novel approaches to expression and detection of oestrus in dairy cows
novel approaches to expression and detection of oestrus in dairy cows novel approaches to expression and detection of oestrus in dairy cows
treatment, followed by AI 48 hours later. However, pregnancy rates did not differ between Ovsynch and Heatsynch protocols (Pancarci et al., 2002). Progestagens can also be used to synchronise oestrus in cattle by use of internal releasing devices; PRID (progesterone-releasing intravaginal device) and CIDR (controlled-internal drug release) are progesterone releasing devices inserted into the vagina. Other devices are implanted into the ear, such as Norgestomet or are feed additives such as MGA (Melengestrol acetate; Yavas and Walton, 2000). Progesterone supplementation maintains progesterone concentration above 1ng/ml which suppresses oestrus and the LH surge, blocking ovulation (Lucy et al., 2004). Progesterone treatments are particularly useful for treating anoestrus; by decreasing LH initially then increasing LH pulsatility by priming hypothalamic centres to induce oestrus and then ovulation (Yavas and Walton, 2000). Progesterone can also overcome cystic ovaries in cows with a persistent dominant follicle that will not ovulate because of continuous exposure to high frequency LH pulses (Garverick, 1997). Administration of GnRH will can also remove the cystic structure by luteinisation (Garverick, 1997). Progesterone devices were initially used for 14-21 days and upon removal oestrus occurred within 3 days incurring a high oestrus response (Macmillan and Peterson, 1993), although conception rates in cows treated for long periods with progesterone are 10- 15% lower than those using short term protocols such as 7-9 days (Lucy et al., 2004). Here short progesterone treatments are now used with a luteolytic dose of PGF 2α 0-2 days before device removal (Lucy et al., 2004). If PGF 2α is administered before progesterone withdrawal there is a higher degree of synchrony (Macmillan and Peterson, 1993) due to removal of any functioning CL. Overall reproductive efficiency is still reportedly low in animals treated with both PGF 2α analogues and progesterone; calving rate was no different between treated (52%) and control (43%) cows (Roche, 1976). Furthermore, cows bred at a detected oestrus compared to fixed timed AI after prior progesterone synchronisation treatments have similar calving rates (Roche et al., 1977). Oestrous synchronisation has merit for synchronising whole herds in block calving systems, removing the need for oestrous detection as fixed time AI can be used (Lucy et al., 2004) and increasing the intensity and duration of oestrous symptoms as more cows are in oestrous at the same time (Hurnik et al., 1975;Van Vliet and Van Eerdenburg, 1996). Synchronisation also 14
educes the incidence of problem cows not showing oestrus as anoestrus and cystic cows can be induced into oestrus (Lucy et al., 2004). Therefore the advantages are that the submission rate of cows can be increased, and although conception rate is not necessarily higher, pregnancy rates may be increased through better detection of oestrus or removing the need for oestrus (Lucy et al., 2004). The availability of hormones and veterinary treatments can vary widely in cost and between countries due to local legislation and regulations. For example, the use of oestradiol is banned in the EU and US, but actively used in Australia and New Zealand. One major consideration in use of synchronisation to remove the need for oestrous detection is whether the benefits outweigh the cost. Profit from return of increased pregnancy rates and shortening the calving interval must outweigh the cost of hormones, labour and potential veterinary treatments for oestrous synchronisation to be widely used. This questions whether an accurate and efficient method of oestrous detection may be more beneficial over use of hormonal treatments as one major negative aspect of synchronisation is the consumer attitude to use of hormones in food production. Oestrous synchronisation is not a tool to improve fertility; the main benefit is improved oestrous detection because of more consistent results in detection. 1.3 OESTROUS DETECTION 1.3.1 General Overview Oestrus is the period of the oestrous cycle which is accompanied by overt behavioural characteristics caused by changing hormonal profiles, which is the signal for the physiological mechanism of ovulation (Roelofs et al., 2010). It has been reported that part of the reproductive decline is associated with the failure to observe oestrus and failure to interpret the signs of oestrus correctly (Reimers et al., 1985). More recently, Van Eerdenburg et al. (2002) reported oestrous detection rates on farm at less than 50%, but showed they could be up to 100% in cows displaying oestrous behaviour, if monitored continuously. Expression of oestrus is a problem as the intensity of oestrus has declined, averaging only 8.5 standing events per cow, and duration of oestrus (time between first and last sign of behavioural oestrus or episode of standing to be mounted) has shortened from 15 to 5 hours (Dobson et al., 2008), lasting only 7 hours 15
- 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 and 24: ecomes the main inhibitor of FSH an
- Page 25 and 26: calf at 40-50 days post partum; inv
- Page 27 and 28: al., 2006). However, aged sperm hav
- Page 29: can occur within 2-3 days, but if t
- 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
educes the <strong>in</strong>cidence <strong>of</strong> problem <strong>cows</strong> not show<strong>in</strong>g <strong>oestrus</strong> as an<strong>oestrus</strong><br />
<strong>and</strong> cystic <strong>cows</strong> can be <strong>in</strong>duced <strong>in</strong><strong>to</strong> <strong>oestrus</strong> (Lucy et al., 2004). Therefore<br />
the advantages are that the submission rate <strong>of</strong> <strong>cows</strong> can be <strong>in</strong>creased, <strong>and</strong><br />
although conception rate is not necessarily higher, pregnancy rates may be<br />
<strong>in</strong>creased through better <strong>detection</strong> <strong>of</strong> <strong>oestrus</strong> or remov<strong>in</strong>g the need for<br />
<strong>oestrus</strong> (Lucy et al., 2004).<br />
The availability <strong>of</strong> hormones <strong>and</strong> veter<strong>in</strong>ary treatments can vary widely <strong>in</strong><br />
cost <strong>and</strong> between countries due <strong>to</strong> local legislation <strong>and</strong> regulations. For<br />
example, the use <strong>of</strong> oestradiol is banned <strong>in</strong> the EU <strong>and</strong> US, but actively<br />
used <strong>in</strong> Australia <strong>and</strong> New Zeal<strong>and</strong>. One major consideration <strong>in</strong> use <strong>of</strong><br />
synchronisation <strong>to</strong> remove the need for oestrous <strong>detection</strong> is whether the<br />
benefits outweigh the cost. Pr<strong>of</strong>it from return <strong>of</strong> <strong>in</strong>creased pregnancy rates<br />
<strong>and</strong> shorten<strong>in</strong>g the calv<strong>in</strong>g <strong>in</strong>terval must outweigh the cost <strong>of</strong> hormones,<br />
labour <strong>and</strong> potential veter<strong>in</strong>ary treatments for oestrous synchronisation <strong>to</strong><br />
be widely used. This questions whether an accurate <strong>and</strong> efficient method <strong>of</strong><br />
oestrous <strong>detection</strong> may be more beneficial over use <strong>of</strong> hormonal<br />
treatments as one major negative aspect <strong>of</strong> synchronisation is the<br />
consumer attitude <strong>to</strong> use <strong>of</strong> hormones <strong>in</strong> food production. Oestrous<br />
synchronisation is not a <strong>to</strong>ol <strong>to</strong> improve fertility; the ma<strong>in</strong> benefit is<br />
improved oestrous <strong>detection</strong> because <strong>of</strong> more consistent results <strong>in</strong><br />
<strong>detection</strong>.<br />
1.3 OESTROUS DETECTION<br />
1.3.1 General Overview<br />
Oestrus is the period <strong>of</strong> the oestrous cycle which is accompanied by overt<br />
behavioural characteristics caused by chang<strong>in</strong>g hormonal pr<strong>of</strong>iles, which is<br />
the signal for the physiological mechanism <strong>of</strong> ovulation (Roel<strong>of</strong>s et al.,<br />
2010). It has been reported that part <strong>of</strong> the reproductive decl<strong>in</strong>e is<br />
associated with the failure <strong>to</strong> observe <strong>oestrus</strong> <strong>and</strong> failure <strong>to</strong> <strong>in</strong>terpret the<br />
signs <strong>of</strong> <strong>oestrus</strong> correctly (Reimers et al., 1985). More recently, Van<br />
Eerdenburg et al. (2002) reported oestrous <strong>detection</strong> rates on farm at less<br />
than 50%, but showed they could be up <strong>to</strong> 100% <strong>in</strong> <strong>cows</strong> display<strong>in</strong>g<br />
oestrous behaviour, if moni<strong>to</strong>red cont<strong>in</strong>uously. Expression <strong>of</strong> <strong>oestrus</strong> is a<br />
problem as the <strong>in</strong>tensity <strong>of</strong> <strong>oestrus</strong> has decl<strong>in</strong>ed, averag<strong>in</strong>g only 8.5<br />
st<strong>and</strong><strong>in</strong>g events per cow, <strong>and</strong> duration <strong>of</strong> <strong>oestrus</strong> (time between first <strong>and</strong><br />
last sign <strong>of</strong> behavioural <strong>oestrus</strong> or episode <strong>of</strong> st<strong>and</strong><strong>in</strong>g <strong>to</strong> be mounted) has<br />
shortened from 15 <strong>to</strong> 5 hours (Dobson et al., 2008), last<strong>in</strong>g only 7 hours<br />
15
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