J.E. Tilton

The effects of post-weaning progestagen treatment (Regumate) of early-weaned primiparous sows on subsequent reproductive performance

This study investigated the effects of feeding the orally active progestagen, altrenogest (Regumate) post-weaning on the subsequent reproductive performance of early weaned sows. Ninety (90) Large White/Landrace first parity sows were randomly assigned to three treatments. Treatment 1 (EW) and treatment 3 (CW) sows were weaned on day 12 and day 24 post-partum, respectively while treatment 2 sows (EW-R) were weaned on day 12 post-partum and received an individual daily dose of 20 mg of Regumate on days 13 to 24 post-partum inclusive. Each sow was mated naturally at least twice at the first post-weaning or post-treatment oestrus and slaughtered on days 25-28 of pregnancy to determine the number of corpora lutea and embryos. Regumate-to-oestrus and weaning-to-oestrus intervals were similar for EW-R and CW sows (6.2 vs. 5.6 days). However, both intervals were significantly shorter (P < 0.01) than the weaning-to-oestrus interval of EW sows (7.3 days). An excellent synchronization of oestrus was achieved with Regumate treatment with 97% of treated sows in oestrus within 7 days of Regumate withdrawal compared with 64% for EW sows (P < 0.01) and 87% for CW sows (P > 0.05). Treatment with Regumate resulted in a significant increase in ovulation rate (16.9 vs. 15.4 and 14.9 for treatments EW-R, EW and CW, respectively; P < 0.05) and a non-significant increase in early embryonic survival (77% vs. 68% vs. 68% for treatments EW-R, EW and CW, respectively; P > 0.05). These results indicate that Regumate feeding is a potential management tool to alleviate the diminished reproductive performance associated with early weaning regimes since it leads to successful control of oestrus, higher ovulation and embryo survival rates and thus a greater potential litter size.

Time of the preovulatory LH surge in the gilt and sow relative to the onset of behavioral estrus

Two experiments were conducted to study the time of occurrence of the preovulatory LH surge in pigs. Sampling every ten minutes in six cycling gilts before and after onset of standing estrus revealed the preovulatory surge began from 8 hr before to 12 hr after the lordosis reflex was elicited. Three of six gilts initiated the preovulatory LH release coincident with the onset of estrus. Data from 28 postpartum sows, with samples drawn every six hours commencing with the onset of estrus, indicated maximum LH levels were present at the first observance of estrus. Six of the 28 sows had an LH peak 18-24 hr after the onset of estrus.

Plasma luteinizing hormone during pregnancy in the pig

Abstract Three chronically catheterized Duroc gilts were used to characterize the pattern of plasma LH in the systemic circulation during pregnancy. Blood samples were collected four times daily (08.00, 12.00, 16.00 and 20.00 h) from the second day of estrus until day 7 postpartum in one pig and to 108 and 98 days of gestation in the remaining two. The concentration of plasma LH fluctuated in a pulsatile manner throughout the studied periods of gestation in all three pigs, with decreasing amplitude towards parturition. Significant correlations between the decline of LH levels and the day of pregnancy were found, and the equations for the linear regression lines are presented. It is suggested that the level of LH in early and mid-pregnancy mimics LH concentrations in the midluteal phase of the estrous cycle.

Utero-ovarian venous concentrations of prostaglandin E2 (PGE2 and prostaglandin F2α (PGF2α) following PGE2 intrauterine infusions

Abstract The uterine horns and utero-ovarian veins of nine crossbred mature gilts were bilaterally cannulated on day 9 of the estrous cycle (day 0 - first day of estrus). Each uterine horn in treated gilts (N=5) was infused with 150 μg PGE 2 in 3 ml of saline at 0900 h on day 12, 15 and 18 of the estrous cycle. Control gilts ( N =4) received 3 ml saline intrauterine infusions on the corresponding day. Blood samples were collected from the utero-ovarian veins 15 min before each infusion and for the following 6 h with 15, 30 and 60 min intervals through the first, second and third two-hour periods, respectively. Venous concentrations of PGE 2 and PGF 2 α were determined by radioimmunoassay procedures. Infusion of PGE 2 resulted in an immediate elevation in PGE 2 concentration in utero-ovarian venous drainage. Coincident elevations of PGF 2 α utero-ovarian venous concentrations were observed after PGE 2 infusion. Plasma PGF 2α concentrations in the utero-ovarian veins were elevated (P 2 treated gilts for one hour post-treatment. The duration of PGE 2 and PGE 2 α elevations as well as the peak values were influenced by day of the cycle.

The effect of intrauterine infusions of prostaglandin E2 on luteal function in nonpregnant gilts.

Two trials were conducted to study the effects of intrauterine infusions of prostaglandin E2 (PGE2) on luteal function in nonpregnant gilts. Cannulae were surgically implanted on day 9 postestrus into the lumen of each horn with a cephalic vein cannula inserted for collection of peripheral blood. Intrauterine infusions of 0, 25, 75 or 200 microg of PGE2 were initiated at 0900 h on day 12 and administered thereafter every 12 hr until estrus or day 22 in the first trial. The second trial protocol included an increase in the dose of PGE2 administered as well as the frequency of infusion. Infusion of 0, 200, 300 or 400 microg PGE2 was begun at 0300 h on day 12 and continued every 6 hr until estrus or day 22. Cephalic plasma samples for progesterone analysis were collected every six hours from 0300 h on day 11 to 2100 h on day 26 in both trials. In Trial 1 mean plasma progesterone concentrations for all treatments were not different (P>0.05) from the controls on any given day of the estrous cycle. Interestrous interval was unaffected by intrauterine infusion of PGE2. The mean plasma progesterone concentrations for all treatments were not different (P>0.05) from the controls on days 11-18 of the estrous cycle in Trial 2. However, plasma progesterone concentrations for the 200-microg and 300-microg PGE2 groups appeared to be greater than the controls on days 14 and 15, indicating a possible delay in the decline of progesterone for these groups. The mean plasma progesterone concentrations for the treatment groups were lower (P<0.05) than the controls on days 20-26 of the cycle. treatment cycle length did not differ (P>0.05) from previous cycle length; thus treatment with PGE2 had no effect on interestrous interval. PGE2 may have retarded the decline of progesterone secretion by the corpus luteum in some cases, but at these dosages and frequencies of administration PGE2 was ineffective in prolonging luteal maintenance.

Endocrine changes associated with spontaneous luteolysis in sows. I. Temporal relationships among prolactin, prostaglandin F2α, progesterone and LH

Abstract Five multiparous sows were cannulated via the cephalic and utero-ovarian vein during the mid-luteal phase. Blood samples were drawn hourly for assessment of prolactin, luteinizing hormone (LH), progesterone and prostaglandin F 2α (PGF 2α ). Both peripheral prolactin and PGF 2α utero-ovarian venous concentrations increased following luteolysis. After luteal regression, episodic pulse height of prolactin and PGF 2α increased 2.5 and 2.0-fold, respectively. A tendency for synchrony of the prolactin and PGF 2α pulses was observed when progesterone utero-ovarian venous concentrations declined below 100 ng/ml plasma. Peripheral LH concentrations were essentially similar throughout the experiment with smaller fluctuations after luteolysis. The coincidental occurrence of prolactin and PGF 2α pulses suggests a temporal relationship may exist between these hormones during the post-luteal period.

Myometrial LH/hCG receptors during the estrous cycle and pregnancy in pigs

Receptors for luteinizing hormone/human chorionic gonadotropin (LH/hCG) have been identified in porcine, rabbit, rat, and human myometrium. To determine the estrous cycle and pregnancy related changes in the receptor capacity and affinity, radioreceptor assays were performed with membrane homogenates of porcine uterine tissues. Cycling gilts were divided into four experimental groups: I (n = 6), day 1-2; II (n = 5), day 6-7; III (n = 5), day 11-12; and IV (n = 6), day 18-20 of the estrous cycle. Pregnant pigs were divided into three experimental groups: I (n = 5), day 35-40; II (n = 5), day 65-70; and III (n = 4), day 95-105 of pregnancy. The concentrations [femtomoles/mg protein (fmol/mg protein)] and affinities of unoccupied LH/hCG binding sites were characterized in all samples of myometrium. Receptor concentrations were highest (P < 0.01) in groups II and III (19.3 +/- 2.5 and 35.8 +/- 2.1 fmol/mg protein, respectively), and was lowest in groups I and IV (5.3 +/- 1.4 and 7.5 +/- 0.7 fmol/mg protein, respectively). Receptor affinity constants (Ka) were consistent (P > 0.05) throughout the estrous cycle [I, (5.1 +/- 1.5) x 10(9); II, (3.0 +/- 0.8) x 10(9); III, (3.2 +/- 0.9) x 10(9); IV, 5.5 +/- 0.7 x 10(9) 1m-1]. Plasma hormone concentrations of progesterone, estrogen and LH were typical of values noted at these times. During pregnancy, receptor concentrations were greatest (P < 0.05) in group II (85.4 +/- 18.5 fmol/mg protein). In groups I and III receptor numbers were 10.8 +/- 2.3 and 26.7 +/- 6.6 fmol/mg protein, respectively. The Ka in group I was 10 times greater (P < 0.05) than Ka in groups II and III, (I, 3.1 +/- 0.9 x 10(10) lm-1; II, 3.4 +/- 0.3 x 10(9) lm-1; III, 3.3 +/- 1.1 x 10(9) lm-1). Plasma hormone concentrations typically found during pregnancy were noted. The function of these LH/hCG binding sites remains unknown; however, changes in receptor capacity during the estrous cycle and pregnancy support a role for modulation of the receptor by hormonal factors.

Effects of various mating stimuli on pituitary release of luteinizing hormone in the gilt

Abstract Twenty-four nulliparous crossbred gilts approximately 9 months of age were assigned to either a naturally mated (NM), artificially inseminated (Al) or non-mated control group (C). All gilts were fitted with indwelling cephalic cannulas for collection of blood samples for subsequent hormonal analyses every 10 min for the first 24 hr of the periestrous period. Plasma luteinizing hormone (LH) concentrations were not affected by type of mating. The mean duration of the LH surge for Al group was less than the C or NM groups (44.5 vs 67 and 87 hr (P 05). Area under the LH release curve and number of episodic surges were not different for the three treatments. Length of standing estrus and exposure time to back pressure were not different among treatment groups. The results suggest that stimulation of the pelvic region during either natural mating or artificial insemination did not enhance release of LH. Mated gilts did exhibit different secretory patterns of LH release than non-mated gilts.

Pituitary and ovarian responses of postpartum dairy cows to progesterone priming and single or double injections of gonadotropin-releasing hormone.

Utilizing single or double pulses of gonadotropin-releasing hormone (GnRH), with or without progesterone pretreatment, we induced ovulation in dairy cows on day 14 postpartum. In experiment 1, neither progesterone priming nor repetitive injection of GnRH enhanced pituitary LH or FSH secretion compared to a single GnRH injection. However, pretreatment with 100 mg progesterone tended (P<0.1) to enhance luteal progesterone secretion during the induced cycle. We confirmed this observation in a second experiment by utilizing a larger number of cows. Cows given 100 mg progesterone prior to a single 200 microg injection of GnRH exhibited higher (P<0.05) concentrations of serum progesterone on days 12 and 16 of the induced cycle (days 26 and 30 postpartum). These results suggest that progesterone pretreatment may influence luteal progesterone secretion following ovulation. This appears to occur via an ovarian mechanism which is independent of pituitary gonadotropin secretion.

Ovarian steroid secretion changes after hCG stimulation in early pregnant pigs

Administration of human chorionic gonadotropin (hCG) to promote ovarian steroid secretion near the time of recognition of pregnancy was evaluated. Neither 500 or 1000 IU of hCG caused a significant increase in luteal function as determined by progesterone (P(4)) concentrations in peripheral blood following treatment on Day 12. Estradiol concentrations were elevated (P<0.01) for the 500 IU hCG group on Days 13, 14, 15 and 16 versus the control group. The 1000 IU of hCG group had three-to five-fold greater (P<0.01) estradiol concentrations than controls on Days 14, 15 and 16 post mating. Treatment with hCG also reduced (P<0.05) the number of resorbed embryos. The results suggest that hCG treatment on Day 12 of pregnancy reduced embryo loss and influenced peripheral estradiol secretion patterns.