NADIS disease forecast – sheep (October)
NADIS is a network of 40 veterinary practices and six veterinary colleges monitoring diseases of cattle, sheep and pigs in the UK. |
October 2004
By Neil Sargison BA VetMB DSHP FRCVS
NADIS Sheep Disease Forecast
Weather conditions during September and October were mostly wet and mild, giving rise to foot lameness and worm problems in many flocks.
Besides management of these important production limiting diseases, the focus for many flocks is now on mating management.
Most sheep farmers are currently concerned about the profitability of their businesses following the mid term review of Agenda 2000, with decoupling of subsidies from production from 1st January 2005.
Subsidy capping will mean that the single farm payment will amount to less than what is currently earned from ewe annual premium and hill livestock compensatory allowances.
Furthermore, while the basis of payments will vary between devolved Government areas, modulation involving an increasing rate of transfer of subsidy to environmental development and other schemes, will further reduce the level of support over the next few years.
Thus, many sheep producers will need to improve the economic productivity of their flocks to remain profitable.
The single farm payment should free farmers from many of the complicated rules governing livestock premium payments, thus enabling more flexible sheep disease management and improved production efficiency.
The identification of potentially production limiting diseases and management changes to improve sheep health will therefore become more worthwhile. There will be more incentive to cull rather than retain for subsidy potentially poorly-productive thin or lame ewes.
Cobalt deficiency
There were several NADIS reports of cobalt deficiency in lambs this autumn. The higher incidence of the disease compared with Autumn 2003 is probably related to subtly different patterns of pasture growth associated with different weather conditions.
THE EFFECTS OF COBALT DEFICIENCY ARE INSIDIOUS IN ONSET AND THE PROBLEM IS OFTEN NOT DIAGNOSED UNTIL SIGNIFICANT ECONOMIC LOSS HAS RESULTED, ASSOCIATED WITH DELAYED LAMB FINISHING
Cobalt deficiency therefore provides an example of where identifying the potential for disease before it occurs and altering management accordingly can improve the economic productivity of the flock.
Severely cobalt deficient lambs frequently appear empty, pot bellied and depressed in appearance. Severely affected animals are sometimes pale and anaemic, although in these cases the differential diagnosis of haemonchosis should be investigated.
A WATERY DISCHARGE ASSOCIATED WITH A LOW-GRADE CONJUNCTIVITIS WAS OFTEN PRESENT AT THE EYES
Cobalt is required for the manufacture of vitamin B12, which is used in the liver for energy production. Growing animals have a higher requirement for vitamin B12 than adults, but the requirements of pre-ruminant animals are low. Consequently, clinical signs are most commonly reported in weaned lambs during the summer.
The relationship between cobalt concentrations in soil or herbage and the vitamin B12 status of lambs is complex, and it is difficult to predict a ‘bad’ season in advance.
Soil pH above the optimum range of 5.8 – 6.3 can affect cobalt availability and soil compaction may reduce pasture uptake of cobalt. Pasture cobalt uptake is lowest when pasture growth is rapid and in mature pasture.
Pasture grown on waterlogged soil has a higher cobalt concentration than pasture grown on well-drained soils. Plants differ in their ability to accumulate cobalt, although when soil cobalt is low the concentrations in all plant species are low.
The diagnosis of cobalt deficiency is usually based on serum vitamin B12 concentrations, which reflect the immediate dietary cobalt intake.
However, yarding for a period of more than 6 hours before sampling, concurrent liver fluke infection and poor handling of samples can result in markedly elevated values.
Furthermore, unless animals are severely deficient, the individual variation in serum vitamin B12 concentrations is high, and it is recommended that a minimum of 7 samples be collected.
If your lambs have been slow to finish this year, the problem may have been caused by more than just poor pasture quality.
It might therefore be prudent to check the cobalt status of your lambs. Your vet can advise you about the diagnosis and management of cobalt deficiency and other potential causes of ill thrift such as worms or selenium deficiency in your lambs.
Flushing ewes
The lambing percentage achieved by hill flocks varies considerably. Some of this variation arises from differences in soil type, climate, altitude and topography, which cannot be influenced by management, other than to modify their effects.
Furthermore, achieving high lambing percentages in hill flocks is not always desirable, because the hill grazing cannot support the metabolic requirements of ewes carrying and rearing twins.
Such production may only be sustained by a high level of supplementary feeding, which may be both uneconomic and impractical. Nevertheless, it is possible to increase the lambing percentage of some hill flocks in a sustainable manner by managing the ewes to ensure optimal ovulation rates and embryonic survival.
In order to achieve optimal ovulation rates, hill ewes should ideally be in body condition score 2.5 to 3.0 (on a scale of 1 – 5).
The transverse processes of their lumbar vertebrae should be well covered, but readily palpable when pressed firmly. Ewes which are in poorer body condition generally respond to a rising plane of nutrition for at least 3 weeks before and continuing for about 3 weeks after mating.
The response to flushing is less defined in heavy ewes (body condition score more than 4.0), but weight loss should always be avoided during the mating period, because it results in a reduced ovulation rate.
Nutritional management between weaning and the following mating is therefore critical to ensure optimal body condition at mating. There is some breed variation in response to flushing with Scottish Blackfaces responding well while some types of Cheviots respond poorly.
RAMS HAVE ALREADY BEEN TURNED OUT TO MOST LOWGROUND FLOCKS, AND WILL BE INTRODUCED TO HILL EWES DURING THE NEXT FEW WEEKS
Achievement of optimal body condition score before mating is also important to ensure that ewes maintain adequate body condition throughout late pregnancy and lambing, thus avoiding pregnancy toxaemia and mastitis problems, while enabling high lamb survival rates and good milk production.
On selenium deficient pastures ewes and lambs may also benefit from selenium supplementation before mating. Your vet can advise you about the potential benefits of selenium supplementation in your flock.
Worming ewes before mating
New recommendations for the treatment of internal parasites in sheep (available at the National Sheep Association’s website: www.nationalsheep.org.uk ) discourage the routine dosing of ewes before mating, on the basis that it may select for anthelmintic resistance.
However, while in most cases dosing sheep before mating may be unnecessary, the benefits are not clearly defined. Thus, the risks associated with not dosing at this stage are unknown.
Practical experience suggests that provided they are in good body condition, dosing ewes before mating has little effect on subsequent lambing percentages.
However, in New Zealand, reduced fertility has been identified in ewe flocks with mean faecal egg counts at mating greater than 100 eggs per gram, possibly due to an effect on ovulation rate.
This effect is probably only important when ewes are in poor body condition, but illustrates the need to control parasite burdens. Dosing ewes before mating may also reduce the risk of disease associated with worms such as Haemonchus contortus.
HAEMONCHOSIS CAN RESULT IN SEVERE DISEASE IN SHEEP OF ALL AGES FOLLOWING INTRODUCTION TO PREVIOUSLY NAIVE FLOCKS
General recommendations about the need to dose ewes before mating cannot be made. Basing the decision to dose ewes before mating on monitoring of faecal worm egg counts may prove to be more sustainable than simply adhering to traditional practices.
Ewe faecal egg counts at this time of year are best performed on individual samples from 7 to 10 animals rather than pooled samples.
The reason for this is illustrated by the following results from two flocks of mixed-aged Greyface ewes.
| Flock 1 | Flock 2 | |
| Faecal egg count based on a carefully pooled sample (eggs per gram) |
50 | 550 |
| Individual faecal egg counts (eggs per gram) |
0 | 0 |
| 100 | 0 | |
| 200 | 0 | |
| 0 | 2650 | |
| 0 | 0 | |
| 150 | 0 | |
| 0 | 0 | |
| 0 | 0 | |
| 100 | ||
| 0 |
On the basis of the pooled sample results, a decision might have been made to dose the ewes in flock 2, but not those in flock 1. However, while the pooled result from flock 1 was low, four of the10 ewes had significant worm egg counts, which might justify dosing.
The high pooled result from flock 2 was derived from only one ewe, which was probably suffering from concurrent chronic disease, such as Johne’s. Dosing this flock before mating would not be beneficial.
Pink eye
Several outbreaks of pink eye (ovine infectious keratoconjunctivitis) were reported in during September and October. Pink eye occurs in sheep of all ages, but tends to be more severe when it is seen in ewes than in lambs.
The first sign of pink eye is tear staining extending from the corner of one or both eyes, associated with conjunctivitis.
As the disease progresses the cornea becomes cloudy and blood vessels are seen prominently at the periphery of the eye. The ocular discharge becomes thicker and pus-like as the disease progresses.
When both eyes are severely affected sheep become temporarily blind, resulting in handling difficulties and losses due to misadventure. In most cases, healing occurs over a period of several weeks, eventually leaving only a faint corneal scar.
However, in extreme cases the anterior chamber of the eye may ulcerate, rupture and become secondarily infected, resulting in permanent blindness. Acquired immunity following infection is poor and many cases relapse.
THE INCIDENCE OF PINK EYE IS HIGHEST IN WINTER MONTHS
The primary causative organisms are believed to be Chlamydia psittaci and Mycoplasma conjunctiviae, either alone or in combination, but several other bacteria may also be involved in a secondary role.
Outbreaks in recently weaned lambs may be associated with high stocking rates, dust, long grass and flies which have been contaminated by tear secretions of infected animals. Handling of the face and head of lambs when drenching may also provide a means of spread.
Clinically recovered animals may harbour the causative organisms for several months and may be a source of re-infection of other animals in subsequent years when their immunity has waned.
The disease is painful and prompt treatment of affected animals is usually recommended to mitigate against the risk of permanent blindness. Treatment is tedious and usually involves the topical application of aureomycin as a puffer or ointment.
There is some evidence to support the use of intramuscular injections of long acting oxytetracycline, which may be a practical treatment method in some flocks. Your vet can advise you about the treatment and management of pink eye in your flock.
Foot lameness
The incidence of lameness has increased over the past month, most reported outbreaks being characterised by inflammation of the interdigital space, under-running of the sole and hoof wall, overgrowth of the hoof wall and an unpleasant smell, characteristic of footrot.
FOOTROT IS AN IMPORTANT WELFARE CONCERN AND SEVERELY AFFECTED SHEEP LIKE THIS REQUIRE IMMEDIATE ATTENTION. THE MAIN FOCUS SHOULD HOWEVER BE ON PREVENTION RATHER THAN TREATMENT OF INDIVIDUAL AFFECTED ANIMALS
Different management regimes are required for different causes of lameness. Clinical assessment of individual cases is therefore important and veterinary attention should be sought when the diagnosis is not clear.
The objective of footrot control is to combat the problem during the transmission stage of the disease, usually during the summer when few lame sheep are seen, rather than to wait until animals are severely lame. This should involve routine foot bathing by walking through 3% formalin or standing for more than 15 minutes in 10% zinc sulphate.
The addition of a squirt of washing-up liquid aids the penetration of zinc sulphate solution. It is essential that the sheep are stood in a dry area for at least 30 minutes afterwards.
It is useful if sheep can be moved onto ‘clean’ pasture after treatment (Dichelobacter nodosus, the causative bacteria of footrot only survives on pasture for a maximum of 4 days during optimal warm and wet weather conditions, and for a much shorter period during dry weather). Foot paring is only necessary when there is gross overgrowth of the horn, or for the treatment of individual lame sheep.
Vaccination can also be a useful adjunct for the control of footrot. An initial course of two injections 4 – 6 weeks apart is usually recommended, followed by booster doses in advance of high-risk periods in spring and autumn.
Vaccination provides protection against infection for about 4 – 6 months, but alone does not eradicate footrot and can prove expensive.
In many flocks, vaccination is targeted at specific high-risk groups of animals, such as rams before mating. Some local tissue reaction can occur at the footrot vaccination site.
Furthermore, footrot-vaccinated sheep cannot be subsequently treated with injectable moxidectin because of a risk of fatal allergic reaction.
Once footrot has become established in a flock, a more radical approach is needed, involving foot paring, foot bathing and antibiotic treatment using either 1ml/30 kg MICOTIL under the skin or 1 ml/5 kg DEPOCILLIN (note that the DEPOCILLIN dose rate is double the standard rate) into the muscle.
Some cases never respond to treatment and should be culled. Vaccination can also be used in the face of a severe outbreak, but is not usually warranted.
PARENTERAL ANTIBIOTIC INJECTIONS CAN BE USEFUL FOR THE TREATMENT OF ADVANCED FOOTROT LESIONS, ALTHOUGH NON RESPONSIVE SEVERELY AFFECTED SHEEP SHOULD BE CULLED
Foot paring should only be undertaken when there is gross overgrowth of the hoof horn. 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.
Your vet can advise you about the diagnosis and management of foot lameness in your flock. The subject has been covered in various NADIS sheep disease focus articles.
Acute liver fluke
Within traditional liver fluke areas, the risk of acute liver fluke is high this year, associated with a wet summer.
In other areas, where the weather during the first part of the summer was drier, the risk will be lower, because snail populations may not have established.
YOU MUST ASSESS THE RISK OF ACUTE LIVER FLUKE IN YOUR FLOCK AND TREAT YOUR SHEEP ACCORDINGLY
The flukicides which are available in Britain differ in their efficacy against immature and adult F. hepatica.
For the treatment of acute liver fluke disease 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.
“Safe” pasture is seldom available on typical hill farms in fluke areas, so 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. After treatment animals should be provided with good quality nutrition.
Triclabendazole has a meat withdrawal period of 56 or 28 days, depending on the product used.
Unfortunately, in some western areas of Scotland and Ireland, the annual need for repeated flukicide treatments has led to the emergence of triclabendazole resistance. The solutions for fluke control in these flocks are not obvious.
Treatment of all sheep and cattle in May to remove adult flukes and prevent egg shedding and the potential for snail infection is useful, but does not totally remove the problem. All of the available flukicides are effective against adult flukes.
Flukicide |
Doserate |
Meat |
| TRICLABENDAZOLE (kills early immatures and adults) (eg. FASINEX 5%) |
1 ml/5kg |
56 days |
| NITROXYNIL (kills late immatures and adults) (eg. TRODAX 34%) |
1.5 ml/50kg |
60 days |
| CLOSANTEL (kills late immatures and adults) (eg. FLUKIVER) |
1 ml/5kg |
42 days |
| ALBENDAZOLE (only kills adults) (eg. VALBAZEN 2.5%) |
3 ml/10kg |
8 days |
Biosecurity to avoid introduction of triclabendazole resistant flukes is not straightforward, because liver fluke can be introduced with cattle and wildlife. Away from the triclabendazole resistant fluke areas, introduced sheep should be dosed with nitroxynil or closantel to remove triclabendazole resistant flukes.
However, when sheep are introduced between September and December, depending on local conditions, this treatment should be delayed for 3 to 4 weeks, to enable early immature flukes to become susceptible.
This strategy will not be 100% effective, so some vets recommend sequential treatment of introduced sheep with both triclabendazole and nitroxynil or closantel on arrival.
However, this practice is not without risk associated with subjecting sheep to concurrent treatments with potentially dangerous drugs.
Brassica poisoning
Many tail-end lambs throughout the country have now been moved onto Brassica crops for finishing. Brassica crops provide a balanced source of carbohydrate, protein, fibre and minerals and are a very useful sheep feed.
However, when fed exclusively, lambs seldom achieve growth rates which would be predicted on the basis of the feed analysis. This is because Brassica crops also contain several important toxic substances which cause depressed appetite.
The list of toxic substances includes:
nitrates
photosensitive substances
haemolytic anaemia factors
oxalates
glucosinolates (goitrogen precursors, which can induce iodine deficiency)
sulphur and molybdenum (which can induce copper deficiency)
TAIL-END LAMBS HAVE NOW BEEN MOVED ONTO BRASSICA CROPS FOR FINISHING
One particularly important toxic substance is a haemolytic anaemia factor, S-methylcysteine sulfoxide (SMCO). SMCO is converted by bacterial fermentation in the rumen to dimethyl disulfide, which causes haemolysis (red blood cell destruction).
Severity of the disease is proportional to the SMCO content of the crop. When present in small amounts, the toxin results in poor growth rates. However, when SMCO is present in high concentrations, lambs become anaemic with haemoglobinuria (red urine), progressing rapidly to death.
SMCO concentrations in plants can be analysed and Brassica crops categorised as low or high potential risk. However, SMCO increases with the age of the crop, so even low risk varieties can become potentially hazardous as they reach maturity or if they are fed to excess.
To avoid these risks, long-keep store lambs should not be grazed on Brassica crops for prolonged periods and animals should be provided with a pasture run-off or supplementary feed.
The diagnosis of haemolytic anaemia is based on the history of grazing potentially high-risk Brassica crops, clinical signs in affected animals and post mortem findings from freshly dead animals of jaundice, haemoglobinuria and anaemia, with congestion of the internal organs. Blood samples from sick animals are dark red and watery.
When the disease is suspected, animals should be removed from the crop and carefully introduced to supplementary feed.
The list of other sheep diseases reported during August 2004 includes:
Several outbreaks of systemic pasteurellosis in lambs (NADIS disease focus October 2004)
Johne’s disease in ewes
jaagsiekte in ewes
pneumonia in lambs
polioencephalomalacia (CCN) in lambs
photosensitisation in hill lambs
magpie injury to the backs of rams
pizzle rot in rams
The management of all of these diseases has been described in recent NADIS sheep disease forecasts. Your vet can advise you about the diagnosis of these problems 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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