Ovine Johne's Disease - what you need to know
06/19/23 • 22 min
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OJD – an iceberg disease
Ovine Johne's Disease (OJD) is endemic across NSW after its detection on the Northern Tablelands in May 2023. While the infection was traditionally considered a southern disease, a number of cases across the Northern Tablelands have been diagnosed over the past 12 months. OJD is said to be an iceberg disease. For ever one animal showing signs of OJD another 25 most likely are sub clinically infected and show no signs. So that visibly impacted animal is the tip of the iceberg.
Ovine Johne’s disease (OJD) is an incurable, infectious wasting disease of sheep. OJD is caused by the sheep strain of the bacterium Mycobacterium paratuberculosis, which leads to the intestinal wall slowly thickening, causing reduced absorption of nutrients from the intestine. This eventually leads to severe loss of condition – infected sheep can waste away and die.
The bacteria are passed in the manure of infected animals, contaminating pasture and water supplies and spreading infection to other susceptible sheep. Once a flock is endemically infected with OJD, it is difficult to eradicate.
OJD is often not diagnosed in a flock until a significant proportion of the flock is already infected and deaths are occurring. There is often no sign for the first few years – that is why it is often referred to as a ‘silent but costly disease’. Infected sheep can be shedding the bacteria in their manure for a considerable period (sometimes years) even though the flock still looks healthy, but they are contaminating the pasture and infecting other sheep.
http://www.ojd.com.au/
http://www.ojd.com.au/publications/
OJD and Crohns
https://r.search.yahoo.com/_ylt=Awr933VrTJBkDE4ApAk36At.;_ylu=Y29sbwNncTEEcG9zAzIEdnRpZAMEc2VjA3Ny/RV=2/RE=1687207147/RO=10/RU=https%3a%2f%2fwww.foodstandards.gov.au%2fpublications%2fdocuments%2fedit_Report_JD%2520and%2520CD-%2520Final%2520Dec%25202004.pdf/RK=2/RS=NnhmukaeZ5y5g06X7280P2l6eXs-
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Get in touch to share sheeping stories or questions anytime!
OJD – an iceberg disease
Ovine Johne's Disease (OJD) is endemic across NSW after its detection on the Northern Tablelands in May 2023. While the infection was traditionally considered a southern disease, a number of cases across the Northern Tablelands have been diagnosed over the past 12 months. OJD is said to be an iceberg disease. For ever one animal showing signs of OJD another 25 most likely are sub clinically infected and show no signs. So that visibly impacted animal is the tip of the iceberg.
Ovine Johne’s disease (OJD) is an incurable, infectious wasting disease of sheep. OJD is caused by the sheep strain of the bacterium Mycobacterium paratuberculosis, which leads to the intestinal wall slowly thickening, causing reduced absorption of nutrients from the intestine. This eventually leads to severe loss of condition – infected sheep can waste away and die.
The bacteria are passed in the manure of infected animals, contaminating pasture and water supplies and spreading infection to other susceptible sheep. Once a flock is endemically infected with OJD, it is difficult to eradicate.
OJD is often not diagnosed in a flock until a significant proportion of the flock is already infected and deaths are occurring. There is often no sign for the first few years – that is why it is often referred to as a ‘silent but costly disease’. Infected sheep can be shedding the bacteria in their manure for a considerable period (sometimes years) even though the flock still looks healthy, but they are contaminating the pasture and infecting other sheep.
http://www.ojd.com.au/
http://www.ojd.com.au/publications/
OJD and Crohns
https://r.search.yahoo.com/_ylt=Awr933VrTJBkDE4ApAk36At.;_ylu=Y29sbwNncTEEcG9zAzIEdnRpZAMEc2VjA3Ny/RV=2/RE=1687207147/RO=10/RU=https%3a%2f%2fwww.foodstandards.gov.au%2fpublications%2fdocuments%2fedit_Report_JD%2520and%2520CD-%2520Final%2520Dec%25202004.pdf/RK=2/RS=NnhmukaeZ5y5g06X7280P2l6eXs-
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Previous Episode
Critical colostrum - how important is it?
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Colostrum is the first milk a newborn lamb will receive from its mother. A concentrated mix of vitamins, minerals, fats, protein, carbohydrates, antimicrobials, growth and immune factors. It acts as a laxative, aids ewe and lamb bonding, provides energy for thermoregulation and acts as a vital source of immunoglobulins required for passive immunity against intestinal and respiratory pathogens. Lamb morbidity and mortality has a significant impact on sheep production systems with the majority of pre-weaning losses occurring within the first two weeks of life. Poor quality and quantity of colostrum in the first 24 hours plays a significant role in lamb death, disease, future growth and reproductive performance.
Immediately postpartum, the lamb experiences an environmental and microbial assault. Lambs have a small surface area to weight ratio, once exposed to the environment, they lose heat quickly and require a boost of rapidly usable energy to aid essential thermoregulation. Cold, wet and windy conditions accelerate heat loss and add extra stressors. Colostrum is vital to stave off hypoglycaemia and hypothermia as it is energy dense with fats, lactose and non-immune proteins necessary to generate heat. Approximately 150-290ml/kg of colostrum is required in the first 24 hours depending on weather conditions, ideally with 50ml/kg received immediately after birth (Banchero, 2015).
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Next Episode
Have ewe got cleavage! Tips on sheep udders and teats.
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The Ovine mammary gland is an intricate structure composed of secretory tissue (Parenchyma) and supporting ligaments, venous, lymphatic, adipose and nervous tissue (Stroma). There are two mammary glands divided by a suspensory ligament contained within the udder as shown in the Ovine udder anatomy diagram.
Mammary Gland Development
The development of the mammary gland (mamogenesis) commences in the embryo and continues through to lactation. Ewe lambs are born with cistern, teats and some large ducts. Alveoli and interlobular ducts develop several months after birth along with fat and connective tissue. During pregnancy and in response to estrogen and progesterone, the concentration of blood vessels and secretory cells increases, with new alveoli and duct formation continuing for several weeks post lambing.
Lactation
In the last trimester of pregnancy, changes in the concentration of circulating hormones and growth factors induces lactogenesis, enabling milk production. Nutrients, white blood cells and antibodies are transported to the secretory alveoli by surrounding blood vessels and lymphatic tissue. The secretory epithelial cells produce milk particles from the nutrients absorbed from stromal tissue. Milk globules, composed of milk particles and cytoplasmic fluid, are moved to the inner lumen by pinch off part of the cell wall in a process known as apocrine secretion. In response to external stimuli, nerves innervating the udder signal the release of oxytocin from the brain, which acts on the myoepithelial layer causing the alveolus to contract and forcibly expel milk from the lumen into the network of ducts and down to the gland cistern. Suckling or manual milking causes milk to pass through the annular ring into the teat cistern where it is ejected from the teat through the streak canal. Shortly after milking, the teat sphincter closes preventing milk leakage and infection.
In sheep and goats approximately 50-70% of the milk is stored in the glands cistern unlike 20% in cattle. Sheep with larger gland cistern can store more milk and cope with less frequent milking, which is beneficial for dairy sheep.
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