Johne's Disease (paratuberculosis) - signs and prevention

Johne's Disease (pronounced "Yo nees") is a disease that affects the intestines of mostly ruminants. It is caused by a hardy bacteria called Mycobacterium paratuberculosis.

Johne's disease is most commonly observed in dairy cows, but may also affect beef cattle, sheep, and goats.

The strain that affects sheep is different than the one that affects cows, though there is an intermediate strain that sheep are susceptible to. While cattle experience diarrhea, in sheep, Johne's tends to be a wasting disease. Control of the disease in infected flocks is difficult due to the lack of a reliable live animal test. Vaccination will reduce the number of clinical cases in a flock, but will not prevent all animals from becoming infected. Colostrum from other sources (cows, goats) may be a source of infection in sheep flocks.

What are the signs of Johne's disease and how can I tell if my flock has Johne's disease?

This disease is hard to detect. The signs of Johne's disease are vague and months can pass after infection before they appear. Weight loss in animals with a good appetite may be the only indication as diarrhea is not a common sign in sheep, unlike what is seen in cattle. Infected sheep may appear unthrifty and wool break/poor fleece condition may also be noted. The signs of Johne's disease can be confused with the clinical indications of other conditions such as parasitism, OPP (ovine progressive pneumonia), CLA (caseous lymphadenitis) or malnutrition. Of course, more than one problem may be occurring - for example, sheep eventually succumbing to Johne's disease had improved clinically after treatment for parasites. Because of the slowly progressive nature of the infection, signs of Johne's disease are usually not seen until animals are adults.

How do sheep get Johne's disease?

Johne's disease typically enters a flock when an apparently healthy, but infected animal is introduced. This animal contaminates the premises (feed, ground, water) by shedding the organism in its manure. The organism is then ingested by other sheep. Lambs are thought to be most susceptible to infection and their suckling manure-contaminated teats are another route of infection. It is also possible that a ewe in the later phases of the infection can shed M. paratuberculosis into her milk and colostrum, thus transmitting it to her lambs.

How can you prevent your animals from getting Johne's disease?

The best way to avoid this chronic infectious disease of course is to be as certain as possible that animals brought into the flock are not infected with M. paratuberculosis. Johne's disease test-negative flocks are the best sources of animals for purchase. Since many flock managers have not yet test for the infection, assess the entire flock (not just the animals you intend to buy) for body condition. Ask the owner about the cull rate and common cause for culling - how many animals were thin/unthrifty for no confirmed reason? Check the body condition of the dam of lambs you intend to purchase and have her tested if you have suspicions (tests on sheep less than one year old are not likely to be informative unless exhibiting signs of the infection).

Following general rules of sanitation are helpful in blocking transmission of the infection. Feeders and waterers should be designed to minimize the likelihood of fecal contamination. Lambing should occur in clean, dry areas. Animals with weight loss or diarrhea should be segregated from the rest of the flock and tested.

Sheep Synchronisation Tips

A high ovulation rate (O/R) is the obvious first step in achieving a high lambing percentage.

Effect of ewe live weight

Live weight has two effects:

(1)  The static (live weight) effect

·         Heavy ewes have higher ovulation rates (and more lambs) than light ewes.

·         Twinning (percentage of twin births to total births) increases by about 6% per 4.5 kg increase in ewe live weight — i.e. 1.3% per kg increase.

·         This effect operates up to at least 70 kg live weight and there is no evidence of a decline at the top end of this range. Barrenness increases markedly under average weight of 40–45 kg for Mutton-based breeds and 35–40 kg in Merinos.

High ewe live weight and live weight gain during mating causes high O/R - for each extra kg of ewe weight there will be 1.3% higher lambing percentage.

·         Comparisons of poorly reared and well-reared ewes show that while the poorly reared ewes have fewer multiple ovulations; this is probably a function of their lower adult live weight.

(2)  The dynamic (live weight gain or "flushing") effect

·         Some trials have shown ewes gaining weight quickly (e.g. 0.5–1.0 kg per week) just before mating had higher ovulation rates than ewes of similar weight with low or no weight gain.

·         However some results showed that ovulation rate was more dependent on ewe live weight at oestrus than on previous changes.

#Seasonality of ovulation rate

·         Most sheep breeds are seasonal breeders and fewer eggs are shed in the first cycles of the breeding season in early autumn.

·         The first cycle of each season features a "silent heat" — i.e. ewes ovulate but do not show oestrus.

·         Highest lambing percentage coincides with mating mid-season depending on location. Higher numbers of abnormal eggs may be shed near the beginning and end of the breeding season.

Each successive ewe oestrus during the breeding season has about 0.15 more eggs shed.

#Synchronisation

 ·         Synchronisation may be used to get ewes ovulating simultaneously (e.g. to facilitate timing of artificial insemination) and/or to induce ewes to cycle out of season.

·         The two ways of doing this are by using rams or hormonal treatment.

Use of #rams ("ram effect")

 * The introduction of rams early in the breeding season stimulates ewes to ovulate within 3–6 days (without showing oestrus if this is the first ovulation of the breeding season) and show oestrus about 17 days later.

·         Ewe flocks stimulated by the ram effect are thus likely to be synchronised.

·         Rams introduced several weeks before normal onset of oestrus may have no effect and late introduction will only stimulate those few ewes, which have not begun cycling.

Synchronisation can be used to get ewes ovulating simultaneously by using hormones or rams.

·         Rams used for synchronisation may be entire or vasectomised. Some poor results with rams vasectomised for one year or longer have been reported and this may be due to reduced libido in these rams.

·         High libido vasectomised rams are most effective and should be introduced up to a week before normal if using as teasers (i.e. to stimulate ovulation and oestrus).

Rams introduced early in the breeding season, either vasectomised or entire, will stimulate ewes to ovulate within 3-6 days.

·         Some breeds are more effective, with indigenous rams are usually superior to Merino’s.

Hormonal synchronisation can be used to:

 ·           stimulate first oestrus (e.g. first oestrus in young ewes or an early first oestrus for older ewes)

·     synchronise ewes to show oestrus at the same time (e.g. to condense lambing or for artificial insemination) during the normal breeding season

·         Controlled internal drug sponges containing progestagens (synthetic analogues of progesterone) are most commonly used.

·         Results are more heavily influenced by operator skill and timing of insemination than product type.

·         The sponge is inserted in the vagina and withdrawn after several days.

·         The ewe typically shows oestrus within three days after withdrawal within the normal breeding season.

·         This time varies depending on dose level of progestagen, type of device or sponge used and whether pregnant mare's serum gonadotropin (PMSG) is also used to stimulate greater ovulation rate.

·         Ewes not fertilised at this oestrus will return to oestrus about 16–17 days later and remain generally synchronised. This is useful when planning a return visit for an AI technician.

Synchronisation for out of season breeding usually requires PMSG also to stimulate ovulation.

·         Prostaglandin injections can also be used for synchronisation but are not common.

·         Ask a vet about synchronisation or hormonally induced oestrus if planning to use it for the first time.