SELLS Animal Health Update May 2021

SOUTH EAST MONTHLY DISEASE SURVEILLANCE RESULTS  

Alex Stephens District Veterinarian Yass.

Your local District Vet can help you to investigate, diagnose and manage herd health or mortality issues in your herd or flock. They provide impartial advice and can assist you with disease management and your biosecurity plan. Each month we provide this report of diseases and issues detected and managed in the last month by producers, their veterinarians and animal health advisors.

Grass tetany was found to be causing deaths in a mob of older Angus beef cattle with 6-month-old calves at foot grazing short lush green grass. For more information on this disease see the article below.

Pregnancy toxaemia caused deaths 2-4 weeks prior to lambing, in well-conditioned twin and triplet bearing ewes. On one property this was caused by an outbreak of pink eye which interrupted the grazing of the ewes. On another property there was a case in triplet bearing ewes, caused by harsh weather. On a third hypocalcemia was an inciting cause.  Read more about this disease in the article below.

Ewe deaths were seen on a property where the weight of the heavy twin bearing gravid uterus caused spontaneous vaginal rupture with resultant gut herniation and rapid progression to death. This is a very rarely seen disease thought to be a result of the great season creating large heavy lambs and a very heavy uterus.

Barber’s pole worm was found to be causing anaemia and deaths in a mob of wethers due for drenching. These sheep did not display the classic bottle jaw signs but instead presented with weakness and death.

Bottle jaw is best investigated with faecal egg counts for worms and fluke, to rule out these diseases, where these are negative and weight loss is noted Johne’s disease should be ruled out with a test or a postmortem. Ovine Johne's disease has been diagnosed on a few properties this month, where persistent weight loss was investigated.

Pink eye has been causing eye disease requiring management in both cattle and sheep properties.

Flystrike in sheep has persisted very late into autumn this season caused by the rainy weeks followed by warm weather.

Selenium deficiency was found to be the cause of retained foetal membranes in a herd of beef cattle. Selenium deficiency can cause immunosuppression and depressed fertility in cattle.

Bovine respiratory disease complex occurred in a mixed group of recently purchased weaner calves.  More than 20% became sick requiring treatment and 2.5% died.  This is a multifactorial disease with stress factors such as weaning, viruses and comingling playing a large part when it strikes in the backgrounding industry.

Pestivirus caused a 15% loss of pregnancies in a batch calving dairy herd along with at least 8% of the calves born to that batch being born persistently infected (PI). Vaccination against this disease using Pestigard® might seem expensive but can be regarded as good long-term insurance, as when this disease strikes, as it moves in and out of naïve herds infecting pregnant cows, it causes a large financial hit.

Footrot in sheep has continued to require a large amount of the District Veterinarian time. Feet did not really dry out in the summer and then conditions in autumn have been suitable for spread in many regions. Lameness investigations are being conducted as well as trace forwards, trace backs and neighbour inspections around infected properties. We also assist producers with the creation and implementation of their eradication or management programs.

GRASS TETANY

Nicole Romness and Bruce Thompson – 4^th Year University of Sydney

What is it:

Grass tetany, otherwise known as hypomagnesaemia, is a fatal metabolic disorder in ruminants associated with low levels of magnesium in the blood. Despite the primary cause being low magnesium in the diet, high concentrations of sodium and potassium in the forage are known contributing factors.

Causes and Who is at Risk:

Grass tetany is a multifactorial disease. High risk conditions for grass tetany include:

1. Pasture: animals grazing grass dominant pasture or lush cereal crops, animals grazing grasses with high moisture content resulting in increased gut transit time and decreased absorption, animals recently removed to different paddock
2. Soil: acid sandy soils, heavy use of nitrogen and/potash fertilisers (high sodium and potassium levels interfering with magnesium absorption)
3. Animal: cattle are the most susceptible but is also reported in sheep and goats. Over-represented classes of cattle include:
4. Older cows with calves during winter and spring
5. Older cows grazing lush grass-dominant pasture
6. Dairy cows in peak lactation
7. Thin or overweight cattle
8. Angus cattle and associated cross-breeds.

Diagnosis

Diagnosis is typically based on clinical signs, history and environmental factors. Blood testing can also be conducted to confirm a diagnosis. Signs include incoordination, excitation, convulsions and sudden death. Heightened aggression has also been reported in some cases which can be a useful sign to differentiate between grass tetany and disorders that cause similar signs.

Treatment

Treatment of grass tetany involves supplementation  with magnesium. Injections of calcium and magnesium in the form of a 4-in-1 flow pack under the skin work to quickly correct the disorder. Injection is then followed up with oral supplementation of magnesium which is available in products such as lick blocks, slow release capsules, and magnesium oxide or magnesium sulphate powder added to feed.

Prevention

Prevention of grass tetany centers around magnesium supplementation and elimination of factors that inhibit magnesium absorption in the gut.

Management options to aid in prevention include:

• feed good quality hay or silage to increase roughage and energy intake
• limit high potassium feed (such as lush grass dominant pasture)
• move lactating cows to high dry matter, high legume pasture
• provide shelter
• limit stress
• correct soil acidity with lime or dolomite (dolomite contains magnesium).

Magnesium supplementation can be added to hay or pasture. A lactating cow requires 2g of magnesium per 1kg dry matter or around 50-70g/head/day of magnesium sulphate. Adding 3g of magnesium sulphate per 1kg of hay is usually sufficient, or 1kg magnesium sulphate per 350kg hay roll. Hay can be soaked or sprayed with a solution of magnesium sulphate powder mixed with water. For pasture supplementation, spray dry magnesium oxide up to 30kg/ hectare every 3 weeks or magnesium sulphate 20kg/hectare every 2 weeks during high risk periods.