novel approaches to expression and detection of oestrus in dairy cows

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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 78
fertility and oestrous expression. However success of this type of study depends on the heritability of the trait, where heritability of oestrous expression is low, but also the number of phenotypic records of that trait (Berry et al., 2012). To improve upon this study multiple measurements for oestrous expression could be used such as maximum activity at oestrus, percentage increase in activity at oestrus, days to first episode of high activity and days to commencement of luteal activity. Furthermore, using physiological measurements of oestrus gives a more accurate interpretation of oestrus that is less affected by management factors and the environment. 3.4.2 Implications of a Genomic Approach Implications of using genomic selection over traditional genetic selection are that the improvements in genetic gain are realised quicker than using traditional selection methods. Therefore identification of SNPs for improved oestrous expression could lead to inclusion of SNPs in breeding programmes and thus aid reversal of the decline in oestrous detection rates. Genomic selection is a revolutionary technology enhancing dairy cattle breeding, with the amount of information on a molecular level rapidly increasing due to sequencing of the bovine genome in 2003 (http://www.hgsc.bcm.tmc.edu/projects/bovine). Studying SNPs and their variation and making links between physiological data allows this information to be used in selection programs and incorporation into the fertility index (Berglund, 2008). Because of the low heritability of reproductive traits, h2=
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NOVEL APPROACHES TO EXPRESSION AND
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TABLE OF CONTENTS TABLE OF CONTENTS
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2.2.3 Statistical Analyses ........
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5.3 RESULTS .......................
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Furthermore, automated software was
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LIST OF FIGURES Figure 1.1 Hormonal
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LIST OF TABLES Table 1.1 Trends in
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LIST OF ABBREVIATIONS ˚ ˚C μM 2D
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CHAPTER 1 - Introduction & Literatu
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the past 50 years and duration of o
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Oestrus growing follicle (Staigmill
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ecomes the main inhibitor of FSH an
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calf at 40-50 days post partum; inv
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al., 2006). However, aged sperm hav
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can occur within 2-3 days, but if t
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educes the incidence of problem cow
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oestradiol, the LH surge and ovulat
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The secondary signs of oestrus can
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There are also changes in normal be
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engage in more natural behaviours i
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1983). Exact explanations and mecha
Page 43 and 44: 2006) and disruption of LH secretio
Page 45 and 46: 1.4.3.2 Milk Yield and Nutrition Di
Page 47 and 48: influence the ability of the ovary
Page 49 and 50: cyclicity can be delayed if dietary
Page 51 and 52: indication for the optimal time to
Page 53 and 54: calving), 3) pre-breeding heat date
Page 55 and 56: 1.5.2 Physiological Changes Physiol
Page 57 and 58: 1.5.2.3 Body and Milk Temperature T
Page 59 and 60: physical activity and stage of the
Page 61 and 62: caused by the general environment t
Page 63 and 64: may be gained. This is because data
Page 65 and 66: In summary the objective was to for
Page 67 and 68: diet, with concentrates at milking.
Page 69 and 70: oestrus was defined as 3 consecutiv
Page 71 and 72: The interaction between parity and
Page 73 and 74: individual oestrus was not signific
Page 75 and 76: Table 2.4 The effects of the intera
Page 77 and 78: (361 vs. 578 points, respectively,
Page 79 and 80: oestrous expression with increasing
Page 81 and 82: the blood (Sangsritavong et al., 20
Page 83 and 84: CHAPTER 3 - Single Nucleotide Polym
Page 85 and 86: population owing to previous select
Page 87 and 88: Table 3.1 Cont. Follicle Stimulatin
Page 89 and 90: 3.2.4 Sequencing of DNA in the Labo
Page 91 and 92: was achieved. PCR products were rem
Page 93: 3.4 DISCUSSION The objectives of th
Page 97 and 98: CHAPTER 4 - Development of a Novel
Page 99 and 100: In summary UWB seems a good option
Page 101 and 102: Initial tests were carried out to i
Page 103 and 104: Therefore this demonstrates that X
Page 105 and 106: which is most important for achievi
Page 107 and 108: Figure 4.9 Horizontal - Vertical Di
Page 109 and 110: that UWB is matching the ‘truth
Page 111 and 112: mounting cow. For example height ch
Page 113 and 114: Backpack 1 st put on in AI stalls E
Page 115 and 116: Cows’ behaviour was assessed at 5
Page 117 and 118: or that the cows were in an area of
Page 119 and 120: plane, but mostly in achieving high
Page 121 and 122: Develop techniques for analysis of
Page 123 and 124: in elastic silicone moulded over a
Page 125 and 126: and time of mount, duration of moun
Page 127 and 128: observed matched with increases in
Page 129 and 130: 5.3 RESULTS Results demonstrate pos
Page 131 and 132: Figure 5.2 Graph showing mounting b
Page 133 and 134: Table 5.1 Results from POC 2 showin
Page 135 and 136: Table 5.3 Efficiency and accuracy o
Page 137 and 138: oestrus and oestrus it is clear to
Page 139 and 140: P4 Concentration, ng/ml P4 Concentr
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P4 Concentration, ng/ml P4 Concentr
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Activity Activity Activity Activity
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5.4 DISCUSSION The aim of this work
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averaged 70% which was lower than t
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when the cows lie down, especially
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the level of oestrous activity was
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technology larger herds must be mon
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monitoring could also monitor non-l
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antennae which could affect accurac
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predispose cows to illness e.g. met
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CHAPTER 6 - Overall Discussion & Co
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oestrus, h 2 =0.27 (Lovendahl et al
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The final section of this thesis de
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ate. By using UWB in a commercial s
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provides an insight the potential o
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BLOWEY, R. (2005) Factors associate
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ovine gonadotrophin releasing hormo
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GINTHER, O. J., KOT, K., KULICK, L.
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associated with embryonic survival
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ody condition at parturition on end
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Signs in a 24-h Tie-Stalled Dairy H
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SHERMAN, E. L., NKRUMAH, J. D., MUR
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Influence of negative energy balanc
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