A ProMED-mail post
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International Society for Infectious Diseases
Date: Wed 18 May 2011
Source: Warwick Daily News [edited]
Four emerging cattle diseases are threatening Australian dairy herds,
according to one of Australia's top cattle veterinary experts. Cattle
veterinarian Dr Rob Bonanno will focus on 4 emerging cattle diseases
when he addresses the Australian Veterinary Association's Annual
Conference in Adelaide this week [15-20 May 2011].
"These 4 new diseases are a fatal cattle liver disease [acute bovine
liver disease] thought to be caused by an annual grass and a plant
fungus, lameness caused by hairy heel warts [digital dermatitis],
haemorrhagic bowel syndrome, and the growing issue of zinc toxicity,"
Dr Bonanno said.
"Many of these new cattle diseases have become increasingly common
due to the extremely wet weather conditions we have been having in
recent months. A trend towards larger herd sizes is also correlated
with many emerging diseases of importance."
Acute bovine liver disease (ABLD)
---------------------------------
has been recorded in Western Australia, South Australia, Tasmania,
and Victoria and it is not clear if it is associated with warm, humid
conditions and the presence of an annual grass called rough dog's
tail.
Digital dermatitis or hairy heel wart
-------------------------------------
has become one of the leading causes of lameness in confinement dairy
herds in North America and Europe and is being diagnosed increasingly
in Australia, especially on farms that have adopted intensive systems
of production. The disease is caused by exposure of the feet to a
slurry of manure resulting from poor drainage or poor hygiene
protocols, damage caused by rough flooring, or poor pathways and muddy
conditions.
Haemorrhagic bowel syndrome (HBS)
---------------------------------
is being reported with increasing frequency in lactating dairy cattle
in recent years. This sometimes presents as a cause of sudden death,
but also sudden milk drop, abdominal pain, and loss of appetite. The
exact cause is not known but risk factors may include rumen and post
rumen acidosis and fungal and bacterial infections.
Zinc toxicity
-------------
is rarely seen in Australia, but can be a symptom of the use of
excessive supplementation in the diet to prevent facial eczema, or
zinc sulphate contamination of feed. Signs can include anorexia,
diarrhoea, chronic constipation, and reduced milk yields.
Dr Bonanno says removal of animals from affected paddocks when the
1st signs of disease appear is critical to prevent new cases and to
limit the toxic damage to mildly affected animals, with "aggressive
early treatment" able to save many cows.
--
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[Acute Bovine Liver Disease (ABLD)
----------------------------------
This is a very severe liver condition, the cause remains elusive.
Previously known as phytotoxic hepatitis, acute bovine liver disease
(ABLD) is a disease of beef and dairy cattle. As the name implies,
this is an acute disease with a sudden onset and clinical signs are
most often related to the liver. While it can and does affect cattle
of any age, it is most often seen in animals over 6 months of age.
Those herds of highest risk tend to be the larger herds.
In the case of those that do not die immediately, clinical signs
observed are related to photosensitization -- a severe type of
sunburn. There are two types of photosensitization: one is primary,
where the agent causing photosensitization does not affect the liver;
the second form is where the agents causing photosensitization are not
removed by the liver because the liver is damaged and cannot remove
them. The cattle are agitated, distressed, possibly due to pain of the
sunburn and will seek shade. The sunburn occurs on udders, muzzles,
vulvas, the base of horns and other light skinned areas of the body
such as white faces or legs. These animals are usually depressed,
often with a fever and frequently with a drop in milk production.
There are a few animals that survive; recovery is prolonged and
infection in the infected skin and udders (mastitis) requires
treatment. Anti-inflamatories, antibiotics and treatment for mastitis
are required. The earlier treatment is provided the better the chances
for survival, however long recovery may be.
Rough Dog’s Tail (_Cynosurus echinatus_) is an annual grass that
has been associated with ABLD. What is unknown is whether this is an
indicator of some factor or whether the plant is directly involved.
The plant is not known to be toxic. Warm moist times of the year also
seem to have more cases of ABLD.
Hairy heel warts (HHW)
----------------------
There are some factors that seem to be common among dairies with this
syndrome: herds larger than 200-500 cows; muddy holding pens; and
purchased replacement heifers. The therapy of choice is topical
oxytetracycline with precautions taken to prevent antibiotic residue
in milk or meat. Footbaths commonly are used in herds with HHW but are
not as effective as topical antibiotics.
Hemorrhagic bowel syndrome (HBS)
--------------------------------
This is an acute enteritis with an 80-100 percent mortality. The
bacterium _Clostridium perfringens_ and the fungus _Aspergillus
fumigatus_ have both been implicated in the cause of HBS, but neither
can be linked definitively or consistently to the condition. Acute
signs of HBS include profound depression, tachycardia (rapid heart
rate), decreased milk production, abdominal distension, ruminal
stasis, and dark clotted blood in the feces. Segmental lesions
localized to the jejunum are observed at necropsy. Affected areas of
jejunum contain frank hemorrhage with rapid to immediate clotting,
which forms functional occlusion of the lumen of the small intestine.
Treatment of acutely affected cows with supportive care (fluids,
anti-inflammatories, dextrose] and antimicrobial agents has generally
been ineffective. Common risk factors include season of the year, some
geographical locations, usually the 2nd lactation, and larger herd
sizes.
Zinc intoxication
-----------------
Clinical signs vary based on the duration and degree of exposure.
Signs in cattle include a decrease in weight gain, possibly from mild
anorexia, and a decrease in milk production. - Mod.TG]
[Photo of hairy heel wart:
Image ofRough Dog’s Tail grass (_Cynosurus echinatus_) at:
http://lv-twk.oekosys.tu-berlin.de/project/amanos/plantfamilies/images/Graminae/Cynosurus-echinatus_IMGP7982.jpg>
- Mod.JW]
[see also:
2009
----
Acute bovine liver disease - Australia: (TS) 20090418.1468]
....................................................................sb/tg/mj/ejp/jw
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