Time of ovulation and reproductive performance over three parities after treatment of primiparous sows with PG600

Primiparous sows from a commercial pig farm in central Brazil were utilized to investigate the effect of post-weaning gonadotrophins (given during summer) on estrus, time of ovulation and reproductive performance over three parities. One group of sows (PG600) was treated with a combination of 400 IU equine chorionic gonadotrophin (eCG)+200 IU human chorionic gonadotrophin (hCG) (PG600) 24h after weaning (n=420), whereas the control group received saline (n=408). In a subset of sows (n=150), estrus was detected and time of ovulation was determined by transcutaneous ultrasound. Treatment with PG600 increased the percentage of primiparous sows in estrus within 10 days after weaning (94.8% versus 79.7%) and reduced the first weaning-to-estrus interval (5.3 days versus 8.0 days) relative to control sows (P<0.05). Although the duration of estrus was longer (P<0.05) in sows given PG600 (65.7 h versus 61.0 h), the interval from estrus to ovulation was not different (P>0.05) between PG600 and control sows (46.6 h versus 43.3 h). Treatment with PG600 did not affect (P>0.05) rates of return-to-estrus and farrowing over three parities, but it increased the number of total piglets born (P<0.05) in the second parity (11.2 versus 10.4), thereby minimizing the magnitude of second-litter syndrome. Culling rates from the first to the fourth parity were 26.7 and 24.5% (P>0.05) for PG600 and control sows, respectively. In conclusion, PG600 given 24 h after the first weaning reduced the weaning-to-estrus interval and increased the size of the second litter.     

Estrogen induces estrus unaccompanied by a preovulatory surge in luteinizing hormone in suckled sows

The objective was to determine if progressive changes occurred in incidence of estrus and patterns of luteinizing hormone (LH) after estradiol benzoate (EB) administration at three stages of lactation. Estradiol benzoate (800 micrograms) was injected at the beginning of the second (7.8 +/- 0.3 days, range 7-8, n = 4), third (15.6 +/- 0.3 days, range 15-16 days, n = 5), or fourth (23.3 +/- 0.5 days, range 22-24, n = 4) wk of lactation. Interval to estrus (h) and proportion in estrus (in parentheses) were 72 (1/4), 88.5 (4/5), and 99 (4/4; pooled SEM = 3.5) for the second, third, and fourth weeks, respectively. Only one animal ovulated during lactation (third week). This animal had a progesterone concentration of 17 ng/ml 1 wk after estrus and an LH concentration above 2.0 ng/ml for 72 through 90 h after EB. In other sows, LH remained less than 1.0 ng/ml after EB. Patterns of LH after EB in sows treated during the fourth week of lactation were increased to a maximum of 0.76 ng/ml by 120 h after EB, which was greater than for those treated during the second or third week (maxima of 0.38 and 0.32 ng/ml, respectively; pooled SEM = 0.07; p less than 0.05). Concentrations of LH in sows that exhibited estrus were greater both before and after treatment than in sows that did not exhibit estrus after EB (p less than 0.05). By 2 wk after weaning, 8 sows had ovulated (6 of these exhibited estrus), and there were no effects of stage of lactation on these responses. We concluded that the behavioral responsiveness to EB increased as lactation progressed. The increased LH in sows treated during the fourth week indicated a partial recovery of the positive feedback response to EB. These data suggested that separate mechanisms caused behavioral and gonadotropin responses to EB in lactating sows.     

Effect of PG600 and adjusted mating times on reproductive performance in weaned sows

The administration of PG600 to sows at weaning induces >90% of sows to return to estrus within a week, but farrowing rate and litter size are often not improved. This study evaluated the effects of adjusted artificial insemination (AI) times based on weaning to estrus interval (WEI) and estrus to ovulation interval (EOI) following PG600. All sows were given PG600 at weaning and allotted to adjusted (ADJ, n=47) or non-adjusted (NA, n=46) mating times after the onset of estrus. Adjusted mating involved: (1) 2-3 days WEI, AI at 36 h and 48 h; (2) 4 days WEI, AI at 24h and 36 h; (3) 5 days WEI, AI at 12h and 24h; and (4) 6-7 days WEI, AI at 0 h and 12h. Mating for NA occurred at 0 h and 24h after onset of estrus. There was no effect of treatment on return to estrus (92.9% versus 92.5%) or ovulation (92.7% versus 92.5% for ADJ and NA, respectively). The proportion of first AI occurring within 24h prior to ovulation was increased (83.8% versus 50.0%) and closer to ovulation for ADJ compared to NA treatment (19.4h versus 27.3h, P<0.05). Treatment did not influence (P>0.10) the proportion of second AI occurring within 24h of ovulation (72.8% versus 56.6%) but did influence (P<0.05) the interval from second AI to ovulation for ADJ compared to NA (10.6h versus 3.3h). The ADJ treatment increased (P<0.05) the proportion of sows that received an AI within 24h before ovulation (98.8% versus 87.0%). However, treatment did not influence pregnancy (87.4%) or farrowing (79.5%) rates but the NA treatment tended to increase (P<0.10) total number of pigs born (11.8 versus 8.9). In conclusion, while AI times for ADJ appeared to occur within optimal periods, farrowing rates were not improved and litter size decreased, suggesting that two AI at 12h intervals and closer to the time of ovulation may be detrimental. Overall, these data suggest that for sows injected with PG600 at weaning and receiving two AI, breeding at 0 h and 24h after onset of estrus is recommended.     

Effect of exogenous gonadotropins on the weaning-to-estrus interval in sows

The efficacy of PG 600 (400 IU PMSG and 200 IU hCG) for accelerating the onset of estrus was determined for sows weaned during the summer. Yorkshire sows (average parity = 4.6), nursing 8.6 +/- 0.2 pigs (mean +/- SEM) were weaned after 27.7 +/- 0.4 d of lactation and were treated intramuscularly with either PG 600 (n = 35) or with 0.9% saline (n = 35). Sows were checked for estrus once daily in the presence of a mature boar. Treatment with PG 600 increased (P < 0.05) the percentage of sows in estrus within 7 d after weaning (97.1 vs 82.9%). Relative to controls, sows given PG 600 expressed estrus sooner (3.8 +/- 0.1 d vs 4.5 +/- 0.1 d; P < 0.01). Sows exhibiting estrus within 7 d after treatments were artificially inseminated 0 and 24 h after first exhibiting estrus. The percentage of inseminated sows that farrowed tended to be higher (P < 0.07) for control than for PG 600-treated sows (96.6 vs 82.3%). The number of pigs born live was similar (P > 0.1) for sows treated with PG 600 and with saline, and was 12.7 +/- 0.6 and 11.7 +/- 0.7, respectively. Pigs farrowed by saline-treated sows, however, tended to be heavier (P < 0.09) than pigs farrowed by sows treated with PG 600 (1.49 +/- 0.06 kg vs 1.34 +/- 0.06 kg). In summary, PG 600 accelerated the onset of estrus in sows weaned during the summer. Sows mated during the induced estrus, however, tended to have a lower farrowing rate and farrowed lighter pigs than control sows inseminated during a natural estrus occurring within 7 d after weaning.     

Effect of altering suckling intervals of early-weaned pigs on rebreeding performance of sows

Sows on two commerical farms were assigned to have their pigs weaned after a 3-week lactation (control, n=160) or after a 3-week lactation that included a 48-hr period of interrupted nursing before weaning (altered-suckling, n=122). Sows in the altered-suckling groups were paired, and each member of a pair was separated from both litters during the alternate 12-hr periods. Thus during the final 48 hr before weaning, each sow in the altered-suckling group had two 12-hr periods when no litters were present and two 12-hr periods when two litters were present. On farm 1, interval from weaning to estrus was 12.8 +/- 0.8 days for control sows compared to 8.4 +/- 1.0 days for sows in the altered-suckling group (P<.01). On farm 2, interval from weaning to estrus did not differ between sows in the control group and those in the altered-suckling group (6.2 vs 6.1 days, P>.05). Thus altered-suckling was effective in reducing the interval from weaning to estrus only when the normal rebreeding interval was prolonged (farm 1). Conception rates at first breeding and subsequent litter sizes did not differ between treatments. Altered-suckling may improve reproductive performance of sows in situations where prolonged postweaning anestrus is a problem.     

The duration of ovulation in pigs, studied by transrectal ultrasonography, is not related to early embryonic diversity

The duration of ovulation in pigs was studied by transrectal ultrasonography. The number of preovulatory follicles was counted on both ovaries at 30-minute intervals from 36 hours after the onset of estrus (Group A: naturally ovulating sows that were group-housed and were inseminated and caged during scanning) or 40 hours after treatment with human chorionic gonadotropin (hCG) (Group B: tethered sows that had been induced to ovulate but were not inseminated). The duration of ovulation was (mean+/-SD) 1.8+/-0.6 hours (range 0.75 to 3.25) in Group A (n=13) and 4.6+/-1.7 hours (range 2.0 to 7.0) in Group B (n=8). The difference was significant (P<0.01). In Group A and B sows, respectively, the course of ovulation, expressed as the relation between the relative follicle count (percentage of the maximum follicle count; Y) and the time (percentage of the duration of ovulation; X) was: Y = 104.3( *)e(-0.023( *)X) (R(2)=0.95) and Y = 98.9( *)e(-0.018( *)X) (R(2)=0.92). The onset of ovulation occurred at approximately two-thirds of the duration of the estrus (Group A: 67+/-6%; Group B: 60+/-10%). Group A sows were artificially inseminated and were slaughtered at 98+/-8 hours (range 77 to 110) after ovulation. The difference between the maximum follicle count and the corpora lutea count was zero or only 1 in 81% (21 26 ) of the ovaries. Embryonic diversity (within-litter SD of the number of nuclei or of the number of cell cycles) was not related to the duration of ovulation, neither at the level of ovary nor of sow (P>0.05). In conclusion, transrectal ultrasonography was found to be an appropriate nonsurgical method of studying the duration of ovulation in pigs. The duration of ovulation varied both between sows and between groups of sows, and was not related to early embryonic diversity.     

Timing of insemination relative to ovulation in pigs: effects on sex ratio of offspring

The objective of the present study was to identify effects of the interval between insemination and ovulation in pigs on the sex ratio and sex ratio dispersion of offspring. Crossbred sows that had farrowed 2 to 9 litters were weaned (Day 0) and came into estrus between Days 3 and 7 after weaning. Ultrasonography was performed every 6 h, from 12 h after the onset of estrus until ovulation had been observed. The sows were inseminated once at various intervals from the onset of estrus. At farrowing, the numbers of viable piglets and dead piglets were recorded per sow. In four 12-h intervals between insemination and ovulation (36 to 24 h before ovulation, 24 to 12 h before ovulation, 12 to 0 h before ovulation and 0 to 12 h after ovulation), the total number of piglets was (mean+/-SEM) 10.8+/-1.2 (n=15); 13.4+/-0.7 (n=23); 13.2+/-0.9 (n=21); and 12.1+/-1.0 (n=16), respectively (P>0.05). The percentage of male piglets per litter in the four 12-h intervals was 52.1+/-3.6, 50.5+/-2.7, 54.9+/-2.8 and 47.8+/-4.5, respectively (P>0.05). Sex ratio was not influenced by litter size (P>0.05), and its distribution was normally dispersed (i.e., as expected under a binomial distribution) in all 4 intervals between insemination and ovulation (P>0.05).     

Two days of pulsatile GnRH infusion beginning 4 days before weaning in sows initiates a wave of follicular growth that is not sustained after weaning

Intervals to estrus and ovulation in weaned sows depend partially on the diameter of ovarian follicles at weaning. The objective was to determine if follicular diameter in sows could be increased by a 48h period of GnRH infusion before weaning and whether this pre-weaning growth would advance follicular development after weaning. The posterior vena cava was cannulated in eight sows at 10+/-1 day after farrowing. Sows were randomly assigned to receive intravenous treatment with either 2mL of GnRH (1microg/mL; n=4) or 2mL of saline (n=4) every 0.5h for 48h beginning 94h before weaning. The average follicular diameter and the number of follicles within diameter classes were determined daily by ultrasonography. Serum LH concentrations increased on the first infusion day but serum LH was equal to control on the last infusion day (P<0.077). The GnRH infusion increased the average diameter of ovarian follicles (P<0.001). Serum estradiol increased (P<0.001) and serum FSH decreased (P<0.016) coincident with GnRH-induced follicular development but these changes were reversed within 24h after the end of the infusion period. Follicles that grew in response to GnRH regressed and were replaced by a new population of follicles within 4 days after weaning. Within the experimental model for the present study, a GnRH infusion increased follicular growth in lactating sows but follicles could not be sustained beyond the end of GnRH infusion.     

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.     

Effect of boar contact on follicular development and on estrus expression after weaning in primiparous sows

Boar contact can induce ovarian activity, advance estrus and stimulate estrous behavior in sows. High amounts of boar contact can, however, suppress estrous behaviour. The present study with primiparous sows was designed to compare sows that had contact with a teaser boar during detection of estrus, with sows that had no boar contact at all. Number of sows detected in estrus within 9 d after weaning, onset and duration of estrus, follicular dynamics and timing of ovulation were studied. Boar contact increased the number of sows that ovulated and showed estrus from 14 of 47 to 24 of 47 (P < 0.05). Average timing of ovulation was later for sows with boar contact (165 h vs 150 h after weaning). Duration of estrus, detected without a boar, was similar in the two groups. For the sows with boar contact, duration of estrus detected with a boar was longer than estrus detected without a boar (56 vs 38 h; P < .01). Follicular dynamics were not affected by boar contact; boar contact only increased the number of sows with ovulation. Ovulatory sows showed a larger increase in follicular diameter (P < 0.01) from weaning to Day 4 after weaning (from 2.3 to 5.4 mm) than anovulatory sows (from 2.5 to 4 mm). Anovulatory sows did not show follicular growth after Day 4. It is concluded that boar contact can increase the number of sows that ovulate and show estrus after weaning. Estrous behavior does not seem to be suppressed by contact with a teaser boar, compared to sows without boar contact.     

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.     

Fertility of sows following artificial insemination at a gonadotrophin-induced estrus coincident with weaning

Two experiments were performed to examine sow fertility following the pre-weaning injection of gonadotrophin. In experiment 1, sows received PG600 2-days pre-weaning (PW2), on the day of weaning (W) or received no injection and served as controls (CT1). Compared to controls, the injection of PG600 resulted in shorter (P<0.02) wean-estrus intervals and more (P<0.05) sows exhibiting estrus by 7 days after weaning (4.5+/-0.2, 5.1+/-0.3, 6.1+/-0.3 days, and 81.3, 82.9, 68.8%, for PW2, W, and CT1, respectively). No effect of treatment was apparent for farrowing rate or subsequent litter size. In experiment 2, PG600 was injected at 4 days pre-weaning (PW4) and then either GnRH or hCG was injected at the time of weaning. Control (CT2) sows received no injections. Injection of PG600 was associated with shorter (P<0.0001) wean-estrus intervals and a higher (P<0.003) farrowing rate (1.1+/-0.2, 5.1+/-0.2 days, and 94.8, 78.5% for PW4 and CT2, respectively). There was no effect of treatment on subsequent litter size and results were the same for GnRH and hCG treated sows. We conclude that injection of gonadotrophins prior to weaning will result in very short wean-estrus intervals and that, when combined with a hormonally controlled ovulation, sow fertility may be enhanced.     

Relationship of vaginal impedance with speed of return to oestrus after weaning, oestrous behaviour, parity and lactation length in cyclic sows

The effect of weaning to oestrus interval, oestrus duration, parity, lactation length, breed and their interactions on changes of vaginal impedance in sows after weaning and during oestrus was examined. The impedance measurements were carried out by a four-electrode method. The interval from weaning to oestrus was significantly longer in sows with the length of lactation 21-25 days than 26-30 days and 31-36 days and in primiparous than multiparous sows. The interval from weaning to oestrus was negatively correlated with the length of lactation (r=-0.21; P<0.05), parity (r=-0.36; P<0.01) and oestrus duration (r=-0.26; P<0.01). The weaning to oestrus interval, oestrus duration, parity and lactation length had a significant effect and the breed of sows had no influence on the vaginal impedance in peri-oestrus. The decrease of vaginal impedance after weaning was delayed in sows with a longer weaning to oestrus interval and in primiparous than multiparous sows. The decline of vaginal impedance during peri-oestrus was more gradual in sows with a longer interval from weaning to oestrus, shorter lactation, primiparous sows and sows with the length of oestrus 36 h and 72 h and more. The nadir of vaginal impedance occurred earlier before oestrus in sows with a shorter oestrus. The interaction of weaning to oestrus interval with parity and oestrus duration and the interaction of oestrus duration with parity significantly affected the vaginal impedance in weaned sows. In conclusion, the weaning to oestrus interval, oestrus duration, parity and lactation length considerably influence the vaginal impedance in sows during peri-oestrus. The findings indicate that the impedance technique may be a useful method for a study of factors and processes that accelerate or slow down the return to oestrus after weaning and affect oestrus duration in sows.     

The influence of time of insemination relative to time of ovulation on farrowing frequency and litter size in sows, as investigated by ultrasonography

The objective of this experiment was to identify the optimal time of insemination relative to the time of ovulation, based on ultrasonographic detection of embryonic survival at 10 days after ovulation, number of sows farrowing, and litter size. Furthermore, the possible value of the interval from weaning to onset of estrus for prediction of the time of ovulation was examined. Crossbred sows (n = 143) that had farrowed 2 to 9 litters were weaned (Day 0) and observed for estrus every 8 h from Day 3 until end of estrus. Ultrasonography was performed every 6 h, from 12 h after onset of estrus until ovulation had been observed. The sows were inseminated once at various time intervals from ovulation. At Day 16, 25 of the sows were slaughtered and their uteri were flushed for embryos. In the remaining sows, the number of viable and dead piglets and mummified fetuses per sow was recorded at farrowing, with the sum of the 3 constituting the total number of piglets born per sow. The highest number of embryos recovered per sow was found after insemination during the interval from 24 h before to 4 h after ovulation. The lowest frequency of non-pregnant sows and the highest total number of piglets born per sow were found after insemination from 28 h before to 4 h after ovulation. Consequently, the optimal time for insemination was found to be in the interval 28 h before to 4 h after ovulation. The interval from weaning to onset of estrus and from onset of estrus to ovulation were negatively correlated, allowing a rough prediction of the time of ovulation from the interval from weaning to onset of estrus.     

Relationships between LH, FSH and prolactin secretion and reproductive activity in the weaned sow

Blood samples were collected from primiparous sows via indwelling jugular cannulae at 15-min intervals for 12 h before and for 24 h (2 sows) or 48 h (10 sows) after weaning and then every 4 h until behavioural oestrus. Weaning to oestrus intervals ranged from 3 to 10 days and 2 sows showed no signs of oestrus and had not ovulated by Days 11 and 16 after weaning. Prolactin concentrations in plasma decreased significantly (P less than 0.001) and reached basal levels 1-2 h after weaning in all sows whilst plasma progesterone concentrations remained basal until approximately 30 h after the preovulatory LH surge in sows that ovulated. Elevated concentrations of prolactin or progesterone during the post-weaning period were, therefore, not responsible for delayed restoration of cyclicity. Overall, mean LH concentrations rose significantly (P less than 0.001) from 0.22 +/- 0.02 during the 12-h period before weaning to 0.38 +/- 0.03 ng/ml during the 12-h post-weaning period. After weaning, pulsatile and basal LH secretions were markedly increased for sows that showed an early return to oestrus (less than or equal to 4 days) compared with sows showing a longer weaning to oestrus interval but a correlation did not exist between either of these LH characteristics and the time taken to resume cyclicity. Mean LH concentrations before weaning were, however, inversely related (r = -0.649; P less than 0.05) to the weaning to oestrus interval. Overall, mean FSH concentrations rose significantly (P less than 0.001) from 151.1 +/- 6.2 (s.e.m.) ng/ml in the 12-h period immediately before weaning to 187.7 +/- 9.7 ng/ml in the subsequent 12-h period but there was no correlation between FSH concentrations, before or after weaning, and the interval from weaning to oestrus. However, a significant correlation was apparent between ovulation rate and peak concentrations of the rise in FSH after weaning (r = 0.746; P less than 0.05) and overall mean FSH values (r = 0.645; P less than 0.05). It is concluded that both LH and FSH concentrations in peripheral blood rose in response to removal of the suckling stimulus at weanling. The increase in LH pulse frequency associated with weaning was not directly related to the weaning to oestrus interval although a specific pattern of LH secretion was observed in sows showing an early return to oestrus (less than or equal to 4 days).(ABSTRACT TRUNCATED AT 400 WORDS)     

Opioid inhibition of luteinizing hormone secretion in the postpartum lactating sow

Twelve lactating sows were used at 22.4 +/- 0.8 days postpartum to determine whether endogenous opioid peptides (EOP) are involved in the suckling-induced inhibition of luteinizing hormone (LH) secretion. Four sows each received either 1, 2, or 4 mg/kg body weight of naloxone (NAL), an opiate antagonist, in saline i.v. Blood was collected at 15-min intervals for 2 h before and 4 h after NAL treatment. All sows were then given 100 micrograms gonadotropin-releasing hormone (GnRH) in saline i.v., and blood samples were collected for an additional h. Pigs were weaned after blood sampling. At 40 h after weaning, sows were treated and blood samples collected as during suckling. Serum concentrations of LH after treatment with NAL were similar for all doses; therefore, the data were pooled across doses. During suckling, serum concentrations of LH were 0.41 +/- 0.04 ng/ml before NAL treatment, increased to 0.65 +/- 0.08 ng/ml at 30 min after NAL treatment, and remained elevated above pretreatment concentrations for 120 min (p less than 0.05). Naloxone failed to alter serum concentrations of LH after weaning. These data indicate that EOP may be involved in the suckling-induced suppression of LH secretion and that weaning may either decrease opioid inhibition of LH secretion or decrease pituitary LH responsiveness to endogenous GnRH released by NAL.     

Changes in the hypothalamic-hypophyseal-ovarian axis of primiparous sows following weaning or pulsatile gonadotropin releasing homrone administration and weaning

Lactating primiparous sows were used to examine relationships among hypothalamic gonadotropin releasing hormone (GnRH), serum, and anterior pituitary gonadotropins and follicular development after weaning or after administering GnRH pulses (1.5 ug) once hourly for 72 h before weaning. Control sows were either slaughtered at 0 or 72 h after weaning or were cannulated for collection of blood samples until 24 h after estrus. Sows pulsed with GnRH were either slaughtered 72 h after beginning of GnRH treatment or were cannulated for collection of blood samples until 24 h after estrus. Exogenous GnRH pulsed hourly during 72 h prior to weaning stimulated follicular growth as demonstrated by an increase in number of surface follicles >5 mm in diameter and a decrease in number of follicles <5 mm in diameter. Interval (h) from weaning to an increase in estradiol (>16 pg/ml) was less in GnRH-pulsed than in control sows (P < 0.05), but hours from weaning to estrus were similar between groups. Amounts of GnRH in the medial basal hypothalamus (MBH), stalk median eminence (SME), and hypophyseal portal area (HPA) were similar among control sows killed at 0 or 72 h and sows pulsed with GnRH. Serum concentrations of luteinizing hormone (LH) and frequency of release of LH were similar between GnRH-pulsed and control sows, but concentrations of LH and follicle stimulating hormone (FSH) in anterior pituitary were lower in GnRH-pulsed sows than control sows. Administration of GnRH for 72 h prior to weaning in primiparous sows stimulated follicular growth as manifested by increased secretion of estrogen; however, the amount of follicular growth was apparently inadequate to hasten the onset of estrus after weaning.     

Early-weaned sows: altrenogest therapy, estrus, ovulation, and reproductive performance

Early weaning is a technique used to increase swine health status, and may cause consequences in reproductive performance of sows. An experiment was performed to evaluate these effects in a herd of sows, with weaning at 9 or 10 days post-farrowing, located in west of Minas Gerais, Brazil. Large-White sows (n=102), with three or four previous parturitions were randomly allocated to three treatment groups: T1: artificial insemination (AI) at first post-weaning estrus of the sows; T2: AI at second post-weaning estrus, T3: AI at first estrus, after an administration of a daily individual dose of 20 mg of altrenogest from 5 to 8 days post-weaning. The duration of the first post-weaning estrus did not differ among treatment groups; however, the second estrus of the T2 group was of shorter duration relative to the other treatment groups (P< or =0.035). Ovulation occurred earlier at the second estrus of the T2 group, compared with the T1 and T3 groups (P< or =0.027), being similar to that at the first estrus of T2 group (P=0.177). The relationship of the timing between ovulation and estrus was similar among treatment groups (P> or =0.221). There was no difference in farrowing rate among treatment groups (P> or =0.313). The T2 group produced a mean of 2.5 more piglets per litter (P=0.002). In conclusion, the use of altrenogest did not increase the reproductive performance of early-weaned 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.     

Stag exposure advances the LH surge and behavioral estrus in Eld's deer hinds after CIDR device synchronization of estrus

The impact of male presence or absence on the timing of the preovulatory LH surge and estrus was studied in 3 experimental groups (n = 6/group) of Eld's deer hinds pretreated with intravaginal progesterone-releasing devices (CIDR-type G) as follows: Group 1 = indirect male contact barn; Group 2 = direct male contact barn; and Group 3 = male isolation barn. For all hinds, the duration of the preovulatory LH surge averaged 2.5+/-0.5 h, whereas mean peak preovulatory and basal LH concentrations were 2.9+/-0.2 ng mL(-1) and 0.27+/-0.03 ng mL(-1), respectively. Nine of 12 male-exposed hinds exhibited a preovulatory LH surge within 24 to 32 h postCIDR device withdrawal, whereas 0 of 6 male-isolated hinds exhibited a preovulatory LH surge during the same time period. Onset of behavioral estrus (45.2+/-2.3, 52.7+/-5.7 and 66.3+/-1.8 h, respectively) was significantly advanced (P<0.05) after CIDR device withdrawal in male exposed hinds (Groups 1 and 2) compared with male isolated hinds (Group 3). These data suggest that stag exposure is important for modulating the timing of the preovulatory LH surge and behavioral estrus after synchronization of estrus with exogenous progestagens.