Abstract
BackgroundEconomically important milk production traits including milk volume, milk fat and protein yield vary considerably across dairy goats in New Zealand. A significant portion of the variation is attributable to genetic variation. Discovery of genetic markers linked to milk production traits can be utilised to drive selection of high-performance animals.A previously reported genome wide association study across dairy goats in New Zealand identified a quantitative trait locus (QTL) located on chromosome 19. The most significantly associated single nucleotide polymorphism (SNP) marker for this locus is located at position 26,610,610 (SNP marker rs268292132). This locus is associated with multiple milk production traits including fat, protein and volume. The predicted effect of selection for the beneficial haplotype would result in an average production increase of 2.2 kg fat, 1.9 kg protein and 73.6 kg milk yield.An outstanding question was whether selection for the beneficial allele would co-select for any negative pleiotropic effects. An adverse relationship between milk production and udder health traits has been reported at this locus. Therefore, a genome wide association study was undertaken looking for loci associated with udder traits.ResultsThe QTL and production associated marker rs268292132 was identified in this study to also be associated with several goat udder traits including udder depth (UD), fore udder attachment (FUA) and rear udder attachment (RUA). Our study replicates the negative relationship between production and udder traits with the high production allele at position 19:26,610,610 (SNP marker rs268292132) associated with an adverse change in UD, FUA and RUA.ConclusionsOur study has confirmed the negative relationship between udder traits and production traits in the NZ goat population. We have found that the frequency of the high production allele is relatively high in the NZ goat population, indicating that its effect on udder conformation is not significantly detrimental on animal health. It will however be important to monitor udder conformation as the chromosome 19 locus is progressively implemented for marker assisted selection. It will also be of interest to determine if the gene underlying the production QTL has a direct effect on mammary gland morphology or whether the changes observed are a consequence of the increased milk volume.
Highlights
Important milk production traits including milk volume, milk fat and protein yield vary considerably across dairy goats in New Zealand
A chromosome 19 quantitative trait locus (QTL) associated with goat udder health traits in the NZ goat population We report a single genome wide significant QTL for several udder health traits including udder depth, fore udder attachment and rear udder attachment (Table 2 & Fig. 1)
A QTL signal was detected for teat angle and udder furrow at the same locus but did not reach genome wide significance
Summary
Important milk production traits including milk volume, milk fat and protein yield vary considerably across dairy goats in New Zealand. A previously reported genome wide association study across dairy goats in New Zealand identified a quantitative trait locus (QTL) located on chromosome 19. The most significantly associated single nucleotide polymorphism (SNP) marker for this locus is located at position 26,610,610 (SNP marker rs268292132) This locus is associated with multiple milk production traits including fat, protein and volume. Genetic gain focused on production for the dairy goat population in New Zealand is limited largely to within farm selection and some buck transfers between farms. This has resulted in considerable unrealised marker driven selection potential which led to the search for and discovery of quantitative trait loci (QTL) for milk production traits in a subset of the population. The non-synonymous C636R mutation in bovine Mannose Receptor C Type 2 (MRC2) gene increased muscularity in meat breeds but caused Crooked Tail Syndrome [6, 7]
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