PHYSIOLOGY AND ENDOCRINOLOGY SYMPOSIUM: How single nucleotide polymorphism chips will advance our knowledge of factors controlling puberty and aid in selecting replacement beef females1,2,3,4

Abstract

ABSTRACT:The promise of genomic selection is accurate prediction of the genetic potential of animals from their genotypes. Simple DNA tests might replace low-accuracy predictions for expensive or lowly heritable measures of puberty and fertility based on performance and pedigree. Knowing with some certainty which DNA variants (e.g., SNP) affect puberty and fertility is the best way to fulfill the promise. Several SNP from the BovineSNP50 assay have tentatively been associated with reproductive traits including age at puberty, antral follicle count, and pregnancy observed on different sets of heifers. However, sample sizes are too small and SNP density is too sparse to definitively determine genomic regions harboring causal variants affecting reproductive success. Additionally, associations between individual SNP and similar phenotypes are inconsistent across data sets, and genomic predictions do not appear to be globally applicable to cattle of different breeds. Discrepancies may be a result of different QTL segregating in the sampled populations, differences in linkage disequilibrium (LD) patterns such that the same SNP are not correlated with the same QTL, and spurious correlations with phenotype. Several approaches can be used independently or in combination to improve detection of genomic factors affecting heifer puberty and fertility. Larger samples and denser SNP will increase power to detect real associations with SNP having more consistent LD with underlying QTL. Meta-analysis combining results from different studies can also be used to effectively increase sample size. Highdensity genotyping with heifers pooled by pregnancy status or early and late puberty can be a cost-effective means to sample large numbers. Networks of genes, implicated by associations with multiple traits correlated with puberty and fertility, could provide insight into the complex nature of these traits, especially if corroborated by functional annotation, established gene interaction pathways, and transcript expression. Example analyses are provided to demonstrate how integrating information about gene function and regulation with statistical associations from whole-genome SNP genotyping assays might enhance knowledge of genomic mechanisms affecting puberty and fertility, enabling reliable DNA tests to guide heifer selection decisions.

Heifer fertility and carry over consequences for life time production in dairy and beef cattle

“…Age at puberty, which in turn is associated with growth rate and mature size, has a moderate estimated heritability of 0.25 to 0.4 (Martin et al, 1992;Snelling et al, 2012). In dairy cows, milk production is positively correlated with size (Lin et al, 1987) which has contributed to selection for larger animals even though these are not necessarily the most efficient.…”

The impact of cow nutrient status during the second and third trimesters on age at puberty, antral follicle count, and fertility of daughters

“…A novel finding in this study was that heifers that calved in the first 21 d of their first calving season had greater numbers of antral follicles detectable by ultrasonography at 14 months of age. Antral follicle count has been reported as an indicator of fertility in heifers and cows in a numbers of studies (Cushman et al, 2009;Mossa et al, 2012;Tessaro et al, 2011); however, there have also been studies where antral follicle count did not reflect fertility in cattle (Snelling et al, 2012;Starbuck-Clemmer et al, 2007). Mossa et al (2012) reported a tendency for dairy cows with low follicle numbers to have an increased number of services per conception and lower pregnancy rates in a seasonal production system.…”

PHYSIOLOGY AND ENDOCRINOLOGY SYMPOSIUM: Factors controlling puberty in beef heifers1

“…As the second speaker of the symposium, Snelling et al (2012) speculated that simple tests for DNA variants among animals (i.e., SNP) may replace low-accuracy predictions for expensive or lowly heritable measures of puberty and fertility based on performance and pedigree. Although several SNP from the BovineSNP50 assay have tentatively been associated with reproductive traits including age at puberty, antral follicle count, and pregnancy observed on different sets of heifers, sample sizes are too small and SNP density is too sparse to definitively determine genomic regions containing causal variants affecting reproductive success.…”

“…In looking toward the future, larger samples and denser SNP chips will increase power to detect real associations with SNP having more consistent linkage disequilibrium with underlying QTL. Snelling et al (2012) concluded by presenting example analyses to demonstrate how integrating information about gene function and regulation with statistical associations from whole-genome SNP genotyping assays might enhance knowledge of genomic mechanisms affecting puberty and fertility, thereby enabling reliable DNA tests to guide heifer selection decisions. Funston et al (2012), the third speaker for the symposium, discussed nutritional aspects of developing replacement heifers.…”

“…The Physiology and Endocrinology Symposium on "Factors controlling puberty in beef heifers" encouraged attendees to consider novel nutritional management approaches to hasten the onset of puberty in beef heifers (Lamb et al, 2011;Funston et al, 2012), to apply basic knowledge gained through research to hormonally manipulate the reproductive process to improve reproductive success (Perry, 2012), and to consider new technologies such as SNP that may play a future role in selecting beef heifers for reproductive success (Snelling et al, 2012). The 2011 Physiology and Endocrinology Symposium enhanced our understanding of the latest nutrition, physiology, and genetic research on puberty in beef heifers.…”