N.R. Lambe

Prediction of lamb carcass composition and meat quality using combinations of post-mortem measurements.

Various post-mortem measurements (carcass weights, conformation and fatness classes, external carcass dimensions, eye muscle dimensions, subcutaneous fat depth, pH and temperature) were recorded on 197 Texel (TEX) and 200 Scottish Blackface (SBF) lamb carcasses. The potential use of these measurements to predict carcass composition and key meat quality traits was investigated, to enable categorisation of carcasses in the abattoir and/or for use in genetic improvement programmes. By combining different measurements, accurate predictions of dissected carcass muscle weight (adjusted R(2) 0.93 in TEX, 0.88 in SBF) and fat weight (adjusted R(2) 0.84 in TEX, 0.87 in SBF) were achieved, and moderate predictions of intra-muscular fat (adjusted R(2) 0.56 in TEX, 0.48 in SBF), whilst shear force was predicted with low to moderate accuracy (adjusted R(2)<0.33 across breeds and cuts). Sex, eye muscle dimensions and subcutaneous fat depth improved predictions of carcass composition and intra-muscular fat, whilst pH or temperature provided little additional benefit for these traits, but increased prediction accuracies for shear force. These results could contribute to the development of automated carcass grading systems or help inform breeding decisions.

In vivo measurements of muscle volume by automatic image analysis of spiral computed tomography scans

This study investigates the accuracy of an automatic image analysis method that was developed for spiral computed tomography scans (SCTS), with the objective of calculating the volume of muscle in the hind leg (HLMV CT ) and lumbar region (LRMV CT ) in lambs. The first step in the image analysis method was the isolation (segmentation) of the muscle regions in each image of the SCTS, using a new program that was implemented in the Sheep Tomogram Analysis Routines software (STAR). Due to the differences of muscle shape in the regions investigated, the new segmentation program applies different segmentation paths in specific subregions. These were automatically identified by the program based on skeletal landmarks. After the segmentation was completed, the muscles areas were automatically measured by counting the pixels representing muscle in each image; the volumes were calculated by adding the muscle areas of each image multiplied by the depth of the image (inter-slice distance). The accuracy of these measures of muscle volume was evaluated, using regression analysis, by comparing HLMV CT and LRMV CT to the hind leg and lumbar region muscle weights measured after dissection (HLMW D , no. =240, and LRMW D , no. =50, respectively) of Texel (TEX) and Scottish Blackface (SBF) female and male lambs slaughtered in 2003-04. The effects of breed, sex and year on the association (SCTS v . dissection) were evaluated. There was a strong association between HLMV CT and HLMW D ( R 2 =97·4%), which only increased slightly ( R 2 =97·7%) when breed was included in the model. This indicates that HLMW D can be estimated directly from HLMV CT with a high degree of accuracy. For the lumbar region, the association was high ( R 2 =83·0% to 88·8% depending on the model) but lower than in the hind leg, probably because the automatic segmentation isolates only the areas of the longissimus lumborum and multifidi muscles. Breed had a significant effect on the prediction of LRMW D from LRMV CT , as well as sex in the case of the TEX lambs. The results indicated that the predictions of LRMW D from LRMV CT require different equations for very divergent breeds such as TEX and SBF.

Muscularity and eating quality of lambs: Effects of breed, sex and selection of sires using muscularity measurements by computed tomography

Differences in muscularity of the hind leg (HL) and lumbar region (LR) were investigated between sexes (ram vs ewe lambs), breeds (Scottish Blackface, SBF vs Texel, TEX) and progeny of high- and low-muscularity sires (HM, LM) (n=471). The influence of these factors on meat eating quality (MEQ) was also examined (n=229). TEX lambs had 16% greater muscularity than SBF in both regions, whilst differences between sire groups were 4%. Ewe lambs had slightly higher values of muscularity for the HL than rams, but values were similar for the LR. Meat from SBF lambs had higher tenderness, stronger lamb flavour and higher overall liking than TEX meat. Sex had a weak influence with ram lambs having a stronger abnormal flavour and lower overall liking in the LR only. No significant differences in MEQ were found between HM- and LM-sired lambs, suggesting that improvements in muscularity would not have unfavourable effects on MEQ.

Prediction of total body tissue weights in Scottish blackface ewes using computed tomography scanning

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 (R 2 = 80 to 99%) but bone weight was predicted less accurately (R 2 = 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).

Testing selection indices for sustainable hill sheep production – lamb growth and carcass traits

Two selection indexes, one intended for lamb producers and finishers and one for store lamb producers, were derived using genetic parameters for carcass and maternal characteristics from Conington et al. (2001) and economic values from Conington et al. (2004). This paper summarizes responses to selection for lamb traits only, after 5 years of selection (1998 to 2003) on two farms using these selection indexes. The index for lamb producers and finishers, evaluated on farm 1, with a flock size of 680 ewes, includes economic weightings for maternal traits as well as carcass weight, fat and conformation grades, whereas the index for store lamb producers, evaluated on farm 2, with a flock size of 580 ewes, only includes economic values for maternal traits and lamb growth to weaning. Three selection lines of Scottish Blackface sheep per farm were created with the first lambs born to each line in 1999. These lines were selection (S), control (C) and industry (I); they were of equal size on each farm. Five top- and five average-performing ram lambs were selected each year for the S and C lines respectively using a multi-trait best linear unbiased prediction (BLUP) implementation of the indexes. The I-line used four mature rams bought from industry, selected on appearance only, i.e. adherence to breed ‘type’. Results showed that 5 years after the implementation of the index, the S line had significantly higher index scores than the C or I lines on both farms. The means (s.d.) for the average index scores in 2003 are 114 (328), 119 (371) and 451 (328) (farm 1), and −8 (146), −11 (130), and 250 (129) (farm 2) for the C, I and S lines, respectively, giving predicted net differences (S-C) of £3·38 (farm 1) and £2·58 (farm 2) per ewe. Phenotypic responses showed significant S v. C differences in weaning weight on both farms. As predicted from previous analyses, no changes in carcass quality traits were seen at farm 1 although S-line carcass weights tended to be heavier than those from the C or I lines. The results show that genetic improvement using multi-trait selection indices has been successful and it is a viable, long-term strategy to improve levels of production for hill sheep in extensive environments.

Evaluating the effects of a single copy of a mutation in the myostatin gene (c.*1232G > A) on carcass traits in crossbred lambs

This study evaluated the effects of the ovine c.*1232G>A myostatin mutation (MM) on carcass traits in heterozygous crossbred lambs sired by Texel and Poll Dorset rams using ultrasound, CT scanning, carcass classification and VIA. In experiment 1, MM was associated with increased loin depth (+2.8%) and area (+3.2%). MM-carriers had significantly higher CT-estimated lean weight and proportion (2 to 4%) and muscle to bone ratio (by ~3%), in both experiments, and muscle to fat ratio (28%) in experiment 2. Muscle areas in three cross-sectional CT scans, were higher (2 to 5%) in MM-carriers. In experiment 2, fat-related measurements were significantly lower in MM-carrier lambs but this was not seen in experiment 1. A significant increase in muscle density, indicative of lower intramuscular fat, in MM-carriers shows that meat quality characteristics need attention. Carrying MM significantly decreased carcass fat scores. VIA did not detect any significant MM effects.

Use of meat quality information in breeding programmes

This chapter discusses the inclusion of meat quality information in livestock breeding programmes which could provide permanent and cumulative genetic improvements in these traits with continued selection. Reasons why meat quality information is not more widely used in current breeding programmes are considered. Measurement techniques, genetic parameters and breeding programme designs that could be exploited to successfully incorporate meat quality traits are discussed, as well as suggestions of possible future directions for the inclusion of meat quality traits in livestock breeding programmes.

Seasonal changes in tissue weights in Scottish Blackface ewes over multiple production cycles

Hill ewes undergo large changes in body fat and muscle weight throughout the annual production cycle as they contend with the pressures of reproduction and lactation, as well as harsh environmental conditions. This study modelled seasonal changes in fat and muscle weights in Scottish Blackface hill ewes throughout their productive lifetime using random regression statistical techniques. Scottish Blackface ewes (no. = 308) were scanned using computed tomography (CT) four times per year, from 2 until 5 years old. Heritabilities of tissue weights were estimated at 2-weekly intervals throughout the productive life of the ewe. Genetic correlations between tissue weights at the same point in the production cycle at different ages, and between tissue weights at different events within each annual production cycle were predicted. Animal solutions from random regression analyses were used to estimate tissue weights, from pre-mating at 2 years old to weaning at 5 years old. The effects of litter size in the current and previous production years on fat and muscle weights were investigated. Correlations between CT tissue weights and those predicted by a sin/cos random regression model were 0.87, 0.84, 0.88 for carcass fat, internal fat and muscle respectively. Heritabilities ranged from 0.31 to 0.90 for carcass fat weight, 0.21 to 0.68 for internal fat weight and 0.26 to 0.57 for muscle weight, throughout the productive lifetime of the ewe. Heritabilities were highest during mating for fat weights, and during the dry period and lambing time for muscle weights. Heritabilities of tissue weights in 3-year-old ewes were higher than in other age groups. Genetic correlations were 1.00 between tissue weights at the same scanning event at different ages, but ranged from close to zero to 0.97 between scanning events within age groups. Clearly environmental variation across time was large. The number of lambs produced in both the current and the previous year influenced tissue levels. Ewes that did not produce lambs (barren) in a given year carried more muscle during that year than ewes producing lambs. As ewes aged, barren ewes carried increasingly more carcass fat and muscle than ewes with lambs. Barren ewes also had significantly more muscle during the following year than ewes that had weaned lambs. Ewes that reared twins had significantly less carcass fat the following year than singleton-bearing or barren ewes. These effects of previous litter size increased significantly with age.

The effect of conditioning period on loin muscle tenderness in crossbred lambs with or without the Texel muscling QTL (TM-QTL)

A Texel muscling quantitative trait locus (TM-QTL) has been identified on chromosome 18, which increases loin muscling, but may also have a negative impact on mechanically-measured loin tenderness in crossbred lambs, depending on conditioning time. This study investigated the influence of a range of conditioning times (3, 5, 7 or 9 days) on the effect of TM-QTL on loin muscle tenderness. Using Texel rams heterozygous for TM-QTL, mated to non-carrier Mule ewes, heterozygous (n=45) and wild-type (n=50) crossbred lambs were produced. Weight of the valuable Longissimus lumborum muscle was higher in TM-QTL carriers than non-carriers, when compared at a fixed age (+11.5%; P=0.038), with the same trend at a fixed carcass weight (+10.2%; P=0.064). Toughness, measured by shear force, was significantly higher in samples from TM-QTL carriers than non-carriers, after conditioning for 3 days (P=0.002), 5 days (P=0.003) or 7 days (P=0.03), but was not significantly different after 9 days of conditioning (P=0.32). Compared to non-carrier lambs, the proportion of samples above consumer acceptability thresholds for toughness was greater in the TM-QTL carrier lambs after 3 and 5 days of conditioning, similar at 7 days, but lower at 9 days. The results suggest that the negative effect of TM-QTL on loin tenderness in crossbred lambs can be overcome by conditioning for more than 7 days. Marketing of TM-QTL carrier lambs through companies that use enhanced processing protocols could be beneficial, due to higher loin muscle weights, without negative effects on meat quality.

Beef primal cuts expressed as proportions of overall matured carcass weights (carcass balance) in Aberdeen Angus cross and Limousin cross steers and heifers

Introduction “Carcass balance” or the proportion of overall beef carcass weight that is present in various primal cuts in both the hindquarter (HQ) and forequarter (FQ) segments has a considerable effect on the commercial value of each carcass. As part of a wide ranging study to examine animal performance and quality attributes of beef cattle, the objective of the current experiment was to quantify the proportions of various primal cuts within beef carcasses from both Aberdeen Angus cross (AAx) and Limousin cross (LIMx) steers and heifers slaughtered through a commercial abattoir.