novel approaches to expression and detection of oestrus in dairy cows

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In the non-pregnant cow the corpus luteum undergoes luteolysis around day 17. Oxytocin produced by the corpus luteum binds to oxytocin receptors on the endometrial membrane, stimulating pulsatile release of prostaglandin F 2α (PGF 2α ) (Flint and Sheldrick, 1983). Oxytocin receptor concentration in the uterus increases throughout the cycle, especially from day 15 to 17 (Robinson et al., 1999), binding oxytocin and inducing the episodic secretion of PGF 2α from the uterine endometrium. PGF 2α controls CL breakdown, causing decreased progesterone concentrations, reducing the inhibitory effect of high progesterone concentrations (Robinson et al., 2001). This removes the negative inhibition of GnRH secretion resulting in increased LH secretion stimulating increased oestradiol concentrations observed during the follicular phase. In the pregnant cow the conceptus must signal its presence in order to prevent luteolysis. Progesterone inhibits oxytocin receptor expression in the early to mid luteal phase (Robinson et al., 2001) but the conceptus must signal its presence by producing the maternal recognition of pregnancy signal, interferon tau (IFNτ). The antiluteolytic effects of IFNτ physiologically signal the presence of the conceptus (Demmers et al., 2001). This occurs between days 16-18 when the trophectoderm has produced sufficient quantities of IFNτ and thus prevents the increase in oxytocin receptors. However for IFNτ to be produced the trophoblast must have begun to elongate from spherical to filamentous; no IFNτ production occurs if the embryo is still spherical, regardless of day of the oestrous cycle (Robinson et al., 2006). Pulsatile release of PGF 2α from the uterus is blocked because IFNτ inhibits oxytocin receptor expression on the endometrium. This occurs because oestrogen (which induces oxytocin receptor expression) is reduced by pathways decreasing oestrogen receptor concentrations (Demmers et al., 2001), and progesterone concentrations remain high which are necessary to maintain pregnancy. 1.2.2 Management of Reproduction Management of reproduction is important as improved reproductive efficiency is essential for efficient milk production and strongly influences the profitability of the herd. Strict management parameters must be adhered to in order to produce one calf per cow per year, to keep within an optimal calving interval of approximately 365 days; including a gestation period of approximately 270 days. Therefore to keep within the desired calving interval, depending on the management scenario, cows must be in 8
calf at 40-50 days post partum; involving the steps of uterine involution, resumption of oestrous cycles, expression and detection of oestrus and insemination (Royal et al., 2000a). This is more important when producers operate to a block calving regime when cows have to be in calf at strict intervals, usually within 60-90 days post partum or they risk being culled for infertility. Although it is still important to try and adhere to a strict calving interval when employing all year round calving, as it is not always desirable to have extended calving intervals, due to fluctuation in yield with stage of the lactation curve. One of the largest contributors to extended calving intervals however, is the percentage of cows ovulating that are not detected in oestrus, causing the biggest losses to the dairy industry (Van Vliet and Van Eerdenburg, 1996;Peralta et al., 2005). Cows must be detected in oestrus so that artificially insemination (AI) coincides with ovulation at the optimal time for conception to occur. Bulls are more accurate at determining true oestrus, but there are major benefits associated with the use of AI, which explains the popularity of AI, and highlights further the importance of oestrous expression and detection. 1.2.2.1 AI vs. Natural Service One of the main reasons for reproductive technologies, namely AI, are to increase reproductive potential and control breeding for genetic gain so that desirable characteristics are inherited. This approach involves the need for accurate oestrous detection, whereas bulls can detect pheromones and oestrus much more accurately (Lopez-Gatius et al., 2005). However, although bulls are advantageous in this context, and can ‘clean up’ fertilising cows when AI has failed (Lima et al., 2009) they can be dangerous on farm, and diseases are more readily transmitted (Dobson et al., 2008). AI allows for smaller quantities of semen to be used than is the case during natural mating, therefore genetically superior bulls can fertilise a greater number of cows by using AI. Predicted transmitting abilities (PTAs) are readily available and included in the Fertility Index, for selection of desirable daughter traits when choosing a suitable bull for AI thus controlling heritable traits (Flint, 2002;Wall, 2003). Another advantage of using AI in the dairy industry is the ability to use sexed semen. Heifer calves are required to expand the herd and increase progress with herd 9
Page 1 and 2: NOVEL APPROACHES TO EXPRESSION AND
Page 3 and 4: TABLE OF CONTENTS TABLE OF CONTENTS
Page 5 and 6: 2.2.3 Statistical Analyses ........
Page 7 and 8: 5.3 RESULTS .......................
Page 9 and 10: Furthermore, automated software was
Page 11 and 12: LIST OF FIGURES Figure 1.1 Hormonal
Page 13 and 14: LIST OF TABLES Table 1.1 Trends in
Page 15 and 16: LIST OF ABBREVIATIONS ˚ ˚C μM 2D
Page 17 and 18: CHAPTER 1 - Introduction & Literatu
Page 19 and 20: the past 50 years and duration of o
Page 21 and 22: Oestrus growing follicle (Staigmill
Page 23: ecomes the main inhibitor of FSH an
Page 27 and 28: 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 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 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
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
Page 141 and 142:
Page 143 and 144:
Page 145 and 146:
Page 147 and 148:
Activity Activity Activity Activity
Page 149 and 150:
Page 151 and 152:
Page 153 and 154:
5.4 DISCUSSION The aim of this work
Page 155 and 156:
averaged 70% which was lower than t
Page 157 and 158:
when the cows lie down, especially
Page 159 and 160:
the level of oestrous activity was
Page 161 and 162:
technology larger herds must be mon
Page 163 and 164:
monitoring could also monitor non-l
Page 165 and 166:
antennae which could affect accurac
Page 167 and 168:
predispose cows to illness e.g. met
Page 169 and 170:
CHAPTER 6 - Overall Discussion & Co
Page 171 and 172:
oestrus, h 2 =0.27 (Lovendahl et al
Page 173 and 174:
The final section of this thesis de
Page 175 and 176:
ate. By using UWB in a commercial s
Page 177 and 178:
provides an insight the potential o
Page 179 and 180:
BLOWEY, R. (2005) Factors associate
Page 181 and 182:
ovine gonadotrophin releasing hormo
Page 183 and 184:
GINTHER, O. J., KOT, K., KULICK, L.
Page 185 and 186:
associated with embryonic survival
Page 187 and 188:
ody condition at parturition on end
Page 189 and 190:
Signs in a 24-h Tie-Stalled Dairy H
Page 191 and 192:
SHERMAN, E. L., NKRUMAH, J. D., MUR
Page 193 and 194:
Influence of negative energy balanc
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