Search

Innate immune response to a lipopolysaccharide (LPS) challenge varies among sheep breeds. How different breeds respond to bacterial infections impacts management practices of sheep producers. Hence, clinical response, acute-phase response, and gene expression of pro- and anti-inflammatory markers in peripheral white blood cells (WBCs) were examined after an LPS challenge in Dorset and Suffolk ewes. Ewes received either PBS or 2.5 µg/kg LPS (i.v.) 4 to 5 d after onset of synchronized estrus. Blood was collected via jugular venipuncture intermittently for 24 h to determine WBC counts. Rectal temperatures and observations of behavioral/physical appearances were recorded hourly. After LPS, WBCs decreased the first hour (P = 0.0001) and rectal temperatures (P < 0.0001) increased through 4 h; both returned toward normal 6 h after challenge. Suffolk ewes exhibited greater changes in temperature (P = 0.03) and behavioral/physical responses (P < 0.0001) than Dorset ewes and had an enhanced acute-phase response demonstrated by increased concentrations of plasma haptoglobin (P = 0.04), as well as cortisol concentrations (P = 0.03). Real-time PCR was completed on buffy coat homogenates for expression of pro-inflammatory [CXCL8, IL-6, interferon gamma (IFNG), complement component 3 (C3), toll-like receptor 4 (TLR4), prostaglandin synthase 2 (PTGS2)] and anti-inflammatory [IL-10, superoxide dismutase 2 (SOD2), forkhead box P3 (FOXP3), peroxisome proliferator-activated receptor gamma (PPARG), mannose receptor C type 1 (MRC1), transforming growth factor β (TGFβ)] genes. After LPS treatment, gene expressions increased for CXCL8 (P = 0.0003), TLR4 (P = 0.004), SOD2 (P < 0.0001), and C3 (P = 0.003), while PPARG (P = 0.006) and MRC1 (P = 0.003) decreased. Overall, Dorset ewes had greater expression of TLR4 (P = 0.003), IL-10 (P = 0.045), PPARG (P = 0.002), FOXP3 (P = 0.001), and SOD2 (P = 0.0002), whereas Suffolk ewes had greater expression of IL-6 (P = 0.0007), IFNG (P = 0.02), PTGS2 (P = 0.0002), and C3 (P = 0.008). Suffolk ewes also displayed greater expression of IL-6 (P = 0.002) and C3 (P = 0.0004) in response to LPS. In conclusion, differences in gene expression may explain the enhanced inflammatory response in Suffolk ewes and may predispose Suffolk ewes to be more responsive to bacterial infection than Dorset ewes.

Ability to select service sires that minimize partial or complete losses of pregnancy could have major economic impacts in sheep production systems. This study tested the null hypothesis that survival of potential progeny did not vary with breed type of service sire or among individual rams. Data included 980 ewes on 10 farms; each ewe was pregnant to 1 of 67 rams of 12 breeds. Number of conceptuses was estimated once during pregnancy by ultrasonography, either transrectal (embryos) or transabdominal (fetuses), and was compared with number of lambs born to estimate losses. Data were examined first for number of lambs born and second for documented losses. Individual service sires affected number born (P < 0.001), which varied from 0.70 to 2.45 lambs per pregnant ewe. The main effects of breed type on lambs born were not significant, but breed types of both service sires (P < 0.0002) and ewes (P < 0.001) interacted with diagnosed number of conceptuses. Lambs born varied with ewe age (P < 0.0001) and among farms (P < 0.0001), and statistically, farms interacted with number of diagnosed conceptuses (P < 0.0001); season had no effect. In documented losses, there were both main effects of individual service sire and a service sire × number of diagnosed embryos interaction (P < 0.005). Thus, ewes bred to some rams were more apt to lose single pregnancies, whereas ewes bred to other rams were more apt to lose 1 or more embryos or fetuses from multiple pregnancies. Breed type of service sire affected (P < 0.05) prenatal death. Complete losses of single conceptuses tended to be greater in ewes bred to black-faced or hair-type rams (service sire breed type × number of diagnosed conceptuses; P < 0.09). Breed type of ewes also varied in incidence of complete losses (P < 0.05); hair-type ewes (46%) lost more (P < 0.02) documented conceptuses from examination to birth than black-faced (27%), white-faced (20%), or dairy-type (25%) ewes. Greater losses of singles than of multiples occurred in black-faced (37% vs. 18%) and hair-type (64% vs. 27%) ewes than in other breeds (ewe breed type × number of conceptuses; P < 0.03) per ewe. Surprisingly, purebred conceptuses were lost less often (24%) than crossbreds (36.4%; P < 0.002). Selection of rams based on records of prenatal losses in ewes they serviced may be a method to decrease embryonic and fetal wastage. However, further study to determine repeatability of differences among service sires from year to year will be required.

Problem: Spontaneous mastitis or induced infections mimicking mastitis reduce pregnancy rates in ruminants. The effect of immunization with either a mastitis-related pathogen component, peptidoglycan-polysaccharide (PG-PS), or killed Streptococcus pyogenes on pregnancy outcome was investigated., Method of Study: Ewe lambs were immunized with PG-PS (n = 50) or killed bacteria (n = 50) or were not immunized (control, n = 100). Titers of PG-PS immunoglobulin G (IgG) were detected by enzyme-linked immunosorbent assay (ELISA). Ewes were bred by rams at synchronized estrus. All immunized ewes and half of the ewes not immunized were challenged with PG-PS on day 5 after breeding. Pregnancy maintenance was evaluated., Results: Although the proportion of ewes pregnant at day 42 after breeding did not differ among treatments, the probability of pregnancy decreased with total dose of PG-PS (P < 0.05)., Conclusions: Immunization of ewe lambs with PG-PS or killed S. pyogenes did not improve pregnancy maintenance. Furthermore, the toxic streptococcal component decreased pregnancy rate in immunized sheep in a dose-dependent manner.

The effects of progesterone (P4) on follicular growth and fertility in ewes were examined. In Experiment 1, 22 ewes received either one or three packets of P4 (5 g/packet) or an empty packet subcutaneously (sc) from Days 5 to 15 of the estrous cycle (estrus = Day 0). On Day 6, P4-treated ewes received 12.5 mg of prostaglandin F2 alpha. Follicles > or = 3 mm in diameter were observed via transrectal ultrasonography daily from Day 4 through estrus, corpora lutea (CL) were observed 5 to 7 d after estrus. Ewes with low (LOW; < or = 1 ng/ml; n = 5), intermediate (MED; >1 and <2 ng/ml; n = 10), or normal (NOR; > or =2 ng/ml; n = 7) P4 in jugular plasma on Days 7 through 15 differed in follicular development. The largest follicle at estrus was larger in ewes with LOW vs. MED and NOR P4 (7.8 +/- 0.3 vs. 6.9 +/- 0.2 mm; P < 0.05). Treatments differed in proportions of multiple-ovulating ewes, in which the oldest ovulatory follicle was first observed before Day 10 (LOW: 3 of 3, MED: 6 of 10, NOR: 0 of 5, respectively; P < 0.05). Estradiol was higher early in the treatment period in LOW ewes than in MED and NOR ewes (day x treatment; P < 0.05). In Experiment 2, ewes received 5 mg of P4 in corn oil (low progesterone [LP]; n = 51) or 2 ml of corn oil (CON; n = 49) sc every 12 hr on Days 6 through 14 of the estrous cycle before mating. LP ewes received 15 mg of prostaglandin F2 alpha on Day 6. Mean serum P4 on Days 7 through 15 was 0.6 +/- 0.1 ng/ml in LP and 1.9 +/- 0.1 ng/ml in CON ewes. Eleven LP and 12 CON ewes were scanned daily from Day 4 through mating, and in all ewes (n = 93), CL were counted 10 d after mating and embryos were counted at 25, 40, and 60 d of gestation. In multiple-ovulating ewes, day of cycle of appearance was earlier for the oldest (Day 6.1 +/- 0.8 vs. 10.4 +/- 0.8) but not second oldest (Day 11.7 +/- 1.0 vs. 12.2 +/- 0.9) ovulatory follicles in LP compared with CON ewes. The conception rate was lower in LP (72%) than in CON ewes (98%; P < 0.01). However, numbers of CL 10 d after mating, and in pregnant ewes, numbers of embryos 25 d after mating and lambs born, did not differ with treatment. In summary, low P4 increased the size of the largest follicles and the age of the oldest ovulatory follicles. Embryos resulting from the ovulation of older and younger follicles in the same ewe did not differ in their ability to survive.

Effects of day of estrous cycle and induced luteal regression on follicular dynamics in ewes were examined. In Exp. 1, ewes received PGF2 alpha (i.m.) on d 5, 8, or 11 after estrus (d 0) or saline on d 14 (n = 27, 27, 31, and 29, respectively). Ewes were laparotomized before treatment and again 48 h after induced estrus to record numbers, sizes, and locations of follicles > or = 2 mm and corpora lutea (CL). The two largest follicles (designated F1 and F2) and any of equal size (F1.5 and F2.5) were marked with India ink in stroma around the follicle. Ewes treated on d 8 ovulated fewer F1 and F1.5 (39%) than ewes treated on d 5 (69%; P < .05); d 11 (51%) and 14 (56%) were intermediate. In Exp. 2, ewes received PGF2 alpha on d 5 or 8 (n = 15/d). Ovaries were examined with transrectal ultrasonography daily from 4 d before PGF2 alpha until ovulation, and on d 5 and 8 after ovulation. Diameters, locations, and ranks (at time of PGF2 alpha) of follicles > or = 2 mm and CL were recorded. Ewes treated on d 8 ovulated fewer F1 and F1.5 (35%) than ewes treated on d 5 (86%; P < .05). Ovulatory follicles at time of PGF2 alpha were larger on d 5 (4.7 +/- .2 mm) than on d 8 (4.0 +/- .2 mm; P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

This study was conducted to determine the effects of the corpus luteum (CL) of pregnancy and(or) the previously gravid uterine horn (g-UH) on the incidence and site of ovulation and the duration of luteal function in postpartum (PP) ewes. Ewes were laparotomized at d 60 to 80 of gestation and assigned to one of four groups: 1) single g-UH, CL left intact (SI, n = 35); 2) single g-UH, CL removed (SR, n = 30); 3) twin g-UH, CL on both ovaries left intact (TI, n = 21); and 4) twin g-UH, CL removed from one ovary (TR, n = 32). On d 20 PP, the number of follicles on each ovary was determined at laparoscopy, and ewes received (i.m.) 750 IU of hCG. Ovarian structures were determined at laparoscopy on d 24 PP. Blood samples were collected daily from d 20 to 40 PP and assayed for progesterone. more follicles (P < .05) were observed at laparoscopy on d 20 PP in SI/TI than in SR/TR groups (8.4 vs 6.0, respectively; SE = .4). Overall, 52% of the ewes had visible CL 4 d after hCG, and 73% of the ewes had elevated levels of progesterone by 7 d after hCG. The number of g-UH (S vs T) or status of the CL (I vs R) did not affect these responses. For SR ewes with hCG-induced CL on a single ovary, the incidence of CL formation on the ovary adjacent to g-UH was less (P < .05) than that for SI ewes (0 vs 57, respectively). Removal of the CL from S ewes, but not from T ewes, reduced follicular development and ovulation in response to hCG. Perhaps there is a positive systemic effect of the CL of pregnancy on postpartum ovarian function in ewes.

Three experiments were performed to study effects of decreased concentrations of estradiol-17 beta (E2) on lifespan and function of ensuing ovine corpora lutea (CL). In experiment 1, 52 follicles were collected from 10 ewes and placed into individual culture with 0 or .01 microCi 3H-androstenedione (10 ng; 3H-A) and 0, 10(-11), 10(-9), 10(-7), or 10(-5) M of a nonsteroidal aromatase inhibitor, CGS16949A (CGS). Concentrations of E2 secreted into the medium, and synthesis of estrogens as estimated by formation of 3H-water from 3H-A were decreased by 10(-5) and 10(-7) (P < .01), but not 10(-9) or 10(-11) M CGS. In experiment 2, luteolysis was induced in 24 ewes by injection of PGF2 alpha on days 5 to 10 of the estrous cycle (0 hr). Ewes received 0, 0.5, 1.0, 2.0 or 4.0 mg CGS per kg BW i.v. at -12, 0, 12 and 24 hr, and an ovulatory dose of hCG at 36 hr. Jugular (P < .001) and vena caval (P < .001) concentrations of E2 were decreased by CGS at all doses tested for 8 to 10 hr, but had returned to levels similar to control ewes by the time of the next injection. Concentrations of E2 around the time of the LH surge were similar in control and treated ewes. During the subsequent luteal phase, concentrations of progesterone (P4) were similar in control and treated ewes. Thus, transient decreases in E2 during the follicular phase were not deleterious to the subsequent luteal phase. In experiment 3, luteolysis was induced in 18 ewes by injection of PGF2 alpha on days 6 or 7 (0 hr) of the estrous cycle. Ewes received 0 or 1 mg CGS per kg BW i.v. every 8 hr from 0 to 40 hr. Ovulation was induced with hCG at 36 hr. CGS reduced jugular (P < .001) and vena caval (P < .001) concentrations of E2, prevented an endogenous surge of LH (P < .05) and increased (P < .001) concentrations of FSH. All ewes had ovulated a marked follicle by 72 hr, but onset of the luteal phase, as assessed by concentrations of P4, was delayed (P < .01) in ewes receiving CGS. Delayed luteal phases were not solely attributable to the presence of new CL or to luteinization of follicular cysts. When data were aligned according to the day ewes were observed in estrus, profiles of P4 did not differ with treatment.(ABSTRACT TRUNCATED AT 400 WORDS)

Two experiments, each arranged as a 2 x 2 factorial, were conducted in ewes to examine direct effects of bovine follicular fluid (bFF) on follicular development and luteal function and to further characterize follicular development and luteal function after pituitary stalk transection (SS). In Exp. 1, ewes were sham-operated or SS on d 6 of an estrous cycle and received 5 ml of saline or bFF three times daily on d 5 through 11 of the same cycle. In Exp. 2, all ewes were SS on d 6 of an estrous cycle and treated with saline or bFF three times daily on d 5 through 11 and with ovine FSH (60 micrograms; NIADDK-oFSH-16) or saline (1.2 ml) from d 7 to 11. In Exp. 2, ewes were ovariectomized on d 11 to assess effects of treatments on follicular development and luteal function. In both experiments, concentrations (ng/ml) of FSH on d 7 were suppressed (P less than or equal to .005) by bFF compared with saline (.50 +/- .17 vs 1.63 +/- .15) and remained suppressed (P less than or equal to .005) through d 11 (.46 +/- .12 vs 1.54 +/- .12). Replacement therapy (oFSH) restored concentrations of FSH. Concentrations of LH were not affected by bFF but were elevated (P less than or equal to .05) 1 d after SS (d 7; .88 +/- .09 vs .56 +/- .09) and remained elevated (P less than or equal to .05; 1.31 +/- .20 vs .65 +/- .11) from d 6 through 11. Concentrations of progesterone were unaffected by SS.(ABSTRACT TRUNCATED AT 250 WORDS)

Current methods for obtaining venous blood from the reproductive organs of livestock often have a low rate of success or involve intensive surgical procedures that may impair ovarian function. Therefore, the caudal vena cava was catheterized via the lateral saphenous vein to determine the feasibility of using this method for chronic sampling of blood draining from the reproductive organs of ewes (n = 6), cows (n = 6), and gilts (n = 7). Blood samples were collected at 2-cm (ewes and gilts) or 5-cm (cows) intervals during insertion of catheters. Correct placement, defined as the position at which plasma concentrations of progesterone or estrogen were at least threefold greater than in jugular venous plasma, varied among species and among animals within species. It seemed, however, that a majority of catheters would be placed correctly if secured at 48 to 52 cm in ewes, 52 cm in gilts, and 90 to 100 cm in cows. Saphenous vein catheters were secured for sequential sampling of vena caval blood during the follicular phase of ewes (n = 25), cows (n = 4), and gilts (n = 5). Catheters remained patent for the duration of sampling in all individuals. Concentrations of estrogen in jugular and vena caval plasma were correlated (ewe P less than .0003; cow P less than .0001; gilt P less than .0001). Profiles of progesterone and estrogen revealed an episodic pattern of secretion in vena caval but not jugular plasma. Catheterization of the vena cava via the saphenous vein is a relatively simple and noninvasive method for obtaining blood containing uterine and ovarian hormones before their metabolism.

Two experiments were conducted in ovariectomized, pituitary stalk-transected ewes to determine if dopamine (DA), norepinephrine (NE) or serotonin (5-HT) alter secretion of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and prolactin (PRL). In experiment 1, ewes were infused (iv) with saline (control), DA (66 micrograms/kg/min), NE (6.6 micrograms/kg/min) or 5-HT (6.6 micrograms/kg/min). Treatments did not alter pulse frequency, but 5-HT increased (P less than .05) amplitude of pulses of LH and mean concentrations of LH, DA and NE were without effect on basal secretion of LH. DA but not NE or 5-HT decreased (P less than .05) the release of LH in response to gonadotropin hormone-releasing hormone (GnRH, 25 micrograms, im). Concentrations of FSH were not affected by treatments. Secretion of PRL was reduced (P less than .05) by treatment with DA and NE but not 5-HT. Each amine reduced (P less than .05) the release of PRL in response to thyrotropin-releasing hormone (TRH; 3 micrograms, im). In experiment 2, ewes were given DA at doses of 0, 0.66, 6.6 or 66.0 micrograms/kg/min, iv. No dose altered basal LH, but each dose reduced (P less than .05) basal and TRH-induced release of PRL. Key findings from these studies include direct pituitary action for: (1) 5-HT enhanced basal secretion of LH, (2) suppression of GnRH-induced secretion of LH by DA. (3) DA and NE inhibition of PRL secretion, and (4) DA, NE and 5-HT inhibition of release of PRL in response to TRH.

In the present study, effects of dopamine (DA) and ovarian secretions on release of luteinizing hormone (LH) and prolactin (PRL) were examined using two methods of withdrawal of progesterone. Eight to 10 d after estrus, 36 ewes were assigned to one of six treatments: 1) lutectomy; 2) lutectomy and DA; 3) ovariectomy; 4) ovariectomy and DA; 5) ovariectomy and estradiol-17 beta or 6) ovariectomy, estradiol-17 beta and DA. Estradiol-17 beta was administered by Silastic implants inserted during surgery. Immediately after surgery, ewes were infused iv with DA (6.6 micrograms X kg-1 X min-1) or saline for 48 h. Infusion of DA did not affect secretion of LH after surgical removal of the corpus luteum. In lutectomized ewes, concentrations of LH in serum increased between 0 and 12 h from .5 to 3.3 ng/ml, declined between 12 and 16 h and then plateaued at 1.1 to 1.5 ng/ml. In contrast, concentrations of LH in ovariectomized ewes increased between 0 and 12 h and then remained at 3 to 5 ng/ml. Surges of LH occurred between 40 and 50 h postsurgery in eight of 12 lutectomized ewes, 11 of 12 ovariectomized ewes with implants of estradiol-17 beta and zero of 12 ovariectomized ewes. The magnitude of the surge of LH was higher in lutectomized ewes than in ovariectomized ewes with implants of estradiol-17 beta. Infusion of DA inhibited release of PRL, but there was no effect of method of progesterone withdrawal. Lutectomized ewes, but not ovariectomized ewes with implants of estradiol-17 beta, had a surge of PRL associated with the surge of LH.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of 0, 0.66 and 6.6 micrograms/kg per min of dopamine (DA) and of 0, 0.06 and 0.66 micrograms/kg per min of serotonin (5-HT) on secretion of luteinizing hormone (LH), estradiol-17 beta and progesterone were examined in ewes during luteal regression and the follicular phase. Onset of luteolysis was synchronized with two injections of 7.5 mg prostaglandin F2 alpha (PGF2 alpha) (i.m.) given 3 h apart in ewes which were 12-14 days postestrus. Ewes were infused intravenously with DA, 5-HT or a combination of DA and 5-HT for a 60-h period beginning at the time of the first PGF2 alpha injection. Neither DA nor 5-HT influenced the decrease in plasma concentrations of progesterone following PGF2 alpha. Effects of DA and 5-HT on tonic secretion of LH changed during the infusion. During the first 12 h, increasing doses of DA depressed and increasing doses of 5-HT increased mean concentrations of LH in plasma in a linear manner (DA, P less than 0.01; 5-HT, P less than 0.05). Between 16 and 34 h, 6.6 micrograms/kg per min of DA continued to suppress LH, however, 5-HT was no longer stimulatory to secretion of LH. DA was unable to inhibit secretion of LH after 40 h. Also, between 0 and 34 h, concentrations of estradiol-17 beta in plasma were decreased by infusion of DA (P less than 0.01). Interval from PGF2 alpha to onset of the preovulatory surge of LH, magnitude of the surge and duration of the surge were not altered by infusion of either DA or 5-HT.

Two experiments (Spring and Fall) were conducted in ovariectomized ewes to determine changes in pituitary hormone secretion immediately after pituitary stalk-transection. Ewes underwent either pituitary stalk-transection (SS), sham-transection (SH) or administration of anesthesia only (AO). Stalk-transected, but not sham-operated or anesthetized ewes had polyuria and polydipsia for 7 to 14 days after surgery. Concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin were measured in peripheral blood samples collected every 10 minutes for a six-hour period. Results were comparable for each season. During the six hours following surgery or removal from anesthesia, concentrations of LH declined in all ewes, but more slowly in SS ewes. No differences in patterns or mean concentrations of FSH were observed. Immediately after surgery, concentrations of prolactin were elevated, then declined in SH and SS ewes. The decrease was greater in SH than SS ewes. Data are consonant with the view that hypothalamic inhibition as well as LHRH stimulation regulate gonadotropin release by the pituitary.

Three experiments were conducted to examine the relationship between systemic concentrations of luteinizing hormone (LH) and estradiol-17 beta (E2) after withdrawal of progesterone in cycling ewes. In Exp. 1, ewes were assigned randomly to one of three treatments: laparotomy (C), removal of the luteal ovary (ULO), or ULO plus anesthesia with sodium pentobarbital for 6 h beginning 4 h after surgery. Anesthesia was used in an attempt to block the expected increase in tonic secretion of LH. Patterns of LH and E2 in these three groups did not differ during the 24-h experimental period. In Exp. 2, a longer period of anesthesia was utilized. Forty-eight ewes were assigned at random to one of four treatments: C, ULO, lutectomy or an intrafollicular injection of prostaglandin F2 alpha (PGF2 alpha). One-half of the ewes in each group were anesthetized with sodium pentobarbital from initiation of treatment (0 h) until 10 h after surgery. Sodium pentobarbital did not suppress the increases in LH and E2 after progesterone withdrawal. The regression of concentrations of E2 on concentration of LH was not significant. In Exp. 3, ewes were infused with either saline or dopamine after receiving an im injection of PGF2 alpha. Tonic secretion of LH increased after 4 h in ewes infused with saline, but not in ewes infused with dopamine. Despite the suppression of LH, concentrations of E2 increased in dopamine-treated ewes as in control ewes. Therefore, the initial increase in E2 after a decline of progesterone in cycling ewes is independent of increases in LH.

A study was done to test whether ovulatory follicles destined to form subfunctional corpora lutea differed from normal ovulatory follicles in steroidogenic function. Twenty-five ewes were treated with prostaglandin F2 alpha on d 11 of the estrous cycle, then unilaterally ovariectomized before (n = 13) or after (n = 12) the surge of luteinizing hormone (LH) at the induced estrus to collect "control" follicles, which would have produced normal corpora lutea. In 15 ewes, the second ovary was removed 63 to 84 h later to collect "treated" follicles before (n = 7) or after (n = 8) the second expected surge of LH. Five ewes (control) were allowed to ovulate from the remaining ovary at first estrus and another five (treated) at the second estrus (3 to 4 d later). Treated ewes had lower serum progesterone than control ewes during the ensuing cycle (P less than .05). Treated follicles contained less estradiol in the theca (4.4 +/- .6 vs 10.0 +/- 2.5 ng; P less than .05), less androstenedione (.1 +/- .1 vs 1.0 +/- .2 ng) and estradiol (.5 +/- .1 vs 2.9 +/- 2.2 ng) in the granulosa (P less than .05) and less progesterone in the follicular fluid (.8 +/- .4 vs 3.3 +/- .8 ng; P less than .05) than control follicles, when removed before the surge of LH. Follicles removed after the surge of LH did not differ. In conclusion, ovulatory follicles with low steroidogenic function became corpora lutea that secreted lower-than-normal quantities of progesterone.

Two studies were conducted to determine the distribution of follicles on the ovarian surface in ewes. In Exp. 1, the effect of the corpus luteum on the distribution of follicles was investigated on d 9, 12 and 14 postestrus in unilaterally ovulating ewes. Follicles (greater than or equal to 2 mm diameter) were inventoried by size and distance from the center of the corpus luteum or corpus albicans. There were more small follicles (less than or equal to 4 mm diameter) on d 9 than on d 12 and 14, Although the ovary bearing the corpus luteum had a greater number of large follicles, no positive relationship of the corpus luteum to the diameter of the closest follicle or the distance of the largest follicle was found. In Exp. 2, follicles were inventoried on ovaries from ewes during the estrous cycle, postpartum anestrus, seasonal anestrus and the peripuberal period. During the estrous cycle, two apparent waves of follicular growth were noted. In addition, during the luteal phase the luteal ovary consistently had a larger follicle than the nonluteal ovary. When estimates were made of the effects of size of follicle on distance of the follicle from the reference structure and of distance on size of follicle, presence of luteal tissue, and day of estrous cycle were found to influence the variances. In addition the interaction of these characteristics affected the variation of size or distance. Weighting the distribution of ovarian structures for relative ovarian mass allowed an examination of localization of structures to standardized ovarian areas. More follicles and corpora lutea were found in the middle of the ovary than on the ends. Although the numbers of follicles in a standardized area were correlated with ovarian mass, occurrence of corpora lutea in a standardized area was not significantly correlated with ovarian mass. Collectively, these results are indicative of a local effect by the corpus luteum on the diameter of the largest follicle and a systemic effect on the number of follicles. In addition, because specific regions appear to be more favorable for follicular activity and ovulation, a precise local effect of the corpus luteum is difficult to determine.

Two experiments were conducted in peripuberal ewe lambs to determine (a) the influence of the first luteal structure [most frequently a transient (i.e., 1 to 4 d) structure] on subsequent ovarian activity and (b) a role for the uterus in its demise. In Exp. 1, 21 lambs were assigned randomly on the day of the first rise in progesterone in the plasma to (1) sham-operation, (2) removal of the nonluteal ovary, (3) removal of the luteal ovary and (4) removal of the luteal ovary plus progesterone replacement (5 mg given three times 12 h apart, initiated at surgery). No effect of treatment on subsequent ovarian activity was observed. In Exp. 2, four of 14 lambs were assigned randomly to be hysterectomized before their first rise in progesterone. The remaining 10 lambs, (five each) were sham-operated or hysterectomized on the day of the first rise in progesterone. All hysterectomized lambs (N = 9) exhibited a rise in progesterone and maintained elevated concentrations of progesterone, whereas sham-operated lambs initiated estrous cycles. Oviducts and uteri collected from lambs hysterectomized on the day of the first rise in progesterone in Exp. 2 were flushed for presence of oocytes and none were found. Similarly, no retained oocytes were found in histological preparations of first luteal structures obtained from eight lambs ovariectomized in Exp. 1. Concentrations of luteinizing hormone (LH) and prolactin were determined in daily samples collected from 19 lambs in Exp. 1. Luteinizing hormone increased and became more variable as lambs matured, whereas prolactin decreased with no detectable change in variability. It is concluded that the transient luteal structure is not required for sexual maturation and that its lifespan is uterine dependent.

The objectives of this study were to determine 1) the ability of charcoal-extracted bovine follicular fluid (bFF) to suppress endogenous follicle stimulating hormone (FSH) at various stages of the estrous cycle and 2) the effects of suppression of FSH on luteal function and lengths of the current and subsequent estrous cycles. Twenty-six mature ewes were assigned randomly to receive 5 ml of either bFF or saline, subcutaneously, at 8-h intervals on d 1 through 5 (bFF n = 6; saline n = 3), d 6 through 10 (bFF n = 6; saline n = 3) or d 11 through 15 (bFF n = 6; saline n = 2) of the estrous cycle (d 0 = estrus). Blood was collected daily beginning at estrus and continued until the third estrus (two estrous cycles) or 40 d; more frequent samples were collected 2 h prior to initiation of treatment (0600), hourly for the first 8 h of treatment, then every 4 h until 0800 on the first day after treatment, and finally at 1600 and 2400 on that day. Plasma concentrations of FSH were lower (P less than .001) in bFF-treated than in saline-treated ewes. Treatment with bFF reduced (P less than .05) plasma concentrations of progesterone during the current but not during the subsequent estrous cycle. Treatment with bFF did not affect plasma concentrations of estradiol-17 beta. Administration of bFF on d 11 through 15 of the estrous cycle lengthened the interval from the decline in progesterone to estrus and the inter-estrous interval by approximately 3 and 4 d, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of domperidone, a peripheral dopamine receptor antagonist, on secretion of LH and prolactin were studied during the luteal phase and following administration of PGF2 alpha. Since hyperprolactinemia has been reported to inhibit secretion of LH in ewes, effects of thyrotropin-releasing hormone (TRH) also were examined. Ewes 8-10 days post-estrus were assigned to be treated with: 1) vehicle (n = 5); 2) 0.3 mg domperidone (n = 6); 3) 1.0 mg domperidone (n = 6); 4) 3 micrograms TRH (n = 6); or 5) 10 micrograms TRH (n = 6) every 4 hours for 60 hr. Luteal regression was induced with PGF2 alpha at 12 hr after initiation of treatments. During the luteal phase, pulses of LH were more frequent (P less than .05) and the amplitudes of these were higher (P less than .05) in ewes treated with domperidone or TRH than in control ewes. These changes in LH occurred even though each treatment elevated markedly concentrations of prolactin in plasma. After induction of luteal regression, mean of LH and frequency of LH discharges were similar in all groups. However, in ewes treated with the 1.0 mg/4 hr dose of domperidone the pulse amplitude was greater than in the other groups (2.3 vs 1.1 ng/ml). Dose-response relationships and the magnitude of the prolactin release following domperidone or TRH varied with time. Treatments did not affect the timing of the LH surge or the increase in progesterone associated with the subsequent cycle.(ABSTRACT TRUNCATED AT 250 WORDS)