Selection indices for lean meat production in sheep

Simm, G.; Dingwall, W.S.

doi:10.1016/0301-6226(89)90052-3

Cited by 109 publications

(88 citation statements)

References 7 publications

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“…Subsequently, Stanford, Jones, and Price (1998) published a review of methods for predicting lamb carcass composition with reference to the use of ultrasound for predicting body/carcass composition in sheep. Simm, Lewis, Grundy, and Dingwall (2002) referred that in vivo measurements most widely used have been ultrasonic measures of fat and muscle depth or areas and found from their experimental results that substantial responses can be achieved by selecting sheep on an index of live weight and ultrasonic measurements of fat and muscle (Simm, 1992;Simm, Dingwall, & Lewis, 1993).…”

Section: Introductionmentioning

confidence: 99%

In vivo estimation of lamb carcass composition by real-time ultrasonography

et al. 2006

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The objective of this study was to evaluate the accuracy of ultrasonography to measure fat thickness in live lambs and predict carcass composition to find a system that can assess carcass composition easily and accurately, without damage to the product and can improve carcass classification.Fat thickness (FTh) between the 12th and 13th ribs and between the 3rd and 4th lumbar vertebrae, was measured in vivo using realtime ultrasound, in 67 Churra Galega Bragançana males (mean weight 36.0 kg, range 21.5-47.0 kg), using an ALOKA SSD-500V equipped with two probes (5 and 7.5 MHz) in order to predict carcass composition. The most satisfactory correlation between carcass and ultrasound measurements was between the 3rd and 4th lumbar vertebrae fat thickness (FTh). The first variable admitted in the models to predict carcass composition (live weight, LW) explained between 63% and 96% of the total variation of the weight of the components of the carcass. In fact, 96% of the variation in total amount of muscle was accounted for by live weight. The inclusion of the ultrasound measures with the 7.5 MHz probe improved, in all prediction equations, the coefficient of determination (R 2 ) with a substantial reduction in the residual standard deviation (RSD). In relation to the subcutaneous fat of the carcass, 85% of the variation was explained by live weight and the FTh 12-13 7.5 measurement. In the prediction model for total carcass fat weight, live weight and ultrasound fat thickness measurement explained 88% of the variation. The results indicate that in vivo ultrasound fat thickness measures in association with live weight can be used to predict carcass composition in Churra Galega Bragançana lambs.

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Section: Introductionmentioning

confidence: 99%

In vivo estimation of lamb carcass composition by real-time ultrasonography

et al. 2006

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“…Breed improvement in both cases has been achieved through the subjective appraisal of breed characteristics and perceived commercial (eg carcass) characteristics, and latterly through intensive selection within structured breeding programmes known as sire reference schemes. The current selection uses a selection index designed to improve the yield of lean meat (Simm and Dingwall, 1989). Therefore, genetic change has been achieved without knowledge of the underlying genetic architecture of the breeds.…”

Section: Introductionmentioning

confidence: 99%

Increased heterozygosity and allele variants are seen in Texel compared to Suffolk sheep

et al. 2003

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In this study, the Suffolk and Texel sheep breeds were compared for microsatellite marker heterozygosity throughout seven chromosomal regions in the sheep genome. A total of 623 Texel animals and 489 Suffolk animals in five and three half-sib families, respectively, were genotyped for microsatellite markers across the seven different chromosomes. Using the observed allele frequencies, the expected levels of heterozygosity were calculated for each family. The expected levels of heterozygosity did not significantly differ between the breeds across all regions studied. However, levels of expected heterozygosity were 32% higher in Texel animals on chromosome 4 due to a region of increased heterozygosity between BMS648 and BM3212. The number of allelic variants significantly differed between the breeds, solely due to a region of increased number of alleles on chromosome 20. This region of higher numbers of allele variants in the Texel breed extended from the MHC to c. 15 cM distal to the MHC region incorporating markers OMHC1, CSRD226, TGLA387 and BM1818, which had 3.30, 7.02, 3.09 and 6.75 more alleles in Texel than in Suffolk animals, respectively. No difference was observed in the variance of allele frequency between the two breeds. It is proposed that previous selective sweeps may have reduced numbers of alleles and levels of heterozygosity in the Suffolk breed.

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“…These were cooperative breeding schemes where reference rams were shared among flocks to create connectedness and facilitate within-breed genetic evaluation. The rams were selected according to a lean growth index designed to increase carcass lean growth, while constraining fat growth at a constant age end point (Simm and Dingwall, 1989). Sires were chosen from the top and bottom 5% of available rams based on index score and categorized as 'high' or 'low' lean growth index.…”

Section: Methodsmentioning

confidence: 99%

Heterogeneous variances and genetics by environment interactions in genetic evaluation of crossbred lambs

Márquez

Haresign

Davies

et al. 2015

Animal

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Accounting for environmental heteroscedasticity and genetics by environment interaction (G × E) in genetic evaluation is important because animals may not perform predictably across environments. The objectives of this study were to evaluate the presence and consequences of heteroscedasticity and G × E on genetic evaluation. The population considered was crossbred lambs sired by terminal sires and reared under commercial conditions in the UK. Data on 6325 lambs sired by Charollais, Suffolk and Texel rams were obtained. The experiment was conducted between 1999 and 2002 on three farms located in England, Scotland and Wales. There were 2322, 2137 and 1866 lambs in England, Scotland and Wales, respectively. A total of 89 sires were mated to 1984 ewes of two types (Welsh and Scottish Mules). Most rams were used for two breeding seasons with some rotated among farms to create genetic links. Lambs were reared on pasture and had their parentage, birth, 5 week, 10 week, and slaughter weights recorded. Lambs were slaughtered at a constant fatness, at which they were ultrasonically scanned for fat and muscle depth. Heteroscedasticity was evaluated in two ways. First, data were separated into three subsets by farm. Within-farm variance component estimates were then compared with those derived from the complete data (Model 1). Second, the combined data were fitted, but with a heterogeneous (by farm) environmental variance structure (Model 2). To investigate G × E, a model with a random farm by sire (F × S) interaction was used (Model 3). The ratio of the F × S variance to total variance was a measure of the level of G × E in the population. Heterogeneity in environmental variability across farm was identified for all traits ( P < 0.01). Rank correlations of sire estimated breeding value between farms differed for Model 1 for all traits. However, sires ranked similarly (rank correlation of 0.99) for weight traits with Model 2, but less so for ultrasonic measures. Including the F × S interaction (Model 3) improved model fit for all traits. However, the F × S term explained a small proportion of variation in weights (<2%) although more in ultrasonic traits (at least 10%). In conclusion, heteroscedasticity and G × E were not large for these data, and can be ignored in genetic evaluation of weight but, perhaps, not ultrasonic traits. Still, before incorporating heteroscedasticity and G × E into routine evaluations of even ultrasonic traits, their consequences on selection response in the breeding goal should be evaluated.

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Selection indices for lean meat production in sheep

Cited by 109 publications

References 7 publications

In vivo estimation of lamb carcass composition by real-time ultrasonography

In vivo estimation of lamb carcass composition by real-time ultrasonography

Increased heterozygosity and allele variants are seen in Texel compared to Suffolk sheep

Heterogeneous variances and genetics by environment interactions in genetic evaluation of crossbred lambs

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