Swelling Disease in Angora Goats

– By Dr. Erin Masur DVM When a goat person hears the words “swelling disease,” they may first think of common conditions such as a big head or bottle jaw. However, “swelling disease” or “Swelsiekte” refers to a strange condition of Angora goats that causes acute spontaneous edema of the underside. This condition was first reported in the 1970s in South Africa. Since then, there have been reports in Australia, New Zealand, Britain, and the United States. Researchers have explored numerous theories since the 1970s, yet significant ambiguity exists regarding this condition. Let’s explore what we do and don’t know.

We must review how blood and blood vessels function in a normal, healthy state to understand the possible explanations for swelling disease. Let’s focus on two major bodily fluids: blood and interstitial fluid. It’s common knowledge that blood runs through our blood vessels, but we don’t often think about interstitial fluid, which flows outside and around the body’s cells.

Blood comprises plasma, red blood cells, white blood cells, and platelets. Interstitial fluid is composed mostly of water but can contain a variety of macromolecules and micromolecules. Blood’s plasma is in constant flux with interstitial fluid because the two can seep across the porous membranes of the smallest, most delicate blood vessels, called capillaries. Different capillary categories have different permeability grades or how “leaky” they are.

As blood plasma and interstitial fluid flow from one bodily space to another, they may transfer molecules back and forth to each other depending on how big those molecules are and how leaky the capillaries are in their area of the body. Albumin and globulin are two essential macromolecules carried by the blood plasma and the interstitial fluid. These ubiquitous, essential proteins are considered large in terms of molecular size.

Because they’re large, their concentration in one fluid versus another influences how those fluids interact across the permeable capillary lining. “Oncotic pressure” refers to when there’s enough albumin and globulin in the blood plasma to attract water out of the interstitial space, across the capillary lining, and into the blood vessel space. In a normal, healthy animal, the balance of albumin and globulin in the blood plasma is almost equal to that of the interstitial fluid.

By understanding these concepts, we can begin understanding the nuts and bolts of swelling disease. Any cause of inflammation in the immune system increases capillary permeability, resulting in “capillary leak syndrome.” As the capillary lining becomes more permeable, it allows albumin to leak from the blood plasma and into the interstitial space, creating low oncotic pressure. This draws fluid into the interstitial space, and if enough of it accumulates, it can result in edema (or swelling) visible to the naked eye.

While capillary leak syndrome is a universal response to inflammation in mammals, Angora goats suffer more severe swelling than other goat breeds. But what causes this process to get started in the first place? Well, there’s the source of debate about the origins of swelsiekte.

One of the most straightforward theories to accept relates to gastrointestinal parasites such as the brown stomach worm, barber pole worm, or coccidia. These parasites are typically correlated to low plasma protein, drawing an easy conclusion that ties in with albumin leakage. The first study to test this theory concluded that while worms could be an underlying cause, the swelling disease seems to develop only when an additional condition coincides with worms (Snyman, 2005).

A follow-up study agreed that even when Angoras are artificially infected with large amounts of worms, they don’t go on to develop any significant signs of swelling disease. They also reported that goats artificially infected with coccidiosis developed moderate swelling disease. Still, they feared this correlation was weak and concluded that gastrointestinal parasites alone do not cause swelling disease.

“Swelling disease” or “swelsiekte” refers to a strange condition of Angora goats that causes acute spontaneous edema of the underside. This condition was first reported in the 1970s in South Africa.

Another more complicated theory concerns the complex relationship between the brain, the adrenal glands, stress hormones, and blood sugar. In a healthy animal, a section of the brain called the pituitary sends messages about stress triggers to little glands in the abdomen called the adrenals.

Under stress, the pituitary releases a hormone that stimulates the adrenals to produce cortisol, commonly called the “stress hormone.” The stress hormone then travels through the body, causing several different responses. One of the ways the body responds to stress hormones is to call upon the organs that store the ingredients for blood sugar and begin assembling it. This response ensures the body can maintain its blood sugar in times of stress.

However, in animals with adrenal glands that don’t produce enough stress hormone when signaled, normal blood sugar isn’t maintained during stress. Should there be an additional external factor, such as a cold weather snap, blood sugar becomes even more depressed. What causes an animal to have unproductive adrenal glands?

The explanation could be congenital hypoadrenocorticism — simply put, it’s genetics. After many years of genetic selection for premium mohair, the Angora goat may have genetically drifted toward adrenal glands that can’t perform normally. A 2015 study cast doubt upon this theory when it found that cortisol levels in Angoras with swelling disease aren’t much different than in Angoras without. However, some have theorized that because proteins bind to cortisol, abnormal protein levels in swelling disease could be causing measurement errors (Hobson, 2015, pending publication).

With no strong resolutions regarding hypoadrenocorticism, another path to explore is high-stress triggers. Stressors that researchers have studied are cold weather patterns, weaning, castration, and handling for drenching and dipping.

When researchers analyzed the relationship between swelling disease and stressors, the most significant swelling appeared when a sudden onset of cold, wet weather immediately followed shearing. Kids between weaning and 18 months are more likely to develop swelling, most likely due to underdeveloped acquired immunity at this age. Some would postulate that the stress theory is related to the hypoadrenocorticism one in that animals under acute stress produce cortisol and experience inflammation.

While the mystery of the cause still evades us, fortunately, there are some clear guidelines for preventing swelling disease. Avoiding sudden weather patterns when scheduling events such as weaning is an important strategy. Using thorough pain control for procedures like tail docking and castration is also helpful in reducing stress associated with these procedures. Improving handling techniques during events like shearing is another useful preventative tool. Improving the overall nutritional plane of the herd and optimizing healthy protein intake is a supportive measure to offset the risks of swelling disease.

To diagnose swelling disease, a producer can be reasonably confident the sudden onset of edema along the underside of an Angora goat is confirmatory. A goat with swelling disease may act normally and have no other symptoms except the swelling. A complete blood count and blood chemistry are helpful to confirm the diagnosis with a veterinarian, especially when determining the associated prognosis.

Although many goats with swelling disease spontaneously resolve, some need intensive treatment to avoid fatality. As far as we can tell, swelling disease isn’t transmissible. Still, it stands to reason that if one goat becomes affected, a producer may want to explore potential stressors amongst his herd to prevent it from happening to others.

One of the most exciting things about goat medicine is that in comparison to human medicine or canine and feline medicine, so much territory is unexplored. Research is a slow process, and even after decades of observing and studying this condition, we’ve only been able to rule out weak correlations.

Returning to basic biological concepts such as plasma proteins and capillary permeability helps us understand which paths to explore. In the meantime, as farmers and shepherds, the best we can do is keep updated with new information and use recommended preventative measures. It seems safe to say that you’re exempt from this mysterious problem unless you own Angoras. If you do raise Angoras, this topic should be on your radar as the story develops.

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DR. ERIN MASUR DVM is a livestock veterinarian located in the northeast with a passion for small ruminant parasitology. On her own farm, she raises sheep, ducks, and children. You can keep up with her research at EarlyBirdWorm.com, or check out her services at SheepRockVet.com. For more frequent updates, you can find her on social media by searching for Sheep Rock Vet or Fork You Farms.

SOURCES:

• Hobson, Mackie. (June 2, 2002). Swelling Disease (Sweldiekte) – The Capillary Leak. SA Mohair Grower’s Assoc. https://www.angoras.co.za/ article/swelsiekte-swelling-disease-in-angora-goats.
• Hobson, Mackie. “Swelling Disease (Swelsiekte) — The role of the inflammatory process.” SA Mohair Grower’s Association, 2 June 2022, https://www. angoras.co.za/article/swelsiekte-possible-role-of-the-inflammatory-process. Accessed 28 Aug. 2023.
• Hobson, Mackie. “Swelling Disease (Swelsiekte) — Theories and Trials conducted.” SA Mohair Grower’s Association, 2 June 2022, https://www. angoras.co.za/article/swelsiekte-theories-tested-and-trials-conducted. Accessed 28 Aug. 2023.
• Hobson, Mackie. “Weaning and the First 18 Months Continued from Last Edition…” Mohair News, 12 Mar. 2021.
• Snyman, M.A., and A.E. Snyman. “The possible role of Ostertagia circumcincta, coccidiosis and dietary protein level in the development of swelling disease in Angora goat kids.” Journal of the South African Veterinary Association, vol. 76, no. 2, 2005, pp. 63–68. • Sullivan, Melissa, et al. Ventral Oedema in Angora Goats, Flock & Herd, Jan. 2014, www.flockandherd.net.au/other/reader/ventral-oedemaangora-goats.html.