Research and Development s9

Department for Environment, Food and Rural Affairs CSG 15

Research and Development

Final Project Report

(Not to be used for LINK projects)

Two hard copies of this form should be returned to:
Research Policy and International Division, Final Reports Unit
DEFRA, Area 301
Cromwell House, Dean Stanley Street, London, SW1P 3JH.
An electronic version should be e-mailed to
Project title / To investigate the use of X-ray CT scanning in the prediction of carcass
conformation in hill sheep & to use this information in a breed improvement programme
DEFRA project code / LS0202
Contractor organisation and location / ADAS Consulting Limited, ADAS Redesdale
Rochester, Otterburn
Newcastle on Tyne, NE19 1SB
Total DEFRA project costs / £ 199,606
Project start date / 01/10/97 / Project end date / 31/03/02
Executive summary (maximum 2 sides A4)
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CSG 15 (Rev. 6/02) 2

Hill sheep, as well as having a major role in maintaining the rural environment and economy of upland areas are, because of the stratified structure of the UK sheep industry, the second most important genetic contributors to total slaughter lamb carcasses. Traditionally, hill sheep have been selected for their ability to survive and produce lambs in harsh environments. This has tended to favour the development of smaller and hardier breeds which produce carcasses of small size and of moderate conformation which do not achieve the target carcass specification for the main domestic and export markets. It is against this background, with Defra-funding, that ADAS Redesdale is collaborating with the Institute of Rural Studies, Aberystwyth in a long-term experiment which aims, through genetic selection, to improve the carcass quality (weight and conformation) of hill sheep.

Within this project, good progress had been made in increasing carcass weights but progress towards improving carcass conformation was being hampered by inadequate live animal measures of carcass conformation. Developing a more accurate predictor of conformation in live animals was fundamental to the success of this and other breed improvement projects which aim to improve carcass conformation. X-ray Computer Tomography (CT) is an imaging technology developed for medical applications but its use in animal science, including measures of carcass traits in live animals, is becoming better understood. Work to date has concentrated on using CT for assessing carcass composition in sheep and has been confined to mainly terminal sire breeds. No information was available on the use of CT for predicting conformation in live hill lambs nor on its applications within a breed improvement programme for carcass conformation of hill sheep maintained under harsh environments. The aims of this experiment were to establish CT scanning protocols for predicting conformation in live Scottish Blackface sheep and to use this information, incorporated into an appropriately designed selection index, within the established breed improvement programme for carcass quality in Scottish Blackface sheep at ADAS Redesdale.

In 1997, eighty lambs were selected from a number of ADAS Redesdale’s commercial flocks (to provide maximum variation in the measured parameters) and these were used to calibrate the X-ray CT scanner. Lambs used for the calibration study were also subjected to half-carcass and joint tissue dissection. Originally, it was planned that from 1998 to 2001, on average 250, lambs born to nucleus flock and control flock ewes combined would be CT scanned in late August/early September each year. This was achieved in 1998, 1999 and 2000 but, due to movement restriction imposed as a consequence of foot and mouth disease (FMD), was not achieved in 2001. Totals of 250, 247 and 264 lambs were CT scanned in 1998, 1999 and 2000 respectively. For the calibration study, CT scans were taken from: caudal ischium, ISC (gigot), mid-femur, FEM (gigot), hip joint, HIP (gigot), 5th lumbar vertebra, LV5 (loin), 2nd lumbar vertebra, LV2 (loin), 8th thoracic vertebra, TV8 (chest/shoulder) and 6th thoracic vertebra, TV6 (chest/shoulder). For the routine CT scanning done in 1998, 1999 and 2000, CT scan information was collected for ISC, LV5 and TV8 only. In addition to CT scan information, a number of field assessments including live weight, ultrasonic muscle depth and width, and fat depth were made on each lamb..

These data collectively were used to establish the effectiveness of CT scanning to predict tissue proportions in the whole and specific regions of the carcass and to derive a selection index incorporating CT scan information to improve carcass conformation as part of a breed improvement programme.

To develop an effective selection index requires estimates of means, phenotypic standard deviations, heritabilities and correlations (phenotypic and genetic) for and between a large number of carcass and production variables. These were obtained from several sources. Firstly, animals from the calibration study provided base phenotypic data as did information collected on nucleus and control flock lambs CT scanned in 1998 and 1999. Secondly, the SAC Hill Sheep database provided 1352 records on field performance (including ultrasound measurements) and shoulder dissections after slaughter for Blackface lambs. Of these, 399 lambs had full half-carcass dissections. Finally, relevant data from the literature were used to provide additional information on some traits.

It has been possible to establish that ischium (ISC), lumbar (LV2 & LV5) and thoracic (TV6 & TV8) CT scans were the best predictors of absolute tissue weight and tissue proportions across the entire carcass. Leg muscle and bone tissue weights and proportions were best predicted from the ISC scan while fat weight was better described by the hip (HIP) or femur (FEM) CT scans. LV5 was the best predictor for all tissue weights and proportions in the loin. In the thorax, both TV (6 & 8) CT scans returned similar accuracies for tissue weights and proportions. The results clearly showed that CT scans gave results superior to subjective conformation scoring, ultrasound and the other in vivo techniques used for predicting absolute carcass tissue size, carcass tissue %, and tissue distribution. Furthermore, CT described conformation more independently of fat and live weight than did MLC conformation scores.

The calibration study also indicated that a more rigorous description of conformation and its components would be needed before CT scan information could be successfully incorporated into a selection index to improve carcass conformation. From the literature, a number of important points were identified which should be addressed in any selection index designed to improve carcass conformation. In developing a selection index to improve carcass conformation within this project, it was decided therefore that conformation was a function of body composition (fat (F) %, bone (B) % and muscle (M) %), regional tissue distribution and tissue shape (muscularity). To be successful, any selection strategy for conformation must simultaneously increase both M:B and M:F ratios. From over 250 derived selection indices, it was possible to identify one which in theory at least achieved these objectives.

A selection index incorporating CT scan information (CT index) was used to select nucleus flock replacements for the first time in 1999. Data derived from two lamb crops only have provided an early indication that this selection index will be successful in improving carcass conformation of hill sheep. Carcass conformation of nucleus flock lambs is significantly better than that of control (unselected line) lambs after only two intakes of animals selected using the revised CT index. While this is a very encouraging result, it can only be validated fully by evaluating further lamb crops bred using the CT index. It is recommended, therefore, that the study be continued in its present form for a further two years.

CSG 15 (Rev. 6/02) 2

Project
title / To investigate the use of X-ray CT scanning in the prediction of carcass
conformation in hill sheep & to use this information in a breed improvement programme / DEFRA
project code / LS0202
Scientific report (maximum 20 sides A4)
To tab in this section press the tab key and the Control key together
Press the DOWN arrow once to move to the next question.

CSG 15 (Rev. 6/02) 2

INTRODUCTION

Hill sheep, as well as having a major role in maintaining the rural environment and economy of upland areas are, because of the stratified structure of the UK sheep industry, the second most important genetic contributors to total slaughter lamb carcasses (MLC, 1988). Traditionally, hill sheep have been selected for their ability to survive and produce lambs in harsh environments. This has tended to favour the development of smaller and hardier breeds which produce carcasses of small size and of moderate conformation which do not achieve the target carcass specification for the main domestic and export markets (Merrell and Haresign, 1996).

It is against this background, with initially MAFF-funding and latterly Defra-funding, that ADAS Redesdale is collaborating with the Institute of Rural Studies, Aberystwyth in a long-term experiment which aims through genetic selection to improve the carcass quality (weight and conformation) of hill sheep. Within this project, good progress had been made in increasing carcass weights but progress towards improving carcass conformation was being hampered by inadequate live animal measures of carcass conformation (Merrell, 2001). Developing a more accurate predictor of conformation in live animals was fundamental to the success of this and other breed improvement projects which aim to improve carcass conformation. Whereas ultrasonic measures of fat depth and muscle depth or area have been shown to enhance the accuracy of selection for lean meat production (Simm, 1992), these measures are proving inadequate for selection for carcass conformation in this project.

X-ray Computer Tomography (CT) is an imaging technology developed for medical applications but its use in animal science, including measures of carcass traits in live animals, is becoming better understood. Work to date has concentrated on using CT for assessing carcass composition in sheep (Simm and Dingwall, 1989) and has been confined to mainly terminal sire breeds (Vagen and Jopson, 1996). In addition, muscularity is increasingly being advocated as preferable to conformation as a measure of the shape of lamb carcasses (Jones et al., 2002). This is because, unlike conformation, muscularity when defined as 'the thickness of muscle relative to skeletal dimensions (de Boer et al., 1974) is independent of carcass fatness’. CT scan information provides potentially an ideal means by which to assess accurately muscularity. No information was available on the use of CT for predicting conformation in live hill lambs nor on its applications within a breed improvement programme for carcass conformation of hill sheep maintained under harsh environments.

The aims of this experiment were to establish CT scanning protocols for predicting conformation in live Scottish Blackface sheep and to use this information, incorporated into an appropriately designed selection index, within the established breed improvement programme for carcass quality in Scottish Blackface sheep at ADAS Redesdale.

MATERIALS AND METHODS

Animals and husbandry

Purebred Scottish Blackface male and female lambs drawn from a number of commercial flocks and from a selected (nucleus) and unselected (control) flock maintained at ADAS Redesdale were used for this study.

In 1987, eighty lambs were selected from a number of ADAS Redesdale’s commercial flocks (to provide maximum variation in the measured parameters) and these were used to calibrate the X-ray CT scanner. The management of these lambs was typical of a progressive Northumberland hill farming system. Following pregnancy diagnosis in late February, twin-bearing ewes were housed and single bearing ewes continued to graze areas of semi-natural rough grazing (SNRG). After lambing, ewes with twin lambs were initially turned out to sheltered, improved pastures before being transferred back to SNRG on average 28 days after lambing. Single bearing/rearing ewes lambed outdoors and the lambs were reared on SNRG throughout. The lambs were weaned in August and this approximately coincided with them being CT scanned.

The management of lambs born to nucleus and control flock ewes was similar to that described for commercial flocks at ADAS Redesdale with two notable exceptions. To increase rates of genetic gain, for the nucleus flock, artificial insemination and Multiple Ovulation and Embryo Transfer (MOET) techniques were used and lambs were therefore born to surrogate mothers. As recipient ewes were implanted with a single embryo only, the majority of lambs (>75%) were reared as single lambs. Only those ewes that failed to conceive to MOET and were mated naturally at the next oestrous cycle or were control flock ewes (which were naturally mated only) had any chance of producing twin lambs. Using MOET necessitated some minor changes to normal management and husbandry. All nucleus (donor) and recipient ewes were transferred from SNRG to inbye field initially and then housed for a short period immediately before and during the mating period. This was done for the induction of superovulation and to facilitate semen collection, AI, embryo collection and embryo transfer. Control flock ewes were confined to inbye fields at this time to facilitate pedigree mating by natural service. To facilitate management at lambing time, all recipient and control flock ewes were housed immediately before the start of lambing, and were returned to SNRG within ten days after lambing.

Originally, it was planned that from 1998 to 2001, on average, 250 lambs born to nucleus flock and control flock ewes combined would be CT scanned in late August/early September each year. This was achieved in 1998, 1999 and 2000 but, due to movement restriction imposed as a consequence of foot and mouth disease (FMD), was not achieved in 2001. Totals of 250, 247 and 264 lambs were CT scanned in 1998, 1999 and 2000 respectively.