Utvidet evaluering av skjeletthelse hos gris ved hjelp av computer tomografi (CT)

In 2008, Norsvin was the first swine breeding company in the world to employ advanced diagnostic imaging computed tomography (CT, CAT-scanning) in selection of breeding boars. Images were first used for automated quantification of lean meat and fat percentage, and later validated for manual scoring of articular osteochondrosis in the BIONÆR-project ?Robust pigs? 199598. In project 244212 ?Expanded use of CT? one was to investigate if other developmental orthopaedic problems; knock/bow leggedness, hump-/swayback and shoulder blade shape associated with ulcers also could be scored with CT. If the problems turned out to be due to heritably predisposed osteochondrosis, it would be possible to reduce prevalence through selection and thus achieve improved health, welfare, durability and productivity for Norwegian pigs. With respect to knock/bow leggedness, osteochondrosis was the decidedly most common problem in the growth plates. It was discovered that the disease had the same cause in growth plates as in joints, and when the cause is the same, the heritable predisposition is probably also similar. The examined pigs had straight legs, but modern pigs reach finishing weight by approximately 5 months, and knock/bow leggedness from osteochondrosis manifests from 5 months upwards. Osteochondrosis in growth plates is therefore possibly not that important to finishing pigs, but one should probably still select against it in boars to ensure that breeding sows have straight legs that are as evenly loaded as possible and therefore minimally disposed for claw- or joint problems later in life. For hump-/swayback, the back of 37 pigs with undesirable score on conformation evaluation was examined and, surprisingly, the vertebrae of 30 of the pigs had completely normal shape in CT scans. One likely explanation was that osteochondrosis had led to osteoarthritis in the small facet joints on one side of the spine in three pigs; these pigs may have compensated through posture and thus received a poor conformation score due to soft tissue inflammation without concurrent altered bone shape. In the 7 pigs with abnormal shape vertebral body osteochondrosis had led to wedged single or fused bones. Bones that were shorter on the underside bulged upwards and led to humpback; whereas the back in front of and behind humps often bulged in the opposite direction, in the absence of wedged bones. This secondary, opposite bulging may have been more noticeable on the surface, illustrating how challenging back conformation scoring can be in pigs. Osteochondrosis behaved differently in the shoulder blade than most other places, leading to new bone formation resulting in permanent shape change. Computer programs for automated extraction and characterisation of shoulder blade shape were developed, and used to estimate heritability and correlation to ulcers. In practice, this means Norsvin can now select CT-scanned boars for optimal shoulder blade shape in breeding sows simply by pressing a button on a computer Norsvin already had the most advanced procedure for CT-evaluation of osteochondrosis in joints, lean meat and fat percentage. Osteochondrosis does, however, occur in other sites and is the single-most important, heritably predisposed disease that influences growth of a durable skeleton. CT is optimally suited for whole-body scoring of osteochondrosis, but manual evaluation is too labour-intensive to be practicably possible. It is already feasible to select for optimal shoulder blade shape through the pressing of a single button; we can now see how we have to proceed to achieve the same for osteochondrosis in growth plates and vertebral bodies. We hope to be able to pursue this in future, as it will maintain Norsvin?s position as the company with the most advanced, comprehensive and sophisticated approach for ensuring health, welfare, durability and sustainability in swine production in the world.

Siden 2008 har norske svineprodusenters samvirke, Norsvin, brukt avansert billeddiagnostikk i form av computer tomografi (CT) for å velge hvilke råner som skal bli fedre til den neste generasjonen griser. Med CT kan man måle kjøtt- og fettprosent i levende individer. I prosjektet «Robust gris» fra 2010-2014 ble også bruk av CT til å undersøke den arvelige sykdommen osteochondrose som kan gi løse biter i ledd, smerte og bevegelsesproblemer hos både slaktegris og avlsgris også utredet. Formålet med prosjektet det nå søkes om er å undersøke muligheten for å utvide bruken av CT til å omfatte andre viktige problemstillinger i skjelettet som potensielt også kan skyldes arvelig osteochondrose. Problemstillingene det gjelder er beinstillingsfeil (hjulbeint/kalvbeint), ryggform (nedoverbrutt rygglinje, såkalt dokkrygg) og formen på skulderbladet, da særlig former som kan disponere for utvikling av trykksår over bogen hos avlspurker. Utfordringene i prosjektet er at det må identifiseres minst 10 griser som må gå ut av produksjon eller avl på grunn av hver av de tre aktuelle problemstillingene. Disse grisene må undersøkes med CT før det gjennomføres full obduksjon av de relevante skjelettdelene for å stille en definitiv diagnose av årsaken. Det viktigste spørsmålet i prosjektet er å svare på om problemstillingene skyldes ren anatomisk utforming, ervervet eller arvelig sykdom, inkludert arvelig osteochondrose. Anvendelse av resultater er direkte avhengig av svaret på dette spørsmålet: dersom problemstillingene skyldes arvelig sykdom så kan forekomsten av slike problemer reduseres gjennom målrettet utvalg av individer til avl. Observasjonene i prosjektet vil da danne grunnlaget for anbefalinger for hvordan slikt utvalg kan gjennomføres basert på CT undersøkelse av levende råner.