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The onset of ovarian activity post partum was investigated by measuring progesterone concentrations in milk samples, in two dairy herds consisting of 118 cows with an average milk yield of 8340 kg FCM. Samples were taken three times a week till 50 days post partum. In 17 cows (14.4%) anoestrus occurred. The daily milk yield in this group was 2.65 kg FCM higher than the average yield in the group returning to oestrus before day 50 post partum. In cows returning to oestrus within 50 days post partum the first rise in progesterone was detected on average 27.6 days after calving. In first calvers (31.4 +/- 10.2) and in multiparous cows in the winter period (26.9 +/- 9.4) the onset of ovarian activity was delayed compared to start of ovarian activity in the summer period. In the first cycle only 28% of the cows had a normal luteal phase (12-17 days), 36% of the cows had a shortened luteal phase (less than 6 days), and 24% of the cows had a short luteal phase (6-11 days). In 12% of the cows the luteal phase was longer than 17 days. In the second cycle 56% of the cows had a normal luteal phase while 17% had a shortened luteal phase, and 17% had a short luteal phase. Pregnancy rates after first insemination in cows with a short dioestrus (10-25 days) were higher than in cows with a prolonged dioestrus (26-50 days). On the basis of these result it might be expected that postponing the first insemination until the second or even the third cycle in high-yielding cows will have only a marginal effect on the number of open days and a large effect on the number of inseminations per pregnancy.

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The purpose of this study was to find the economically optimal period of first conception in gilts, addressing the issues of lifetime reproductive performance and expected herd life. A profit equation was used to combine the effects into one economic parameter. The data were from 14,910 gilts on 54 farms throughout The Netherlands. The average number of pigs born alive in the first litter increased with older age at conception. In the second litter a similar, but much smaller, effect was observed. Age at first conception had no effect on number of pigs born alive in the third or greater litter. Gilts bred at an older age had a shorter expected herd life than gilts bred at a younger age. Evaluating the reasons for culling revealed that infertility became a more important reason with increasing age at first conception. The proportion culled for infertility increased linearly from 18% at conception on d 200 to 24.5% at conception on d 300. Combining the effect of litter size and herd life led to the conclusion that the profit per gilt (sow) was not significantly affected by her age at first conception. It is concluded that the optimal economic age at first conception was considered to be approximately 200 to 220 d of age when the cost of housing and feed of the gilt from entry to first conception were taken into account.

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The sensitivity of the pituitary to GnRH in early and late anoestrus and the indirect response of the ovary were investigated in six adult beagle bitches. Plasma concentrations of LH and oestradiol were determined after i.v. injection of graded doses of GnRH (0, 0.01, 0.1, 1, 10 and 100 micrograms kg-1). The responses were measured by the LH and oestradiol concentration profiles over time. The responses of LH and oestradiol were significantly dose dependent (P = 0.002 and P < 0.001, respectively). The responses of LH and oestradiol were significantly higher (P = 0.02 and P = 0.001, respectively) in late anoestrus than in early anoestrus. The responses of LH and the responses of oestradiol were positively correlated (r = 0.97, P = 0.001). It is concluded that during the course of anoestrus in the bitch pituitary sensitivity to GnRH increases while the ovary responds accordingly.

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After synchronization of oestrus, normally cyclic heifers (n = 31) received 2500 iu pregnant mares' serum gonadotrophin (PMSG) i.m. and had a progesterone-releasing intravaginal device (PRID) without the oestradiol capsule inserted on day 10 of the oestrous cycle and received 15 mg prostaglandin(PG) i.m. 48 h later. PRIDs were removed 96 h after insertion and 16 heifers received 1.0 mg GnRH i.m. while the controls (n = 15) received 10 ml saline i.m. All heifers were injected with anti-PMSG i.v. 10 later. Peripheral blood concentrations of PMSG, progesterone, oestradiol and LH were compared. Ovaries were collected on death 7 days after the GnRH or saline injection and the number of corpora lutea counted. Heifers were considered to have responded well (> 60 pmol l-1) or poorly (< 60 pmol l-1) to superovulation on the basis of the oestradiol concentration 24 h after PG administration. During PRID treatment, LH concentrations remained at basal values. In the heifers treated with GnRH, a single LH surge occurred 2.3 +/- 0.1 h (SD) after the GnRH injection with a maximum concentration of 14.6 +/- 2.3 (SEM) micrograms l-1 and a duration of 6-8 h. In 12 of the 15 control heifers, LH concentrations remained low (range 0.10-1.94 micrograms l-1) during the 72 h following the saline injection; three controls showed a spontaneous LH surge at 18, 23 and 23 h after the saline injection, respectively, with a maximum concentration of 6.0-12.5 micrograms l-1 and a duration of 10-12 h.(ABSTRACT TRUNCATED AT 250 WORDS)

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Normally cyclic heifers (n = 34) received 2500 iu pregnant mares' serum gonadotrophin (PMSG) i.m. at day 10 of oestrus, and 15 mg prostaglandin (PG) i.m. at day 12. Thereafter, a monoclonal antibody against PMSG was administered i.v. before (n = 24), at (n = 6) or shortly after (n = 4) the preovulatory LH surge. Peripheral blood concentrations of LH and oestradiol were compared; follicular development was monitored by daily ultrasound scanning; and the numbers of preovulatory-sized follicles and ovulations were counted 96 h after injection of PG following death. Anti-PMSG treatment before the LH surge inhibited the LH surge in 16 heifers (67%). In these heifers, the initial increase in oestradiol concentration upon PMSG stimulation to 167.5 +/- 35.0 pmol l-1 was terminated immediately after anti-PMSG treatment and decreased rapidly to basal values, while the number of preovulatory-sized follicles remained constant until 68 h after PG injection; on average 0.4 +/- 0.1 ovulations were counted. In the remaining eight heifers, five animals showed an immediate, but temporary, 20-60% drop in oestradiol concentration after anti-PMSG treatment. In all eight heifers 25% of the preovulatory-sized follicles ovulated. Treatment with anti-PMSG at or shortly after the LH surge did not affect the pattern of oestradiol concentration, but a significantly higher ovulation rate was observed in the animals treated shortly after the LH surge: 20.3 +/- 2.6 versus 6.3 +/- 2.3 in animals treated at the LH surge, which corresponded to 76% and 24% of the preovulatory-sized follicles monitored shortly before the period of multiple ovulation.(ABSTRACT TRUNCATED AT 250 WORDS)

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One hundred and forty-six Dutch cross Friesian cows were selected from a local slaughterhouse and synchronised with norgestomet. The 134 cows with a normal progesterone pattern after the removal of the norgestomet implant were treated intramuscularly with 3000 iu pregnant mare's serum gonadotrophin (PMSG) on day 10 followed by 22.5 mg prostaglandin 48 hours later. Blood samples were collected daily and at hourly intervals from 30 to 54 hours after the prostaglandin. The 113 cows with a pre-ovulatory peak of luteinising hormone (LH) were divided into three groups: 37 control cows (group 1) received a placebo six hours after the LH peak; 42 cows (group 2) received anti-PMSG six hours after the LH peak and 34 cows (group 3) received anti-PMSG 18 hours after the LH peak. All the cows were inseminated 10 hours after the LH peak. Six or seven days after insemination the cows were slaughtered and the embryos were evaluated after flushing the ovaries, and the numbers of corpora lutea, cysts and follicles on the donor ovaries were counted. Treatment with anti-PMSG had no significant effect on the numbers of corpora lutea or the numbers of embryos compared with the control group. The mean (+/- sem) numbers of corpora lutea were 14.7 +/- 1.4, 16.3 +/- 1.4 and 16.6 +/- 1.4 for groups 1, 2 and 3, respectively. The numbers of transferable embryos were 3.5 +/- 0.6, 4.1 +/- 0.7 and 5.0 +/- 0.7 for groups 1, 2 and 3, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

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A transvaginal ultrasound guided follicular aspiration technique was developed for the repeated collection of bovine oocytes from natural cycling cows. In addition, the feasibility of using this method for collecting immature oocytes for in vitro embryo production was also evaluated. Puncturing of visible follicles for ovum pick-up was performed in 21 cows over a three month period. All visible follicles larger than 3 mm were punctured and aspirated three times during the estrous cycle on Day 3 or 4, Day 9 or 10 and Day 15 or 16. The mean (+/- SEM) estrous cycle length after repeated follicle puncture was 22.2 +/- 0.3 days. The mean total number of punctured follicles per estrous cycle was 12.6 +/- 0.3. The largest (P<0.05) number of follicles punctured (5.1 +/- 0.3) for ovum pick-up was on Day 3 or 4 of the estrous cycle. The overall recovery rate of 541 punctured follicles was 55%. Most oocytes (P<0.05) were aspirated from follicles smaller than 10 mm. Following in vitro maturation and fertilization (IVM/IVF), 104 oocytes were transferred to sheep oviducts. Six days later, 75 ova/embryos were recovered, after flushing the oviduct of the sheep, of which 24% developed into transferable morulae and blastocysts. In this study, a reliable nonsurgical, follicular aspiration procedure was used for the repeated collection of immature oocytes which could be used successfully for in vitro production of embryos. This procedure offers a competitive alternative to conventional superovulation/embryo collection procedures.

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Repeated transvaginal ultrasound guided puncturing of visible follicles was performed for ovum pick-up (OPU) during Periods A and B, each of which lasted 3 mo. During Period A, 10 cows (A) were used in the study. Period B commenced 1 mo after Period A and two groups of animals were used. The first group (B1) consisted of 9 of 10 cows from Group A. The second experimental group of animals in Period B consisted of 11 cows (B2) which had not been submitted to previous puncture. During the study, all visible follicles larger than 3 mm were punctured and aspirated three times, on Day 3 or 4, Day 9 or 10 and Day 15 or 16 of the estrous cycle. The mean estrous cycle length (+/- SEM) after repeated follicle puncture did not differ among the three groups and was 22.3 +/- 0.4, 22.5 +/- 0.4 and 22.1 +/- 0.3 d for groups A, B1 and B2, respectively. The mean total number (+/- SEM) of punctured follicles per estrous cycle in Group A (13.1 +/- 0.5) was significantly larger than in Groups B1 (11.2 +/- 0.4) and B2 (11.6 +/- 0.4). The largest number of follicles punctured for ovum pick-up in all three groups was always on Day 3 or 4 of the estrous cycle: 4.9 +/- 0.3 follicles; the mean (+/- SEM) number of punctured follicles on Day 9 or 10 and Day 15 or 16 was significantly (P<0.05) lower: 3.4 +/- 0.2 and 3.9 +/- 0.2, respectively. In Period A, primarily 3- to 5-mm follicles were punctured per estrous cycle, while 6- to 10-mm follicles were predominantly punctured in Period B (P<0.05). Recovery rate of oocytes on Day 3 or 4, Day 9 or 10 and Day 15 or 16 were 53, 50 and 52%, respectively. Most oocytes (P<0.05) were aspirated from follicles smaller than 10 mm.

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Sixty dairy buffaloes (second to fourth lactation) from a large buffalo farm were used to compare the effects of single intramuscular injections of 100 micrograms gonadotrophin releasing hormone (GnRH), 250 micrograms GnRH or saline given on day 14 post partum. The buffaloes had calved at the end of the breeding season (December). Milk samples for progesterone determination were taken at the time of injection and then three times a week either until first insemination or until around day 90 post partum. GnRH given at 14 days post partum resulted in quicker completion of uterine involution, earlier resumption of ovarian activity, shorter intervals between calving and conception and a better first service conception rate in non-suckled dairy buffaloes. Differences between the results obtained by a GnRH dose level of 100 micrograms and 250 micrograms were non-significant. In the post-treatment period cases of prolonged luteal activity were common in all groups of buffaloes. Therefore the sequential administration of GnRH and prostaglandin is suggested for the management of post-partum reproductive activity in problem herds.

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The role of prolactin and LH in the control of the function of the corpus luteum in the dog was studied. Experiments were performed to interfere with the secretion of a) prolactin by administering a dopamine agonist and b) LH by desensitisation with a long-acting LHRH and by stimulation. Treatments with prolactin-lowering dosages of bromocriptine, (20 micrograms/kg body weight twice a day, orally; n = 8) which started between day 1-5 (n = 4) and day 20-24 (n = 4) of the luteal period resulted in a similar pattern of progesterone, concentration in peripheral blood in both groups. The progesterone release in the second half of the luteal period (13.1 +/- 1.8% (sem) of the progesterone release of the total luteal period) was significantly lower than in control dogs (24.7 +/- 2.2%). Treatment at about day 30 of the luteal period with LHRH CR (1.34 mg, intramuscularly; n = 3), which significantly suppressed the LH level, did not reduce the progesterone release in the second half of the luteal period, 21.3 +/- 4.7% compared to 24.7 +/- 2.2% in the control dogs. The endogenous LH peak resulting from treatment with LHRH had no effect on the progesterone concentration in the blood. It is concluded that prolactin is the main luteotrophic factor in the cyclic dog during the second half of the luteal period.

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The ovaries of 59 pluriparous cows of unknown reproductive history were palpated, scanned and dissected on the day of slaughter to compare the accuracy of rectal palpation and transvaginal ultrasonography with a 5 MHz linear array for the detection of corpora lutea and follicles. The rectal palpation was first carried out to judge the presence of follicles of more than 5 mm diameter, and corpora lutea which were classified as young (days 1 to 4), mid-cycle (days 5 to 16) or old (days 17 to 21) according to morphological criteria. The cows were then examined for follicles and corpora lutea by ultrasonography and the corpora lutea were again classified directly as young, mid-cycle or old according to their appearance. The cows were then slaughtered, their ovaries dissected, and the follicles over 5 mm in diameter were counted and the corpora lutea were classified in the above mentioned age categories. For the detection of a mid-cycle corpus luteum the sensitivity and predictive value of rectal palpation were, respectively, 83.3 per cent and 73.2 per cent and for ultrasonography the sensitivity and predictive value were 80.6 per cent and 85.3 per cent, respectively. However, both techniques were inaccurate for the detection of young and old corpora lutea. For detecting follicles ultrasonography was a significantly better method than rectal palpation. Ultrasonography detected 95 per cent of follicles larger than 10 mm whereas rectal palpation detected only 71 per cent of these follicles. Both techniques failed with follicles 5 to 10 mm in diameter; only 21.5 per cent were detected by rectal palpation and 34.3 per cent by ultrasonography.

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We compared three methods for diagnosing early pregnancy in cattle: 1) a trans-rectal ultrasound scan of the uterus, 2) a cow-side enzymeimmunoassay (EIA) milk progesterone test 3) a radioimmunoassay (RIA) milk progesterone test. Scanning of the uterus was performed in 148 cows. These cows were not detected in estrus before scanning, which took place between Days 21 and 33 after insemination (AI). A considerable difference was noted between the reliability of the scannings performed at an early stage (Days 21 to 25) and those performed at a later stage (Days 26 to 33). The sensitivity and specificity of the ultrasound examination between Days 21 and 25 were only 44.8% and 82.3%, respectively, but were 97.7% and 87.8% between Days 26 and 33, respectively. Milk samples were collected on the day of AI. (Day 0) and 21 days later. Samples that were positive in the EIA test always contained more than 1 ng/ml progesterone (P4); however, 20% of the negative EIA samples contained also more than 1 ng/ml P4. Only 59% of the animals showing a negative EIA test on Day 0 and a positive test on Day 21, indicating pregnancy, calved, while 16% of the cows with a negative test on Day 0 and Day 21, indicating nonpregnancy, turned out to be pregnant. Of the 82 animals with P4 levels lower than 1 ng/ml on Day 0 and higher than 1 ng/ml on Day 21, only 61.0% calved. All 14 cows with low levels both on Day 0 and Day 21, indicating nonpregnancy, were found to be not pregnant. The influence of both early embryonic death and the accumulation of intrauterine fluids on the accuracy of these tests are discussed.

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The optimal time for mating bitches was determined by measuring the progesterone concentration in peripheral blood three times a week after the start of vulval bleeding. Of 104 bitches with reduced fertility 81 (78 per cent) became pregnant and of 112 bitches with normal fertility 105 (94 per cent) became pregnant. Of 121 bitches mated once, 102 (84 per cent) became pregnant, and of 95 bitches mated more than once, 84 (88 per cent) became pregnant. The mean (+/- sd) interval between the start of vulval bleeding and the optimal time for mating in 88 bitches was 11.8 +/- 3.1 days. The blood progesterone concentration appears to be an excellent indicator of the best time for mating, particularly in bitches with reduced fertility.

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To determine whether prolactin has luteolytic properties during the first part of the luteal period, hysterectomy was performed in four dogs, in which prolactin had been chronically suppressed by bromocriptine administration. The concentration of progesterone in the peripheral blood decreased upon hysterectomy during the first part of the luteal phase and regained normal values after about seven days. The progesterone patterns during the perisurgical period in these dogs were similar to those patterns observed in dogs hysterectomised without bromocriptine treatment. It is concluded therefore that, in the dog, luteolytic properties can not be attributed to prolactin.

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Nonlactating Dutch-Friesian cows were selected from a local slaughterhouse and synchronized with Syncro-Mate B. Cows with a normal progesterone pattern were treated with PMSG (3,000 I.U. i.m.) on Day 10 followed by PG (Prosolvin 22.5 mg) 48 h later. Blood samples were collected daily and at hourly intervals from 30 h after PG. Monoclonal anti-PMSG (Neutra-PMSG) was administered i.v. at 5.8 h after the LH peak in 16 cows; controls (n = 16) did not receive Neutra-PMSG. For comparison, 16 additional cows were superovulated with FSH-P in decreasing doses, twice a day (total 32 mg), starting at Day 10. All cows were inseminated at 10 h after the LH peak. Embryos were evaluated on Days 6 and 7 after flushing upon slaughter (recovery 87%). The number of corpora lutea and follicles on the donor ovaries were counted. No significant differences in the concentrations of progesterone and LH were observed between the three superovulation groups. Upon Neutra-PMSG, PMSG in blood was completely neutralized, it was decreased to < 0.5 ug/l at AI from 7.0 ug/l at the LH peak. The number of transferable embryos was significantly higher after Neutra-PMSG (9.1 per cow) than without Neutra-PMSG (5.3). or upon FSH-superovulation (4.6). The number of cysts on the ovaries of Neutra-PMSG-treated cows was reduced similarly to that after FSH-superovulation. Treatment with Neutra-PMSG shortly after the LH peak positively affects final follicular maturation in PMSG-superovulated cows and results in a nearly two-fold increase of transferable embryos.

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Five dogs were hypophysectomized on Day 4 and 9 on Day 18. Prolactin and LH stimulation tests showed that hypophysectomy was complete in 6 dogs only. In these dogs, the progesterone concentration was measured in the peripheral blood; it decreased sharply immediately after surgery. It regained normal values in 3 of the 4 dogs hypophysectomized on Day 4, and remained low in the 2 dogs hypophysectomized on Day 18. This indicates that, in the dog, luteal function is autonomous during a certain period. The luteal period of the 3 dogs hypophysectomized on Day 4 was shorter than that of control animals, although the time of onset of luteal regression appeared to be similar. This indicates that pituitary luteotrophic support is required during the second part of the oestrous cycle of the dog.

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Between days 24 and 32 after mating/insemination, 881 pigs (785 pregnant and 96 not-pregnant) were tested for pregnancy on a commercial farm with a linear-array real-time ultrasound scanner. 5-7 Days later, 785 of these animals (708 pregnant and 77 not-pregnant) were tested again with A-mode equipment by farm employees. Confirmation of pregnancy was based on recorded farrowings or abortions; confirmation of non-pregnancy was based on return to oestrus and rebreeding, recorded non-farrowing, or inspection of the uterus of culled animals at the slaughterhouse. From the number of correct positive (a), incorrect positive (b), correct negative (c) and incorrect negative (d) diagnoses, a sensitivity (a/a + d) of 100% versus 97.5%, a specificity (c/c + b) of 90.6 versus 55.8%, a positive predictive value (a:a + b) of 98.9% versus 95.3% and a negative predictive value (c:c + d) of 100% versus 70.5% were calculated for the real-time ultrasound technique versus A-mode technique. It was concluded that real-time ultrasound scanning provides a very accurate technique for pregnancy diagnosis in pigs, enabling immediate decision making on treatment or culling of animals diagnosed as non-pregnant.

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Progesterone levels in peripheral blood of dogs were analysed during the cycle in which hysterectomy (n = 5) or sham surgery (n = 3) was performed as well as during the cycle of dogs (n = 5) hysterectomized at least one year prior to this study; the data were compared with the findings in control dogs (n = 3). The averages of the duration of the luteal period observed in the three experimental groups were not significantly different from those of control dogs. Immediately after surgery, the progesterone level decreased from 25 to 50% of the presurgical level, but returned to presurgical level in about four days. Prolactin levels were elevated for about 30 h after surgery. Nevertheless, the averages of the mean prolactin levels for each animal during the luteal period of the experimental groups were not significantly different from those of control dogs. It is concluded that in the dog, the uterus is not involved in the lifespan of the cyclic corpus luteum.

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Both prolactin and the suckling stimulus are involved in the suppression of LH levels during lactation in the sow. Reduction of the prolactin level by treatment with bromocriptine will result in a significant increase of the LH level, followed by a further significant increase after weaning. The suppression of LH release by the two factors is caused by a blockade at the hypothalamic level. The LH-response to an injection of LHRH is not affected by the presence or absence of prolactin and the suckling stimulus and therefore rules out the pituitary as the primary target organ.

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The development of pre-ovulatory bovine follicles from the onset of oestrus until ovulation may be divided into four phases on the basis of the patterns of the steroid levels in the follicular fluid. Changes in the morphology of the follicular wall and the oocyte coincide with these patterns. Prior to the pre-ovulatory LH surge steroid synthesis is directed towards the production of oestradiol-17 beta, and androstenedione is the major substrate of aromatase. After the LH peak, steroid synthesis switches to the production of progesterone shortly prior to ovulation. The membrana granulosa cell-layer shows morphological luteinization at the time. The elevated levels of LH and FSH observed in the follicular fluid suggest that changes in the micro-environment of the maturing bovine oocyte are regulated by these gonadotrophins.

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