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DNA – Tests in sheep to verify Genetic Descent

The growing interest in agricultural technology and the fact that breed societies increasingly require DNA parentage tests to confirm the identity of animals, renders it a good time to consider compiling a DNA profile database for all stud animals. Worldwide, DNA profile tests are accepted as the standard to confirm the pedigree for breeding farm animals and to ensure the integrity of flock records. breeders can therefore ensure that there is no doubt about the correctness of their breeding lines by performing these tests. DNA profile analysis and parentage tests are increasingly applied in sheep farming and contribute significantly to the improvement of breeding programs.

The accuracy of parentage tests is therefore very important for the registered sheep industry. Accurate estimation of paternity is also of great value to commercial sheep farmers. Such tests enable them to track the performance of their rams and identify sires and sire-lines that produce superior performing offspring.

Establishing parentage by using DNA profiles is based on identification of specific standard DNA markers known as microsatellites. These genetic markers are used to construct a DNA “blueprint” of an animal. The basic theory of verifying descent is based on two principles:

  • The identification of genetically inherited markers that remain unchanged and
  • The knowledge that all animals receive two copies of each marker, one from the mother and one from the father.

The DNA profile of a sheep, used to establish parentage, consists of 16 specific genetic markers with two alleles each, as specified by the International Society for Animal Genetics (ISAG), To establish parentage, the lamb’s DNA profile is compared with that of the nominated ewe and possible ram. Since half of the lamb’s DNA comes from the ewe and half from the ram, both parents must contribute one allele to each marker. To be absolute sure of the parentage, both parents should be tested.

The illustration below indicates the complete affirmation of the genetic descent of a lamb

Parentage is only confirmed when all 16 pairs of alleles can be traced, one from the ewe and one from the ram – 15 out of 16 or 14 out of 16 is not good enough.

One of each of the two alleles of the genetic markers present can be traced to the ewe and the ram.

Verification of parentage is of great value to any breeder and result in the following advantages:

  • DNA-profiles enables individual identification (this is especially important in stock theft cases).
  • DNA-profiles are essential for verification of genetic descent.
  • Verification of genetic descent provides important information on flock dynamics.
  • It can be verified which ram bred which offspring (this is also especially important for commercial farmers). In this way, the most fertile rams are also identified.
  • The mating ability of rams can be assessed.
  • The Consumer Act permits the buyer the right to expect that all information about any purchase be correct and verified. Therefore, both the breed society and the breeder (seller) can be held responsible for all information on an auction catalogue. Legal consequences may follow on providing faulty information to the buyer.

Editorial Comments:
The council of Dohne Merino Breed Society decided that parentage verification is mandatory for all Dohne Merino rams taken to AI stations for the purpose of freezing semen from 2020 onwards. Breeders are further encouragedto test at least all young rams selected for own use and those to be sold as AA stud rams, to protect their own integrity. This information is very handy to market the accuracy of breeding values of a stud. The motivation for this decision is twofold in nature:

  1. As rightly noted above, accurate parentage of breeding animals is entrenched in the Consumer Act. Any consumer can insist on verifying parentage of, for example, a ram purchased at a production sale. By performing routine testing, each breeder not only strengthens his/her credibility when selling rams and protects integrity of his/her data, but also promotes the breed at international level.
  2. The use of genomics to stay ahead of technology is non-negotiable. The sooner DNA material is stored, the greater the competitive advantage that can be achieved. The starting point, of course, is that DNA material should be available of all animals that have a major genetic influence on the breed. Building a bank of accurate DNA material is now required. Individual breeders within the breed who are already participating in the program, will enjoy a competitive advantage that cannot be overtaken in the future.

Breeders must take hair samples from the foreleg of each ram involved as well as that of his father and mother, for analysis. As the information of more animals becomes known – for example, a ram’s father that has already been analysed, it will become necessary to analyse the animal and its mother only, or even just the animal itself.

Care must be taken to remove hair together with their follicles. The follicle, not the hair, is required for analysis. A large enough sample (estimated at least 60 follicles) must be sealed in an envelope and clearly marked with the animal’s complete identity. Note that NO contamination should occur with samples from other animals. At this stage, the cost of establishing such a parentage at Unistel is approximately R165 (excluding VAT). These costs may change, and breeders should please contact the laboratory of their choice for more specific information before taking samples.

Note that these samples can be stored indefinitely for complete genomic analysis. Other cell material such as an uncontaminated blood sample may also be used for such analysis as required by the specific laboratory.

Die toenemende belangstelling in tegnologie in landbou en die feit dat telerverenigings toenemend vereis dat ouerskap van diere bewys moet word met DNS ouerskaptoetse, maak dit ‘n goeie tyd om oorweging te skenk daaraan om ‘n DNS- profiel databasis van stoetdiere op te bou. DNS-profiel toetse word wêreldwyd as die standaard vir teelbevesting van plaasdiere aanvaar en om die integriteit van kudderekords te verseker die verbetering van teeltprogramme.

Die akkuraatheid van ouerskaptoetse is dus baie belangrik vir die geregistreerde skaapbedryf. Akkurate vaderskapbepaling is ook van groot waarde vir kommersiële skaapboere aangesien sulke toetse hulle in staat stel om die prestasie van hulle ramme te volg en om vaars en vaarlyne te identifiseer wat hoë prestasie nageslag produseer.

Ouerskapvestiging met behulp van DNS-profiele berus op identifikasie van bepaalde standaard DNS merkers bekend as mikrosatelliete. Hierdie genetiese merkers word gebruik om ‘n DNS “bloudruk” van ‘n dier op te stel. Die basiese teorie oor teelbevestiging berus op twee beginsels:

  • Die identifikasie van geneties geërfde merkers wat onveranderd bly en
  • Die kennis dat alle diere twee kopieë van elke merker besit waarvan een vanaf die ma en een van die pa afkomstig is.

Die DNS-profiel van ’n skaap, wat vir ouerskapbepaling gebruik word, bestaan uit 16 verskillende genetiese merkers soos deur die International Society for Animal Genetics (ISAG) gespesifiseer, met twee allele elk. Om ouerskap te bevestig, word die lam se DNS-profiel met díe van die genomineerde ooi en moontlike ram vergelyk. Aangesien die helfte van die lam se DNS van die ooi en helfte van die ram afkomstig is, moet albei ouers een alleel by elke merker bydra. Om seker te wees van ouerskap moet verkieslik beide ouers getoets word.

Die onderstaande illustrasie dui aan die volledige bevestiging van teling van ‘n lam.

Ouerskap word slegs bevestig indien al 16 pare allele herlei kan word, een vanaf die ooi en een vanaf die ram – 15 uit 16 of 14 uit 16 is nie goed genoeg nie.

Een van elk van die twee allele van die genetiese merkers teenwoordig, kan herlei word na die ooi en die ram.

Ouerskapbevestiging is van groot waarde en verseker die volgende:

  • DNS-profiel ontleding maak individuele identifikasie moontlik (dit is veral belangrik by veediefstalsake).
  • DNS-profiele is noodsaaklik vir teelbevestiging.
  • Teelbevestiging verskaf belangrike inligting oor trop- dinamika.
  • Daar kan bepaal word watter ram watter aanteel geteel het (dit is veral ook van belang vir kommersiële boere). Sodoende word die vrugbaarste ramme identifiseer.
  • ‘n Ram se dekvermoeë kan bepaal word.
  • Die Verbruikerswet vereis dat ‘n koper die reg het om daarop aan te dring dat alle inligting oor sy aankope korrek is en bevestig kan word. Dus kan ‘n vereniging asook die teler verantwoordelik gehou word vir alle inligting in ‘n veilingkatalogus. Sou die inligting foutief wees kan daar regsgevolge wees.

Redaksionele Kommentaar:
Die raad van die Dohne Merino Telersgenootskap het besluit dat verifiering van ouerskap vanaf 2020 verpligtend is vir alle Dohne Merino ramme wat na KI-stasies geneem word vir die doel om saad te vries. Dit word aanbeveel dat alle jong ramme wat vir eie gebruik geselekteer word asook diè wat as AA-stoetramme verkoop gaan word, se ouerskap te laat toets om hulle eie integriteit te beskerm. Telers kan dit gebruik om die akkuraatheid van hulle teeltwaardes te bemark. Die motivering vir hierdie besluit is tweerlei van aard nl.

  1. Soos tereg hierbo opgemerk, is akkurate ouerskap van teeltdiere in die verbruikerswet verskans. Enige verbruiker kan aandring op verifiering van ouerskap van ‘n ram wat op byvoorbeeld ’n produksieveiling aangekoop is. Roetine toetse deur elke teler, versterk nie alleen die geloofwaardigheid van die ras op internasionale vlak en by kuddeboere nie, maar beskerm die integriteit van die teler.
  2. Die gebruik van genomika om tegnologies voor te bly, is ononderhandelbaar. Hoe gouer DNS-materiaal gestoor word, hoe groter is die kompeterende voordeel wat behaal kan word. Die beginpunt is natuurlik dat DNS-materiaal beskikbaar moet wees vir alle diere wat ’n groot genetiese invloed uitoefen op die ras. Die opbou van ’n bank van akkurate DNS-materiaal is nou nodig. Individuele telers binne die ras wat nou reeds aan die program begin deelneem, sal ’n vorentoe ’n kompeterende voordeel geniet wat nie ingehaal kan word nie.

Telers moet haar monsters op die voorbeen van elke betrokke ram asook sy pa en ma neem vir ontleding. Namate die inligting van meer diere bekend raak – byvoorbeeld ’n ram se pa is reeds ontleed, mag dit naderhand nodig wees om net die dier en sy ma of selfs net die dier self, te laat ontleed.

Sorg moet gedra word dat die hare met follikel en al uitgetrek word. Die follikel, nie die haar nie, word benodig vir ontleding. ’n Groot genoeg monster (na skatting minstens 60 follikels) moet in ’n koevert verseel en duidelik gemerk word met die dier se volledige identiteit. Let op dat daar GEEN kontaminasie met monsters van ander diere moet plaasvind nie. Op hierdie stadium is die koste van so ’n ouerskapbepaling by Unistel ongeveer R165 (BTW uitgesluit). Hierdie koste kan verander en telers moet asseblief die laboratorium van hulle keuse kontak vir meer spesifieke inligting voor monsterneming.

Let daarop dat hierdie monsters onbeperk gestoor kan word vir volledige genomiese ontleding. Ander sel-materiaal soos ’n ongekontamineerde bloedmonster kan ook gebruik word vir sulke ontledings nagelang van die spesifieke laboratorium se vereistes.