G.L. Williams

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.

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.

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.

Use of altrenogest alone or in combination with PMSG to control the preovulatory LH surge in gilts

Sixty-four cycling gilts were used to study the effects of altrenogest (AT) alone or in combination with pregnant mares serum gonadotropin (PMSG). PMSG was administered at different times before and after AT removal and the variations in onset of the preovulatory LH surge, estrus and the interval to peak LH concentrations were studied. Each gilt was individually administered 15 mg AT daily in the ration for 14 consecutive days, with the day of AT removal designated as day 0. PMSG (750 I.U.) was injected SC at day −1, 0 and 1 (N=16treatment). Sixteen control gilts (C) received a saline (1 ml) injection on the last day of AT feeding. Percentages of gilts failing to exhibit estrus were: PMSG−1 (0%), PMSG−0 (0%), PMSG+1 (6.2%) and controls (31.2%). Mean intervals( ± SEM) from last feeding of AT to onset of the preovulatory LH surge were 104±5, 99±3, 106±3 and 103±5 h for the PMSG−1, PMSG−0, PMSG+1 and C groups, respectively. Time from last feeding of AT to onset of standing estrus was 116±6, 107±4, 112±3 and 112±4 h, respectively, for the four groups. The respective mean LH peak values were 5.5±0.7 (P<0.01), 8.9±0.8, 8.2±0.9 and 9.2±0.7 ng/ml for the PMSG−1, PMSG−0, PMSG+1 and C groups. Injection of PMSG on the day after last AT feeding caused a greater (P<0.05) synchrony of occurrence of the onset of estrus and the preovulatory LH peak. These results indicate that when a combination treatment of AT and PMSG is given, greatest synchrony of estrus and ovulation most likely occurs when the PMSG treatments are administered 24 h after termination of the progesterone agonist.

In vitro metabolism of ovarian steroids by bovine whole blood and plasma

Experiments were conducted to evaluate the effects of time and temperature on the potential of bovine whole blood (WB) or plasma (PL) to metabolize the ovarian steroids progesterone, estradiol-17β and testosterone. During a radioimmunoassay study (Experiment 1), we observed a temperature and time-dependent reduction (P<0.001) of plasma progesterone concentrations in samples incubated as WB at 5, 15, 25, or 35C for up to 48 hr. Most notable was the observation that 27% of progesterone present in controls was lost when WB was incubated at 5C for 48 hr and a 17% reduction was observed when PL samples were incubated at 35C for 48 hr. Immunoreactive estradiol-17β concentrations (Experiment 2) in PL and WB incubates were not affected by time or temperature. However, immunoreactive testosterone concentrations increased more than 3-fold by 48 hr in WB incubates held at 35C. To examine the latter observation further, 3H-progesteone was incubated with WB at 35C, followed by extraction and thin-layer chromatography (Experiment 3). Results generally supported RIA findings and revealed the presence of significant 17α-hydroxylase, 17–20 lyase and aromatase activity. Heretofore this has not been considered to occur outside major steroid metabolizing organs.