novel approaches to expression and detection of oestrus in dairy cows

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season of attainment of puberty can influence age at puberty in heifers (Schillo et al., 1983). Seasonal changes in peripheral concentrations of gonadotrophins have been reported (Critser et al., 1987), which could explain the influence of season and photoperiodic variations in activity levels at oestrus. An increase in LH release in cows has been reported in summer compared to winter (Hansen et al 1982), perhaps related to the effects of oestradiol, as described for the sheep (Legan et al., 1977). This might explain how photoperiod can affect reproductive behaviour, especially oestrous expression. 2.4.2 Effect of Milk Yield on Increase in Activity There was an association between increasing milk yield and declining activity and oestrous expression. This trend follows the widely recognised change in cattle reproductive physiology recorded over the past 50+ years, coupled with rapidly increasing milk production since the 1950s (Lucy, 2001). The average increase in yield from 2010/11 to 2011/12 is 241 litres per cow with the average yield at 7617 litres per cow per annum (provisional 2012 data; DairyCo, 2012a). However poor conception rates still persist (Royal et al., 2000a;Butler, 2003). High milk yields have been reported to affect oestrous expression. Harrison et al., (1990) reported that low yielders showed stronger oestrous expression than high yielders. When comparing the duration of oestrus in high and low yielders, low yielders had a longer duration of oestrus, 10.9 vs. 6.2 hours. Total standing events was also increased, 8.8 vs. 6.3, as was total standing time, 28.2 vs. 21.7 seconds (Lopez et al., 2004). Studies of activity also concur with the results of the current study where there was a clear pattern between high milk production and lower activity at oestrus (Yániz et al., 2006). Lopez-Gatius et al. (2005) also reported that for each 1kg increase in milk yield walking activity at oestrus decreased by 1.6%. Possible explanation for the effects of milk yield on reduced activity at oestrus is through the interlinking reproductive and somatotropic axes which can be influenced by metabolite levels and influence hormone production (Chagas et al., 2007). High yielding animals require a high plane of nutrition, which increases the rate of metabolic clearance by the liver, rapidly removing steroid hormones, oestradiol and progesterone from 64
the blood (Sangsritavong et al., 2002). This results in lower circulating oestradiol and a reduced duration in the system (Lopez et al., 2004), which could impact on oestrous expression. Furthermore NEBAL related to high producing cows (discussed in Section 2.4.1.1) can affect the level of oestrous expression. NEBAL attenuates LH pulse frequency which inhibits oestradiol secretion which in turn prevents ovulation. Low energy status coupled with supressing LH pulses also seems to reduce the responsiveness of the ovary to LH, again inhibiting the production of oestradiol (Butler, 2003) with subsequent impacts upon oestrous expression. Furthermore NEBAL is strongly associated with low levels of blood glucose, insulin and IGF-1 post partum which can limit oestradiol production by the dominant follicle. Metabolic demand causes a reduction in levels of glucose, insulin ang IGF-1. Glucose and insulin are associated with the upregulation of LH receptors in the ovary. Indeed insulin and IGF-1 are linked as IGF-1 production is affected by circulating insulin concentrations. IGF-1 levels are also directly related to energy levels are correlate with oestradiol concentrations. This results in an alteration of the sensitivity of the response of the pituitary gland to GnRH, affecting LH pulses, influencing ovarian follicular development and the capability of the follicles to produce oestradiol (Butler, 2003). Milk yield is also affected by season and photoperiod thought to be associated with the effects of increasing IGF-1 related to long day photoperiod increasing milk yield (Dahl et al., 2000). Therefore oestrous expression may be affected through increased yield and the effects of IGF- 1 influencing oestradiol production. 2.4.3 Activity Increase and Conception Rate In the current study when activity was increased, the probability of conception occurring increased although this results was not significant (P=0.064). Out of 773 inseminations at observed oestrus only 243 resulted in pregnancy. It has been reported that the probability of conception occurring increases with increasing oestrous number (Darwash et al., 1997b). Also the chance of a cow conceiving is increased with greater oestradiol levels (Lopes et al., 2007;Perry et al., 1991). Pre-ovulatory follicle size has been directly related to oestradiol concentration on the day of AI (P
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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
Page 29 and 30: can occur within 2-3 days, but if t
Page 31 and 32: educes the incidence of problem cow
Page 33 and 34: oestradiol, the LH surge and ovulat
Page 35 and 36: The secondary signs of oestrus can
Page 37 and 38: There are also changes in normal be
Page 39 and 40: engage in more natural behaviours i
Page 41 and 42: 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: oestrous expression with increasing
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 and 94: 3.4 DISCUSSION The objectives of th
Page 95 and 96: fertility and oestrous expression.
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
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Figure 5.2 Graph showing mounting b
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Table 5.1 Results from POC 2 showin
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Table 5.3 Efficiency and accuracy o
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oestrus and oestrus it is clear to
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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
Page 193 and 194:
Influence of negative energy balanc
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