As explained by Ms. Charné Rossouw-Claassen, a division manager for animal genetics, in the 2023 Brangus Journal, genetic testing is well-known in scientific communities but can still be confusing for agricultural producers. Understanding the different DNA technologies and how they can be used to meet specific breeding goals is crucial. Ms. Rossouw-Claassen identifies three main areas of genetic livestock testing: simple-heritable trait testing, parentage testing, and genomic value testing.
All genetic testing is based on the principle of heredity—the concept that half of an animal’s genetic information comes from its mother (dam) and the other half from its father (sire). An international DNA marker panel has been developed to verify an animal’s parentage. DNA markers are divided into alleles, with one allele inherited from each parent. A calf’s DNA marker profile will be a random combination of both parents' alleles. For parentage to be valid, the calf’s DNA markers must show one identical allele from the mother and one from the father at each marker.
In genetics, mutations can sometimes occur, though they aren’t always beneficial. Some mutations found in Brangus cattle include:
- Arthrogryposis Multiplex (curly calf): Affected calves are stillborn with contracted, elongated limbs and a twisted spine.
- Alpha-Mannosidosis: A nervous system disease that is fatal. Affected animals usually do not make it to sexual maturity.
- Development duplication: A very high probability of early embryonic death. Calves are usually born with multiple limbs, if additional limbs are removed early, they can have a good chance at a full life.
- Contractual Arachnodactyly: of affected calves born, most can walk, survive and suckle. They have reduced range of motion in their upper limb joints (stifle, hip and heel).
- Horn genes: Calves that are affected do not naturally develop horns.
- Double Muscling: The suppression of myostatin protein enhances muscle growth.
- Osteopetrosis (Marble bone): Typically characterized by premature stillbirths – 10 days to one month before term, inferior brachygnathia, easily broken long bones and impacted molars.
- Neuropathic Hydrocephalus: Calves affected are stillborn with an excessively large skull, with little to no spinal cord or brain material.
- Syndactyly (Mulefoot): Characterized by merging of the claws in one, two, three or in some cases four legs.
Genetic Evaluation:
Genomic testing uses thousands of DNA markers, called single nucleotide polymorphisms (SNPs), to link phenotypic and genetic characteristics and calculate an animal’s genetically improved breeding value. The 50K SNP chip is the most common genomic test for cattle, studying around 54,000 markers evenly distributed across the bovine genome. This test generates a genomic profile for each animal, providing valuable insights for selecting breeding stock.
Pedigree and performance data are crucial to the accuracy of genetic merit predictions. Genotyping younger animals improves the accuracy of these predictions by giving a 'snapshot' of their genetics before investing in them. This early genetic insight helps producers identify economically important traits, like reproduction and meat tenderness, and make informed breeding decisions.
With the advancement of genetic technology, producers can now have greater confidence in their herd’s bloodlines and use testing to select for desired traits while eliminating undesirable ones. This allows for early decision-making regarding breeding stock and enhances the overall efficiency of breeding programs.
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