NADIS is a network of 40 veterinary practices and six veterinary colleges monitoring diseases of cattle, sheep and pigs in the UK.
By Neil Sargison BA VetMB DSHP FRCVS
NADIS Sheep Disease Forecast
Most lowground flocks are now well into the second cycle of the mating period.
Ram harnesses or raddle are employed in most flocks to provide reassurance that the rams are working, to batch ewes for hosing and lambing management and to provide information that can be used retrospectively to investigate the cause of poor scanning results.
Some use harnesses from the onset, progressively changing to darker colours, some apply raddle only when the rams are first turned out, to confirm that they are working, and some fit harnesses after 17 days to spot any ewes returning to oestrus.
RADDLE AND HARNESS CRAYON MARKS CAN PROVE USEFUL TO INVESTIGATE PROBLEMS SUCH AS A HIGH BARREN RATE, LOW SCANNING PERCENTAGE OR PROTRACTED LAMBING PERIOD
For most lowground flocks, the target should be about 90% of ewes conceiving during the first 18 days of the mating period and a barren rate of less than 4% after 2 cycles.
Provided that ewes are cycling and rams working, there are few advantages to be gained by leaving rams with the ewes for more than 36 days. The management of the small number of ewes that conceive over a prolonged period after 36 days is often uneconomical.
RAM HARNESSES SHOULD BE A COMFORTABLE FIT AND REGULARLY CHECKED AND ADJUSTED TO AVOID BRISKET SORES. INFECTED BRISKET SORES OFTEN INVOLVE THE CARTILAGE OF THE STERNUM AND RESPOND POORLY TO ANTIBIOTIC AND SUPPORTIVE TREATMENT. HOWEVER, STRESSFUL GATHERING TO ADJUST HARNESSES SHOULD ALSO BE AVOIDED.
There have been several reports of ewes being marked for a second time after 17 days.
There are several possible causes for this problem, including:
ewes not cycling at the time of ram introduction due to:
• inappropriate breed of sheepa high proportion of ewe lambs or gimmers in the flock
• the latitude and altitude of the farm
• stress associated with unskilled handling or persistent rain
fertilisation failure due to:
• unsound rams
• an inappropriate ram:ewe ratio
• unsuitable mating paddocks
early embryonic mortality due to:
• severe undernutrition
• persistent stress
• selenium deficiency
• border disease
Most cases reported this year have been associated with unsound rams. While swapping rams between groups after 18 days, use of chaser rams or mobbing ewes into bigger groups may ensure satisfactory pregnancy rates, lambing periods will be protracted, perinatal lamb mortality rates high and lamb finishing dates delayed.
These cases re-enforce the message that rams should always be checked for breeding soundness before the mating period.
There were numerous reports during October and November of lameness in sheep, associated with warm and damp weather. Many cases were due to footrot, which usually proves difficult to manage at this time of year, because by the time that severely lame sheep are identified, the disease is present in a high proportion of the flock.
THE TREATMENT RESPONSE IN ADVANCED CASES OF FOOTROT IS VERY POOR
The objective of footrot control is to combat the problem early during the transmission stage of the disease, usually during the early summer when few lame sheep are seen. At this early stage, control is achieved by regular foot bathing in 3% formalin or 10% zinc sulphate and standing in a dry area for 30 minutes afterwards, with the aim of preventing spread of infection.
However, control is difficult when the problem is addressed after infection has spread throughout the flock and most sheep have underrunning and overgrowth of the hoof walls.
In these cases it is necessary, but usually impractical to pare feet before footbathing, and at best cure rates are very low. (Great care should be taken to avoid excessive or over-zealous foot paring, which can result in severe lameness, or may even predispose to footrot itself.)
Antibiotic treatment using either a subcutaneous injection of tilmicosin, or intramuscular injection of penicillin at double the standard dose rate improves the treatment response in some cases.
Vaccination can be a useful adjunct to the management of severe outbreaks, but is expensive, leads to unpleasant injection site reactions, only affords short lived protection, and is incompatible with the use of moxidectin injections for worm or scab control.
NOT ALL LAMENESS PROBLEMS ARE CAUSED BY FOOTROT
A group of 15 lame Texel rams was examined to decide whether or not footrot vaccination would be worthwhile. Two of the rams had elbow arthritis, two had interdigital fibromas, three had scald (or possibly benign or early footrot), and the remainder had shelly toe, with horn separation and trapping of grit.
Footrot vaccination would have been unnecessary, ineffective and expensive.
ELBOW ARTHRITIS IS A COMMON CASUE OF CHRONIC LAMENESS IN ADULT SHEEP
In another case, a group of 500 Greyface ewes was examined, because of lameness which didn’t respond to footbathing in zinc sulphate. There was a suggestion that the problem might have been due to digital dermatitis and a request for antibiotic powder to use in a footbath.
Closer examination showed the cause of this particular problem to be footrot, which was unresponsive to treatment due to the advanced stage of the disease in the flock.
Antibiotic footbathing would have been ineffective, irresponsible and expensive. These two cases highlight the value of achieving a veterinary diagnosis before treating lame sheep.
About 20% of a January-lambing flock of Suffolk ewes were found to be barren when scanned at the beginning of November. The barren rate in this flock was usually about 8%. The scanner reported that in some cases, ewes appeared as if they had been pregnant, but subsequently resorbed their foetuses.
The scanning percentage of 179% for the remaining ewes was also disappointing, when compared with 200% during normal years.
The barren ewes were from different age groups and had been mated to 3 different rams. The ewes were in mixed body condition, with some of the barren ewes being fat, while others were unexpectedly lean (score 2 on a scale of 1 – 5).
Serological tests for toxoplasmosis and border disease were all negative. However the plasma concentrations of the protein, albumin of 10 barren ewes were low, while their plasma concentrations of the protein, globulin were elevated.
Low albumin concentrations in barren ewes are often related to liver disease, while high globulin concentrations indicate an inflammatory response.
Furthermore, serum concentrations of the enzyme GLDH were elevated, indicating acute liver disease. These findings were consistent with a diagnosis of sub acute liver fluke disease. This diagnosis was confirmed by the identification of small numbers of liver fluke eggs in the faeces of 2 of 10 barren ewes.
THE DIAGNOSIS OF LIVER FLUKE CAN BE CONFIRMED BY THE IDENTIFICATION OF EGGS IN FAECES
The ewes were also scouring and had unexpectedly high faecal worm egg counts averaging 269 per gram. This finding was unusual and probably associated with lowered immunity due to their altered protein balance.
Sub-acute liver fluke disease is caused by the parasite Fasciola hepatica, which has a two host life cycle involving snails and a variety of mammalian species including sheep, cattle, goats, deer and rabbits.
The seasonal appearance of the disease is determined by the effects of moisture and temperature on the snail populations and free-living stages of F. hepatica. Sub-acute disease is caused by massive liver damage due to the presence of up to 1000 migrating immature flukes. Severely affected animals are lethargic, pale and breathless.
Sudden deaths may occur when animals are handled, as a result of liver rupture. Poor reproductive performance is often associated with subacute liver fluke.
POSTMORTEM FINDINGS OF HAEMORRHAGIC TRACTS IN THE LIVER
The diagnosis of subacute liver fluke is straightforward whenever moribund or dead animals are available for euthanasia and postmortem, but can be problematic when a postmortem examination is not possible.
Fluke eggs are not always found in the feaces because the disease is principally caused by immature flukes. In these cases, measurement of blood protein and liver enzyme concentrations can be useful.
The diagnosis of sub-acute liver fluke in the case described was unexpected, because the flock was kept on a mostly arable farm in the south-east of Scotland, away from the traditional liver fluke areas.
Furthermore, the forecast liver fluke disease risk for 2004/5 was not particularly high, associated with a mostly dry early summer. However, despite the overall low risk, small permanently boggy areas present on most farms may provide ideal snail habitats.
In the case described, the problem was associated with a drainage ditch which ran alongside the field grazed by the ewes during the summer and autumn. While neither sheep nor cattle had been introduced for several years, liver fluke caused serious problems in the south-east of Scotland during the autumn and winter months 2001/2 and 2002/3.
Infected snails could, therefore, have been washed into the ditch from higher farms, or resident snails could have been infected by liver fluke carried onto the farm with wildlife.
HABITATS ARE PRESENT ON MANY FARMS, EVEN IN DRIER EASTERN REGIONS, WHICH COULD SUPPORT POPULATIONS OF FLUKE INFECTED SNAILS
Subacute liver fluke was diagnosed during November on four other farms served by the same veterinary practice in the south-east of Scotland.
For the treatment of acute liver fluke it is necessary to use triclabendazole which has good efficacy against early immature flukes. When “safe” dry pasture is available, a single treatment is given before moving the sheep.
However, when such pasture is not available, repeated treatments at 3 week intervals are required throughout the high risk period of autumn and early winter. Careful animal handling is necessary and some deaths may occur despite treatment.
Triclabendazole resistance is an emerging problem in some western parts of the UK, resulting from the need to dose sheep numerous times every year for fluke control. Your vet can advise you about alternative fluke control options if you suspect triclabendazole resistance in your flock.
Concern was raised when 260 of 1100 April-born Greyface cross Suffolk and Texel lambs failed to reach finishing weights by mid October. These lambs had only gained about 150 g/day during the summer and autumn months, when growth rates in excess of 300 g/day should have been achievable.
IT OUGHT TO BE POSSIBLE TO FINISH MOST SPRING-BORN LOWGROUND LAMBS BY THE END OF AUGUST, BEFORE PASTURE WORM LARVAL CONTAMINATION BECOMES PRODUCTION LIMITING
The lambs had been orally dosed with ivermectin at 4 – 6 week intervals throughout the summer. Two weeks after dosing during October, faecal samples were submitted from 6 lambs for a routine drench check.
Their faecal worm egg counts were 100, 250, 50, 0, 50 and 50 eggs per gram, indicating that the wormer had not been effective. This drench check was followed up 2 weeks later by a faecal egg count reduction test, which showed the presence of resistance to all three anthelmintic groups.
Reports of multiple anthelmintic resistance are becoming more commonplace. Future worm control and the achievement of economically sustainable lamb growth rates will become difficult in these flocks, highlighting the importance of doing everything possible to avoid the emergence of the problem in your flock.
Anthelmintic resistance is discussed in this month’s Sheep Disease Focus article.
The list of other sheep disease problems reported during October and November 2004 includes:
pink eye in ewes
Johne’s disease in ewes
orf in feeding lambs
CCN in ewes
enzootic pneumonia in lambs
systemic pasteurellosis in lambs
These subjects have all been described in recent NADIS sheep disease forecast articles. Your vet can advise you about their management in your flock.
• While every effort is made to ensure that the content of this forecast is accurate at the time of publication, NADIS cannot accept responsibility for errors or omissions. All information is general and will need to be adapted in the light of individual farm circumstances in consultation with your veterinary surgeon.
Copyright © NADIS 2002
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