Osteochondrosis in pigs diagnosed with computed tomography: heritabilities and genetic correlations to weight gain in specific age intervals

Abstract

The aim of this study was to develop a method for scoring osteochondrosis (OC) by using information from computed tomography (CT), as well as to estimate the heritability for OC scored by means of CT (OCwCT) of the medial and lateral condyles at the distal end of the humerus or the femur of the right and left leg and the sum of these scores (OCT). In addition, we were aiming at revealing the genetic relationship between OCwCT traits and growth in different periods (days from birth to 30 kg (D30), days from 30 to 50 kg (D30_50), days from 50 to 70 kg (D50_70), days from 70 to 90 kg (D70_90), days from 90 to 100 kg (D90_100) and days from birth to 100 kg (D100)). The OCwCT was assessed for 1449 boars, and growth data were collected for these 1449 boars and additional 3779 boars tested in the same time period. All boars were tested as part of the Norsvin Landrace boar test and in the same test station. Heritabilities for OCwCT on anatomical locations varied from 0.21 (s.e. 5 0.08) on the medial condyle of the right humerus to 0.06 (s.e. 5 0.06) on the lateral condyle of the left femur, whereas OCT exhibited the highest heritability ( h 2 5 0.31, s.e. 5 0.09). Genetic correlations between OCT and OCwCT for the anatomical locations ranged from 0.94 (s.e. 5 0.07) for OCT and OCwCT score for the medial condyle of the humerus right side to 0.26 (s.e. 5 0.39) for OCT and the lateral condyle of the femur left side. Genetic correlations between D30 and OCT were medium high and unfavourable (r g 5 20.74). As the boar gain weight, the relationship between growth rate -expressed as number of days spent growing from one interval to the next -and OCT decreased to 0.12 (s.e. 5 0.19, i.e. not significantly different from zero) for the trait D90_100 kg. These changes of genetic correlation coefficients coincide with the maturing of the joint cartilage and skeletal structures. In this study, we demonstrate that CT could be used for selection against OC in breeding programmes in pigs and that the genetic correlations between growth periods and OC are decreasing over time.

Genetic trends of conformation traits and genetic correlations to osteochondrosis in boars

“…However, a OCT score of 6 can be obtained in several ways, for example, a score of 4 on one location and a score of 2 on another location, or a score of 1 on six of the eight locations. The scoring is described in detail by Aasmundstad et al (2013).…”

“…To the best of our knowledge, this data material is the first in which CT is used to carry out an in vivo measurement of OC, a procedure described by Aasmundstad et al (2013). In vivo measurements facilitate the phenotyping of the selection candidates themselves, thereby increasing the accuracy of the EBV, which leads to increased genetic gain.…”

“…However, the animals were not assessed for conformation traits before slaughter. After 2008, the half-sib test ended and the flow of OC phenotypes stopped until 2012, when an OC breeding value based on the OC measurements from CT was implemented in the breeding goal (Aasmundstad et al, 2013). With the implementation of CT, the in vivo measurement of OC and conformation scoring can be acquired on the same animal, thus improving the accuracy of the selection.…”

“…Assessment of OC using CT OC was scored by using CT as described in detail by Aasmundstad et al (2013). In a study described by Olstad (2014), a cohort of piglets was serially scanned from two to eight times at biweekly intervals with conventional CT, Aasmundstad, Gjerlaug-Enger, Grindflek and Vangen and then, following the last scan for each piglet, a postmortem sectioning of distal femur into slabs were performed.…”

“…The OCT trait is the total score of OC assessed on the medial and lateral condyles at the distal end of both the humerus and femur of the right and left leg based on images from CT; hence, evaluation was conducted on eight anatomical locations for each boar. For each location, a score between 0 and 5 was assigned (Supplementary Figure S3), based on the assessment scale described by Aasmundstad et al (2013), and all animals were judged by the same trained assessor.…”