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.Keywords: Genetic parameters, Video image analysis, lamb carcasses, EUROP classification, lean meat yield, ultrasound measurements. YFIRLIT Erfðastuðlar fyrir skrokkeiginleika lamba maeldum með rafraenum aðferðum, EUROP flokkun og mati á lifandi lömbum.Arfgengi vöðvahlutfalls lambaskrokka og EUROP flokka sem metnir voru baeði rafraent (VIAscan®) (n=18.680) og af matsmönnum í sláturhúsi (n=26.795) var metið ásamt erfða-og svipfarsfylgni þessara eiginleika við maelingar og dóma á lifandi lömbum (n = 9.930), (ómmaelingar, stig fyrir frampart og laeri ásamt legglengd). Erfðafylgni milli EUROP flokkunar matsmanna og VIAscan® flokkunar var 0,94 fyrir holdfyllingu og 0,82 Icel. Agric. Sci. 28 (2015), 3-14 www.ias.is http://dx.doi.org/10.16886/IAS.2015.01 4 ICELANDIC AGRICULTURAL SCIENCES fyrir fitu. Arfgengi holdfyllingarmats var 0,32 fyrir VIAscan® og 0,35 fyrir sláturhúsmat og arfgengi stiga fyrir fitu var 0,29 og 0,31. Arfgengi nýtingar (LMY) metin með VIAscan® sem kg nýtanlegt kjöt í hverjum skrokkhluta (frampartur, hryggur, laeri) var...

Sources of bias, genetic trend and changes in genetic correlation in carcass and ultrasound traits in the icelandic sheep population

“…The heritability of CF (Table 3) was in line with other studies for the Icelandic breed, 0.27 (Saevarsson 1999) and 0.31 (Einarsson et al, 2015). Einarsson et al (2015) found the Icelandic CF score to be genetically the same (r g =0.99) as the measure of tissue depth over 12 th rib, the tissue depth having higher heritability (0.58).…”

“…Conington et al 1998, Maxa et al 2007). Previous studies with the Icelandic breed on fixed weight bases have shown the same (Einarsson et al 2015, Saevarsson 1999.…”

“…Einarsson et al (2015) found the Icelandic CF score to be genetically the same (r g =0.99) as the measure of tissue depth over 12 th rib, the tissue depth having higher heritability (0.58). This could explain that heritability for the Icelandic CF is reported to be higher than published estimates for other breeds in general, (e.g.…”

“…for shoulder and leg conformation of lambs. These measures have high genetic correlation with the carcass scores (Einarsson et al 2015). Selection of replacements based on these traits is therefore likely to affect genetic analysis for the carcass traits.…”

“…Saevarsson (1999) estimated a genetic correlation of 0.48 between CC and CF in Icelandic sheep, using one year of slaughter house data. Einarsson et al (2015) estimated a correlation of 0.40 with data from [2007][2008]. According to the theory, selection for less fat and more muscle will gradually lead to antagonistic genetic correlation between the two traits and change the possible rate of genetic gain accordingly (Falconer 1989).…”