FACT SHEET August Lameness in Sheep

Transcription

1 FACT SHEET August 213 Lameness in Sheep

2 Why is lameness in sheep so important? Lameness in sheep can be a very painful condition and presents a poor image for the industry. Lame sheep are less competitive when it comes to feeding in groups and because of their weakened condition, are more susceptible to other diseases. There are also knockon effects such as reduced fertility and ultimately, fewer lambs reared. Persistently lame ewes lose body condition and have reduced milk yields, which affects the growth of their lambs. Affected lambs also perform poorly and their growth can be reduced by between 8% and 18%. Managing and treating lameness is costly both in terms of labour time as well as the medicines and chemicals used to treat it. Reductions in the productivity and efficiency of sheep has been estimated to cost the UK sheep industry 24m annually. Recent estimates from Ireland put the total annual per flock costs of managing and treating ewe lameness at.55/ewe for flocks with 5% lameness and 4.22 /ewe for flocks with 25% lameness prevalence. The total per flock costs of lameness in lambs of these levels was estimated to cost.14 and.4 per lamb. For flocks with very high lameness levels (59% has been recorded) the costs will be considerably more. Footrot has distinct stages that progress from between the digits towards the sole of the hoof, and underrunning the sole of the hoof towards the outer hoof wall (abaxial wall). Sometimes you cannot see early stages of underrun footrot but it can be felt by placing your thumbnail along the inside of the hoof which, if necessary, should be done with great care. The extent of the underrunning can be judged by how far your thumb enters underneath the sole. Footrot scores The extent of such damage is limited by predisposing factors such as host resistance to disease, presence of prolonged wetness and presence of other hoof conditions that can affect the hoof integrity. Hooves can be readily classified into the following 5 groups according to the progression and severity of footrot, which can be used to gauge the effectiveness of control strategies over time. Footrot score: Footrot score: 1 Footrot score: 2 What are the main causes of lameness? Fig 1: Normal hoof. No signs of any foot lesion, infection or irritation. Footrot score: 3 Fig 2: Mild interdigital dermatitis ( scald ) with some loss of hair. Slight to moderate inflammation confined to interdigital skin and may involve erosion of epithelium (skin surface). Fig 3: More extensive interdigital dermatitis (skin inflammation) and necrotising (skin death) inflammation of interdigital skin. Footrot score: 4 Footrot The most common cause of lameness is footrot, which is an infectious hoof condition caused mainly by Dichelobacter nodosus, an anaerobic bacterium which occurs naturally only in the feet of ruminants affected by footrot. Fusiformis necrophorum is often considered to be the main pathogen in the predisposition and early stages of initiation of footrot. Footrot is characterised by infection of the interdigital skin (between the hoof digits) usually referred to as scald (inflammation) and if left untreated, can then underrun the sole of the hoof. Both presentations can often cause the animal considerable pain which is why it becomes lame. Fig 4a & 4b: Severe interdigital dermatitis and underrunning of the horn of the heel and sole. Fig 5: Severe interdigital dermatitis and underrunning of the horn of the heel and sole and with underrunning extending towards the walls of the hoof

3 Contagious Ovine Digital Dermatitis (CODD) This condition is considered to be a very infectious and severe cause of lameness that is distinguishable from classical footrot in that a primary lesion commences at the coronary band (at the top of the hoof, i.e. at the junction where hoof meets hair) with subsequent invasion and underrunning of the hoof wall from the coronary band down towards the toe causing detachment, then shedding of the horn capsule (Fig. 6). The damage to the corium (the tissue that connects the horn to the bone) may be so severe that regrowth of the horn can be permanently affected. Typically, there is also loss of hair extending 35cm above the coronary band. The organisms responsible are thought to be treponemes (a microscopic bug) and similar to digital dermatitis problems in cattle. Shelly hoof Shelly hoof ( white line degeneration, Fig. 7) in sheep is a noninfectious condition that occurs when the hoof wall becomes detached from the laminar corium (the tissue that bridges the gap between the bone and the horn). The space then becomes impacted with debris leading to infection, pain and lameness. Sometimes this infection travels right up to the top of the hoof and can burst through the skin at the coronary band (top of the hoof). Mild shelly hoof usually does not impact adversely on sheep although it can act as an entry point for harmful bacteria. The causes of shelly hoof are reported to be unknown in sheep although several theories exist as to the reason why shelly hoof is a problem for some flocks. The type of ground on which flocks are managed, nutritional deficiencies and breeding have been suggested although none of these have been demonstrated beyond doubt. The influence of maternal nutrition and horn development during pregnancy have been established in sheep and nutrition, physiological status and other environmental stressors have been linked to claw quality in dairy cattle but not yet in sheep. Very high prevalence levels in hill breeds has been reported and sometimes is mistakenly labelled as footrot although usually farmers are able to distinguish footrot from shelly hoof. Fig 6 Fig 7 Granuloma (strawberry toe) Strawberry toe is a noninfectious condition that usually presents itself at the point of one or other of the hoof digits where a bulbouslooking growth filled with blood capillaries protrudes from the hoof (see Fig. 8). The main reason why they occur is usually attributed to overzealous hoof paring although this is not the exclusive reason for their occurrence. Interdigital fibroma ( corns ) This condition consists of a growth and protrusion of connective tissue between the digits. They originate from the skin between the digits and are thought to develop in response to trauma, excessive motion or moisture, and abnormal foot and hoof conformation, such as splay toes (Fig. 9). Sometimes they are very small and of no consequence but others can be large and cause friction and skin damage in the interdigital area which can then become an entry point for other hoof problems e.g. footrot. Some animals may have a genetic predisposition to corns. Other causes Less common conditions/infections causing lameness include postdipping lameness, septic laminitis, ulcerative dermatosis (skin disease), bluetongue and footandmouth disease. Trauma (injuries e.g. fractures and ligament and tendon injuries) also cause sheep to become lame. Lameness originating from limb lesions can also be caused by infectious and noninfectious diseases e.g. most sheep farmers will have some lambs with infectious polyarthritis (joint ill) each year. The incidence of joint ill can be minimised by ensuring that ewes are lambed in a clean, dry environment and that lambs take in adequate amounts of protective colostrum within six hours of birth. Dipping navels and providing clean lambing pens or dry lambing fields also help to protect lambs. Erysipelas is caused by a bacterium present in soil. It is not common in sheep but can cause outbreaks of lameness in lambs; if left untreated, lambs become severely debilitated and should be euthanised promptly. Fig Fig 8 Fig 9

4 Controlling lameness Lameness caused by footrot or CODD is often bought in with the arrival of purchased sheep. Some steps to minimise the risk and spread throughout the flock are summarised below. 1. Isolate boughtin sheep (quarantine) away from your flock and footbath them with a zinc sulphate based solution in accordance with the manufacturer s directions. This should be done twice on arrival and again in 71 days. Inspect hooves of all new animals and treat any with signs of footrot. 2. Footbathing will assist in the control of lameness due to footrot or scald. Formalin exacerbates shelly hoof by causing the horn to become more brittle. 3. Vaccination is effective for footrot, but must be repeated at least every year. Recent studies have shown that vaccination for footrot also gives some protection against CODD. 4. The footrot bacteria can live off the sheep for 71 days, especially in mud, so keep sheep pens clean, collect hoof clippings, avoid muddy gateways and fix leaking water troughs. 5. Avoid concentrating feed sources in one area move it around, if practical. (Using a snacker feeder is ideal for this.) Footbath solutions Footbathing with zinc sulphate solution has a disinfecting action on the surface of the hoof and is an important control measure if the problem is scald (footrot score 1 as described on page 2). It does not cure footrot that has become underrun, even if sheep stand in it for 51 minutes as it does not penetrate the horn or sole, although standing in it for this time is more effective than just walking through. Essentially footbathing holds back the problem but does not cure footrot with scores 2 to 4 as described on page 2. For CODD, an antibacterial footbath solution from your vet is required. A clean, dry standing area is required after footbathing to maximise its efficacy Treating footrot You can only be certain WHY your sheep are lame by inspecting individual hooves. This is the first step towards deciding what is the best treatment to use. Affected sheep with footrot or CODD should be given antibiotic treatment as directed by your veterinary surgeon. Usually, for footrot, a longacting antibiotic is administered and repeated if necessary. The earlier the footrot is detected and promptly treated, the lower the contamination to other sheep and the quicker it will be cleared up. Topical ( on the surface antibiotic sprays e.g. purple terramycin spray ) are useful for mild cases of scald or footrot. To trim or not to trim? The rate of hoof growth varies depending on available nutrition, the breed and genetics of the sheep, moisture, and other soil characteristics. Sheep grazed on rocky, dry soil may not require the extent of hoof care needed for sheep in high rainfall areas which need to have their hooves inspected more regularly. Typically, hooves will grow around.1 to.5cm/month and so if an animal is lame in one hoof and doesn t bear so much weight on that hoof, then it can quickly become overgrown (Fig. 1). After successful treatment of footrot, the weightbearing function will be restored and the hoof will begin to be worn away to the same level as the other hooves. Overgrown hooves should be carefully trimmed only to restore the hoof integrity and shape of the hoof so that there is a weightbearing ridge of horn of 2mm (as shown in Fig. 1) around each digit and not trimmed flush with the sole of the hoof. Footrotaffected hooves should not be pared and treated with antibiotics. Contrary to popular belief, it is not necessary to pare feet with footrot to expose the organism to the air. Overparing is painful, and can lead to other problems such as granulomas ( strawberry toe ). Once footrot or CODD have been successfully treated, sometimes there are flaps of loose horn that can be cut off without any damage to the hoof. In contrast to footrot, shelly hoof often leads to having loose pockets between the abaxial (outer) hoof wall and the corium (tissue that attaches the horn to the cleat), which is an ideal harbour for stones, dirt and debris. Trimming away the detached horn in this instance will reduce the risk of further impactment and infection. The outer horn should normally regrow back down

5 Breeding out lameness How much footrot is normal? A simple strategy for selfreplacing flocks with low levels of footrot is to avoid keeping ewe or ram replacements from sheep that are persistently lame, or if they have been treated for being lame. Culling lame sheep is an expensive solution but necessary if they do not respond to treatment, or if they are persistently lame. Research undertaken at SRUC (SAC) reported a genetic basis of around 2% to footrot and the use of breeding to control footrot works best when more than 1% of the flock have one or more hooves affected. Breeding is a longterm solution that shows cumulative benefits over time i.e. annual improvements stack up with the added benefit of having fewer sources of infection. This could be.25.5% progress per annum which is more or less doubled if management techniques are also used to reduce the level of footrotcausing bacteria in pasture. The 5point scoring system explained on page 2 can be used on your breeding flock every year to identify which family groups are more or less resistant to footrot and Estimated Breeding Values (EBVs) for footrot resistance can be produced if a sufficient number of animals are regularly scored. This is now being implemented in Ireland. Some key points Don t breed from sheep that are lame. Identify sheep with coloured marker that are persistently lame, then cull them. Pick rams that are active and up on their feet walking around, rather than lying lazily in the pens at the sale. Ask the owners if their flock is regularly footrotscored and ask to see the results. Inspect the hooves (all of them!) of rams you want to buy. There should be no signs of previous hoof problems or of excessive hoof paring. In a study completed by SAC (now SRUC), very low footrot prevalence of <1% was seen in some flocks with the worst (highest prevalence) being nearly 6%. Average levels for different hoof lesions in GB for the different causes of footrot are shown in Table 1 below and combined from a study undertaken in Northern Ireland by AFBI. Table 1: Prevalence of hoof lesions after inspection if sheep had 1 hoof affected (%) Number of sheep Footrot 1 Shelly hoof Interdigital fibroma White line abscess CODD Granuloma Pedal joint sepsis Misshapen Overgrown Texel 5, Blackface 4, Welsh Mountain Hill breeds Northern Ireland 1, Hoof lesions on 4 point scale described on page Lowland breeds Northern Ireland 1,

6 Further information Contact Further information on lameness in sheep can be downloaded from FAWC Opinion on lameness in sheep: NADIS website: 8% funding is available to eligible businesses towards the cost of onetoone support on animal health via the Farming Connect Whole Farm Plan, please get in touch. For more information on Farming Connect services and events, contact us: PHONE menterabusnes.co.uk WEBSITE /farmingconnect Catch up with all the latest news from Farming Connect by joining our online community. Follow us on: FACEBOOK facebook.com/farmingconnect Farming Connect support, guidance and training is delivered by Menter a Busnes on behalf of the Welsh Government Author: Dr. Joanne Conington, SRUC. 9