Predictors of carcass and meat quality are sought that can be measured in the live animal, preferably at a young age, on-farm, and with minimum stress to the growing animal. Several in vivo methods of assessing these traits indirectly in lambs have been developed, most of which are expensive and require restraint/handling of animals, which can cause stress and affect growth rate. This study investigates the use of linear dimensions obtained from video image analysis (VIA) to assess live weight, carcass composition and meat quality (MQ) in lambs of two divergent breeds, in a non-disruptive way.

Previous studies using X-ray computed tomography (CT) of Scottish Blackface hill ewes have shown that carcass fat, internal fat and muscle are depleted during pregnancy and early lactation and deposited during late lactation and the dry period (Lambe et al., 2003a). Muscle weights and proportions throughout the year are positively genetically correlated with total litter weight reared, largely due to increased litter size. Average weights of lambs reared were positively correlated with carcass fat weight or proportion pre-lambing and internal fat weight pre-mating, but negatively correlated with internal fat proportion pre-lambing (Lambe et al., 2005). However, is genetic potential to mobilise and regain increased amounts of tissue during the year positively associated with the ability to produce more and heavier lambs? The aim of this study was to address this question by relating total loss and gain of fat and muscle in ewes during the annual cycle with lamb production traits.

Computed Tomography (CT) is a non-invasive method used to provide accurate information on body composition of breeding animals. It is being applied in sheep breeding programmes in the UK to predict whole carcass composition in terms of muscle, fat, and bone. Previous studies established the equations to predict the total weights of muscle, fat and bone in different breeds from conventional CT scans. The average prediction accuracies were 92, 96 and 81% for muscle, fat and bone, respectively, in meat sheep and hill breed lambs (Young et al., 2001). Spiral CT scans provide a means of assessing directly the composition of the whole body and its different regions, in addition to muscularity and conformation. Although an automatic procedure to quantify the carcass components in cross-sectional images was developed previously, new software to segment images from spiral CT scans is now being evaluated. The aim of this study was to determine the accuracy of the automated image analysis in the estimation of total muscle volume of the hind leg, which is the most valuable joint.

Hill sheep breeds are required to survive and rear lambs in harsh conditions, and good maternal characteristics contribute to their success. However, improved carcass characteristics are also required to meet market requirements. This paper evaluates lamb performance characteristics after 4 years of selection using indexes tailored to improve overall productivity in different hill sheep production systems.

Computed tomography (CT) gives accurate in vivo estimates of sheep carcass composition based on information provided by cross-sectional CT reference scans (Young et al., 2001). Spiral CT is a novel imaging technology in which contiguous cross-sectional scans of a known thickness are collected. This data allows the reconstruction of images in three dimensions, giving the possibility of a comprehensive assessment of characteristics that are defined in terms of shape, such as conformation and muscularity. The development of automatic procedures for image analysis is of high priority due to the large amount of information contained in the spiral scans. The first step in image analysis is isolating the carcass components of each cross-sectional image, called segmentation. An algorithm to automatically segment the cross-sectional images in the spiral scan was developed, with the objective of investigating in vivo assessments of conformation and muscularity in sheep. The aim of this study was to compare the muscle areas obtained by manual and automatic segmentations.

Thirty cull Scottish Blackface ewes were scanned three times over a period of 1 week using X-ray computed tomography (CT). Cross-sectional CT reference scans were taken at seven anatomical sites per ewe: ischium (ISC), femur (FEM), hip (HIP), 5th lumbar vertebra (LV5), 2nd lumbar vertebra (LV2), 8th thoracic vertebra (TV8) and 6th thoracic vertebra (TV6). Ewes were then slaughtered and dissection measurements collected.

Results of multiple regression analyses suggested that five reference scans allow accurate prediction of total weights of bone, muscle and fat (carcass and internal). The most informative cross-sectional scans were ISC, HIP, LV5, LV2 and TV8, from which prediction equations were derived. Fat and muscle weights were predicted accurately (R2 = 80 to 99%) but bone weight was predicted less accurately (R2 = 56%). Repeatabilities were high for the CT measurements used to predict fat and muscle (0•82 to 0•99) but lower for those used to predict bone (0•19 to 0• 86).

Tissue depletion and repletion were investigated in 142 Scottish Blackface ewes using computed tomography (CT). Ewes of two ages (2 or 3 years) and differing reproductive status (barren, single- or twin-bearing) were studied through one annual production cycle to investigate mobilization of carcass fat (subcutaneous and inter-muscular), internal fat and muscle.

Ewes were CT scanned five times during the 1-year study period: pre-mating; pre-lambing; mid-lactation; weaning; pre-mating the following year. For each animal at each of the five scanning events cross-sectional CT scans were taken at five anatomical sites (ischium, hip, 5th lumbar vertebra, 2nd lumbar vertebra and 8th thoracic vertebra). CT images were analysed to yield areas of carcass fat, muscle and internal fat and total weights of these tissues were estimated at each scanning event using prediction equations derived from a separate calibration data set.

The results show that both carcass and internal fat depots were depleted during pregnancy and early lactation and repleted from mid-lactation to mating the following year. In proportionate terms, internal fat was most labile, but carcass fat contributed more to total weight change because it was a bigger fat depot. Subcutaneous fat was the largest and most labile of the carcass fat depots. Muscle reserves were depleted only when fat reserves had fallen to very low levels. Older ewes carried more carcass fat in total than younger ewes when reserves were low. Mobilization of tissue reserves in twin-bearing ewes was less than in single-bearing ewes, probably due to preferential feeding.

To what extent different fat depots of the carcass are more or less useful to the animal as readily labile energy stores is not clear. A knowledge of how ewes partition and use fat within the carcass is vital in order to estimate the impact of selection to reduce subcutaneous fat on other carcass fat depots. This study was designed to describe changes in the different carcass fat depots over one annual production cycle.