Wednesday, October 15, 2014

Another "Gift" from Last Year's Warm and Dry Winter

To improve the nutritional intake of our ewes during the first two weeks of our breeding season, we've been feeding hay to our breeding ewes since the first of October.  While we have plenty of dry grass, the nutritional value of this forage (which grew last spring), is minimal.  By feeding hay, we hope the ewes will produce more eggs - and a higher percentage of twins next spring.

Our ewes have adapted to this new feeding regime very quickly - whenever they hear my diesel truck now, they run to the fence along the road.  Earlier this week, however, we started noticing that a significant number of ewes in our larger breeding group (our "mules" or crossbred ewes) were losing interest in the hay.  They'd come up with the rest of the sheep, sniff around at the hay, and then wander off down the hill.  Many of them were losing weight (obviously - they'd quit eating), and many of them had nasal discharges.  After consulting with my wife (who's also my veterinarian!), we decided that we were looking at an outbreak of bluetongue virus.  Other sheep ranchers have experienced similar outbreaks this year - now it's our turn!

According to the Merck Veterinary Manual, sheep with bluetongue exhibit some or all of the following symptoms:
"After an incubation period of 4–6 days, a fever of 105–107.5°F (40.5–42°C) develops. The animals are listless and reluctant to move. Clinical signs in young lambs are more apparent, and the mortality rate can be high (up to 30%). About 2 days after onset of fever, additional clinical signs such as edema of lips, nose, face, submandibular area, eyelids, and sometimes ears; congestion of mouth, nose, nasal cavities, conjunctiva, and coronary bands; and lameness and depression may be seen. A serous nasal discharge is common, later becoming mucopurulent. The congestion of nose and nasal cavities produces a “ sore muzzle” effect, the term used to describe the disease in sheep in the USA. Sheep eat less because of oral soreness and will hold food in their mouths to soften before chewing. They may champ to produce a frothy oral discharge at the corners of the lips. On close examination, small hemorrhages can be seen on the mucous membranes of the nose and mouth. Ulceration develops where the teeth come in contact with lips and tongue, especially in areas of most friction. Some affected sheep have severe swelling of the tongue, which may become cyanotic (‘blue tongue”) and even protrude from the mouth. Animals walk with difficulty as a result of inflammation of the hoof coronets. A purple-red color is easily seen as a band at the junction of the skin and the hoof. Later in the course of disease, lameness or torticollis is due to skeletal muscle damage. In most affected animals, abnormal wool growth resulting from dermatitis may be observed."
There are a number of strains of the virus - we've had it one other year in our sheep (we had 3-4 ewes with bluetongue about 4 years ago, and all of them survived).  While there is usually a vaccine available for the virus, we've never used it (it's much like the flue vaccine - the strains in the vaccine must match the strain in the environment in any given year for it to be effective).  What's more, the vaccine is not available this year - the California manufacturer did not produce any vaccine in 2014 due to production problems.  Based on the symptoms we've observed, this year's strain is different than the strain we had previously, but based on the age of the ewes that are showing symptoms, I think our older ewes must have some natural immunity.

The virus is transmitted by a biting midge (we used to call them "no-see-ums").  According to an article recently published by the UC Davis School of Veterinary Medicine:
"bluetongue is most prevalent when midges are abundant in late summer and fall, but there has been speculation over how the virus survives through the winter. When temperatures turn cold and the biting-midge populations plummet, transmission appears to cease for more than six months, but the virus reappears when temperatures warm the following season."
The UCD study found that the virus was able to overwinter in the midge population.

Now I'm a shepherd, not an epidemiologist or entomologist , but based on what I know about insect pests, it would seem that a normally cold and wet winter in our region would be hard on these midges.  Last year's winter was neither wet nor very cold - and I suspect that we have more midges (and more virus) this fall because of the drought.  In other words, the drought has had impacts far beyond the lack of rainfall for those of us who farm or ranch.

Since bluetongue is a virus, we can't treat it directly.  Again, according to Merck:
"There is no specific treatment for animals with bluetongue apart from rest, provision of soft food, and good husbandry. Complicating and secondary infections should be treated appropriately during the recovery period."
Yesterday, I sorted off the 33 ewes that were showing signs of the virus and hauled them to another property (where we still have some green grass).  Normally, I don't like hauling animals during breeding season - I prefer to let the ewes "settle" for 18 days (around the first week of December) after we remove the rams to ensure that they remain pregnant.  However, we felt it was important to isolate these sheep and to provide them with green grass and supplemental feed.  We'll also treat any secondary infections - sometimes sheep with bluetongue can develop additional respiratory infections, which we treat with antibiotics.  And we'll leave them on this alternative pasture until they've fully recovered.  On a positive note, some of them looked much brighter this morning. Flexibility, once again, is a key part of our management system!

While I'm grateful not to face the daily stress of a long commute or a job I hate, I have to admit that ranching can be stressful at times.  The drought, and its associated impacts, have definitely made life more stressful than usual.  I worry about the economic impacts (in terms of added expenses and lower revenue) that bluetongue will cause my business; more profoundly, I hate to see my animals suffering.  I haven't slept well during the last several nights, and getting up extra early to accommodate the additional work of caring for sick sheep has exacerbated my feeling of fatigue.  This morning's rain has helped, but we desperately need cold and wet weather in the coming months.  We need an end to the drought.

1 comment:

  1. "The gift that just keeps on giving" - Good luck my friend!