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    Improving the response to synchronisation programmes of dairy cattle : a thesis presented in partial fulfilment of the requirement for the degree of Doctor of Philosophy in Veterinary Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2014) Sahu, Santosh Kumar
    A gonadotrophin, prostaglandin, gonadotrophin + progesterone (GPG+P4) programme with fixed-time artificial insemination (FTAI) is the current recommended synchronisation programme for both heifers and anoestrous cows on New Zealand dairy farms. However, it is an expensive programme and a better understanding of the role of all of its components would be very useful in developing alternative cheaper programmes. The two components of the programme that are the least understood, in terms of their underlying physiological actions and how they influence the outcome of synchronisation, are the Day 0 gonadotrophin-releasing hormone (GnRH) injection and the progesterone device. Additionally it is well known that energy status has a significant impact on fertility but there is little evidence, particularly under New Zealand conditions, of how energy status affects the response to GPG-based treatments in anoestrous postpartum dairy cows. The effects of a GPG (Day 0: 100 µg GnRH, Day 7: 500 µg PGF2a, Day 9: 100 µg GnRH) programme upon follicular and luteal dynamics, ovulation synchronisation and patterns of oestradiol and progesterone secretion in postpartum anoestrous dairy cows and nulliparous dairy heifers were compared with (i) a GPG programme plus a progesterone insert from Days 0–7 (GPG+P4) and (ii) a GPG+P4 programme from which the first GnRH treatment had been omitted (P+G+P4). Interactions of each treatment with energy balance, as determined by NEFA, IGF-I and insulin concentrations, were also studied in postpartum anoestrus cattle. Finally the conception rate (CR) to fixed time AI of a GPG+P4 programme in which AI was done concurrent with the Day 9 GnRH injection (Cosynch) was compared with a progesterone + prostaglandin programme (P4+PG; Day 0–7: progesterone releasing intravaginal device, morning of Day 6: 500 µg PGF2a, afternoon of Day 9: FTAI) in heifers. The physiological effects of the GPG and the GPG+P4 programmes were similar in anoestrous dairy cows. The inclusion of the Day 0 GnRH still appeared feasible in a GPG programme for treating anoestrous cows as it led to a higher probability of a corpus luteum (CL) on Day 7. In addition, treatment response was significantly affected by the postpartum duration and negative energy balance as evidenced by the significantly higher NEFA concentrations on Days 0, 7 and 9, and a lower insulin concentration on Day 0, in cows that failed to ovulate in response to the synchronisation protocol compared with cows that did ovulate. A clear and significant relationship between NEFA concentrations and ovulation in response to all synchronisation protocols showed that, regardless of the regimen that was used to treat anoestrus, the response was moderated and limited by the degree of negative energy balance. In heifers, the removal of the progesterone-releasing device from a GPG+P4 programme had no effect on follicular dynamics or on the proportion of heifers which ovulated after either the GnRH injection on Day 0 or Day 9. Additionally, unlike the anoestrus cows, omitting the GnRH injection on Day 0 did not result in significantly delayed ovulation at the end of the programme, inasmuch as treatment with P+G+P4 was associated with earlier ovulation than GPG. Furthermore, synchronising heifers with a significantly less expensive programme (P4+PG) resulted in similar CR to synchronising with GPG+P4 (54.8% versus 52.4%, respectively) further confirming that Day 0 GnRH was not essential in heifer synchrony. In conclusion, the higher conception rate in cows treated with a GPG+P4 programme rather than a GPG programme reported previously does not seem to be modulated by the actions on follicular dynamics and improved synchronised ovulation in dairy cattle with postpartum anoestrous (or in nulliparous heifers); however, the treatment response in anoestrous cows can be significantly affected by negative energy balance. In contrast, in dairy heifers, no benefit of Day 0 GnRH or the progesterone device in a GPG+P4 programme suggests the possibility of more cost effective options (e.g. P4+PG) which can lead to a CR as high as those synchronised using a GPG+P4 programme.
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    The use of oestradiol benzoate and progesterone to synchronise oestrus in dairy cattle : a thesis presented in partial fulfilment of the requirements for the degree of Master of Veterinary Science at Massey University
    (Massey University, 1995) Hanlon, David William
    Current oestrus synchronisation regimes for cattle are based on synchronising the end of the progestational phase of the oestrous cycle so that ovulation occurs simultaneously in treated animals. The end of the progestational phase can be synchronised through inducing premature luteolysis using prostaglandin F2α and its analogues or by artificially extending dioestrus using exogenous progesterone treatment. The time taken for subsequent follicular maturation and ovulation tends to be inconsistent between animals, which contributes to the poor fertility obtained following fixed-time insemination after oestrus synchronisation treatments. The variable rate of follicular development occurring after a synchronous decline in plasma progesterone levels is a major limiting factor in achieving a degree of synchrony of oestrus and ovulation which would allow for fixed-time insemination. Controlling the time of ovulation using exogenous oestrogen to induce a preovulatory LH surge is a potential method by which the variability in timing of ovulation may be reduced. Alternatively, re-setting follicular wave patterns in different animals at the commencement of synchrony treatments using exogenous oestrogen, so that follicular wave emergence is synchronised, is another method by which the variability in timing of ovulation could be reduced. A clinical trial was conducted involving 750 dairy heifers in 13 herds to determine the effects of 0.5 mg oestradiol benzoate administered intramuscularly 24 hours after removal of progesterone-containing intravaginal devices (CIDR-B) on the occurrence and timing of oestrus, synchronised pregnancy rate and synchronised conception rate in dairy heifers. Within each herd heifers were randomly allocated to one of two oestrus synchronisation treatments. All heifers received a CIDR-B progesterone-containing intravaginal device with an attached 10 mg oestradiol benzoate capsule for 12 days. Twenty-four hours after CIDR-B removal one group received an intramuscular injection of 0.5 mg oestradiol benzoate and the other group received an intramuscular injection of a placebo. Heifers were inseminated to detected oestrus 48 and 72 hours after device removal. Administration of oestradiol benzoate 24 hours after removal of CIDR-B devices significantly increased the number of heifers exhibiting oestrus within the observation period (96.1%; vs 90.5%, p <0.01). It also altered the onset of oestrus so that significantly more heifers were in oestrus (86.6% vs 72.3%, p<0.01) and conceived (47.1% vs 37,5%, p<0.05) by 48 hours after device removal. The overall synchronised conception rate and synchronised pregnancy rate were unaffected by treatment. The effects of the same oestrus synchronisation treatment, on the time to oestrus, ovulation, and peak LH concentration were examined in dairy heifers. Treatment with oestradiol benzoate tended to reduce the time from device removal to LH peak in randomly cycling heifers (median time to LH peak 40.1 hr vs 63.9 hr, p=0.07), but treatment with oestradiol had no significant effect on the time to LH peak, standing oestrus or ovulation in heifers synchronised during late dioestrus. The effects of oestradiol benzoate on the dominant follicle and corpus luteum of cows treated with progesterone (CIDR-B) at different stages of the oestrous cycle were investigated. Treatment with oestradiol benzoate on day 3 of the oestrous cycle caused atresia of the dominant follicle present at CIDR-B insertion and resulted in the early emergence of the subsequent follicular wave. Treatment with oestradiol benzoate on days 6, 9, 12 and 15 of the oestrous cycle had no effect on follicular characteristics or the emergence of the subsequent follicular wave. Treatment with oestradiol benzoate had no effect on the day of onset of regression of the corpus luteum regardless of the stage of the oestrous cycle at CIDR-B insertion. The effectiveness of re-using CIDR-B devices to synchronise returns to oestrus in non-pregnant dairy heifers was examined. After an initial CIDR-B synchronisation programme in dairy heifers, the used CIDR-B devices were re-inserted 14 or 16 days after first insemination, for a period of 5 days. Re-insertion of used CIDR-B devices significantly increased the number of non-pregnant heifers detected in oestrus and inseminated by 48 hours after device removal (45.2% vs 27.3%, p<0.05, in herds where CIDR's were re-inserted on day 14; 48.8% vs 13.6%, p<0.05, in herds where CIDR's were re-inserted on day 16). Re-insertion at 14 or 16 days after first insemination was equally effective in increasing visible returns to service. Conception rate was unaffected by CIDR-B treatment. In conclusion, intramuscular administration of oestradiol benzoate 24 hours after the removal of CIDR-B progesterone-containing intravaginal devices increases the number of heifers exhibiting oestrus at an earlier time after device removal. The administration of oestradiol benzoate appears to reduce the variability in timing of LH peaks typically occurring in a herd of synchronised heifers due to different stages of follicular development being present at the time of CIDR-B removal. Treatment with oestradiol benzoate at the start of CIDR-B treatment appears to have no significant effect on synchronising follicular wave emergence in different animals other than those in early metoestrus. Administration of oestradiol benzoate after treatment with exogenous progesterone therefore appears to offer the most potential in controlling the time of oestrus and ovulation and allowing for fixed-time insemination.