GR Tissue Research Articles

Accreditation of in-abattoir Dual Energy X-ray Absorptiometry scanning apparatus to predict lamb carcass composition in Australia

Dual Energy X-ray Absorptiometry (DXA) scanners operating at abattoir processing speeds are currently installed in six sheep meat abattoirs around Australia, predicting carcass composition as estimates of computed tomography (CT) determined fat %, lean %, and bone %. This study tested an updated bone-detection algorithm for these DXA scanners. This algorithm improved the precision of prediction for carcass fat% and lean%, but most notably for bone % (R2 = 0.92, RMSE = 0.61 %), compared to the previous algorithm (R2 = 0.51, RMSE = 1.57 %). This was due to improved allocation of bone-containing pixels, resulting from the inclusion of tissue thickness in the bone-detection equation. In a second experiment, the predictions from this new algorithm, along with an automated phantom calibration technique, were assessed relative to their ability to meet the AUS-MEAT accreditation accuracy standards required for predicting CT determined carcass fat%, lean%, and bone%. The DXA met these standards for predicting fat % (range 10.9 % - 37.1 %), lean % (range 49.0 % - 66.2 %), and bone % (range 11.6 % - 25.0 %), across three weight bands of light carcasses (<22 kg), mid-weight carcasses (22-28 kg), and heavy carcasses (>28 kg). This work allowed for the accreditation of DXA, enabling its predictions of carcass composition to be used for trading sheep carcasses in Australia. The accuracy of these predictions far exceed those provided by the historical industry measure of GR tissue depth, and hot carcass weight.

Ultra-wideband microwave precisely and accurately predicts sheepmeat hot carcase GR tissue depth

A portable ultra-wideband microwave system (MiS) coupled with an antipodal slot Vivaldi patch antenna (VPA) was used as an objective measurement technology to predict sheep meat carcase GR tissue depth, tested against AUS-MEAT national accreditation standards. Experiment one developed the MiS GR tissue depth prediction equation using lamb carcasses (n = 832) from two slaughter groups. To create the prediction equations, a two layered machine learning stacking ensemble technique was used. The performance of this equation was tested within the dataset using a k-fold cross validation (k = 5), which demonstrated excellent precision and accuracy with an average R2 of 0.91, RMSEP 2.11, bias 0.39 and slope 0.03. Experiment two tested the prediction equation against the AUS-MEAT GR tissue depth accreditation framework which stipulates predictions from a device must assign the correct fat score, with a tolerance of ±2 mm of the score boundary, and 90% accuracy. For a device to be accredited three measurements captured within the same device, as well as measurements across three different devices, must meet the AUS-MEAT error thresholds. Three MiS devices scanned lamb carcases (n = 312) across three slaughter days. All three MiS devices met the AUS-MEAT accreditation thresholds, accurately predicting GR tissue depth 96.1–98.4% of the time. Between the different devices, the measurement accuracy was 99.4–100%, and within the same device, the measurement accuracy was 99.7–100%. Based on these results MiS achieved AUS-MEAT device accreditation as an objective technology to predict GR tissue depth.

Improved cut weight predictions from DEXA scans of lamb carcasses enables more accurate allocation of cuts to processing plans

The value of precise dual energy X-ray absorptiometry (DEXA) cut weight predictions to lamb allocation to cut plans is unknown. Lambs (n = 191) varying in carcase weight (HSCW) and GR (tissue depth over the 12th rib) were DEXA scanned and boned out to weigh retail cuts. Cut weights were predicted using HSCW; HSCW + GR; HSCW + DEXA and HSCW + DEXA image components in GLM models. DEXA improved cut weight predictions in most cuts (P < 0.05). A dataset of 10,000 carcases was then simulated using the associations between HSCW, GR and cut weights, before being truncated to 4500 lambs representing onel day's HSCW distribution. A lamb Carcase Optimisation Tool scenario was developed with 2–3 cut options per carcase section and cut weight thresholds applied to several cuts. Processing costs, market values and actual cut weights were input into the Optimiser to determine carcase allocation to cut options for optimised profits. This scenario was repeated using the predicted cut weights to determine the cut misallocations caused. DEXA-predicted cut weights produced 16.7% and 8.0% less misallocations than HSCW and GR. DEXA produced 20.8% and 14.3% less misallocations than HSCW and GR in shortloins, and 25.5% and 12.9% less in hindquarters. While cut misallocations have little direct impact on total profits, as product is over and under-valued when misallocated, reducing cut misallocations will improve processor compliance when sorting carcases into cut plans- reducing their need to retrim, downgrade and repackage product or the erosion of customer confidence caused by supplying product not meeting market specifications.

Prediction of lamb carcase C-site fat depth and GR tissue depth using a non-invasive portable microwave system versus body condition scoring

This study compared portable ultra-wide band microwave system (MiS) versus body condition score to predict C-site fat depth, GR tissue depth and eye muscle depth (EMD) in lambs. Experiment 1 assessed MiS and condition score to predict ultrasound measured C-site and EMD (n = 1549). Precision and accuracy was greatest for the MiS measurement with liveweight included in the model, with a C-site predicted RMSEP of 0.58 mm, R2 0.60 and bias of 0.021 mm and an EMD predicted RMSEP of 2.27 mm, R2 0.72 and bias of 0.088 mm. Experiment 2 (n = 900) assessed pre-slaughter MiS scanning and condition scoring to predict carcase GR tissue depth, C-site fat depth and EMD. MiS performed better than condition score for all three carcase trait predictions, regardless of the inclusion of liveweight, with the highest precision and accuracy for GR tissue depth determination with a RMSEP of 3.68 mm, R2 0.63 and bias 0.072 mm.

Prediction of lamb carcase C-site fat depth and GR tissue depth using a non-invasive portable microwave system

The experiment evaluated the ability of portable ultra-wide band microwave coupled with a Vivaldi patch antenna to predict carcase C-site fat and GR tissue depth. For C-site, 1070 lambs, across 8 slaughter groups were scanned and for GR, 286 lambs across 2 slaughter groups. Prediction equations for reflected microwave signals were constructed with a partial least squares regression two-components model and a machine learning Ensemble Stacking technique. Models were trained and validated using cross validation methods in actual datasets and then in datasets balanced for tissue depth. The precision and accuracy indicators of microwave predicted C-site fat depth across pooled and balanced datasets were RMSEP 1.53 mm, R2 0.54, and bias of 0.03 mm. The precision and accuracy for GR tissue depth across pooled and balanced datasets were RMSEP 2.57 mm, R2 0.79 and bias of 0.33 mm. Using the AUS-MEAT fat score accreditation framework this device was able to accurately predict GR 92.7% of the time.

Using dual energy X-ray absorptiometry to estimate commercial cut weights at abattoir chain-speed

This experiment assessed the ability of an on-line dual energy x-ray absorptiometer (DEXA) installed at a commercial abattoir to determine commercial cut weights in lamb carcases at abattoir chain-speed. 200 lamb carcases were scanned using a DEXA that was trained to predict the computed tomography determined proportions of fat, lean, and bone. Models were then trained using hot carcase weight and, DEXA fat% value or GR tissue depth to predict cut weight. Results from validation tests of DEXA models demonstrated excellent precision for predicting cut weight, in most cases describing more than 85% of the variation, and RMSE values that represented between 5 and 13% of the average weight of each cut. For most cuts these weight predictions were superior to those informed by GR tissue depth. This precision was maintained upon validation. Additional analyses utilised pixel information from the fore, saddle, and hind sections of DEXA images. This further enhanced the predictive power of cut weight models.

Characterization of meat sensory quality from different beef breed and residual feed intake selections

Times for the progressive breakdown of 95 lamb carcases were recorded to determine the impact of carcase weight and GR tissue depth on the time and therefore cost to produce value added retail cuts. Further analysis also assessed the potential to use these carcase traits as predictors of fabrication times. Regression modeling demonstrated there was a limited ability to predict the difference in time to fabricate mid value-added (R2 = 0.18) and extreme value-added (R2 = 0.12) cuts compared to traditional cuts, suggesting that other factors need to be considered. However, this study highlighted the significant increases in time required to fabricate more value-added cuts and to breakdown heavier carcases. Furthermore, this study demonstrated the changes to the saleable meat yield as the degree of fabrication increased, such that the average product prices increased ($20.64/kg for mid value added and $28.72/kg for extreme value added) compared to traditional retail cuts ($15/kg) to offset the increased labour of fabricating value-added cuts.

Improvement of rabbit meat microbial quality by feed supplementation with natural sources of polyphenols

Times for the progressive breakdown of 95 lamb carcases were recorded to determine the impact of carcase weight and GR tissue depth on the time and therefore cost to produce value added retail cuts. Further analysis also assessed the potential to use these carcase traits as predictors of fabrication times. Regression modeling demonstrated there was a limited ability to predict the difference in time to fabricate mid value-added (R2 = 0.18) and extreme value-added (R2 = 0.12) cuts compared to traditional cuts, suggesting that other factors need to be considered. However, this study highlighted the significant increases in time required to fabricate more value-added cuts and to breakdown heavier carcases. Furthermore, this study demonstrated the changes to the saleable meat yield as the degree of fabrication increased, such that the average product prices increased ($20.64/kg for mid value added and $28.72/kg for extreme value added) compared to traditional retail cuts ($15/kg) to offset the increased labour of fabricating value-added cuts.

The effect of lamb carcase weight and GR depth on the production of value-added cuts – A short communication

Times for the progressive breakdown of 95 lamb carcases were recorded to determine the impact of carcase weight and GR tissue depth on the time and therefore cost to produce value added retail cuts. Further analysis also assessed the potential to use these carcase traits as predictors of fabrication times. Regression modeling demonstrated there was a limited ability to predict the difference in time to fabricate mid value-added (R2=0.18) and extreme value-added (R2=0.12) cuts compared to traditional cuts, suggesting that other factors need to be considered. However, this study highlighted the significant increases in time required to fabricate more value-added cuts and to breakdown heavier carcases. Furthermore, this study demonstrated the changes to the saleable meat yield as the degree of fabrication increased, such that the average product prices increased ($20.64/kg for mid value added and $28.72/kg for extreme value added) compared to traditional retail cuts ($15/kg) to offset the increased labour of fabricating value-added cuts.

Relationships between live weight, body condition, dimensional and ultrasound scanning measurements and carcass attributes in adult Angora goats

Real-time ultrasound scanning is an accurate non-invasive technique used to improve quality in sheep, cattle and pig meat production but has been overlooked in meat production from heavy goat carcasses. The aims of this study were to: determine subjective and objective carcass attributes of 6year old Angora castrate goats prior to and following slaughter; and determine the relationships between carcass attributes, bodyweight, body condition score (BCS), body dimension measurements and ultrasound measurements using multiple regression modelling. Key attributes were: on-farm bodyweight (range 35–77kg), BCS (1, very thin to 4.3, fat), dimensional frame measures (wither height, heart girth, anterior-posterior circumference, body volume (circumference×girth)), carcass weight (range 11.6–33.2kg), GR tissue depth of carcasses (1–27mm) and the ultrasound measurements of eye muscle depth (EMD, 17–35mm) and subcutaneous fat depth (SFD, 1–6mm). Goats from three genetic backgrounds were grazed on pasture together for 6 years. In the three months preceding slaughter the goats grew from an average live weight of 50.7kg gaining live weight at an average of 117g/d to reach an average live weight of 62kg. There were moderate correlations between all measurements. BCS accounted for 55.1% of the variance in carcass weight, 51.3% of the variance in EMD, (3.2% more than did GR tissue depth) and 59.9% of the variance in SFD. Live weight accounted for 83.8% of the variance in carcass weight. The best prediction equation for carcass weight included terms for live weight, SFD, EMD and sire, accounting for 91.5% of variance. Body dimensional measurements were not as useful as BCS in predicting carcass weight, with the best, body volume, accounting for 5% less of the variance than live weight. The best prediction for the EMD included terms for BCS and carcass weight, accounting for 61% of variance. GR tissue depth was primarily associated with SFD, and in combination with carcass weight and BCS explained 71.9% of the variance. In relation to predicting carcass traits, girth accounted for more of the variance in EMD, SFD and GR tissue depth than wither height or body circumference. If breeders aim to alter the EMD and SFD of Angora goats then ultrasound scanning provided better estimates compared with relying on live weight with or without body condition scoring. Both EMD and SFD were also in the best model for predicting carcass weight. BCS was a useful on-farm measurement for estimating carcass attributes but girth was not as useful as body volume in explaining the variance in live weight.

Herb-clover mixes increase lamb live weight gain and carcass weight in the autumn period

Two experiments were carried out in two consecutive autumns to examine whether herb-clover mixes would improve lamb production compared with a ryegrass-based pasture. The three herbage treatments were: (1) ‘pasture mix’—perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens); (2) ‘plantain mix’—plantain (Plantago lanceolata), white clover and red clover (Trifolium pratense); (3) ‘chicory mix’—plantain, chicory (Cichorium intybus L.), white and red clover. Individual lamb live weight gain, final lamb live weights, carcass weights and GR tissue depths were greater (P < 0.05) in both of the herb-clover mixes in both experiments compared with the pasture mix. However, environmental conditions in the second year resulted in lower stocking rates on the plantain mix. This result suggests that in a dry environment, of the three mixes examined, the chicory mix is the best option for finishing lambs in the autumn.

Mixtures of clovers with plantain and chicory improve lamb production performance compared to a ryegrass–white clover sward in the late spring and early summer period

AbstractA research programme was undertaken over two consecutive years with the purpose of studying the effect of herb–clover swards on lamb production performance year‐round. The focus of this study was on two consecutive late spring and early summer periods (2011, 2012). In each year, three sward treatments were compared on grazed paddocks with 40 lambs ha−1: (i) grass–clover mixture (perennial ryegrass [Lolium perenne L.] and white clover [Trifolium repens]); (ii) plantain–clover mixture (plantain [Plantago lanceolata], white clover and red clover [Trifolium pratense]); and (iii) chicory–plantain–clover mixture (plantain, chicory [Cichorium intybus L.] and white and red clovers). Lambs were weighed at 2‐week intervals, and carcass weights and GR tissue depth measurements were obtained at slaughter. In both years, lambs on treatments (ii) and (iii) had greater (P &lt; 0·05) final live weight, liveweight gain, carcass weight, dressing‐out percentage and GR tissue depth measurements, and lower feed conversion ratio compared to lambs on treatment (i). Lamb production was similar in treatments (ii) and (iii) (P &gt; 0·05) in each year. Therefore, during the late spring and early summer period, herb–clover mixture swards were found to be a superior option to perennial ryegrass–white clover for finishing lambs.

Influence of stocking rate and mixed grazing of Angora goats and Merino sheep on animal and pasture production in southern Australia. 2. Liveweight, body condition score, carcass yield and mortality

The effects of animal species (AS; Angora goats, Merino sheep, mixed-grazed goats and sheep at the ratio of 1 : 1) and stocking rate (SR; 7.5, 10 and 12.5 animals/ha) on the liveweight, body condition score, carcass yield and mortality of goats and sheep were determined in a replicated experiment on improved annual temperate pastures in southern Australia from 1981 to 1984. The pattern of liveweight change was similar for both species with growth from pasture germination in autumn until maturation in late spring followed by weight loss. In winter, sheep grew faster than goats (65 versus 10 g/day, P &lt; 0.05). In mixed-grazed treatments between November and December goats either grew when sheep were losing weight or goats lost less weight than sheep (P &lt; 0.01). Both AS (P &lt; 0.001) and SR (P &lt; 0.001) affected liveweight of sheep and an AS × SR interaction (P &lt; 0.05) affected liveweight of goats. Mixed-grazed sheep were heavier than separately grazed sheep at all SR with a mean difference at 10 and 12.5/ha of 4.6 kg. Mixed-grazed goats at 10/ha were heavier than separately grazed goats from the end of the second year of the experiment, but at 12.5/ha, separately grazed goats maintained an advantage over mixed-grazed goats, with a 9.4-kg mean difference in December (P &lt; 0.05). Body condition scores of goats and sheep declined with increasing SR; they were highest in late spring and were highly correlated with liveweight (r2 &gt; 0.8). Both AS and SR affected (P &lt; 0.001) carcass weight and GR tissue depth as a direct result of differences in liveweight. Adjusting for differences in carcass weight negated AS effects on GR tissue depth. The carcass weights of sheep and goats increased by similar amounts for each 1-kg increase in liveweight. Mortality of sheep (3.1% p.a.) was unaffected by AS or SR. An AS × SR interaction indicated mortality of separately grazed goats at 12.5/ha and mixed-grazed goats at 10 and 12.5/ha were higher (P &lt; 0.05) than all other goat (29 versus 9%) and sheep treatments, primarily because of increased susceptibility to cold stress. Disease prevalence differed between sheep and goats. Mixed grazing of Merino sheep and Angora goats produced complementary and competitive effects depending upon the SR. Goats used summer pasture better but winter pasture less well for liveweight gain than sheep. Angora goats should not be grazed alone or mixed grazed with sheep on annual temperate pastures at SR greater than that recommended for Merino sheep and the evidence indicates a lower SR will reduce risks associated with mortality.

Management of young goats during prolonged fasting affects carcass characteristics but not pre-slaughter liveweight or cortisol

Effects of pre-slaughter management (72 h continual fasting; 24 h feeding within 72 h fasting; 24 h feeding plus 6 h additional transport within 72 h fasting) and of water availability, gender, weaning 3 weeks before slaughter, initial liveweight (LW) and body condition score (CS) on LW, plasma cortisol and carcass characteristics were studied in young goats. The goats (n = 229) were ~16 weeks of age, with a mean ± s.d. LW of 13.7 ± 2.4 kg. Pre-slaughter treatment did not significantly affect LW or carcass weight at slaughter, but goats fed within the fasting period had lighter-coloured meat compared with the continually fasted goats and the goats fed and transported during the fasting period. Interactions between fasting treatment and gender were evident for hot carcass weight (HCW), retail yield (kg) and dress (% pre-fasting LW). Fasting treatment also interacted with water availability for HCW and with weaning status for GR (12th rib, 110 mm from mid-line) tissue depth. Interactions were evident between gender and water availability for LW at slaughter, and between gender and weaning status for retail yield (% HCW). Weaning status interacted with pre-fasting LW to influence LW at slaughter, and fasting treatment interacted with pre-fasting body CS to influence dress (% pre-slaughter LW). The effects of gender, weaning status, water availability, initial LW and CS on the pre-slaughter LW and carcass characteristics were generally consistent with our previous findings on time off feed. The results show benefits of providing high-quality feed and water and of minimising transport of goat kids during prolonged pre-slaughter fasting. They provide additional information for estimation of carcass characteristics of young goats to be marketed for meat and to aid in the further development of welfare standards for goats. Further research on interactions between gender and pre-slaughter management factors that influence goat carcass characteristics and meat quality is warranted.

Comparison of manual assessments of ewe fat reserves for on-farm use

The two systems currently used in Australia for assessing the body reserves of live sheep (fat and condition scoring) were evaluated for their ability to quantify the range of scores within a mob and their ability to discriminate between sheep of varying fatness. Three ewe genotypes (fine Merino, medium Merino and first-cross Border Leicester × Merino) were independently assessed by four assessors experienced in each system (i.e. eight assessors). Twenty-four hours after assessment the ewes were slaughtered in a commercial abattoir and hot carcass measures of tissue depth at the GR site (thickness of tissue over the 12th rib, 110mm from the midline) taken to allow correlation with the assessed live scores. There was at least three times more phenotypic variation in fat score assessment compared with condition score as the fat score assessors used a wider range of scores. Despite this the average repeatability of fat scoring (0.73–0.85) was greater than condition scoring (0.64–0.84) particularly within the fine Merino genotype. Although there was a strong linear relationship between assessments of fat and condition scoring, the regression coefficients comparing the two scoring systems indicated a greater discrimination among animals on fat score across all three genotypes. Furthermore the fat scores had a significantly higher correlation with GR tissue depth measured on the carcass than condition scores. These data indicate that both systems will similarly assess the average body fat reserves of a mob or animals; however, fat scoring achieves greater discrimination when the goal is to identify individuals that are lower or higher than the mob average.

Preslaughter management practices influence carcass characteristics of young goats

Effects of sex, weaning 3 weeks before slaughter, continuous fasting and water deprivation for up to 72 h, and initial liveweight (LW) and body condition score (CS) on LW and carcass characteristics were studied in 231 goats of ~16 weeks of age with a LW of 13.6 ± 2.4 kg (mean ± s.d.). Overall, the animals lost 5.9% of initial LW during the first 12 h of fasting, 7.5% by 24 h, 10.8% by 48 h and 14.1% by 72 h. Weaned goats lost 2.6% more LW than non-weaned goats after 48 h fasting, and animals denied access to water lost 1.5% more LW than those with access to water. Fasting period, weaning status, water availability and CS influenced dressing out percentage determined as percentage initial LW or percentage preslaughter LW. All six factors investigated significantly influenced hot carcass weight (HCW), retail meat yield (kg) and L2 (lumbar eye muscle site) tissue depth. Sex, weaning, fasting period, and initial LW and CS influenced retail meat yield (as a percentage of HCW) and GR (12th rib) tissue depth. Muscle colour score was affected by initial LW, water availability and fasting period. There was also a fasting period × sex interaction for muscle colour. The results provide information for estimation of carcass characteristics of young goats marketed for meat and demonstrate that preslaughter management of young goats influences factors that affect economic returns. They reinforce the need to minimise time off feed and water before slaughter of young goat kids, from both a welfare and an economic perspective, and for further research on preslaughter management factors that may influence welfare of goats and goat meat quality.

Predicting the composition of lamb carcases using alternative fat and muscle depth measures

Hot carcase weight (HCW) and the GR tissue depth (total tissue depth over the 12th rib, 110 mm from the midline) were measured on 312 crossbred (Poll Dorset × Merino) lambs with a mean live weight of 47 kg. At a position 30 mm distal to the lumbar-sacral junction, the depth (RMD) of the rump muscles was measured along with subcutaneous fat depth overlaying the m. gluteus medius (RFD). The subcutaneous fat depth over the m. longissimus (loin) at the 12th rib was measured (Fat C), as was the depth and width of the loin cross section (EMD and EMW, respectively). The right side of each carcase was scanned by a dual energy X-ray bone densitometer and fat and lean weight determined and the percentage of lean and fat content in the carcases calculated. HCW alone accounted for 26% of the variation in percentage lean content (LC), with GR measurement being the single best predictor of LC ( R 2 = 48.1; r.s.d. = 1.89). RFD provided a less accurate and precise estimate of LC ( R 2 = 37.3; r.s.d. = 2.07) than either GR or Fat C ( R 2 = 46.5; r.s.d. = 1.92). Inclusion of HCW with either GR or Fat C provided a small improvement in the amount of variation in LC which could be explained. The measurement of breeding animals by ultrasound includes the terms weight, Fat C and EMD. These predictors when combined explained 49% of the variation in LC whereas by comparison measures of weight, RFD and RMD only explained 42% of the variation in LC. The current method of measuring fat depth over the 12th/13th rib is practical and measurement over the rump does not present an advantage based on the results of this study.

Effects of available nutrition and sire breeding values for growth and muscling on the development of crossbred lambs. 2: Composition and commercial yield

Carcasses from 56 lambs representing male progeny of 3 sires selected for muscling (M sire-type), 3 sires selected for postweaning weight (G sire-type), and 3 control sires (C sire-type) were evaluated. Lambs had been raised on low (LOW) or high (HIGH) planes of available nutrition from 10 days of age to approximately 8 months when they were slaughtered at an average cold carcass weight (CCW) of 21.4 kg. When adjusted for CCW, M lambs had more lean tissue in the loin, a greater depth and width of the M. longissimus thoracis et lumborum at the 12th rib, and a greater weight of major hindlimb muscles than did G or C lambs. Although there was no difference in GR tissue depth due to sire-type at an adjusted CCW, there was less total fat in the carcass of M lambs and the amount of fat in the carcass of M lambs on HIGH nutrition was not greater than that on LOW nutrition, as it was for C and G lambs. This reduced propensity of M lambs to deposit fat in the carcass in response to HIGH nutrition was particularly evident in the loin, with fat-trim from the loin decreasing for M lambs in response to HIGH nutrition, whereas fat trim increased for C and G lambs compared at an adjusted CCW.

Growth and carcass characteristics of prime lambs fed diets containing urea, lupins or canola meal as a crude protein source

Lupin grain typically provides the main source of protein in most lamb finisher diets in Western Australia. The aim of this work was to determine whether alternative sources of nitrogen could provide a less expensive means of achieving the desired rate of liveweight gain and carcass characteristics. Fifty-one crossbred lambs were finished using 3 different sources of crude protein. These sources were either: (i) a control diet consisting of lupins, oats, barley and cereal chaff in which lupins provided 49% of the nitrogen (lupin diet); (ii) a diet consisting of a combination of cereal grain and urea (urea diet); or (iii) a diet in which lupins were partially replaced with expeller canola meal (canola diet). Diets were isonitrogenous (14.4% crude protein) and isoenergetic (10.5 MJ ME/kg DM). Lambs were gradually introduced to the diets over 2 weeks before being fed the diets ad�libitum for 5 weeks.Lambs fed the canola diet performed the best in terms of feed intake and liveweight gain while those fed the urea diet performed the worst. Respective growth rates for sheep fed the canola, lupin and urea diets were 272, 233 and 180 g/day, respectively, with significant (P&lt;0.05) differences only between the canola and urea diets. Equivalent dry matter intakes for the 3 groups were 1660, 1570 and 1380 g/day respectively, with sheep fed the urea diets being significantly (P&lt;0.05) lower than the other two. Acidosis was considered to be a major cause of the poor performance of sheep fed the urea diet, with 3 sheep from this treatment showing inappetance and markedly reduced growth rates ('shy feeders'). Lambs finished on all 3 diets produced acceptable carcasses. Carcass weights followed the trend of growth rates, but there were no significant differences between diets in carcass weight, dressing percentage, GR tissue depth, C�site fat depth, eye muscle area, muscle pH or meat colour. At the price of the feeds used in this trial, the canola meal diet was the cheapest feed per kilogram of liveweight gain despite being the most costly diet per tonne of feed.

Differences in composition, muscularity, muscle:bone ratio and cut dimensions between six lamb genotypes

Carcass measurements and composition data were obtained for 198 lambs representing two sexes (104 cryptorchids, 94 ewes). Dorsal images of 166 of the carcasses were obtained on the slaughter chain using a video camera. The lambs were sired by a selection of Poll Dorset (PD), Texel (T), Border Leicester (BL) and Merino (M) rams, born to Border Leicester × Merino (BLM) and Merino (M) ewes giving 6 genotypes (PD × BLM, T × BLM, PD × M, T × M, BL × M, M × M). From the right hindleg and chump, the following muscles were dissected and weighed: semimembranosus, adductor femoris, semitendinosus, biceps femoris, and quadriceps femoris. The femur was weighed, the length measured and a muscularity value calculated as described by Purchas, et al. (1991, Meat Sci., 30, 181). Merino cryptorchid lambs were significantly ( P < 0.05) leaner, as measured by GR tissue depth (for explanation, see MATERIALS AND METHODS) adjusted to a mean carcass weight of 24.2 kg, than BL × M lambs, but there was no difference between genotypes within the ewe group (mean carcass weight of 17.1 kg). Genotype differences were found for conformation using the EUROP scoring system. Merino lambs had a greater proportion ( P < 0.001) of poorer scores, particularly compared to PD × BLM and T × BLM carcasses. The BL × M carcasses had a significantly ( P < 0.05) smaller m. longissimus thoracis et lumborum area than other genotypes with no difference between carcasses of T and PD sires. Muscularity values for the BL × M and M lambs were significantly ( P < 0.05) lower than the other crosses but not different from each other. Carcasses from T sires had significantly ( P < 0.05) higher muscularity values than those from PD sires. A negative association ( r = −0.56) was found between EUROP scores and muscularity when carcass differences were adjusted for, but significant differences between genotypes for muscularity were not necessarily carried through to differences in EUROP conformation score. BL × M carcasses had the lowest muscle:bone ratio and T × M the highest with M carcasses having similar ratios to carcasses from PD-sired lambs. Only small differences were found between genotypes for composition of the hindleg, the exception being BL × M carcasses of both sexes which were significantly ( P < 0.05) fatter than T × BLM, T × M and PD × M carcasses. Carcasses from T sires had significantly ( P < 0.05) more muscle in the hindleg than carcasses from PD sires, with the differences being greater in the heavier cryptorchids (1.8%) than the ewes (1.1%). There was no consistent effect of genotype on the cross-sectional areas of the round and topside cuts within either sex. Differences between genotypes for the proportion of the carcass attributed to the round were small and only for BL × M ewe carcasses was this cut significantly lighter ( P < 0.05) than from all other genotypes, except the PD × BLM carcasses. This trend was similar for the topside and silverside cuts. A moderate correlation ( r = 0.46; P < 0.001) was found between muscularity values determined by dissection and those predicted using the equations of Hopkins et al. (1996, Proc. Aust. Soc. Anim. Prod., 21, 181) based on carcass width measurements taken from video images.