Author: Phil Scott DVM&S BVM&S CertCHP DSHP DipECBHM FRCVS
Reviewed: Phil Scott DVM&S BVM&S CertCHP DSHP DipECBHM FRCVS 2017
Published: 2009
The components of a biosecurity programme are all good management practices that can increase the profitability of your sheep farming operation.
A good biosecurity regimen should always be in place to improve your farm efficiency, protect neighbouring farms and the countryside, and safeguard animal and human health.
Biosecurity is not just to protect farm animals; it is also to protect you, your family and your farm workers. Disease is not always apparent, especially in its early stages. Any person visiting a sheep farm and not carrying out effective biosecurity measures on entry and on leaving a premises runs the risk of spreading diseases to and from that premises.
Infectious diseases can be spread between sheep farms by:
Biosecurity and biocontainment are words describing programs for infectious disease control:
Biosecurity - aims to reduce/prevent the introduction of new diseases onto a farm from outside sources. Alternatively, 'biosecurity' is the prevention of disease-causing agents entering or leaving any place where farm animals are present.
Biocontainment - aims to reduce/prevent the movement of infectious diseases on the farm
Biosecurity has four major components:
Know the health history of the flocks from which sheep are purchased.
Know the health status of sheep brought into your farm.
Never bring in sheep without knowing their vaccination history
Limit purchases to ewe lambs and gimmers, not older sheep
Quarantine all new arrivals for at least 30 days and preferably until after lambing (pregnant sheep)
Ensure that sheep do not share community pastures/common grazing
Ensure that sheep do not share fence lines with neighbours' sheep.
Ensure that methods of working are designed to minimise where possible the movement of people, vehicles or equipment into areas where sheep are kept.
Keep a record of visitors to your farm
The spread of disease is a serious risk at livestock markets, where animals come into close contact with other, potentially infected, livestock or equipment. There are a number of measures which should be taken to minimise this risk:
Defra's publication Biosecurity Guidance
(http://www.defra.gov.uk/farm/livestock/biosecurity/index.htm PDF 266 KB) contains information for everyone entering a farm on which livestock is kept to minimise the spread of disease.
The only sure way to protect against Bluetongue and Schmallenberg infections is for farmers to vaccinate their animals (vaccine against Schmallenberg virus not currently available but this situation is under review). Your veterinary practitioner will advise on such vaccinations based upon local risk factors including area of the country, lambing time, and history of disease in the region.
All purchased sheep must be treated for internal parasites (parasitic gastroenteritis; PGE) and liver fluke (based upon risk) immediately upon arrival on the farm.
All introduced sheep should be assumed to be sources of multiple anthelmintic resistance and be treated on arrival and yarded for 24-48 hours to ensure that any viable nematode parasite eggs have been voided before they are turned onto pastures which might be grazed by sheep within the next 6 months. The current recommendation is the sequential use of a group 3-ML anthelmintic and either a Group4-AD or Group 5-SI anthelmintic.
Triclabendazole is highly effective at killing all stages of flukes responsible for acute fasciolosis although there are concerns regarding efficacy in certain flocks and veterinary advice should be sought if doubts exist regarding such treatment. Closantel and oxyclosanide are not effective against early stage immature flukes and should be used only in the treatment of subacute and chronic fasciolosis.
Plunge dipping in diazinon dips kills scab mites within 24 hours and provided that sheep are correctly plunge dipped affords residual protection for fourl weeks. This method has the added advantage of eliminating all louse infestations which now affect almost all sheep flocks.
Two subcutaneous injections, seven days apart, of 200 µg/kg ivermectin, provide control of sheep scab. A single intramuscular injection of doramectin at a dose rate of 300 µg/kg of doramectin achieves some persistence but may occasionally be insufficient to provide protection against re-infection for the whole 17 day period during which the scab mite can survive off the sheep. A single subcutaneous injection of moxidectin at a dose rate of 200 µg/kg provides residual protection against sheep scab for at least 28 days, although the UK data sheet recommends two injections 10 days apart for the treatment of disease outbreaks. One injection of long-acting moxidectin at the base of the ear (Cydectin 20mg/ml LA injection 2%, Zoetis) provides protection against infection or re-infection for 60 days. An alternative treatment for lice, if present, is necessary.
Louse infestations can be eliminated by plunge dipping or pyrethroid pour-on preparations.
Freedom from C. abortus infection is best achieved by maintaining a closed clean flock with strict biosecurity.
Various accreditation schemes offer breeding female replacements from flocks declared free of C. abortusinfection but careful consideration must be given to establishing a clean but susceptible flock when the health status of neighbouring flocks cannot be guaranteed. Vaccination offers the best means of control for farms buying breeding replacements from non-accredited sources.
Prevention is best achieved by maintenance of a high health status closed flock; where this is not possible purchased sheep must be kept segregated until after lambing.
Wherever possible sheep producers should maintain a closed flock to prevent purchasing diseased sheep. If purchases are essential, ewe lambs should be bought from known sources rather than old ewes which are often chronic carriers. All purchased stock must be quarantined for one month and examined for footrot before introduction into the main flock. Footbathing, in either 3 per cent formalin or 10 per cent zinc sulphate, should be undertaken three times during this quarantine period.
Contagious ovine digital dermatitis has been introduced onto many sheep farms with severe consequences in terms of numbers of sheep affected, severity of lesions and poor response to conventional treatments.Away-wintering of sheep on dairy farms is considered to be a major risk factor.
Control of this condition depends on regular inspection of all purchased sheep during the quarantine period, the isolation of any sheep found to be lame and prompt treatment with a suitable antibiotic recommended by your veterinary surgeon. You should be aware that this may have to be actually administered by a veterinary surgeon.
The treated animal(s) should be re-examined at intervals to assess efficacy of treatment
Bacteria causing the common sheep respiratory infections, such as pasteurellosis, are ubiquitous and disease is best controlled by vaccination.
Ovine-pulmonary adenocarcinoma (OPA) is a contagious virus-induced tumour of the lungs of sheep. Virus transmission is facilitated by close confinement and can be a significant problem where sheep are housed for long periods during the winter months.
Prevention can be effected by maintaining a closed disease-free flock with double ring fencing. Purchase of breeding replacement stock is the major risk factor. Sourcing replacement stock from flocks free from OPA has obvious advantages but confirmation of such status in the absence of serological tests is not possible. Ultrasound examination of the lungs of all introduced sheep reduces the risk of diseased animals entering the flock; re-examination every six months is strongly recommended in case very early lesions were not detectable at earlier examinations. Ultrasound scanning identifies lung pathology but cannot guarantee freedom from virus infection which could result in disease years later. Biocontainment involves housing sheep for the minimum time and grouping sheep on age rather than litter size or lambing date wherever possible. OPA disease control measures in the field are currently being researched and interested farmers should contact their veterinary practitioner or Dr Chris Cousens at Moredun Research Institute.
Shearing equipment and other handling facilities, such as mobile plunge dippers and feeders are much less important as vectors for disease than purchased animals, which must be inspected before purchase and quarantined for at least two months. The disease is characterised by suppurative necrotising inflammation of superficial lymph nodes particularly the parotid lymph node at the base of the ear.
The National Scrapie Plan no longer operates in the UK. There are many more important diseases upon which to base genetic selection. Purchase sheep from flocks known to be free of scrapie but this is now a major concern.
Visna maedi virus (formerly maedi visna virus). In countries such as the UK, MVV flock control measures are limited to a relatively small number of pedigree flocks. No specific control measures have been adopted by commercial UK farmers for MVV. Purchase accredited pedigree sheep where necessary but no such commercial sheep are available.
There is no practical method to screen young sheep for Johne's disease and the best means of controlling disease is maintain a closed flock or continue to purchase stock from farms where disease has not arisen in their sheep but verification/certification is rarely available.
NADIS hopes that you have found the information in the article useful. Now test your knowledge by enrolling and trying the quiz. You will receive an animal health certificate for this subject if you attain the required standard.
