HEALTH STATUS. Updated: 03/06/2008
The LOWERYE flock is of a high health status and are eligible for export of semen to most countries (and hopefully embryos in the future, once regulations allow). Both pedigree and commercial flocks are MV accredited and Scrapie Monitored. All females and stock sires are of a known scrapie genotype.
Maedi-Visna (MV) is an incurable wasting pneumonia with an incubation period of several years. The disease is primarily spread through contact (being carried on the breath) but can also be passed through blood and colostrum. The accreditation scheme run by the Scottish Agricultural Colleges (SAC) entails routine blood testing of all sheep over 1 year old, or in larger flocks a proportion of all ewes over 1 year old and all rams/new additions to the flock. The flock must be kept segregated from all non-scheme sheep at all times. Separate equipment and housing must be used for the flock unless thorough disinfection is carried out. Show and sale premises are inspected and approved prior to acceptance of accredited stock otherwise accredited status will be lost. If this status is lost then the offending animals or the whole flock must be isolated and be given two tests with an interval of not less than 6 months. This scheme, which was previously administered by the Ministry of Agriculture (MAFF), has prevented the spread of what could be a potentially catastrophic disease in the UK.
Scrapie is an notifiable, incurable brain disease of sheep and goats that has been recorded for several hundred years. It is a similar disease to BSE in cattle and as such, control or eradication has received fresh importance in recent years. MAFF run a Scrapie Monitoring Scheme that entails regular inspections of the flock by a veterinary surgeon and the post mortem analysis of sheep's brains from a proportion of the flock each year to look for evidence of the disease. Flocks proven to be free of the disease are put on to a 'Temporary Scrapie Export Register'. Inclusion on that register is a prerequisite of export of sheep semen and embryos to most countries. Membership of the scheme requires all monitored sheep to be segregated from non scheme sheep (as in the MV scheme). Females cannot be brought into the flock unless they are from another scrapie monitored flock.
During the last few years a genetic test has been developed, Scrapie Genotyping, that involves a small blood sample being taken for DNA analysis. Resistance to scrapie in Charollais sheep has been found to be dependant on the variation of the DNA at codons 136 and 171. Put simply (I'm not a geneticist!), codon 136 can be either A or V, while codon 171 can be Q or R. A sheep will inherit DNA strands from both sire and dam and it's scrapie genotype is expressed as the variation on those codons on each of those strands. Variations are such that the Charollais sheep's genotype can be any of the following:
Strength of resistance is such that there has never been a case of scrapie identified in a sheep with a genotype of ARR/ARR.
This genetic variation is inheritted in such a way that if an ARR/ARR ram is mated to an ARR/ARR ewe, all offspring will be ARR/ARR. If an ARR/ARR ram is mated to an ARR/ARQ ewe, half of the progeny will be ARR/ARR and half will be ARR/ARQ. If an ARR/ARR ram is mated to an ARQ/ARQ ewe, all lambs will be ARR/ARQ. Using an ARR/ARR ram on all ewes will therefore increase the incidence of the scrapie resistant genotype in the flock and, eventually, all sheep will be of the resistant genotype. This will reduce the incidence (some think even eradicate) of this terrible disease.
The Lowerye flock was one of the very first to bite the bullet on scrapie genotyping even though we have never had a clinical case of scrapie on the farm. In 1997 we tested all the females and stock rams in the flock and have since sampled all introduced females whose genotype we could not predict. We also routinely test all potential stock sires each year. Unlike many other flocks that have since 'jumped on the bandwagon', we have not disposed of good females purely for having a susceptible genotype, preferring to keep as wide a pool of genetics in the flock as possible and breed their resistance up. This can, after all, be done in as few as 2 generations. We consider that, although scrapie resistance must be the way forward, the most important attributes of the British Charollais are the terminal sire traits and these must not be lost in order to reduce the incidence of an already rare disease.
The Department of the Environment, Food and Rural Affairs (DEFRA) launched, in Spring 2002, the National Scrapie Plan in an attempt to eradicate the disease from the UK. The plan will involve the large scale genotyping of stock sires in an initially voluntary scheme that will later (most think sooner rather than later) become compulsory for ram producers. The intention was for the scheme to be up and running by the Spring of 2001 but the outbreak of foot and mouth disease in the UK postponed this until the following Spring. I understand that a similar scheme is already in operation in several EU countries.
In February 2002 the National Scrapie Plan (NSP) tested 80 shearling rams and 80 of our December born ram lambs for scrapie genotype. I was pleased with the results obtained in that we only had to cull 3 ram lambs (onto a good Easter trade) and one shearling ram was vasectomised for use as a teaser. All sheep tested had at least one copy of the ARR genotype and only these four had a VRQ genotype and all were from bought in ewes. All of these ewes have now been culled along with any ewes that had been tested ARQ/ARQ, a decision made very much easier by an extremely buoyant cull ewe trade. 80% of the 2001 and 2002 females retained are genotyped ARR/ARR, with the remainder being ARR/ARQ. The intention is to head towards a flock of R1 sheep while preserving the valuable genetics from the less resistant sheep, indeed before culling out the last of the QQ ewes, RQ daughters were retained from most.
The remainder of the 2002 ram lambs (January born) were tested in April with a similar percentage of ARR/ARR lambs and none that had to be culled.
The winter of 2002 saw the introduction of the Ewe Genotyping Scheme by DEFRA where NSP members could have a number of female sheep genotyped for free (apart from the vet's charge for taking blood samples) for management purposes. We tested all of our potential replacement ewe lambs and any ewes that had not been genotyped on codon 136 and which may have harboured a "V" on that codon. We found just 2 ewes that were genotyped ARR/VRQ, which have since been culled.
In the summer of 2003, we again tested the ram lambs and found 85 out 100 to be of the most resistant genotype ARR/ARR. Of the 65 ewe lambs that we retained only 3 are R2, the remainder being R1. Testing in the Spring of 2004 has shown that over 90% of the ram lambs are now R1, the remainder being R2.