Genetic differences based on a beef terminal index are reflected in future phenotypic performance differences in commercial beef cattle

Abstract

The increased demand for animal-derived protein and energy for human consumption will have to be achieved through a combination of improved animal genetic merit and better management strategies. The objective of the present study was to quantify whether differences in genetic merit among animals materialised into phenotypic differences in commercial herds. Carcass phenotypes on 156 864 animals from 7301 finishing herds were used, which included carcass weight (kg), carcass conformation score (scale 1 to 15), carcass fat score (scale 1 to 15) at slaughter as well as carcass price. The price per kilogram and the total carcass value that the producer received for the animal at slaughter was also used. A terminal index, calculated in the national genetic evaluations, was obtained for each animal. The index was based on pedigree index for calving performance, feed intake and carcass traits from the national genetic evaluations. Animals were categorised into four terminal index groups on the basis of genetic merit estimates that were derived before the expression of the phenotypic information by the validation animals. The association between terminal index and phenotypic performance at slaughter was undertaken using mixed models; whether the association differed by gender (i.e. young bulls, steers and heifers) or by early life experiences (animals born in a dairy herd or beef herd) was also investigated. The regression coefficient of phenotypic carcass weight, carcass conformation and carcass fat on their respective estimated breeding values (EBVs) was 0.92 kg, 1.08 units and 0.79 units, respectively, which is close to the expectation of one. Relative to animals in the lowest genetic merit group, animals in the highest genetic merit group had, on average, a 38.7 kg heavier carcass, with 2.21 units greater carcass conformation, and 0.82 units less fat. The superior genetic merit animals were, on average, slaughtered 6 days younger than their inferior genetic merit contemporaries. The superior carcass characteristics of the genetically elite animals materialised in carcasses worth €187 more than those of the lowest genetic merit animals. Although the phenotypic difference in carcass traits of animals divergent in terminal index differed statistically by animal gender and early life experience, the detected interactions were generally biologically small. This study clearly indicates that selection on an appropriate terminal index will produce higher performing animals and this was consistent across all production systems investigated.

Feed and production efficiency of young crossbred beef cattle stratified on a terminal total merit index1

“…The superior carcass metrics of the animals excelling in the terminal index in the present study have also previously been demonstrated by Connolly et al (2016) . Using a national database, Connolly et al (2016) reported that cattle in the very high genetic merit stratum for a terminal index had a 37.1 kg heavier carcass, a 1.98 units superior carcass conformation (scale 1 to 15) and a 1.33 units less carcass fat (scale 1 to 15), relative to cattle in the very low genetic merit stratum.…”

“…The superior carcass metrics of the animals excelling in the terminal index in the present study have also previously been demonstrated by Connolly et al (2016) . Using a national database, Connolly et al (2016) reported that cattle in the very high genetic merit stratum for a terminal index had a 37.1 kg heavier carcass, a 1.98 units superior carcass conformation (scale 1 to 15) and a 1.33 units less carcass fat (scale 1 to 15), relative to cattle in the very low genetic merit stratum. The smaller differences between the very high and very low genetic merit strata reported in the present study, for the same index and the same traits, are likely due to the fact that the difference in terminal index value between adjacent terminal index strata in Connolly et al (2016) was approximately 17% greater than that in the present study (€51.30 vs. €43.72).…”

“…Since the unit of genetic merit in the present study was EBV, the close to unity regression coefficient of phenotypic performance on its respective EBV across all sexes was desired and expected, even considering that the EBV reliability estimates were relatively low. Such a relationship between genetic merit and the respective phenotypic performance has been previously verified in cattle by Connolly et al (2016) , Crews (2002) and McHugh et al (2014) . The genetic standard deviation of feed intake in the national genetic evaluation is 1.29 kg DM/d; the expected mean difference between the top and bottom 10% of a normal distribution is 3.51 standard deviation units.…”

“…The association between genetic merit for individual traits and phenotypic performance in beef cattle has been investigated previously ( Crews, 2002 ; McHugh et al, 2014 ; Judge et al, 2019 ) and several studies have demonstrated the favorable effect of selection for improved animal performance using overall genetic merit selection indexes ( Connolly et al, 2016 ; Berry and Ring, 2020 ). Connolly et al (2016) for example, using a national database, illustrated that genetically elite cattle (i.e., top 25% for a terminal index) had, on average, heavier and better conformed carcasses, with less fat cover, relative to animals of low genetic merit (i.e., bottom 25% for a terminal index). Berry et al (2019b) extended this, documenting heavier yields of higher value primal carcass cuts in cattle excelling on the Irish terminal index.…”

Carcass characteristics of cattle differing in Jersey proportion

“…It is possible, therefore, to use genetically superior (beef) bulls based on a terminal index (Connolly et al, 2016), which would improve the carcass characteristics of the resulting progeny (Clarke et al, 2009;Connolly et al, 2016) but could also achieve this without necessarily increasing calving dystocia (McHugh et al, 2014). Despite detecting a significant interaction between animal genetic merit and subsequent performance depending on whether or not the cattle originated from a dairy herd (bucket reared) or a beef herd (suckled until weaning), Connolly et al (2016) concluded that the biological significance of the interaction was minimal and that a beef terminal index functions equally well irrespective of the origin of the cattle. Hence, strategies do exist to lessen the effect of Jersey bloodline on beef merit while still protecting one of the main benefits of Jersey cows, which is their superior gross efficiency.…”