Plasma progesterone concentration in relation to ovulation rate and embryo yield in Chios ewes superovulated with PMSG

The main purpose of this work was to investigate the relationship between plasma progesterone concentration and the number of ovulations and/or the number of embryos collected from Chios ewes induced to superovulate with various doses of PMSG.The oestrous cycles of the animals were synchronized by means of MAP intravaginal sponges for 14 days and PMSG was injected i.m. (1500 IU, Group 1; 1000 IU, Group 2; 750 IU, Group 3; 500 IU, Group 4; 0 IU, Group 5) at the time of sponge withdrawal. Seven days after sponge removal and 5 days after mating, mid-ventral laparotomy was performed and the uterine horns and/or oviducts were flushed. The number and diameter of corpora lutea (CL), the number of large (diameter > 0.5 cm) anovulated follicles and the total ovarian response (TOR = CL + large anovulated follicles) were recorded. The embryos were examined under a dissecting microscope and evaluated according to morphological criteria. Blood samples were collected once daily for 4 days starting on the day of sponge withdrawal. One more sample was taken on the day of embryo collection. Progesterone concentration was determined using a conventional ELISA.A significant positive correlation was found between plasma progesterone concentration and number of corpora lutea (r = 0.61, P < 0.001), total diameter of corpora lutea (r = 0.63, P < 0.001), total ovarian response (r = 0.63, P < 0.001), number of eggs (r = 0.51, P < 0.001), number of embryos (r = 0.43, P < 0.001) and number of transferable embryos (r = 0.36, P < 0.01) collected per ewe treated. A negative relation between progesterone concentration (≥ 2 ng ml⁻¹) at the beginning of oestrus and number of corpora lutea (CL) was observed. The investigation of the relationship between ovulation rate and plasma progesterone concentration on the day of embryo collection resulted in the calculation of a formula for the prediction of the response of Chios sheep after superovulation with the specific hormonal regimen.     

Reproductive performance of heifers induced to oestrous asynchrony by suprabasal plasma progesterone levels

Suprabasal progesterone concentrations around oestrus have induced disturbances in oestrous behaviour and ovulation. To determine whether fertility in such an altered oestrus can be maintained at normal levels with additional inseminations (AI) until ovulation, fertility was compared in heifers (n = 11) inseminated in normal oestrous cycles and thereafter in cycles in which the animals were treated with progesterone in order to create suprabasal concentrations after luteolysis. The treatment consisted of silicone implants containing 10.6 mg kg⁻¹ of progesterone inserted subcutaneously on Day 8 of the oestrous cycle (day of ovulation designated Day 0) and removed on Day 25. Both in control oestrous cycles and oestrous cycles under progesterone treatment, growth of the ovulatory follicle and ovulation were determined by frequent ultrasound scanning. Blood was collected frequently for further analysis of progesterone, oestradiol-17β and luteinising hormone (LH). Insemination was performed 12 h after onset of standing oestrus. if ovulation did not occur 24 h after AI, heifers were inseminated again until ovulation. Pregnancy was diagnosed by ultrasound 25 days after ovulation.In control oestrous cycles, plasma progesterone decreased to 0.3 ± 0.3 nmol 1⁻¹. Duration of oestrus was 22.9 ± 2.0 h, the interval from onset of oestrus to ovulation was 32.4 ± 2.3 h and the interval from LH peak to ovulation was 28.6 ± 1.4 h. The interovulatory interval was 20.7 ± 0.6 days. In oestrous cycles in treated heifers, progesterone decreased to 1.0 ± 0.3 nmol l⁻¹ (P > 0.10) and the interovulatory interval was prolonged to 23.5 ± 1.0 days (P < 0.05). Standing oestrus lasted 47.2 ± 12.0 h (P = 0.09, n = 7). The interval from the onset of oestrus to ovulation was 59.4 ± 13.0 h (P = 0.08) and the interval from LH peak to ovulation 25.8 ± 1.3 h (P > 0.10). The prolonged oestrus was associated with increased (P < 0.05) growth of the ovulatory follicle and higher (P < 0.05) release of oestradiol-17β. Conception rates were 90% and 46% (P < 0.05), and the numbers of AI per heifer were 1.1 ± 0.1 and 3.4 ± 0.6 (P < 0.01) for control oestrous cycles and after treatment, respectively.The induction of suprabasal concentrations of progesterone caused asynchronies similar to those observed in cases of repeat breeding. The repeated AI did not maintain fertility at normal levels. It is suggested that the extended growth of the ovulatory follicle may cause impaired oocyte maturation or it may alter the maternal milieu owing to the prolonged release of oestradiol.     

Comparative study of the concentrations of peripheral progesterone before and after PGF2α injection between Bos taurus (Brown Swiss) and Bos indicus (Indobrazil) in the tropics

With the object of studying the changes in progesterone concentration during the oestrous cycle and of verifying prostaglandin F_2α (PGF_2α) response in the luteal phase, 10 Indobrazil and 6 Brown Swiss cows, all non-lactating, were bled three times a week during the months of March and April in the Mexican tropics.Progesterone levels in both groups followed a similar pattern, maximum mean levels being reached at day 13 of the cycle (Indobrazil 2.2 ng/ml and Brown Swiss 2.8 ng/ml). No significant differences were found in the progesterone levels throughout the cycle. Nevertheless, a highly significant difference (P < 0.001) was established between breeds with respect to progesterone levels before and after PGF_2α injection. This was possibly due to a seasonal effect on progesterone production in the two types of cow.     

Superovulation in cows: A relationship between progesterone secretion before ovulation and the quality of embryos

Superovulation was induced in 28 cyclic cows by treatment with FSH and milk progesterone concentrations were studied from the initiation of treatment to oestrus. A negative correlation (r= ?0.66; P < 0.001) was observed between the increase in progesterone concentration observed 2 days after the beginning of treatment and the percentage of transferable embryos collected. During this sampling period progesterone secretion was not related to ovulation rate and number of embryos.     

The association between changes in the intravaginal electrical resistance and the in vitro measurements of vaginal mucus electrical resistivity in cattle

A system was developed for measuring in vitro the electrical resistivity (ρ) of vaginal mucus samples collected throughout a complete oestrous cycle from three Hereford × Friesian cows. Measurements of intravaginal electrical resistance (Rv) and mucus electrical resistivity were made in six Hereford × Friesian cows throughout a complete normal oestrous cycle. Both Rν and ρ fluctuated during dioestrus and fell to a minimum value at oestrus. The decrease in ρ was larger than that of Rν. A significant correlation was found between Rν and ρ (P < 0.01; r = 0.56).     

Cervical mucus and oestrous behaviour responses to oestrogens in sheep: Progesterone-oestrogen relationships and role of progesterone pre-treatment

The final dose of progesterone (5, 10, 20 mg) and time to oestrogen injection relative to the final dose of progesterone (24–72 h) had no significant effect on the production of cervical mucus measured 24 h after the injection of 30 μg oestradiol benzoate (ODB). However, there were significant effects on the behavioural oestrous responses (time from injection of oestrogen to onset of oestrus and duration of oestrus). Time to onset of oestrus increased from 18 to 27.8 h with increasing dose of progesterone (P < 0.001) and decreased from 24.8 to 20 h with increasing time to oestrogen injection (P < 0.05). Conversely, the duration of oestrus decreased from 36.2 to 23.8 h with increasing dose of progesterone (P < 0.001) and increased from 29 to 39 h with increasing time to oestrogen injection (P < 0.01).Ovariectomized ewes became refractory to ODB as measured by the cervical mucus response after the fifth sequential daily injection of 20 μg oestradiol benzoate. Progesterone priming was not required to restore subsequent sensitivity to oestrogen treatment. However, there was a positive linear relationship between length of recovery period and level of response to subsequent treatment.It was concluded that: (1) progesterone pre-treatment or priming is not necessary in the cervical mucus bioassay in ovariectomized ewes; and (2) a period of 8–16 days is needed between assays for normal sensitivity to be regained.     

Dietary-induced suppression of pre-ovulatory progesterone concentrations in superovulated ewes impairs the subsequent in vivo and in vitro development of their ova

In the first of three experiments, eight ovariectomised Greyface ewes primed with exogenous progesterone were used to provide quantitative data on the effects of two contrasting feeding levels (0.3 vs. 1.4 × maintenance) on plasma progesterone concentrations. Over the 9 day study period, mean (± SEM) daily progesterone concentrations were 4.3 ± 0.13 and 3.3 ± 0.17 μg l⁻¹ for the low and high feeding regimens, respectively (P = 0.06), indicating that high feed intake suppressed circulating progesterone levels. The second experiment examined the effect in superovulated Finn-Dorset ewes of a diet supplying either 0.6 (Group L, n = 8) or 2.3 (Group H, n = 8) times their daily energy needs for maintenance, from 1 day before introduction of exogenous progesterone to the time of insemination, on plasma progesterone concentrations and the viability of ova recovered 4 days after insemination. Mean (± SEM) plasma progesterone concentrations were 4.5 ± 0.17 μg l⁻¹ and 2.8 ± 0.16 μg l⁻¹ for L and H ewes, respectively, during the 12 day priming period (P < 0.001). Eight hours after progesterone withdrawal, levels had fallen to 0.9 ± 0.06 μg l⁻¹ and 0.8 ± 0.07 μg l⁻¹, respectively, then rose to 17.8 ± 3.01 μg l⁻¹ and 12.9 ± 2.50 μg l⁻¹ (P > 0.10) at ovum collection. Intervals (mean ± SEM) to oestrous onset (14.5 ± 0.38 h) and the luteinising hormone (LH) surge (27.1 ± 0.98 h) were unaffected by feed intake. Mean (± SEM) ovulation rates (8.1 ± 1.57 vs. 7.8 ± 1.10) and numbers of ova recovered (5.0 ± 1.39 vs. 4.8 ± 1.11) were also similar for each group. However, the proportions of ova considered viable (over 32 cells) at recovery were 0.53 and 0.22 for L and H groups, respectively (P < 0.005). Following 72 h culture (Tissue Culture Medium-199 (M199) + 10% foetal calf serum (FCS)), 0.55 and 0.27, respectively, had developed to blastocysts (P < 0.025). Of ova assessed as viable at recovery, similar proportions (0.86 vs. 0.75) from L and H treatments developed to blastocysts, with corresponding nuclei counts (mean ± SEM) of 55 ± 5.2 and 55 ± 13.2. The third experiment used 12 superovulated Greyface ewes, each offered a different feed level within the range 0.6–2.5 × maintenance, to determine the nature of the relationship between feeding level, pre-ovulatory progesterone concentrations and ovum development at Day 2 following insemination and subsequently during 7 day co-culture (M199 + FCS). Increases in feeding level were accompanied by linear decreases in plasma progesterone (r² = 0.79, P < 0.001), the interval to oestrous onset (r² = 0.52, P < 0.01) and timing of the LH surge (r² = 0.32, P < 0.06). Although undetectable at ovum collection, and somewhat equivocal after 4 day culture, high feeding levels prior to ovulation reduced the proportion of ova (0.16 vs. 0.58) developing to or beyond the expanding blastocyst stage after 7 day culture. Quantitative indices of cell division and protein synthesis confirmed this. In conclusion, excessive feeding during follicular recruitment and oocyte maturation in superovulated ewes imparts a legacy of embryonic loss and developmental retardation.     

Ultrasound-monitored ovarian responses in normal and superovulated cattle given exogenous progesterone at different stages of the oestrous cycle

In two experiments with female cattle, responses to synchronisation and superovulation were monitored by transrectal ultrasonography and embryo recovery. Each experiment had both a synchronisation phase to establish a reference oestrus and a superovulatory phase with the oestrous cycle controlled by exogenous progesterone commencing at two specific times. The reference oestrus was controlled using a progesterone releasing intravaginal device (PRID) applied for 12 days with prostaglandin F_2α given 1 day before removal. Experiment 1 had two treatments which differed by the absence (A) or presence (P) of a 10mg oestradiol benzoate capsule on the PRID, while in Experiment 2 all animals were on treatment P. In the superovulatory phase of both experiments treatment P commenced on Day 7 (PRID 7 treatment) or Day 14 (PRID 14 treatment) of the oestrous cycle (oestrus designated Day 0). Superovulation, using equine chorionic gonadotrophin in Experiment 1 and oFSH in Experiment 2, commenced 3 days before PRID removal. Treatment P caused rapid regression of the dominant follicle and corpus luteum (CL) irrespective of when treatment commenced. A second wave of follicular growth was detected after 6–8 days and the dominant follicle grew at 1.1 mm day⁻¹ in the 7 days before oestrus. In contrast, in treatment A of Experiment 1, the dominant follicle either grew slowly and eventually ovulated for cows in the mid-luteal phase, or the dominant follicle regressed and a second wave follicle ovulated if cows were early luteal at PRID insertion. In the superovulatory phase of both experiments the dominant follicle of PRID 7 animals increased in size and then regressed, but in PRID 14 cows, the dominant follicle was regressing before PRID insertion. During superovulation, the number of 7–10 mm follicles was significantly (P<0.001) greater in PRID 7 animals in Experiment 2. In both experiments, half the animals on the PRID 14 treatment maintained a large follicle during the superovulatory phase in contrast to the even sized follicles in animals on PRID 7 treatment. In Experiment 1, the number of grade 1 embryos recovered was significantly (P<0.05) higher for PRID 7 than PRID 14 treatments. In Experiment 2, there were significant differences (P<0.001) in the number of corpora lutea, total ova plus embryos and grade 1 embryos in favour of PRID 7 animals following superovulation. We conclude that the initiation of control of the oestrous cycle with a PRID and subsequent superovulating regime should take account of normal follicular wave status for effective superstimulation and production of viable embryos, and that ultrasonography may usefully be applied to the process.     

Plasma,milk and faecal progesterone concentrations during the oestrous cycle of lactating dairy cows with different milk yields

The hypotheses tested in this study were that neither average progesterone (P4) concentrations in plasma and milk nor average progesterone metabolites concentrations in faeces would differ during an oestrous cycle in two groups of cows with differing daily milk yields. High producing (HP = 8) and low producing (LP = 8) dairy cows were selected randomly for the study. Their oestrous cycles were initially synchronised using P4 and prostaglandin F2alpha. Chromic oxide capsules were administered twice daily to measure total faecal output. Samples of blood, faeces and milk were taken daily throughout one oestrous cycle, plasma and milk P4, and faecal progesterone metabolites (FP4M) assayed. The average daily milk yields in the two groups were 30.8 and 21.9l per day, respectively (P < 0.0001), although daily faecal output was similar in both the groups (HP, 7.7 versus LP, 6.9 kg DM; P = 0.24). Mean plasma and milk P4 concentrations were similar in both the groups (plasma P4, 4.12 versus 4.05 ng/ml; P = 0.3; milk P4, 8.2 versus 8.3; P = 0.9) during dioestrus. Average daily excretion of P4 to the milk was greater in HP than LP cows (252 versus 185 microg, P = 0.04). Neither concentration nor the daily yield of FP4Ms was affected by level of milk yield (concentration: 12.2 versus 11.5 microg/g; daily yield: 89.1 versus 82.9 mg per day; P > 0.05). These data showed that the concentrations of P4 in plasma and milk, and the concentrations and daily yields of FP4M were not affected by the level of daily milk yields which differed by about 41% of the LP average of 21.9l.     

Ovarian cycle approach by rectal temperature and fecal progesterone in a female killer whale,Orcinus orca

This study aimed to validate the measurements of body temperature and fecal progesterone concentrations as minimally invasive techniques for assessing ovarian cycle in a single sexually mature female killer whale. Rectal temperature data, fecal and blood samples were collected in the dorsal position using routine husbandry training on a voluntary basis. The correlations between rectal temperature and plasma progesterone concentration and between fecal and plasma progesterone concentrations were investigated. Fecal progesterone metabolites were identified by a combination of high‐performance liquid chromatography and enzyme immunoassay. Plasma progesterone concentrations (range: 0.2–18.6 ng/ml) and rectal temperature (range: 35.3–35.9°C) changed cyclically, and cycle lengths were an average (±SD) of 44.9±4.0 days (nine cycles) and 44.6±5.9 days (nine cycles), respectively. Rectal temperature positively correlated with the plasma progesterone concentrations (r=0.641, P<0.01). There was a visual trend for fecal progesterone profiles to be similar to circulating plasma progesterone profiles. Fecal immunoreactive progestagen analysis resulted in a marked immunoreactive peak of progesterone. The data from the single killer whale indicate that the measurement of rectal temperature is suitable for minimally invasive assessment of the estrous cycle and monitoring the fecal progesterone concentration is useful to assess ovarian luteal activity. Zoo Biol 30:285–295, 2011. © 2010 Wiley‐Liss, Inc.     

Repeatability of blood serum progesterone levels in dairy heifers on day 7 of the estrous cycle

Thirty normally cycling dairy heifers were used to determine the repeatability of blood serum progesterone levels on Day 7 ± 0.25 d of the estrous cycle. The experimental group consisted of 16 Holsteins and 14 dairy crossbreds ranging in age from 18 to 24 months. Day of the estrous cycle was determined from twice daily observations for standing heat (Day 0). Serum progesterone levels for Day 7 ± 0.25 d were determined by radioimmunoassay from blood samples collected by jugular venipuncture over three to four consecutive estrous cycles. Levels of blood serum progesterone for Day 7 ± 0.25 d ranged from 0.57 to 6.03 ng/ml. Least square means for the Holstein (2.74 ng/ml) and dairy crossbred (3.38 ng/ml) groups were different (P<0.006). The repeatability for levels of blood serum progesterone on Day 7 of the estrous cycle was low (0.0115).     

Timed artificial insemination plus heat II: gonadorelin injection in cows with low estrus expression scores increased pregnancy in progesterone/estradiol-based protocol

The use of tail chalk and estrus/heat expression scores (HEATSC) evaluation is instrumental in identifying cows with greater estrus expression and greater artificial insemination pregnancy rates (P/AI) in cows submitted to timed artificial insemination (TAI), and cows with low or no estrus expression present lower P/AI. It was intended in this study to improve the pregnancy rates in TAI for Bos indicus beef cows, and gonadotrophin-releasing hormone (GnRH) injection was hypothesized to increase pregnancy rates in a TAI program for cows submitted to progesterone–estradiol-based protocols with low or no estrus expression, evaluated by HEATSC. Cows (n= 2284) received a progesterone device and 2 mg estradiol benzoate, after 8 days the device was removed and 1 mg estradiol cypionate, 150 μg of d-cloprostenol and 300 IU equine chorionic gonadotropin was administered. All cows were marked with chalk and HEATSC evaluated (scales 1 to 3) at TAI performed on day 10. Animals with HEATSC1 and HEATSC2 (n= 937) received 100 μg de gonadorelin (GNRH group; n= 470), or 1 ml saline (Control group; n= 467), and cows with HEATSC3 (named HEAT group; n= 1347) received no additional treatment. The larger dominant follicle, evaluated on day 8and at TAI (day 10), was greater in HEAT group (P= 0.0145 and P <0.001, respectively). Corpus luteum (CL) area and progesterone concentration was evaluated on day 17, and CL area was larger in HEAT group, intermediary in Control and lower in GnRH group (Control= 2.68 cm², GnRH= 2.37 cm², HEAT group= 3.07 cm², P <0.001). Greater progesterone concentrations were found in HEAT group than in Control and GnRH groups (Control= 4.74 ng/ml, GnRH= 4.29 ng/ml, HEAT group= 6.08 ng/ml, P<0.001). There was a difference in ovulation rate, greater in HEAT group than GnRH and Control groups (Control= 72.5%; GnRH= 81.25%; HEAT group= 90.71%; P= 0.0024). Artificial insemination pregnancy rates was greater in HEAT group (57.09% (769/1347) than in Control and GNRH groups, with positive effect of GnRH injection at the time of TAI in P/AI (Control= 36.18% (169/467), GnRH= 45.95% (216/470); P<0.0001). In conclusion, GnRH application in cows with low HEATSC (1 and 2) is a simple strategy, requiring no changes in TAI management to increase pregnancy rates in postpartum beef cows submitted to progesterone–estradiol-based TAI protocols, without reaching, however, the pregnancy rates of cows that demonstrate high estrus expression at the TAI.     

Extension of oestrous cycles and prolonged secretion of progesterone in non-pregnant cattle infused continuously with oxytocin

The experimental objective was to evaluate how continuous infusion of oxytocin during the anticipated period of luteolysis in cattle would influence secretion of progesterone, oestradiol and 13,14-dihydro-15-keto-prostaglandin F-2 alpha (PGFM). In Exp. I, 6 non-lactating Holstein cows were infused with saline or oxytocin (20 IU/h, i.v.) from Day 13 to Day 20 of an oestrous cycle in a cross-over experimental design (Day 0 = oestrus). During saline cycles, concentrations of progesterone decreased from 11.0 +/- 2.0 ng/ml on Day 14 to 2.0 +/- 1.3 ng/ml on Day 23; however, during oxytocin cycles, luteolysis was delayed and progesterone secretion remained near 11 ng/ml until after Day 22 (P less than 0.05). Interoestrous interval was 1.6 days longer in oxytocin than in saline cycles (P = 0.07). Baseline PGFM and amplitude and frequency of PGFM peaks in blood samples collected hourly on Day 18 did not differ between saline and oxytocin cycles. In Exp. II, 7 non-lactating Holstein cows were infused with saline or oxytocin from Day 13 to Day 25 after oestrus in a cross-over experimental design. Secretion of progesterone decreased from 6.8 +/- 0.7 ng/ml on Day 16 to less than 2 ng/ml on Day 22 of saline cycles; however, during oxytocin cycles, luteolysis did not occur until after Day 25 (P less than 0.05). Interoestrous interval was 5.9 days longer for oxytocin than for saline cycles (P less than 0.05). In blood samples taken every 2 h from Day 17 to Day 23, PGFM peak amplitude was higher (P less than 0.05) in saline (142.1 +/- 25.1 pg/ml) than in oxytocin cycles (109.8 +/- 15.2 pg/ml). Nevertheless, pulsatile secretion of PGFM was detected during 6 of 7 oxytocin cycles. In both experiments, the anticipated rise in serum oestradiol concentrations before oestrus, around Days 18-20, was observed during saline cycles, but during oxytocin cycles, concentrations of oestradiol remained at basal levels until after oxytocin infusion was discontinued. We concluded that continuous infusion of oxytocin caused extended oestrous cycles, prolonged the secretion of progesterone, and reduced the amplitude of PGFM pulses. Moreover, when oxytocin was infused, pulsatile secretion of PGFM was not abolished, but oestrogen secretion did not increase until oxytocin infusion stopped.     

The relationship between the blood progesterone concentration at early metoestrus and uterine infection in the sow

In a previous study it was shown that gilts inoculated in the uterus during standing oestrus had a better resistance to Escherichia coli infections than gilts that were similarly inoculated within 12 h after the end of the standing reflex (De Winter et al., 1992). In the present study, the changes of blood progesterone concentrations during early metoestrus were investigated. It was also investigated to what extent the onset of endometritis after intrauterine inoculation is correlated to the blood progesterone concentration.In a preliminary study, the plasma progesterone concentration was measured in a group of 11 gilts during early metoestrus, in order to evaluate the average progesterone levels at that stage of the oestrous cycle. A wide variation of blood progesterone concentrations was observed.A second group of 13 gilts was inoculated in the uterus with an E. coli suspension in order to investigate the presence of a correlation between blood progesterone level and susceptibility of the porcine uterus to bacterial endometritis. A third group of six gilts was similarly inoculated with Staphylococcus hyicus. A clear correlation between blood progesterone concentration and susceptibility to endometritis and the development of a vaginal discharge in gilts experimentally inoculated was observed. The gilts with a low blood progesterone concentration at the time of inoculation had less vaginal discharge and a better resistance to endometritis than gilts with a higher blood progesterone concentration. In gilts inoculated with E. coli, as well as those inoculated with S. hyicus, a significant correlation (P < 0.001) existed between the blood progesterone concentration and the development of endometritis. It was concluded that the development of endometritis depends largely on the hormonal environment of the porcine uterus.     

Effects of level of feeding and progesterone dose on plasma and faecal progesterone in ovariectomised cows

The effects of two levels of feeding and two doses of progesterone (P4) on plasma and faecal progesterone metabolites (FP4M) were studied using a total of 24 ovariectomised (OVX), non-lactating, Holstein-Friesian cows. Cows were grazed on improved ryegrass/white clover pastures and allowed ad libitum access to pasture or were restricted to grazing for a total of 4 h per day in two 2 h periods. Progesterone (P4) was administered as one or two, simultaneous, intravaginal progesterone devices (CIDR). The cows were adapted to their pasture supply for 2 weeks before the start of the progesterone treatments. The progesterone devices were administered for 11 days and the cows were dosed with slow release chromic oxide capsules during the P4 treatment to allow faecal output (FO) to be estimated. Daily blood samples for P4 assay and weekly samples for blood metabolite assay were collected. Faecal samples were collected per rectum daily and assayed for pregnanes containing a 20-oxo-, 20alpha- or a 20beta-OH group by enzyme immunoassay (EIA). Daily FO was higher (P < 0.001) for ad libitum than pasture restricted cows (6.3 vs 4.1 kg DM) but was similar for both doses of P4. The average mass of P4 released from a CIDR device over a 11-day period was higher for cows allowed ad libitum pasture compared with those on restricted pasture (0.64 vs 0.60 g; P = 0.04). Plasma P4 concentrations, however, were higher in restricted than ad libitum fed cows (1x CIDR: 1.81 vs 1.41 ng/ml; 2x CIDR: 4.10 vs 3.46 ng/ml). Increasing the progesterone dose significantly (P < 0.001) increased both the concentrations and daily totals of the faecal pregnanes assayed and total FP4M. Restricted pasture cows had higher (P < 0.001) pregnanes and FP4M concentrations than cows fed ad libitum. Daily total faecal pregnane and FP4M did not differ between feeding levels except for faecal 20alpha-pregnane which was highest for ad libitum fed cows (P < 0.05). These results showed that the plasma concentrations of P4 in CIDR-treated OVX cows were negatively associated with the level of feeding. Level of feeding and dose of P4 affected the concentrations of FP4M, but the daily excretion rate of FP4M was not positively influenced by the level of feeding.     

Concentrations of progesterone in the backfat of pigs during the oestrous cycle and after ovariectomy

Small samples of backfat were taken daily during one oestrous cycle and more frequently after ovariectomy from 12 gilts by means of a simple biopsy technique and the levels of progesterone were determined. Compared to the levels of progesterone in peripheral plasma changes in backfat levels during the oestrous cycle were delayed by 1-2 days. Maximal levels with 89.7 +/- 9.2 (mean +/- s.e.m) ng progesterone/100 mg backfat were recorded on Day 15 of the oestrous cycle. It was estimated that, on this day, a total amount of about 36 mg progesterone is stored in the adipose tissue, which is approximately 200 times that present in total blood and corresponds to the daily production of the corpora lutea of the sow on Day 11. Initial half-life of progesterone in backfat after ovariectomy was estimated to be about 34 h compared to an initial half-life of plasma progesterone of about 120 min. The exact calculation of half-lives was, however, confounded by an obvious effect of anaesthesia or surgery on progesterone levels. Changes in backfat or plasma progesterone concentrations were not affected by the fat-to-lean ratio of the gilts. Fat progesterone levels determined in 44 additional pregnant and non-pregnant sows 17 or 20 days after mating indicated that reliable diagnosis of non-pregnant sows was possible on Day 20. It is concluded that the endocrinology of the oestrous cycle in pigs is related to the enormous storage of progesterone in the fat.     

Effects of dexamethasone administration to diestrus cows on systemic progesterone,estrogen and uterine cyclooxygenase production

Parenteral administration of dexamethasone to diestrus cattle can extend the length of the natural estrous cycle. In mice, dexamethasone has been shown to inhibit production of the second isozyme of the cyclooxygenase (COX) enzyme (a rate limiting enzyme in prostaglandin formation). Therefore, the purpose of this study was to determine the effect of dexamethasone on estrous cycle length and COX-1 and -2 production by the uterine endometrium of cyclic cattle.Nine crossbred beef cows that exhibited two previous normal estrous cycles were randomly assigned to two treatments; a control group administered intramuscular injections of vehicle, and a dexamethasone group administered 8 mg of dexamethasone (Azium^®, Schering Corp., Kenilworth, NJ). Both groups received twice daily injections on day 13–22 of the treatment cycle. Uterine endometrial biopsies were collected on days 16, 19 and 22 of the treatment cycle. Blood samples were collected daily on day 13–22 of the treatment cycle for plasma progesterone and estradiol concentrations.The mean treatment cycle length was extended (P < 0.05) in the dexamethasone group (31 d) compared with the control group (24 d). However, no difference was noted in the time to progesterone decline between treatments. In contrast, estradiol levels were lower in the dexamethasone treated animals compared with the control group on day 19 to 22 of treatment. A western blot analysis revealed no COX-2 in the uterine samples of either treatment. The COX-1 isoform was found on all days examined, but no treatment effect was detected. These results suggest that dexamethasone extends the cycle length by inhibiting follicle growth, and that COX-2 may not be involved in prostaglandin formation by the uterus during luteolysis.     

The use of milk progesterone profiles to characterise components of subfertility in milked dairy cows

Milk progesterone (P₄) concentrations of 1682 postpartum (PP) dairy cows during 2503 lactations were used to define and quantify the incidence of atypical ovarian patterns and to assess their impact on reproductive performance. A total of 257 animals (10.94%) with their first significant luteal activity after day 44 PP were considered a result of delayed ovulation type I (DOVI). Prolonged luteal activity (P₄>3 ng/ml for at least 19 days) observed in 170 (7.3%) and 161 (6.35%) animals during first and subsequent cycles was considered a result of the presence of a persistent corpus luteum (CL), respectively denoted as PCLI and PCLII. Following the demise of an oestrous cycle CL, a total of 322 (12.85%) animals showed a delayed ovulation Type II (DOVII) with P₄<3 ng/ml for >12 days. In 238 inseminated animals (9.92%) prolonged luteal activity was followed by the CL demise which may indirectly indicate the incidence of a late embryo to early foetal mortality (LEM). In this study animals during 794 (31.7%) lactations had at least one atypical ovarian pattern before insemination that, in comparison to those with typical P₄ patterns, contributed to a delayed conception (88.2 vs. 106.2 days), higher number of services per conception (1.49 vs. 1.8), lower first service conception rate (60.9 vs. 43.7%) and a reduced total conception rate (92.6 vs. 82.1%), all of which were significantly different at P<0.001. The incidence of PCLI and PCLII before insemination resulted in a higher level of LEM. Milk progesterone monitoring offers an accurate and objective measurement of factors associated with PP ovarian activity which will assist in investigating the genetic and environmental factors affecting fertility.     

Corpus luteum size and plasma progesterone concentration in cows

It is often assumed that a larger corpus luteum will produce more progesterone and generate higher circulating plasma concentrations. The aim of the study was to determine whether the size of the corpus luteum does actually determine circulating plasma progesterone concentrations. Data were collated from a number of studies on various aspects of luteal function in non-lactating dairy cows to allow comparisons to be made between corpus luteum weight and plasma progesterone concentration across the luteal phase. In these studies oestrous cycles had been synchronised and animals slaughtered on day 5, day 8 or day 16 following oestrus. Both corpus luteum weight and plasma progesterone concentration increased between day 5 and day 8. Plasma progesterone concentration but not luteal weight also increased between day 8 and day 16. On day 5 there was a strong relationship between corpus luteum weight and plasma progesterone (R² = 0.64; P < 0.001). However, no such relationship was present on day 8 or day 16. These results indicate that while during the early stage of corpus luteum development a relationship between size and progesterone is present, by day 8 of the cycle, the size of the corpus luteum is no longer of importance in determining circulating progesterone concentrations.     

Control of oestrus in cattle using progesterone coils

Four experiments were conducted to determine the effect of length of treatment, stage of cycle at start of treatment and administration of oestradiol benzoate or progesterone at the start of treatment with intravaginal progesterone coils on oestrous response and fertility. In Experiment 1, the number of heifers in oestrus was affected neither by injection of 5 mg oestradiol benzoate alone or with 200 mg progesterone nor by length of treatment. More heifers (P < 0.05) were in oestrus on day 2 after treatment following a 12-day treatment compared to a 9-day treatment.In Experiment 2, heifers between days 17 and 20 of the oestrous cycle received an injection of either 5 mg oestradiol benzoate alone or with 200 mg progesterone at the start of a 9-day treatment with progesterone coils. Neither the number of heifers in oestrus nor the pattern of onset were affected after treatment. In Experiment 3, heifers between days 0 and 3 of the oestrus cycle received progesterone coils for 9, 12 or 14 days. In addition, animals received (i) no further treatment, (ii) a gelatin capsule adhered to the coil containing 10 mg oestradiol benzoate (iii) a gelatin capsule adhered to the coil containing 200 mg progesterone. Following a 9- or 12-day treatment period heifers receiving the coil with the oestrogen capsule had a high oestrous response ( compared to , P < 0.05). When oestrogen was not given, there was a significant linear effect of duration of treatment on the number in oestrus (9 days, ; 12 days ; 14 days, ; P < 0.05).In Experiment 4, post-partum cows were used to compare a 9- and 12-day treatment period and half the animals in each group received either 5 mg oestradiol benzoate and 200 mg progesterone at the start of treatment or a 10 mg gelatin capsule adhered to the coil. The length of treatment affected the number of heifers in oestrus since were in oestrus after a 12-day treatment period compared with after a 9-day period (P < 0.001). There were no significant differences in the number of cows in oestrus after injection of oestrogen and progesterone ( ) or after the use of the gelatin capsule ( ).