Effects of (artificial) boar stimuli on uterine activity in estrous sows

This study aims to examine influences of specific boar stimuli on uterine activity in estrous sows, by comparing uterine activity in presence of a mature teaser boar and a robot boar with variable stimuli. Nineteen multiparous, cyclic, commercial crossbred sows were used. Intra-luminal uterine pressure was measured using a non-surgical method for 45 min before applying one of four treatments in combination with a back-pressure-test (BPT): (1) robot with olfactory and auditory stimuli (R+O+A) (n=16), (2) robot with auditory stimuli (R+A) (n=16), (3) robot without additional stimuli (R) (n=16), (4) a mature boar (boar) (n=15). After treatment, measurements continued for 30 min. For each measurement, frequency, mean amplitude and mean duration of uterine contractions were determined. Spontaneous frequency of uterine contractions was 18.6+/-0.7 h(-1) on average and did not differ between treatments. Frequency of contractions increased significantly for the boar (+5.6+/-1.3 h(-1); P<0.01), R+O+A (+3.9+/-1.3; P<0.01) and R+A (+2.6+/-1.3; P<0.05). The effect of boar presence on frequency of contractions was greater than the effect of R (P<0.05). Amplitude and duration of contractions were not affected by treatment. The change in frequency was dependent on spontaneous frequency (P<0.01). In conclusion, the higher the level of boar stimuli, the greater the increase in frequency of uterine contractions. The results indicate that the used combinations of artificial boar stimuli do not mimic a 'whole' boar. It is unclear which boar stimuli stimulate maximal uterine activity during estrus.     

Spontaneous electromyographic activity throughout the cycle in the sow and its change by intrauterine oestrogen infusion during oestrus

Two experiments were carried out to monitor influences on the uterine electromyographic activity (EMG) in cyclic gilts with chronic uterine EMG electrodes. In Exp. 1 the EMG was recorded continuously from Day -1 for 24 days and was evaluated for frequency, duration and amplitude. Progesterone and oestradiol in peripheral plasma were measured daily. As high amounts of oestrogens are characteristic for boar semen, in Exp. 2 the influence of seminal oestrogens on uterine contractions at Day 0 (first day of standing reflex) was investigated in gilts with chronic intrauterine catheters. They were infused with 10 ml saline (N = 4) or saline with physiological amounts of oestrogens (5 micrograms oestradiol + 2 micrograms oestrone + 4.5 micrograms oestrone sulphate; N = 4). Sham-treated gilts (infusion catheters, no infusion; N = 5) served as controls. The EMG was recorded for 2 h before and 9 h after infusion. In Exp. 1 the maximal amplitude (2040 +/- 98 microV) and duration (32 +/- 1.7 sec) but the lowest frequency (15.8 +/- 2.1 contractions/h) were found on Day 0. With decreasing oestrogen and increasing progesterone concentrations the frequency increased continuously until Day 5 (63.5 +/- 1.0 contractions/h) while the amplitude (183 +/- 13 microV) and duration (3.3 +/- 0.7 sec) decreased. During Days 6-13 the EMG activity was not detectable. The reverse pattern was found from the onset of luteolysis until the following Day 0. On Day 0 a significant correlation between oestradiol and the duration (r = 0.81; P less than 0.01; n = 10) but not the frequency was observed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Uterine activity, sperm transport, and the role of boar stimuli around insemination in sows

This paper describes changes in spontaneous myometrial activity around estrus, factors that affect myometrial activity, and the possible role of uterine contractions in the process of (artificial) insemination, sperm transport and fertilization. Myometrial activity in the sow increases during estrus. The activity is myogenic in origin, but several factors have been shown to affect myometrial activity. Natural mating stimulates uterine contractions through several mechanisms. The presence of a boar, rather than the act of mating, induces central oxytocin release in the sow and thus increases uterine activity. Estrogens in the ejaculate of a boar can trigger prostaglandin release by the endometrium and thus increase uterine activity. Tactile stimulation of the genital tract (cervix) or tactile stimulation of the back and flanks of the sow during artificial insemination does not cause a release of oxytocin. There is hardly any evidence for the effects of these latter stimuli on uterine activity, and if they are present at all, the effects are very small. Evidence for the effects of synthetic boar odor on oxytocin release and/or uterine activity is inconsistent. The mere presence of a boar during insemination, in contrast, clearly stimulates uterine activity through the release of oxytocin. Hormonal stimulation (intrauterine) of uterine activity with estrogens, prostaglandins, or oxytocins before, during or after insemination generally improves fertilization rate, especially in situations with reduced fertility. Therefore, uterine contractions are believed to play an important role in the transport of sperm cells to the oviducts after insemination. Whether uterine contractions are absolutely necessary for sperm transport through the uterine horns, however, is not clear. Intensive stimulation of uterine contractions using hormones can also reduce the fertilization rate, probably by increasing the reflux of sperm cells during insemination. In this respect, the presence of a boar during AI seems more adequate, as only sows with a low level of uterine activity show an increase in uterine activity in response to this stimulus.     

The in vitro effect of boar semen on the contractility of rat uteri

Contradictory reports in the literature provoked the investigation of a possible oxytocic effect of boar semen on in vitro rat uterus preparations. When fresh boar seminal plasma (SP), dialyzed seminal plasma (DSP) or a filtrate of acetone-extracted seminal plasma (AE) were added to uterine preparations, both the frequency and force of spontaneous contractile activity tended to be depressed. When the uterine preparations were primed with oxytocin (1.6 USP units/100 ml bathing solution), treatment with SP and AE resulted in an increased frequency of contraction but no increase in force. DSP increased neither the frequency nor force of contractions. A solution of salts and organic compounds that approximated the small molecular or dialyzable components of boar semen ("synthetic boar seminal plasma" or BS) affected contractility in a manner similar to SP and AE. When the rat uterus was bathed in a low calcium physiological salt solution, none of the seminal treatments (SP, DSP, AE, or BS) were capable of initiating a contraction. Further, the force of carbachol-induced contractions in these uterine preparations was markedly depressed by these seminal treatments. In contrast, treatment with oxytocin nearly doubled the contractile force. The depressant effect of SP, DSP and AE on both spontaneous and carbachol-induced contractions appeared to be irreversible. Mineral analysis of SP, DSP, AE, BS and the low calcium salt solution showed the SP, AE and BS contained amounts of Ca(2+) and Mg(2+) which could have altered the uterine contractility. In addition, a non-dial-yzable factor in SP appeared to have a similar effect.     

Effect of estrogen formulation and its site of deposition on serum PGFM concentrations, uterine contractility, and time of ovulation in artificially inseminated weaned sows

At the time of artificial insemination, 48 mixed parity sows were assigned by parity to receive 25 microg estradiol-17beta either in oil deposited onto the vaginal mucosa (E-oil), or dissolved in extended semen (E-semen), or received no estrogen and served as controls. All sows were inseminated transcervically 24 h after detection of estrus. The time of ovulation was determined in 15 sows per treatment by transrectal ultrasonography. Concentrations of prostaglandin F2alpha metabolite (PGFM) were determined in blood samples obtained from eight sows per treatment at 1 h intervals from 1 h pre-treatment until 7 h post-treatment. The remaining eight sows per treatment were fitted with a transducer to allow determination of intrauterine pressure changes during 1 h pre-treatment until 5 h post-treatment. There were no differences among treatments for wean to estrus interval, size of ovarian follicles at the time of treatment or the estrus detection to ovulation interval. In all treatments, plasma PGFM concentrations were increased from 1 h after treatment. However, the increase was greater and of longer duration in the E-oil sows (P=0.03) supporting the suggestion that this formulation and route of administration enhanced uterine PGF2alpha release. Compared to controls, both estradiol treatments were associated with myometrial contractions of increased amplitude and duration, supporting a causal link between estradiol treatment, increased uterine PGF2alpha release, and enhanced myometrial contractility.     

The influence of insulin administration after weaning the first litter on ovulation rate and embryo survival in sows

Primiparous crossbred sows (n = 43), lactating for an average of 21.1 +/- 0.1 d and weaning 8.7 +/- 0.1 pigs, were used to evaluate the influence of insulin on ovulation rate and embryo survival. The sows were maintained on 2.3 kg/head/d of a 14% protein gestation diet during pregnancy, fed ad libitum during lactation, given 2.7 kg/head/d from weaning until re-breeding and fed 2.3 kg/head/d after mating. Beginning the day after weaning (Day 0) sows were treated with 0.4 IU/kg body weight (BW) insulin (n = 21) or were administered an equivalent volume of saline (n = 22) for 4 d. Beginning on Day 3 and continuing until Day 14 after weaning, the sows were checked for estrus twice daily and were artificially inseminated using pooled semen from 2 fertile boars. At slaughter (days 30 to 40 of gestation), ovaries and uteri were collected, and the ovulation rate, embryo number and viability, and uterine weight and length were evaluated and recorded. Use of insulin decreased the average interval from weaning to estrus compared with saline by increasing percentage in estrus by Day 14 after weaning (5.0 +/- 0.57 vs 6.9 +/- 0.56 d, respectively; P < 0.03). Ovulation rate, number of embryos, embryo survival, and average uterine length and weight were not influenced by insulin treatment. Overall, insulin affected reproductive efficiency in primiparous sows by increasing the percentage of sows in estrus.     

Uterine motility in the cow during the estrous cycle. II. Comparative effects of prostaglandins F(2alpha), E(2), and cloprostenol

Intrauterine pressure (IUP) changes were recorded in nonlactating, cyclic dairy cows using transcervically placed intraluminal pressure microtransducers. Spontaneous activity was recorded for the first 30 min. Prostaglandins (PG) F(2alpha) (5 mug/kg), E(2) (5 mug/kg), or cloprostenol (0.1 mug/kg) were then injected intravenously (i.v.) at diestrus, proestrus, estrus, and metestrus, and their effects were recorded. The drug administrations did not alter the duration of the estrous cycle of the cows. Single doses of PGF(2alpha) and E(2) significantly increased uterine activity at all stages of the estrous cycle, while cloprostenol had no effect. PGF(2alpha) and PGE(2) increased IUP, frequency, and amplitude during all stages of the estrous cycle. The spontaneous pattern resumed within 20 min postinjection. Partial uterine refractoriness occurred with both PGs. The results indicate that low doses of natural prostaglandins stimulate uterine activity during the estrous cycle in cattle.     

The effect of experimental induced hypocalcaemia on uterine activity in the sow during parturition and post-partum

Uterine activity was measured by monitoring intrauterine pressure changes using ballon-tipped catheters placed in the lumen. An infusion rate of Na(2)EDTA of 35 mg/Kg/h gave a chelation rate equivalent to the rate of calcium mobilisation, and when infused at a level greater than this, resulted in a reduction in plasma calcium concentrations and a concomitant reduction in uterine activity. In three of the four sows infused intrapartum, there was complete cessation of uterine activity; however, plasma calcium concentrations of less than 6 mg 100 ml resulted in a reduction in uterine activity at this stage of parturition. The uterus of the sow post-partum appeared to be more sensitive to the effects of hypocalcaemia with reduced uterine activity when plasma calcium concentrations fell below 8.2 mg 100 ml and complete cessation of activity between 6 and 7 mg 100 ml . Although there was evidence of a delay in the expulsion of piglets in the hypocalcaemic sows, there was no evidence of an increased number of stillborn piglets compared with the two control sows.     

Effect of estradiol-17beta on PGF and total protein content in bovine uterine flushings and peripheral plasma concentration of 13, 14-dihydro-15-keto-PGF(2alpha)

Two experiments were conducted to examine the effect of estradiol-17beta (E(2)-17beta) on content of immunoreactive prostagladin F(2)alpha (PGF, ng) and total protein (TUP, mg) in uterine flushings, as well as concentrations of 13, 14-dihydro-15-keto-PGF(2)alpha (PGFM) in plasma (Pg/ml). In experiment 1, Holstein heifers were utilized in a single reversal trial in which either E(2)-17beta (3 mg in 2 ml saline/ethanol 50:50; n=5) or vehicle alone (n=6) were given intravenously on day 14 or 15 of the estrous cycle (Period 1) following an induced estrus (day of estrus = day 0). Treatment (Trt) groups were reversed in Period 2 (Day 14 or 15 of the second estrous cycle). Jugular venous plasma was obtained before treatment (Oh), and at 5, 6, and 9h posttreatment (PT). Uterine flushings were collected nonsurgically in vivo , per cervix, via Foley catheter at 6h PT (20 ml of .9% saline per uterine horn). E(2)-17beta did not significantly alter (E(2)-17beta vs vehicle; x(-) +/- S.E.M.) PGF (1674 +/- .11 +/- 338.39 vs 1889.91 +/- 400.24 ng; P> .10) or TUP (33.25 +/- 2.57 vs 39.16 +/- 3.04 mg; P > .10). However, E(2)-17beta increased (P < .05) plasma PGFM (E(2)-17beta vs vehicle) after treatment (0h, 113.2 vs 163.8; 5h, 312.5 vs 203.9; 6h, 324.5 vs 198.0; 9h, 323.2 vs 246.8, pg/ml). In experiment 2, crossbred beef cattle received comparable treatments of either E(2)-17beta (n=5) or vehicle (n=5) on day 14 or 15 postestrus. Jugular venous plasma was obtained at 0h PT, and at 6h PT. Uterine flushings (1.9% saline, 20 ml per uterine horn) and peripheral plasma were collected at slaughter. Estradiol-17beta increased PGF (30.07 +/- 5.94 vs 8.46 +/- 2.01 ng; P> <.05) in uterine flushings as well as PGFM in plasma (E(2)-17beta : 55.82 +/- 19.13 pg/ml, at 0h and 89.31 +/- 14.02 pg/ml, at 6h, vs saline: 103.46 +/- 50.73 pg/ml, at 0h and 17.78 +/- 14.22, at 6h). Estradiol-17beta stimulated uterine production and release of PGF and protein as measured in flushings (experiment 2) as well as plasma PGFM responses (experiments 1 and 2). Uterine and/or cervical stimulation of experiment 1 may have masked uterine response to E(2)-17beta.     

Effects of human chorionic gonadotrophin on contractile activity of steroid-primed pig myometrium in vitro

We examined the effects of (a) oestrogen and progesterone on concentrations of luteinizing hormone/human chorionic gonadotrophin (LH/hCG) receptors in uterine smooth muscle in vivo and (b) hCG on spontaneous myometrial contractions in vitro. Ovariectomized gilts received 2 ml corn oil (control; n = 5), 2 mg oestradiol benzoate (n = 6) or 20 mg progesterone (n = 5) for 5 days. Gilts were hysterectomized 8 h after the last injection and longitudinal sections of myometrium were incubated in modified Krebs' solution with 0 or 10 i.u. of hCG (n = 10/gilt) for 4 h at 37 degrees C in 95% O2:5% CO2. After incubation, myometrial sections were placed in a tissue chamber perfused with Krebs' solution and mechanical activity was recorded for 30 min. Cell membrane fractions were prepared from myometrial tissue not used for in-vitro studies and analysed for LH/hCG receptors. Treatment with oestradiol benzoate increased (P less than 0.01) the number of LH/hCG-binding sites compared with gilts receiving corn oil or progesterone. Incubation of myometrium with hCG reduced (P less than 0.01) the frequency and amplitude of spontaneous uterine contractions in gilts treated with oestradiol benzoate. In contrast, hCG had no effect (P greater than 0.05) on the pattern of myometrial contractions in gilts given corn oil or progesterone. These results indicate that oestradiol promotes the synthesis of LH/hCG receptors in pig myometrium and incubation of oestrogen-primed tissue with hCG has a quiescent effect on myometrial contractility.     

The effects of buck teasing on synchronization of estrus in goats after intravulvo-submucosal administration of cloprostenol

A study was conducted on 35 East African shorthorned female goats to determine if a combination of buck teasing and low doses of a prostaglandin (PGF(2) alpha) analogue, cloprostenol, given intravulvo-submucosally (i.v.s.m.) would be suitable for synchronization of estrus. Goats were allotted, with the onset of estrus, to seven groups (n = 5 goats per group). Five of the seven groups received varying doses of cloprostenol: Group 1 (125 mug cloprostenol i.m. per goat); Group 2 (62.5 mug cloprostenol i.v.s.m. per goat); Group 3 (62.5 mug cloprostenol i.v.s.m. per goat plus buck teasing); Group 4 (31.25 mug cloprostenol i.v.s.m. per goat); Group 5 (31.25 mug cloprostenol i.v.s.m. per goat plus buck teasing); Group 6 (buck teasing); Group 7, (2 ml physiological saline i.v.s.m. per goat, control group). Plasma progesterone concentration was measured on day of treatment and for 6 d thereafter. All goats in groups 1, 2, 3 and 5 exhibited estrus within 68 h. Thus, the number of goats receiving low doses of PG-cloprostenol intravulvo-submucosally observed in estrus increased (P < 0.05) with exposure to bucks. Exhibition of behavioral signs of estrus was maximal between 2 and 20 h after onset of signs of estrus. The exposure of females to males prior to intrauterine penetration was an advantage because copious mucus eased penetration.     

Luteinizing hormone,total estrogens and progesterone secretion during lactation and after weaning in sows

Two experiments were conducted to determine changes in serum concentrations of LH, total free estrogens and progesterone before and after weaning in sows. Blood was collected either via indwelling anterior vena cava cannula or by venipuncture and serum hormones were measured by radioimmunoassay. In Exp. I, blood was collected at 15-min intervals for 4 hr on day 7 and day 21 postpartum from three sows on each day. In addition, individual samples were collected from 10 sows on days 4 and 14 postpartum and from 11 sows on days 1, 3 and 5 after weaning (day 23 postpartum). Serum LH ranged from .2 to .8 ng/ml during lactation and averaged 1.1 ± .7, 1.1 ± .7 and 2.7 ± .7 on days 1, 3 and 5 after weaning, respectively. Progesterone was low (< 1 ng/ml) during lactation and averaged 1.9 ± .3, .6 ± .3 and 1.2 ± .3 on days 1, 3 and 5 after weaning. Estrogens were variable during lactation, averaged 121 ± 36 pg/ml on day 1 after weaning and decreased thereafter. Estrus began on day 3 after weaning in 1 sow and on day 5 in the remaining 10 sows.In Exp. II, blood was collected from seven sows at 12 to 24 hr intervals from 2 days before until 5 days after weaning (day 26 postpartum). Mean serum LH was .7 ± .1 ng/ml during 48 hr before weaning and remained unchanged after weaning until day 3 when LH increased to 6.1 ± .8 ng/ml. Serum LH concentrations then declined to 1.3 ± .8 and .9 ± .8 ng/ml on days 4 and 5 after weaning. Total estrogens averaged 31 ± 4 pg/ml during 48 hr prior to weaning and 32 ± 4, 43 ± 17, 28 ± 1, 30 ± 2, 16 ± 2 and 18 ± 2 on days 0 to 5 after weaning. Progesterone increased from 1.0 ± .3 ng/ml 24 hr before weaning to 3.0 ± .3 at weaning and then remained low (< 1 ng/ml) until after ovulation when progesterone increased. Estrus began on day 4 after weaning in all seven sows.Results from these two experiments indicate that in sows: (1) LH is suppressed during early lactation (day 7), gradually increases during late lactation (day 21) and then reaches peak concentrations after weaning near the onset of estrus, (2) estrogens increase between weaning and estrus and decline thereafter, and (3) progesterone rises transiently at weaning and then increases after estrus and ovulation.     

Effect of beta-carotene administration on reproductive function of horse and pony mares

The objective of this study was to determine whether supplemental beta-carotene would influence reproductive function in mares maintained on spring and summer pastures and to characterize plasma carotene concentrations during the estrous cycle. Carotene concentrations in plasma did not vary with day of estrous cycle (P = 0.7455). Mares receiving every other day injections of beta-carotene (400 mg; n = 4) or saline (10 ml; n = 4) during proestrus/estrus did not differ in plasma estradiol (E(2)) concentrations (P = 0.6313), follicle development (P = 0.8068), or plasma progesterone (P(4)) concentrations during the following diestrus (P = 0.4954). Moreover, no differences in plasma P(4) concentrations (P = 0.9047) were detected between mares receiving every other day injections of beta-carotene (400 mg; n = 4) or saline (10 ml; n = 4) during diestrus. However, administration of beta-carotene raised plasma carotene concentrations relative to controls when injected during proestrus/estrus (P = 0.0096) and diestrus (P = 0.0099). Pregnancy rates (P = 0.4900) and number of cycles required for pregnancy (P = 0.2880) were similar for mares administered injections of saline (10 ml; n = 37), beta-carotene (400 mg; n = 37), vitamin A (160,000 IU; n = 38), or vitamin A + beta-carotene (160,000 IU + 400 mg; n = 43), on the first or second day of estrus and on the day of breeding. Therefore, these results collectively suggest that supplemental beta-carotene does not affect the reproductive function of mares fed adequate dietary carotene. Whether supplemental beta-carotene would enhance reproductive function in mares on low carotene diets warrants further investigation.     

The synchrony of prostaglandin-induced estrus in cows was reduced by pretreatment with hCG

The induction of optimal synchrony of estrus in cows requires synchronization of luteolysis and of the waves of follicular growth (follicular waves). The aim of this study was to determine whether hormonal treatments aimed at synchronizing follicular waves improved the synchrony of prostaglandin (PG)-induced estrus. In Experiment 1, cows were treated on Day 5 of the estrous cycle with saline in Group 1 (n = 25; 16 ml, i.v., 12 h apart), with hCG in Group 2 (n = 27; 3000 IU, i.v.), or with hCG and bovine follicular fluid (bFF) in Group 3 (n = 21; 16 ml, i.v., 12 h apart). On Day 12, all cows were treated with prostaglandin (PG; 500 micrograms cloprostenol, i.m.). In Experiment 2, cows were treated on Day 5 of the estrous cycle with saline (3 ml, i.m.) in Group 1 (n = 22) or with hCG (3000 IU, i.v.) in Group 2 (n = 20) and Group 3 (n = 22). On Day 12, the cows were treated with PG (500 micrograms in Groups 1 and 2; 1000 micrograms in Group 3). Blood samples for progesterone (P4) determination were collected on Day 12 (Experiment 1) or on Days 12 and 14 (Experiment 2). Cows were fitted with heat mount detectors and observed twice a day for signs of estrus. Four cows in Experiment 1 (1 cow each from Groups 1 and 2; 2 cows from Group 3) had plasma P4 concentrations below 1 ng/ml on Day 12 and were excluded from the analyses. In Experiment 1, cows treated with hCG or hCG + bFF had a more variable (P = 0.0007, P = 0.0005) day of occurrence of and a longer interval to estrus (5.9 +/- 0.7 d, P = 0.003 and 6.2 +/- 0.8 d, P = 0.005) than saline-treated cows (3.4 +/- 0.4 d). The plasma P4 concentrations on Day 12 were higher (P < 0.0001) in hCG- and in hCG + bFF-treated cows than in saline-treated cows (9.4 +/- 0.75 and 8.5 +/- 0.75 vs 4.1 +/- 0.27 ng/ml), but there was no correlation (P > 0.05) between plasma P4 concentrations and the interval to estrus. In Experiment 2, cows treated with hCG/500PG and hCG/1000PG had a more variable (P = 0.0007, P = 0.002) day of occurrence of and a longer interval to estrus (4.2 +/- 0.4 d, P = 0.04; 4.1 +/- 0.4 d, P = 0.03) than saline/500PG-treated cows (3.2 +/- 0.1 d). The concentrations of plasma P4 on Days 12 and 14 of both hCG/500PG- and hCG/1000PG-treated cows were higher (P < 0.05) than in saline/500PG-treated cows (7.3 +/- 0.64, 0.7 +/- 0.08 and 7.7 +/- 0.49, 0.7 +/- 0.06 vs 5.3 +/- 0.37, 0.5 +/- 0.03 ng/ml). The concentrations of plasma P4 on Days 12 or 14 and the interval to estrus were not correlated (P > 0.05) in any treatment group. The concentrations of plasma P4 on Days 12 and 14 of hCG/500PG- or hCG/1000PG-treated cows were correlated (r = 0.65, P < 0.05; r = 0.50, P < 0.05). This study indicated that treatment of cows with hCG on Day 5 of the estrous cycle reduced the synchrony of PG-induced estrus and that this reduction was not due to the failure of luteal regression.     

Effects of cloprostenol sodium and clenbuterol HCl on reproductive performance in postpartum anestrous cows

Two experiments were conducted to study effects of cloprostenol sodium (cloprostenol) and clenbuterol HCl (clenbuterol) during postpartum anestrus on subsequent reproductive performance in cows. In Experiment I, 96 cows received either 0.5 mg cloprostenol (PGF, n = 25), 364 mg clenbuterol (CLEN, n = 24), 0.5 mg cloprostenol and 364 mg clenbuterol (CLEN+PGF, n = 21) or no treatment (Control, n = 26) on Day 20 post partum. Treatments failed to influence postpartum interval, pregnancy rate or the incidence of short estrous cycles preceding the first normal estrous cycle. In Experiment II, anestrous cows were administered cloprostenol (0.5 mg) on either Day 20 (PGF20, n = 27) or Day 35 post partum (PGF35, n = 25), or served as untreated controls (Control, n = 26). Neither postpartum interval nor pregnancy rate were affected by cloprostenol treatment. In conclusion, treatment of postpartum cows with PGF did not alter the resumption of normal estrous cycles following parturition.     

In vitro contractile activity of porcine myometrium during luteolysis and early pregnancy: effect of oxytocin and progesterone

The present study was undertaken to elucidate the role of OT in myometrial contractility in sows. Spontaneous and OT-stimulated contractions of the inner circular (CM) and outer longitudinal (LM) layers isolated from cyclic (Days 14-16) and early pregnant (Days 14-16) sows were examined in six cyclic and six pregnant sows. In addition, the role of P(4) in the modulation of OT-induced uterine contractions was investigated. The contractile activity of the LM and CM layers was recorded in a tissue chamber filled with Krebs-Ringer solution. Myometrial contractility was expressed as area under the contractility curve (AUC) and frequency of contractions. Myometrial longitudinal and circular muscles exhibited spontaneous contractility in sows during both luteolysis and early-pregnancy. The mean AUC was higher (p<0.05) in the LM layer compared to the CM layer in both cyclic and pregnant animals. In addition, pregnant sows were characterized by higher AUC in both LM and CM layers in comparison to cyclic sows. The CM layer was unresponsive to examined treatments. Oxytocin (1-3x10(-8) and 1-3x10(-7)M) increased the AUC and frequency of contractions of the LM layer in both examined animal groups, being more effective during luteolysis (p<0.001) than early pregnancy (p<0.01). Response of the LM layer to OT appeared to be clearly related to the initial spontaneous level of contractility. This response to OT was inhibited (p<0.05) in the presence of OT antagonist (10(-6)M). Moreover, in pregnant sows, OT-stimulated contractile activity of myometrium was inhibited (p<0.05) by P(4) (10(-5)M). In conclusion, OT receptors present in myometrial cells (especially in the LM layer) are involved in the regulation of contractile activity of porcine myometrium during luteolysis and early-pregnancy. In addition, progesterone appears to be involved in this regulation.     

Induction of parturition in pigs by intravaginal application of the prostaglandin analog cloprostenol

Cloprostenol was deposited in the vaginal lumen of sows on Day 111 of pregnancy at dosages of 100, 125 or 175 g and volumes of 1, 2 or 5 ml, respectively. A control group was treated with physiological saline. In 92 out of 93 prostaglandin-treated sows, parturition commenced approximately 22 h after application, with no significant differences between dose levels or volumes. There were also no differences in the average size and weight of litters born, weaning weight, frequency of postpartum complications or post-weaning fertility. Intravaginal application of cloprostenol is thus a simple and efficient means of inducing parturition in sows.     

Effect of P.G. 600 on rebreeding performance in sows limit-fed during lactation

The objective was to determine whether treatment with 400 IU PMSG and 200 IU hCG (P.G. 600; Intervet America, Inc., Millsboro, DE, USA) at weaning improved rebreeding performance in sows that were limit-fed during lactation. Crossbred sows were allowed ad libitum access to feed or were limited to 3.2 kg of feed/day during an 18-day lactation. At weaning, limit-fed sows received im treatment with P.G. 600 (n = 16) or saline (n = 19) and ad libitum-fed sows received saline (n = 18). The percentage of sows in estrus by day 7 post-weaning was greater (p<0.05), and the weaning-to-estrus interval was shorter (p<0.05), for ad libitum-fed sows compared to limit-fed, saline-treated sows, with limit-fed, P.G. 600-treated sows having intermediate values that were not different from the other two groups. The percentage of sows pregnant and the numbers of corpora lutea and embryos at day 30 post-mating were not different (p>0.1) among groups. In summary, low feed intake during lactation decreased the percentage of sows that displayed estrus within 7 days after weaning and increased the weaning-to-estrus interval. These effects were at least partially remediated by gonadotropin treatment. Pregnancy rate, and litter size at day 30 of gestation, were similar for ad libitum- and limit-fed sows and not affected by P.G. 600 treatment in limit-fed sows.     

Conception rates and serum progesterone concentration in dairy cattle administered gonadotropin releasing hormone 5 days after artificial insemination

The objectives of this study were to determine the effect of administration of exogenous GnRH 5days after artificial insemination (AI) on ovarian structures, serum progesterone concentration, and conception rates in lactating dairy cows. In experiment 1, 23 Holstein cows were synchronized using the Ovsynch protocol. Five days after AI (day 0) cows were assigned randomly to receive either saline (saline; n=11) or 100microg GnRH (GnRH; n=12). To examine ovarian structures, ultrasonography was performed on day 1 and every other day beginning on day 5 until day 13. On days 5 and 13 blood samples were obtained to measure serum progesterone concentrations. All cows in the GnRH-treated group developed an accessory corpus luteum (CL), whereas cows in the saline group did not. Mean serum progesterone concentrations did not differ between GnRH and saline groups on day 5 (1.64+/-0.46ng/ml versus 2.04+/-0.48ng/ml). On day 13 serum progesterone concentrations were greater (P<0.05) in the GnRH group compared with saline (5.22+/-0.46ng/ml versus 3.36+/-0.48ng/ml). In experiment 2, 542 lactating cows, at two different commercial dairies, were used to test the effect of administering GnRH 5 days after AI on conception rates. Cows were synchronized and detected for estrus according to tail chalk removal. Cows detected in estrus received AI within 1h after detection of estrus. Five days after AI, cows were assigned randomly to receive either GnRH (n=266) or saline (n=276). Pregnancy status was determined by palpation per rectum of uterine contents approximately 40 days after AI. There was no effect of farm on conception rate. There was no effect of treatment as conception rates did not differ between GnRH and saline groups (26.7% GnRH versus 24.3% saline). Regardless of treatment, days in milk, parity, milk yield, and number of services had no effect on the odds ratio of pregnancy. In summary, the results of this study indicated that GnRH administered 5 days after AI increased serum progesterone by developing an accessory CL but did not improve conception rates in dairy cattle.     

Myometrial activity and plasma progesterone and oxytocin concentrations in cycling and early-pregnant ewes

Myometrial activity and plasma progesterone (P) and oxytocin (OT) were measured in early pregnant (n = 5) and cycling (n = 5) ewes. Electromyography (EMG) leads and jugular and inferior vena cava (IVC) catheters were surgically placed in ewes about 1 wk before data collection. When ewes returned to estrus, they were bred to either an intact or vasectomized ram. Continuous EMG data were collected, and blood samples were collected twice daily from day of estrus (Day 0) until Day 18. Ewes bred with an intact ram were checked surgically for pregnancy on Day 20. Computerized, quantitative analysis of EMG events showed no difference in signal from the right to left uterine horns, and no differences between pregnant and cycling ewes (p less than 0.05) until Days 14-18 when nonpregnant ewes returned to estrus and had increased EMG activity. The mean number of EMG events 180-900 s in length decreased in pregnant ewes, but this difference was not significant (p less than 0.05). Jugular plasma progesterone (P) levels confirmed corpus luteum (CL) formation in all ewes, and no differences in P between pregnant and nonpregnant ewes were measured until Days 14-18, when cycling ewes underwent luteolysis and pregnant ewes maintained CL. IVC plasma oxytocin concentrations were increased in pregnant ewes compared to concentrations in nonpregnant ewes on Days 5-13 (p less than 0.05), and the difference was largest at Day 6 (means +/- SEM pg/ml: pregnant = 68.7 +/- 13.9, nonpregnant = 30.9 +/- 19.9).(ABSTRACT TRUNCATED AT 250 WORDS)