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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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    A study of the ovarian response of New Zealand Romney ewes sequentially superovulated with pregnant mare's serum gonadotrophin : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Animal Science at Massey University
    (Massey University, 1973) Clarke, Iain James
    A series of experiments investigated the nature and causes of ovarian refractoriness in ewes sequentially treated with Pregnant Mare's Serum Gonadotrophin (P.M.S.G.). 70 ewes were subjected to the following treatments over 3 oestrous cycles of the 1972 breeding season:- 1. Injectcd with P.M.S.G. at each of 3 cycles (cycles 1,2 and 3); 2. Two injections of P.M.S.G. (at cycles 1 and 3) separated by a nornal oestrous cycle; 3. Injected with P.M.S.G. at two successive cycles (cycles 2 and 3); 4. Injected at 1 cycle only (cycle 3). These treatments were replicated at 1000 i.u. and 1500 i.u. P.M.S.G. and 9 ewes acted as an uninjected control group. The ewes were blood sampled and slaughtered at the end of these treatments and ovulation data were obtained by recovery of the reproductive tracts. The terminal ovulation rates showed that ewes were refractory to a second injection of P.M.S.G. and this condition persisted. The refractoriness was to some extent alleviated by the spacing of injections (Treatment 2 above). Biological Inhibition Tests (using mice) analysed the plasma of the above ewes for evidence of anti-gonadotrophins. Although such factors were not detected in the blood of these ewes, the test did reveal antibody production against P.M.S.G. in the plasma of a further group of ewes which had been chronically treated with the hormone for 6 weeks. It was concluded that ovarian refractoriness, which is rapidly attained in sequentially treated ewes, is not due to the development of serological antibodies against the exogenous gonadotrophin. Another experiment, carried out early in the 1973 breeding season, investigated ovarian follicle development in 30 owes whlch were sequentially treated with P.M.S.G. for up to 3 oestrous cycles. Ewes were laparotomised or killed on Day 10 of the oestrous cycles following treatment and measurements on follicle development were taken. A group of control ewes were observed at a similar time to the treated ewes. Counts on ovarian surface follicles dlffered litt1e between treated and control ewes, at each of the observations. However, the ovaries of slaughtered ewes were sectioned to allow estimation of total ovarian follicular populations and to make some assessment of follicular atresia. Ewes slaughtered after 1 injection of P.M.S.G. had lower numbers of normal antral follicles per ovary than did control ewes or ewes observed at similar times after 2 or 3 injections. It was suggested that exhaustion of ovarian follicular populations may precipitate a refractory condition but that this condition persists because of an endogenous hormonal imbalance. Further work should be done to investigate this latter possibility.
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    A study of the reproductive performance of two year-old Romney and Border Leicester X Romney ewes after differential feeding and gonadotrophin treatment : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Animal Science at Massey University
    (Massey University, 1975) Eastwood, Kenneth Charles
    The reproductive performance of 207 first-cross Border-Leicester x Romney (Border-Romney) and Romney 2 year-old ewes was compared after they grazed in the autumn for 2 months at 2 levels of feeding and treatment with 0, 600 or 1200 i.u. Pregnant Mare's Serum Gonadotrophin (PMSG). To induce and synchronise oestrus at the start of the breeding season, intravaginal progestagen sponges were inserted for 14 days. PMSG was injected on day 12 or 13 after first heat and ewes were then run with entire Southdown rams. Each ewe was laparotomised within a week of PMSG injection to record the ovarian activity. Peripheral blood was collected from a sample of ewes at intervals throughout pregnancy and progesterone concentration determined. The number and weight of lambs at birth and at weaning were recorded. High-plane ewes gained 1.39 kg and low-plane ewes lost 1.51 kg over the 2-month period of differential feeding. Following sponge withdrawal and at the next cycle 80% and 90% of all ewes were in oestrus and of these 77% and 80% were mated over 2 and 3 consecutive days, respectively. PMSG did not affect the degree of synchronisation of oestrus but treatment with the drug, improved feeding and injection on day 12 rather than 13, each reduced the mean cycle length. Border-Romney ewes had higher natural ovulation rate, lambing performance and response to PMSG than Romney ewes. PMSG reduced (16%) the conception rate at first service, proportionately more ewes returned to service at prolonged intervals (>20 days), and this "carry-over" effect reduced the incidence of ewes that later became pregnant. There was marked variation in ovarian response to PMSG. However, litter size increased with up to 5 ovulations per ewe despite an increasing percentage of potential lambs lost. Uterine capacity in terms of both number and weight of lambs born was greatest in Border-Romney ewes but exceeded natural ovulation rate in both breeds. Potential reproductive performance is, therefore, limited by the number of eggs released and in practice management factors before and at mating and selection of ewes with a propensity for higher ovulation rates should be emphasised. Lambs born to Border-Romney ewes were heavier at birth and grew more rapidly to weaning. It is likely that part of this superiority of growth rate was related to a greater milk production by these crossbred ewes and this possibility should be investigated further. Diagnosis of ewes with either single- or multiple-bearing pregnancies on the basis of blood progesterone levels (measured either early or late in pregnancy) was found to be no more accurate than other methods (rectal-abdominal palpation, ultrasonics and radiography) currently available. Variation in lamb birthweight within birth rank appeared to limit the accuracy of diagnosis of single- or multiple-bearing ewes late in pregnancy. Liveweight of the ewe and weight of lamb born were antagonistic in their effects on blood progesterone concentration.