novel approaches to expression and detection of oestrus in dairy cows

positives. Therefore it is likely that in reality this study found no true
associations using this experimental approach.
Furthermore the animal numbers used in this study were seriously limited
and a substantial number of cows (at least 20000) would be required to
achieve meaningful results.
3.4.1 Limitations of Study
Limitations of this study are that the animal numbers used in the study
were small and thus seriously limited the study. Although these results
indicate an association between activity and 2 SNPs, the true significance is
questionable. Therefore a much larger population of at least 20000 cows,
but ideally approximately 200000 cows, would be required to assess the
true effects of each SNP and achieve meaningful results. Furthermore,
much larger datasets are needed to make associations between SNPs and
traits of low heritability (Berry et al., 2012). In the current study one
particular limitation is that the effects of certain SNPs (although not
significant) seem greater because of the low frequency of alleles. To
improve this it would be advantageous to have representative cohorts of
cows for each SNP allele. To extend this work it would also be
advantageous to include pedigree information and investigate oestrous
expression of many daughters from a few select sires.
Considerable challenges arise from this type of research relating to the
quality of data collected; the observed effects may be attributable to
closely linked genes, variations in a gene, or result directly from the
experimental design (Veerkamp and Beerda, 2007) thereby occurring by
chance or due to artefacts. Another approach to improve upon the current
study would be to carry out a genome wide association study to assess if
any common genetic variants are associated with a particular trait of
interest. Using this approach to investigate SNPs simultaneously for their
effects on oestrous expression would control the rate of false positives
(Berry et al., 2012) and would avoid random significant associations as
seen in this study. This would allow genes to be identified near the SNP
and allow for further investigation into the causal effects of these genes
(Hoglund et al., 2012) without speculation about the physiological
mechanisms involved. Careful interpretation of the data must also be
carried out to ensure that the association between genotype and
phenotype is plausible, and that the SNP of significance is related to
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