Ongoing Research & Development Projects

PROJECT TITLE: Towards a better understanding of using breeding to control mastisis in sheep and cattle.

DATE OF COMPLETION: June 2005.

PARTNERS: SLS Group, Texel Society

FUNDING: Genesis Faraday ‘Spark’ award.

INTRODUCTION: The purpose of the project was to investigate the opportunities for breeding for resistance to mastitis, to include the use of conventional breeding techniques, molecular genetic markers and other DNA-based technologies. The study was a desk-based review of published literature, and included a modelling component to investigate the economic impact of mastitis in UK sheep flocks.

FINDINGS:

• There is a dearth of genetic information relating to mastitis in meat sheep breeds. All such published knowledge is in dairy cattle and dairy sheep.

• The number of mastitis cases in sheep varies considerably, depending on the method by which they were recorded, on the breed and farm. Up to 46% of cull ewes were due to mastitis in one study, whereas others reported between 5% and 12% of all ewes in a flock having mastitis.

• The onset of mastitis can be at any time during lactation, although the majority of mastitis cases occur up to the first third of lactation. Mastitis that occurs during lactation is largely due to different pathogens than those responsible for mastitis after weaning, which in turn is closely associated with lack of environmental hygiene.

• The economic impact of mastitis in pedigree flocks was investigated using Markov-chain modelling techniques. Using a set of assumptions about key farm parameters that reflect lowland sheep production, including 10% incidence of mastitis, the economic impact per flock is estimated to be £11 per ewe at risk, or 6% of gross margin (GM)

• Some of the key parameters used in the model were sensitive to the analysis. These include the risk of getting mastitis, where a 50% increase (to 15%) leads to a £17 (9%) reduction in GM. Of greatest sensitivity of the assumptions tested was the reduced proportion of breeding stock sales if the ewe was mastitic (default setting was 0.33). If this setting was reduced by 50% to 0.165 then GM rose to £185/ewe, corresponding to a mastitis cost of £6/ewe. However, a 50% increase in this assumption reduced GM to £174/ewe (£17/ewe for mastitis).

• Due to the difficulties encountered from using cases of clinical mastitis (CM) as a breeding goal trait, many dairy breeding programmes currently use the proxy trait, somatic cell count (SCC) as an indicator of resistance to mastitis. SCC is measured in milk, and is positively correlated to CM as well as being an indicator of subclinical mastitis. SCC has a higher heritability (0.04-0.24) than CM (0.001-0.08), which makes SCC a better selection trait for inclusion into breeding programmes.

• The use of SCC in economic selection indexes for high yielding dairy cattle is critical, to stem the correlated increase in mastitis incidence that otherwise occurs. Even though there are no reports of antagonistic genetic associations among resistance to mastitis and production in meat sheep breeds, it is important that they are estimated if selection to reduce mastitis incidence is desirable.

• There are several studies on molecular markers and candidate genes for resistance to mastitis in dairy cattle, and some for dairy sheep. The majority of these genetic factors are located in the MHC gene complex, which is responsible for controlling immune mechanisms. Importantly, despite predictions of responses to selection using the marker(s), no reports were found of the impact that the use of these has on reducing mastitis in practice. This may be because either, (a) it is too soon to report the outcomes of using recently-discovered markers, (b) they are not being / not admitting to being used in selection programmes, or c) SCC is a cheaper and effective alternative.

• The information on markers and candidate genes from the dairy sector can be used along with robust screening methods to detect both clinical and sub clinical mastitis in the Texel breed. Then it is possible to use comparative mapping techniques that facilitate the knowledge cross-over between different animal species for the same or similar traits. It is anticipated that this method will then identify relevant genetic markers that are important for the Texel breed. These markers could be used on their own or integrated in existing breeding programmes. Despite the need to take milk samples from lactating ewes to detect the markers in the initial study, it is possible that their use can negate the need to continue with milk sampling in the future.

PROJECT TITLE: Breeding for resistance to Foot rot.

DURATION: 2005 - 2008.

PARTNERS: SLS Group, SAC Veterinary Services, Blackface Elite, MLC, CBS Technologies, Texel Society, ADAS, Rosemaund, Institute of Rural Sciences, Roslin Institute

FUNDING: This project was funded by EBLEX, QMS, HCC, SEERAD and Innovis through the SLP LINK programme with match funding from Defra

INTRODUCTION: The aim of this project, which has just started, is to develop robust procedures to identify individuals and family groups differing in their genetic resistance to footrot, to enable selective breeding for enhanced foot rot resistance. Using information from Blackface, Texel and Mule sheep, the project will use both molecular techniques and conventional animal breeding strategies to investigate the links between genetic susceptibility and phenotypic expression of foot rot. Together with a comprehensive assessment of the economic benefits of breeding for disease resistance, it will be possible to determine whether or not breeding for enhanced foot rot resistance is a practical and feasible option for the UK sheep industry.

This project will provide options to enable breeders to select animals for enhanced resistance to foot rot, combining both phenotypic measurement and molecular markers. Even in the event that the genetic markers are not sufficiently strongly associated with foot rot resistance in our breeds under UK environments, or they prove to be not economically viable, breeders will still have the option of using Best Linear Unbiased Prediction (BLUP)-based selection to maximise the utility of information from foot rot scoring

FINDINGS: Foot rot project update – May 2007

The main aim of the project is to determine the ‘best’ way to breed foot rot-resistant sheep and this combines information gathered ‘on the hoof,’ together with molecular information generated from blood samples.

Foot scores and blood were collected on Texel sheep on 19 farms between July and October in 2006. The majority of the flocks scored reflected the geographical spread of performance-recording flocks (centred in the north of England and south of Scotland, with some notable exceptions, shown on the map). A total of 3,603 Texel sheep were scored, (farms shown in orange, red and green on the map below) as well as Blackface (blue and green) and Mule (red and pink) sheep, representing a total of 38,584 feet (as all feet were scored separately).

In the Texel breed, the prevalence of foot rot averaged 29% in 2006, however this varied considerably, being less than 1% for a couple of flocks and more than 59% for the worst-affected flock. Interestingly, the results from the questionnaire (sent out to all prospective Signet-recorded Texel sheep society members to identify suitable flocks for foot scoring) were not in accordance with results from the foot scoring, as the flocks that had the highest levels of foot rot did not feel they had a foot rot problem on their farm, whereas the farmer who had the least foot rot, indicated that he had a ‘very bad’ foot rot problem in his Texel sheep. Therefore, Texel breeders who recognise foot rot as the serious economic or welfare problem may be more likely to take measures to reduce the occurrence of the disease in their flocks and so have lower prevalence of the disease.

PROJECT TITLE: Marker assisted selection applied to commercial sheep.

DATE OF SUBMISSION: June 2004.

PARTNERS: Roslin Institute, MLC, Texel Society, Suffolk Society, Charollais Society

FUNDING: LINK funded, with Government funding from Defra and SEERAD, Industrial funding (cash) from EBLEX, in-kind contributions from the Texel Sheep Society, Suffolk Sire Referencing Scheme Ltd and Charollais Sires Ltd.

INTRODUCTION: This is a 3-year project, aimed at taking forward previous QTL results obtained for Muscle Depth in commercial Texel, Suffolk and Charollais sheep. We aim to verify these findings in 'next-generation' sheep, and enable farmers to utilise these results in there breeding programmes('marker-assisted selection').

FINDINGS: After 15 months the project has been successful in recruiting enthusiastic Texel breeders into the project. Preliminary results confirm the QTL for muscle depth, and suggest that this QTL is present in more families than previously thought. We are now calculating EBV's for breeders that take account of background genetic effects as well as the QTL effect. Utilisation of these enhanced EBV's should enable breeders to make faster genetic progress. Additionally, we are currently seeking to verify QTL for nematode resistance in the same families.

PROJECT TITLE: The role of sire referencing schemes in terminal sire sheep to improve the carcase quality of crossbred lambs.

COMPLETED: May 2005

PARTNERS: SLS Group, Institute of Rural Sciences, ADAS Rosemaund, Texel Society

INTRODUCTION: Sire referencing schemes (SRS) are co-operative breeding programmes through which genetic links are created among member flocks by the mutual use of some rams (reference sires). These links allow for across-flock genetic evaluations creating a much larger pool of candidates for selection and thereby the opportunity for substantially quicker rates of genetic progress. Sire referencing schemes were introduced in terminal sire breeds in the UK in the early 1990s. Their goal has been to improve carcase quality by basing selection decisions on an index to improve lean growth rate. In the three largest schemes (Charollais, Suffolk and Texel), after just a decade of sire referencing, Lean Growth index score has increased by approximately 2% per annum.

Selection programmes in terminal sire breeds ultimately must focus on improving carcase quality in crossbred lambs under commercial finishing regimes. Given the progress achieved in index score within SRS, it is both timely and necessary to test the consequence of that progress on the composition of the carcases of crossbred lambs, and their retail value.

In 1997 Defra and the Meat and Livestock Commission (MLC), in collaboration with the Institute of Rural Sciences (IRS), SAC and ADAS, agreed to fund a long-term experiment – the Longwool Project – to develop breeding programmes relevant to crossing sire (Longwool) breeds. Its objective was to produce a selection index to improve carcase quality without compromising the reproductive performance or maternal ability of these breeds or their crossbred daughters.

The Longwool Project involved approximately 4,800 matings of Scottish and Welsh Mule ewes to terminal sire rams over four years (1999 through 2002) at research farms in England (ADAS Rosemaund), Scotland (SAC Edinburgh) and Wales (IRS Aberystwyth). This large resource of recorded Mule ewes provided a unique opportunity to conduct an extensive progeny test of high and low Lean Growth index rams chosen from within SRS in the most numerous meat sheep breeds (Charollais, Suffolk and Texel) in the UK. There were two aims of this progeny test: (i) to compare growth rate, carcase weight and carcase quality (as measured by fat and conformation score, carcase dissection and retail cutting) in commercially finished lambs sired by high versus low index rams; and, (ii) to evaluate the consequences of selection on this index on the finishing and marketing of crossbred lambs given current industry specifications.

The performance of approximately 6,500 terminal sire cross lambs was assessed in the research. These lambs were progeny of 90 Charollais, Suffolk and Texel rams, half high index and half low index, purchased from the respective SRS in these breeds between 1999 and 2002. The lambs were born in March/April each year with live weights recorded at birth, at 5 weeks, 10 weeks, and 16 weeks (weaning) of age, and once they achieved a target finish condition of 3L. At finish, the lambs were ultrasound scanned for muscle and fat depths and visually assessed for conformation. They were then slaughtered at one of two commercial abattoirs [Hamer International Ltd for lambs from ADAS and IRS, and ABP Ltd (Scotland) for lambs from SAC] where carcase weight, conformation and fat score, and estimated subcutaneous fat percentage were recorded. About 1,000 of the carcases were transported to the University of Bristol for further carcase evaluation. The right side of each carcase was processed into retail cuts (including leg steaks, cutlets and chops) while the left side of each carcase was dissected into lean, fat and bone.

FINDINGS: By 10 weeks of age, offspring of high index sires were 0.44 kg heavier than offspring of low index sires.
High index lambs were 1.1 kg heavier in live weight at target finish (3L), which they achieved at a similar age (169 days) as low index lambs.

High index lambs had thicker muscle depths as measured by ultrasound than low index lambs.

Carcases from lambs with high, in contrast to low, index sires had more favourable MLC fat scores, with fewer of the high index carcases being assessed as over-fat (above a 3L).

Assessments on conformation based on the EUROP score suggested carcases from high index lambs were slightly less well conformed although a more detailed 15-point conformation score assigned in the abattoir suggested otherwise.

Cold carcase weights were 0.56 kg more in lambs from high as compared to low index rams.

On average, high index lambs yielded 0.47 kg more saleable meat which translated into increased weights of leg steaks, cutlets and chops.

In 2004, an extra kg of carcase weight was worth £2.62. Since the offspring of high index rams produced an extra 0.56 kg of carcase weight, this corresponds with an increased sale value of £1.47 each. If a ram is used for 3 years, and mated to 50 ewes each year, it would sire approximately 240 reared lambs over its lifetime. Thus a single high index ram would earn an extra £353 for a commercial sheep farmer. On an industry basis, where approximately 10.1 million terminal sire cross lambs are marketed annually, use of high index rams could generate nearly £15 million in additional income to UK sheep producers. Given the higher value of retail meat, the potential return from the increase in saleable meat yield is nearly twice that amount.

These results clearly indicate that selection on Lean Growth index produces crossbred lambs with heavier carcases that yield more saleable lean meat that could generate substantially higher market returns. The wider uptake and use of such breeding technologies would allow the UK sheep industry to increase its competitive edge in meeting domestic and European-wide market demands for quality lean lamb.

Yet, for these benefits to be fully realized, the current system for lamb marketing in the UK needs to be re-assessed. Lamb is marketed based on weight and visual assessments of conformation and fatness. Carcases outside target specifications, including a prescribed weight range, are penalised. This research documented that crossbred lambs sired by high index terminal sire rams can produce carcases at weights exceeding target without becoming overly fat. A consistent mechanism by which sheep producers and meat processors can benefit from that opportunity is thus needed. This likely involves developing: (i) additional lamb products that generate added-value from the cutting of heavier yet lean carcases for the wholesale (e.g. catering; restaurant) and retail (e.g. supermarket) trade; and, (ii) crossbreeding systems by which terminal sire and Mule ewe enterprises co-operate to consistently produce heavier lamb weights (e.g. greater than 28 kg carcasses) to service this trade with an assured market premium. Research in product development and the design of co-operative crossbreeding programmes is therefore needed. In addition, a major knowledge transfer programme focused on improving dialogue and commitments among sheep farmers, abattoirs and processors is a requisite for such opportunities to result in mutual benefits throughout the industry.