Genetic parameters for lamb carcass traits assessed by video image analysis, EUROP classification and in vivo measurements

Abstract

The heritability of yield predictions obtained from video image analysis (VIAscan®) of lamb carcasses (n=18,680) and EUROP classes obtained by abattoir assessors (n=26,795) was estimated, as well as the genetic and phenotypic correlations between VIAscan® traits and in vivo lamb traits (n = 9,930), including ultrasonic measurements, visual conformation score and length of the cannon bone. The main objective of the study was to test the equivalence of EUROP classes obtained by VIAscan® and visual scoring as selection criteria in the breeding work. Genetic correlations between EUROP scores from VIAscan® and from abattoir assessors were 0.94 for conformation and 0.82 for fat score. The heritability of conformation score was 0.32 and 0.35 based on VIAscan® and visual scoring, and 0.29 and 0.31 for the fat score, respectively. Yield predictions as proportions of lean meat of carcass weight from VIAscan® were highly heritable, h 2 ranging from 0.39 to 0.63. Lean meat yield (LMY) estimated as lean weight in major cuts had a direct heritability ranging from 0.17 to 0.21, maternal heritability ranging from 0.09 to 0.11 and a common environmental (c 2 ) effect of 0.22-0.23. Lean meat yield of the whole carcass (LMY_%) had the highest genetic correlation to visual leg score (0.44) while correlations between lean yield of three carcass parts (LegY_%, LoinY_% and ShoulderY_%) and in vivo measurements were low to moderately high and favourable except for loin yield. The EUROP scores obtained by both methods had similar genetic and phenotypic correlations to in vivo traits where conformation scores were highly correlated to visual scores for legs and shoulders and ultrasonic muscle measurements and fat scores were positively correlated to ultrasonic fat measurements and shoulder scores. It is concluded that VIAscan® can be used as a grading tool for the Icelandic sheep industry and measurements of carcass traits obtained from the system would be useful in the national sheep breeding program.