Selection of laboratory rats for fertility components in synchronized estrus using Suisynchron-Praemix. 2. Results of litter development

The following results were obtained from experimental studies into selection of laboratory rats for fertility and random mating with oestrus being synchronised by means of Suisynchron-Pr?mix, through eight generations: --Success of selection without synchronised oestrus was higher than that with synchronised oestrus by selection according to the basic index and with one and the same selection intensity. --Litter size and weight were higher in the selected variants, as a result of increased potential fertility (rate of ovulation). --In the population with selection and synchronised oestrus a negative relationship was found to exist between the directly correlated selection results regarding fertility parameters, on the one hand, and the effect of synchronisation, on the other. --Both the rates of ovulation and litter parameters were lower in the population with selection and synchronised oestrus, as a result of synchronisation. --The effect of synchronised oestrus on the population with selection and synchronised oestrus was partially eliminated owing to selection for fertility.     

SYNCHRONISATION OF OESTRUS IN BEEF CATTLE ARTIFICIAL BREEDING PROGRAMS USING PROSTAGLANDIN F2α

PGF2α either as a subcutaneous injection (8 or 10 mg) or intrauterine infusion (dose 5 mg) successfully synchronised oestrus in beef cattle AI programs. The beef cattle programs were managed by 1 of the following 2 systems.

• 1 Two 10-day insemination periods, 1 for the first and the second for the repeat inseminations. Oestrus was detected and oestrus cows inseminated for the first 4 days of the first period. On the fifth day all cows not inseminated were treated with PGF2α. The treated cattle came into oestrus and were inseminated over the following 2 to 5 days.
• 2 Two PGF2α treatments 10 days apart followed by two 4-day insemination periods. During the first 4-day period, cows exhibiting synchronised oestrus were inseminated. Cows returning to oestrus were inseminated during the second 4-day period, about 18 days after the first period.

Synchronisation of oestrus was not sharp, oestrus being distributed over 7 days, with the majority of cows being in oestrus on the third (42.3%) and fourth (22.4%) days. The route of administration of PGF2α (injection or infusion) did not effect oestrus synchronisation. PGF2α by either route of administration did not effect the fertility of cows inseminated at either the synchronised or subsequent oestrus. Pregnancy rates at the synchronised oestrus were higher when cows were inseminated after detection of oestrus than when they were inseminated without reference to oestrus at a fixed time 3 days after PGF2α treatment (mass injection). Oestrus synchronisation greatly reduced the input of time, labour and feed required during the total program. However, oestrus synchronisation did not alter the overall efficiency of artificial breeding programs measured in terms of the proportion of cattle entering a program that were inseminated and became pregnant. The main problem encountered was drug wastage through unknowingly treating cows and heifers that were not cycling.     

Effects of oestrus synchronisation and fixed-time artificial insemination on the reproductive performance of dairy heifers

AIM: To compare the reproductive performance of heifers after oestrus synchronisation and fixed-time artificial insemination with non-synchronised heifers bred by herd sires. METHODS: Heifers from 10 spring-calving herds were randomly divided into two groups by herd, breed and age. Heifers in one group (the synchronised group, n = 478) were synchronised with a combination of progesterone, oestradiol benzoate and PGF2alpha, and inseminated 50-54 hours after progesterone treatment. Returns to first service were resynchronised with progesterone treatment 16-21 days after the fixed-time artificial insemination. Heifers in the other group (the control group, n = 470) did not receive any treatment and were bred by herd sires. RESULTS: The conception rate of synchronised heifers to the fixed-time artificial insemination was 51.2% and to the artificial insemination after resynchronisation 40.4%. The pregnancy rate at the end of the breeding season was lower (p<0.001) for the synchronised (92.9%) than for the control (97.2%) group. The interval from start of breeding to calving was earlier for synchronised (295.9 +/- 22.5 days, mean +/- s.d.) than for control (298.5 +/- 17.3 days) heifers. CONCLUSION: Results from this study indicate that the oestrus synchronisation programme used in the present study can reduce reproductive performance by increasing the empty rate compared with natural mating.     

Effects of biotechnical management procedures on blood parameters in gilts. 3. Lipids

Suisynchron treatment was applied to platform-kept gilts over 20 days. The dosage was 100 mg per animal and die. This was followed by 1,000 I.U. PMS and 250 I.U. HCG. Artificial insemination was applied five days after the first hormone administration and followed by one Gravigonan injection after another twelve to 15 days. Blood samples were drawn from those animals as well as from 20 gilts synchronised in the above way and another 20 untreated gilts from a production unit during the various phases of treatment and cycle. Those samples were used for assessment of cholesterol, lipoid-P, free fatty acids, triglyceride, and beta-lipoproteids. The levels of free and total cholesterol went up along with Suisynchron feeding, whereas lipoid-P and beta-lipoproteids declined. Free fatty acid levels went down with significance (P less than 0.01), and triglycerides increased (P less than 0.05). Cholesterol levels were not altered by PMS/HCG administration. The levels of lipoid-P, free fatty acids, and beta-lipoproteids rose to their magnitudes prior to Suisynchron treatment. Tirglycerides rose by 50 per cent. At the time of full oestrus triglyceride levels doubled (P less than 0.01). Unimportant rises were recorded also for cholesterol, beta-lipoproteids, free fatty acids, and lipoid-P. In animals with spontaneous oestrus all lipid parameters were ligher than in sows with full oestrus after synchronisation.     

Reproductive performance of lactating dairy cows following oestrus synchronisation with progesterone, oestradiol and prostaglandin

The ability to synchronise onset of oestrus, and hence the time of breeding and calving, offers potential economic and management benefits to dairy farmers, especially in herds with seasonally concentrated calving patterns. A trial involving 2681 cows in 11 seasonal herds was conducted to evaluate the reproductive performance of lactating dairy cows following oestrus synchronisation with a combination of progesterone, oestradiol and prostaglandin. Cows were randomly assigned within herds to synchronised and control groups, balanced for age, date of calving, body condition and breed. Cows in the synchronised group were treated with an intravaginal progesterone-releasing device containing 1.9 g of progesterone and a gelatin capsule containing 10 mg of oestradiol benzoate 10 days prior to the planned start of the breeding season (Day 0). The device was removed 8 days later on Day -2 and a luteolytic dose of prostaglandin F2alpha was administered 2 days prior to removal of the progesterone-releasing device. Returns to service for cows in the synchronised group were synchronised by inserting a previously used intravaginal device during Days 16-21 after the start of the breeding season. Cows in the control group were left untreated. The percentage of cows being inseminated during the first 5 days was 89.0% for the synchronised group compared to 29.7% for the control group. Compared to cows in the control group, those in the synchronised group had a lower conception rate to the first insemination (52.9% v. 64.3%, p<0.001), a lower conception rate to the second insemination (51.8% v. 62.5%, p<0.001), a higher percentage of empty cows at the end of the breeding season (7.3% v. 5.1%, p<0.05), and more insemination services per pregnancy to artificial insemination (2.0 v. 1.6, p<0.001). There was no difference between the synchronised and control groups in the percentage of cows pregnant to artificial insemination (81.8% v. 85.5%, p>0.10). The mean day of conception from the start of the breeding season was advanced (p>0.0 1) by 1.3 days in synchronised cows (19.9 +/- 0.7 days; mean +/- SEM) compared to control cows (21.2 +/- 0.5 days). It is concluded that the oestrus synchronisation regime used in the present study caused a reduction in fertility, which reduced the potential gains from using such a programme to increase reproductive efficiency in dairy cows.     

Comparison of two doses of oestradiol benzoate administered at a resynchronised oestrus on reproductive performance of dairy cows

OBJECTIVE: To compare the effects of two doses of oestradiol benzoate (ODB) administered as part of a treatment designed to resynchronise returns to oestrus on the reproductive performance of cows in a controlled breeding program. DESIGN: Cohort study. PROCEDURE: Lactating dairy cows on two farms were treated to synchronise three successive oestrous cycles. An intravaginal progesterone releasing insert (IVP4) was used to synchronise the first oestrous cycle. The cows were then treated 15 days after the first treatment by reinsertion of an IVP4 that had been used to synchronise the first oestrus and administration of 1.0 mg of oestradiol benzoate (ODB) i.m. at device insertion. The IVP4 device was removed 8 days later and either 0.5 (n = 421) or 1.0 mg of ODB (n = 446) was administered 24 h later. Injections of (ODB) with or without the use of an IVP4 were used to synchronise the third oestrous cycle. Different synchronisation treatments were used to synchronise first and third oestrous cycles but differences were included in statistical models to account for variation in the data. This enabled examination of effects due to differences in the dose of ODB used to synchronise the second synchronised oestrus. RESULTS: The dose of ODB (0.5 or 1.0 mg) administered just before the second synchronised oestrus did not significantly (P > 0.10) affect the cumulative pregnancy rates over three successive rounds of artificial insemination, the mating start date to the conception intervals, the conception rates to the first or second insemination, the proportion of cows submitted for insemination at the second synchronised oestrus or the proportion of cows that were not pregnant yet failed to show signs of oestrous (phantom cows) identified within each herd. CONCLUSION: There was no difference in reproductive performance between cows receiving either 0.5 mg or 1.0 mg ODB after removal of used IVP4 devices that had been inserted to resynchronise them for a second insemination.     

Conclusions on the use of Suisychron in the USSR

Suisynchron was applied to 2,258 gilts, including 850 from breeding farms. Forty-four pigs were checked to elucidate the influence of sexual maturity on the success of oestrus synchronisation. Suisynchron-Pr?mix was fed to the animals over 20 days, the daily dose for each pig having been 5 g. Twenty-four hours were allowed to elapse from the last administration before 1,500 I.U. PMSG were injected. Synchronised oestrus occurred in 81.2 per cent of all pigs between four and six days from serum injection.Fertilisation in response to first insemination was recorded from 72.9 percent of the pigs, their fertility rate being 9.7 piglets from each farrowing sow. The results of oestrus synchronisation obtained from fattening pigs were somewhat inferior to those recorded from pigs of breeding units. Suisynchron and serum of pregnant mares can synchronise oestrus in 91 per cent of all mateable sows with no previous cycle. The fertility rates recorded from such pigs did not exceed 59 per cent or were between 28.9 and 31.9 per cent lower than those recordable from pigs with a cycle history prior to the use of Suisynchron.     

Re-insertion of a progesterone-containing intravaginal device to synchronise returns to oestrus in dairy heifers

Recommendations for oestrus synchronisation of dairy heifers using progesterone-containing intravaginal devices suggest re-insertion of used devices 16 days after first insemination for a period of 5 days to allow a second opportunity for artificial insemination. Controlled studies on the effectiveness of re-using intravaginal devices to synchronise returns to oestrus in non-pregnant dairy heifers are lacking. A clinical trial was conducted involving 750 Friesian heifers in 13 herds. After an initial synchronisation programme, the used intravaginal devices were re-inserted 14 or 16 days after first insemination into half of the heifers in each herd for a period of 5 days. After the first synchronisation programme, 47.5% of heifers remained non-pregnant. Re-insertion of used intravaginal devices for 5 days significantly increased the number of non-pregnant heifers detected in oestrus and inseminated by 48 hours after device removal compared to heifers in which devices were not re-inserted (45.2% v. 27.3%, p < 0.05, in herds where intravaginal devices were re-inserted on day 14; 48.8% v. 13.6%, p < 0.05, in herds where intravaginal devices 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. However, the number of non-pregnant heifers synchronised for a second round of artificial insemination was less than expected. Conception rate to the re-synchronised oestrus was unaffected by the treatment. It is concluded that the additional procedures of CIDR re-insertion, removal, tailpainting and insemination involved in there-synchrony programme, and the relatively low in-calf rate to the re-synchronised round of insemination, reduced the potential benefits of re-synchronisation.     

Effects of biotechnical management procedures on blood parameters in gilts. 2. Protein-bound iodine and copper

Two groups of twelve gilts each kept on platforms were synchronised in two passes over 20 days, using 100 mg Suisynchron per animal and die followed by PMS treatment (1,000 I.U. Intergonan) and HCG treatment (250 I.U.). Complement fixation occurred five days after the first hormone application and was followed twelve to 15 days later by another phase of treatment, using Gravigonan (250 I.U. follicle-stimulating hormone (FSH), 500 I.U. HCG, 1 mg oestradiol benzoate in 10 ml serum of swine). Blood samples were continuously drawn during the various phases of treatment and cycle from the above animals as well as from 20 gilts synchronised in the above way and from another 20 untreated gilts. Protein-fixed iodine and copper levels were assessed from those samples. The protein-fixed iodine and copper levels of the blood were significantly reduced (P less than 0.01) by synchronisation, using Suisynchron. None of the two parameters was particularly affected by PMS and HCG treatments. Blood-borne protein-fixed iodine and copper was increased by administration of gonabione. Both parameters went up further during full oestrus at which date they were higher in untreated animals than in synchronised. (Protein-fixed iodine: 3.50/226micrograms/100 ml; P less than 0.01; copper: 0.283/0.234 mg/100 ml; P less than 0.01).     

Oestrus synchronisation and fertility in black Bengal goats following administration of progesterone/prostaglandin and gonadotrophins.

Oestrus synchronisation, fertility and kidding behaviour were studied in 44 Black Bengal goats. They were divided into six experimental groups: group 1, control; group 2, progesterone; group 3, progesterone, pregnant mare serum gonadotrophin (PMSG) and human chorionic gonadotrophin (HCG); group 4, prostaglandin F2 alpha (PGF2 alpha); group 5, PGF2 alpha, PMSG and HCG; group 6, PMSG and HCG. There was 100 per cent synchronisation of oestrus in the groups treated with progesterone, progesterone with PMSG and HCG, and prostaglandin with PMSG and HCG. In the other two treated groups the synchronisation was between 66 and 75 per cent. In the control group only 50 per cent of the animals came into oestrus during the period of observation. The duration of oestrus varied between 19 and 24 hours except in group 5 where it was 40.87 hours. Animals came on heat between 95 and 137 hours after treatment except in group 5 where the interval was only 18.87 hours. A maximum fertility of 75 per cent was observed in group 4 while the kidding percentage was greatest in group 2. There appeared to be no beneficial effect of superovulation on the number of kids produced. Gestation length was similar in all the groups.     

Estrus and ovulation synchronization in Merino meat sheep. 2. Fertility outcome after estrus and ovulation synchronization with Cloprostenol "Jenapharm" and Gonovet "Berlin-Chemie" and term-oriented artificial insemination]

49 of 102 sheep of one production herd, which had returned to oestrus once or twice within the 1985 breeding season, were treated twice in a nine-day interval with the PGF2 alpha analogue Cloprostenol "Jenapharm". 53 animals received an additional dose of 10 micrograms of Gonavet "Berlin-Chemie". A lambing rate of merely 15% was achieved by subsequent term-oriented artificial insemination. 31 sheep still in oestrus one day after term-oriented artificial insemination were served, bringing the lambing rate from synchronisation of oestrus and ovulation to 26% and the lambing result to 154%. Serving of the remaining sheep in 2 subsequent oestric cycles, on balance, yielded lambing rates and results of the remaining sheep in 2 subsequent oestric cycles, on balance, yielded lambing rates and results which were higher with significance than those recorded from untreated sheep in the same herd.     

Estrogen determination in the urine of heifers during natural and CAP-affected sexual cycle]

With all differences due to environmental effects and individuality, oestrogen secretion actually follows a typical line of dynamics during one normal sexual cycle. Oestrogen curves were found to rise on the seventh and ninth days of the sexual cycle and to reach a maximum level on the last day. Cycle-depending differences between oestrogen concentrations were found to be leveled on the eighth day, when the oestrus had been synchronised by means of CAP. Oestrogens then went down, in response to synchronisation, up to the 15th day. Both the curve proper and the amount of oestrogens in the given cycle, following synchronised oestrus in heifer, practically were congruent with the values recordable from a normal sexual cycle. Two daily CAP doses of 10 mg per individual did synchronise oestrus in heifer and had no side effects on ovarian function over the following sexual cycle.     

Attempts at biotechnical induction of puberty in young female pigs. 2. Effects of various time intervals between one puberty induction with PMS and HCG to the following estrus synchronization on estrus and ovulation in animals about 190 days old

A biological engineering approach to induce puberty in 125 young female fattening pigs aged 190 days was undertaken on the basis of a mixture of 500 IU PMS (Prolosanserum, Dessau) with 250 IU HCG (Gonabion, Dresden). The injections were made subcutaneously. Pronounced oestrus symptoms were recorded from the external genital organs of 80% of the probands up to ten days after injection, associated with toleration in 52.8% of them. Toleration usually started on the fourth to sixth days after injection. Cycles began to develop in 57.1% up to the next oestrus period. Animals with -/x weight increase per die of 400 g exhibited lower responses. Results in terms of heat and ovulation were lower along with shorter intervals, when oestric synchronisation was undertaken 53, 32, and 17 days after the induction of puberty (20 days Suisynchron, Bernburg; 750 IU PMS).     

Steroid hormone levels in follicular fluid of swine with spontaneous estrus and ovulation synchronization

The steroid hormones oestradiol 17 beta, oestrone (E1), testosterone (T), and progesterone (P) were quantitatively determined in follicular fluids in the pre-oestric phase of pigs with spontaneous oestrus and synchronised ovulation. As a whole, mean steroid hormone concentrations exhibited characteristic curves in spite of a relatively wide scatter of individual values. Drastic decline in oestrogen concentration in pigs with spontaneous oestrus and synchronised ovulation was accompanied by rise of P levels, while T values stayed relatively constant. As compared to spontaneous oestrus, treatment for synchronised ovulation caused significantly higher increases in follicular T levels. Positive (P) or negative (E1, T) correlations were found to exist between follicle size and steroid hormone concentration. Conclusions are suggested for further studies.     

Synchronisation of lambing with low doses of dexamethasone in Chios ewes--short communication

The purpose of the present study was to investigate the feasibility of improving the synchronisation of lambing after oestrus synchronisation and artificial insemination (AI). To this end, low doses of dexamethasone 21-isonicotinate (DEX) alone or in combination with prostaglandin F2a (PG) were used in five treated groups (n = 20 each) and one control group (n = 136) of Chios ewes. On day 143 of pregnancy 1.5 mg DEX was given in Group 5, while on day 146 the following treatments were applied: 0.0375 mg PG in Groups 4 and 5, and 1, 1.5 and 2 mg of DEX in ewes of Groups 1, 2 and 3, respectively. The control ewes received no treatment. The 1.5 and 2 mg dose of DEX was more effective in synchronising labour as regards the treatment to lambing interval and the proportion of ewes that gave birth within 3 days. However, obstetrical manipulations were needed, and dead lambs were born when 2 mg DEX was used. It was concluded that lambing can be safely synchronised in Chios ewes with 1.5 mg DEX given on day 146, without affecting the viability of lambs and without parturition complications.     

Oestrus detection techniques and insemination strategies in Bos indicus heifers synchronised with norgestomet-oestradiol

SUMMARY Oestrus was synchronised in 57 Bos indicus heifers using norgestometoestradiol and pregnant mare serum gonadotrophin. Oestrus was detected by observations made at six-hourly intervals, using oestrogen-treated and chin-ball harnessed steers, heatmount detectors, tail-paint and visual observation. Heifers were inseminated once at either a fixed time of 49.2 ± 0.4 h (mean ± SE; n = 29) after implant removal or 12.6 ± 1.5 h (n = 28) after oestrus was detected. The mean (± SE) time to the onset of oestrus was 47.1 ± 1.9 h, while 90% of heifers recorded in oestrus were detected within 66 h of implant removal. Heatmount detectors were significantly more efficient at detecting oestrus than chin-ball harnessed steers, tail paint or visual observation (P < 0.001). A higher pregnancy rate was obtained in heifers inseminated after oestrus detection compared with heifers inseminated at a fixed-time (57.1 vs 34.5%; P = 0.043) and a higher pregnancy rate was obtained in heifers classified as easy to inseminate compared with heifers classified as difficult to inseminate (57.8 vs 0%, P < 0.001). We conclude that heatmount detectors are an efficient means of detecting oestrus in synchronised B indicus heifers and that pregnancy rates can be increased when insemination follows oestrus detection compared with a fixed-time insemination regimen.     

Studies on the use of megestrol acetate for estrus synchronization in heifers

Megestrol acetate has been tested for its applicability to synchronisation of oestrus in 463 mature heifers in the framework of preclinical and clinical experiments. Clinical tests and studies in the context of laboratory diagnostics have shown that 40 mg/die megestrol acetate, administered in two applications with twelve hours in-between and over 15 days, are necessary for maximum synchronisation effect. The resulting oestrus was found to be prolonged, with ovulations taking place within two or three days. Technological requirements in this context are discussed. Megestrol acetate is found to be suitable for oestrus synchronisation in heifer. Tests conducted under industrialised conditions have shown conception rates to be identical with those obtained by administration of chloromadinone acetate.     

The effect of timing of administration of oestradiol benzoate on characteristics of oestrus,timing of ovulation and fertility in Bos indicus heifers synchronised with a progesterone releasing intravaginal insert

OBJECTIVE: To compare the timing of onset of oestrus and ovulation, characteristics of oestrus, and fertility in Bos indicus heifers synchronised with a progesterone releasing intravaginal insert (IVP4) and administration of oestradiol benzoate (ODB) either at the time of removal of the insert or 24 h later. Design: Cohort study. PROCEDURE: Bos indicus and Bos indicus cross heifers were treated on two farms (Farm A, n = 273; Farm B, n = 47) with an IVP4 for 8 days with 1.0 mg of ODB administered at the time of device insertion and 250 mg of cloprostenol at the time of device removal. Heifers in the ODB-0 group were administered 0.75 mg of ODB at the time of device removal while heifers in the ODB-24 group were administered the same dose of ODB 24 h after device removal. Heifers were inseminated once daily after detection of oestrus. Heifers not detected in oestrus by 72 h after removal of inserts were inseminated at that time. Oestrus was detected in heifers on Farm A using heatmount detectors while on Farm B oestrus in heifers was monitored using radiotelemetry of mounting pressure. Ovarian follicular development was monitored daily in 30 heifers on Farm B from the time of administration of inserts until ovulation to a maximum of 96 h after removal of inserts, and again 11 days after removal of inserts (Day 19). A blood sample was collected from all heifers on Farm B on Day 19 and analysed for plasma concentration of progesterone. Pregnancy was diagnosed 6 to 8 weeks after insemination. RESULTS: Administration of ODB at the time of removal of inserts shortened the time interval to oestrus and ovulation (P < 0.001), increased the number of mounts recorded during oestrus (P = 0.04) and reduced the odds of pregnancy (P = 0.03). The proportion of heifers ovulating on Farm B was 67% and was not affected by treatment group (P = 0.61). The mean diameter of the largest follicle measured in ovaries was greater at the time of removal of inserts (9.1 +/- 0.6 vs 10.7 +/- 0.4; P = 0.03) and at the expected time of the LH surge (8.1 +/- 0.4 vs 11.5 +/- 0.3 mm; P < 0.001) in heifers that ovulated compared to heifers that failed to ovulate, respectively. Emergence of a new follicular wave was not detected during the synchronisation treatment in heifers that failed to ovulate. Concentrations of progesterone in plasma on Day 19 were less in non-pregnant heifers (P = 0.05) compared to heifers subsequently diagnosed as pregnant to insemination and were affected by the diameter of the ovulatory follicle (P = 0.01). CONCLUSION: Administration of ODB at the time of removal of inserts can shorten the time interval to oestrus and ovulation and can reduce fertility when insemination is carried out once daily. Further work is needed to determine if prolonged suppression of follicular development, anovulatory oestrus and premature ovulation occuring in some heifers is associated with administration of ODB.     

Conception rates in cows after various synchronisation techniques using progesterone releasing intravaginal devices

The effects of different treatments for oestrus synchronisation on the incidence of oestrus and fertility levels in dairy cows were studied in 2 experiments. In Experiment 1, 200 lactating cows were allotted to 5 groups and the treatments imposed were either; 1: Untreated controls, 2: An injection of 0.5 mg of cloprostenol followed 13 days later by a progesterone releasing intravaginal device (PRID) inserted for 12 days, 3: A PRID, with a capsule containing 10 mg of oestradiol benzoate (ODB) attached, inserted for 12 days, 4: A PRID inserted for 12 days with 0.5 mg of cloprostenol administered 24 h before PRID removal or, 5: As for 4 but 14 days after fixed-time insemination a second PRID was inserted for 12 days. Treated cows were inseminated 56 h after PRID removal and at an observed oestrus during the subsequent 30 days. The control group was inseminated at an observed oestrus during this 30-day period. For treatments 2, 3, 4 and 5, respectively, the percentage of cows showing oestrus by 60 h after PRID removal was 70, 40, 67 and 43 and conception rates to the fixed time insemination were 34, 33, 49 and 29%. Calving rates of cows inseminated at an observed oestrus during a 30-day period were 70, 75, 70, 83 and 82% for treatments 1, 2, 3, 4 and 5, respectively. In Experiment 2, 60 lactating cows were divided into 2 groups and the treatments imposed were either 1: An injection of 0.5 mg of cloprostenol followed 13 days later by a PRID inserted for 12 days or 2: As for 1 but 14 days after fixed-time insemination a second PRID was inserted for 12 days. Treated cows were inseminated 56 h after PRID removal and at an observed oestrus over a period from the first insemination to 6 days after removal of the second PRID. For treatments 1 and 2, respectively, 73 and 71% of cows showed oestrus by 60 h after removal of the first PRID and 40% and 46% conceived to the fixed time insemination. The conception rates to inseminations over the treatment period were 73 and 70% for treatments 1 and 2, respectively. None of the treatments resulted in conception rates which were lower than those of control cows provided that treated cows were reinseminated at observed oestrus. Treatment 4 provided the most practicable technique for oestrus synchronisation.     

Oestrus synchronisation with a prostaglandin analogue: I. Systems in lactating dairy cattle

Three trials were completed to compare different regimes for the use of an analogue of prostaglandin F₂ alpha(“Estrumate”: ICI) in the breeding management of herds of lactating dairy cows with seasonally concentrated calving patterns. The first regime involved two injections of ‘Estrumate’ 11 days apart, followed by insemination, either at 72h and 96h after the second injection, or at the first observed oestrus. Every cow had calved at least 40 days before the first injection. The second regime involved a single ‘Estrumate’ injection given to every cow not inseminated during the first seven days of the breeding programme. Treated cows were inseminated when observed in oestrus within 48h of injection, or at 72h and again at 96h. The third regime utilised the technique of tail-painting during the pre-mating period to identify groups of cycling cows which were subsequently givena single injection of “Estrumate” and inseminated 72h lateror at a subsequent behavioural oestrus.

All regimes significantly altered the conception pattern from that obtained in untreated herd-mates. The variable incidence of post-partum anoestrus, genuine short oestrous cycles and the degree of precision in oestrus synchronisation in lactating dairy cows resulted in many animals being unnecessarily injected and/or inseminated. The third regime overcame most of these problems and could have application in many largeherds. The identification of cycling animals and insemination at detected oestrus are important components of programmes using prostaglandins for the purpose of oestrus synchronisation in lactating cows in seasonal dairy herds.