for a period of five years. If any significant results are obtained before that, the project will be terminated at that stage.

Any Angora producers who experience swelling disease outbreaks, are kindly requested to contact Dr Gretha Snyman at Tel no. 049 842 1113 during office hours.