Serum profiles of luteinizing hormone,progesterone and total estrogens during the canine estrous cycle

Serum levels of LH, total estrogen and progesterone were measured daily by radioimmunoassay during proestrus, estrus and early diestrus in five beagle bitches. Occurrence of the LH peak relative to the onset of estrus was quite variable ranging from 3 days before to 7 days after the onset of estrus. Serum LH levels were elevated for 3 days with a peak value of 25 ± 2 ng/ml reached 2.4 days after the start of estrus. LH levels were ≤ 2 ng/ml when measured at other times during the estrous cycle. Estrogen titers ranged from 84 ± 39 pg/ml at 9 days before the LH peak to 175 ± 15 pg/ml coincident with the LH peak. A broad estrogen peak was evident beginning 5 days before and continuing for 5 days after the LH peak. An estrogen surge was seen in 4 of 5 dogs immediately preceding or coincident with the LH peak suggesting that LH release in the bitch is triggered by a sharp elevation in estrogen levels. Serum progesterone levels rose from ≤ 5 ng/ml before the LH peak to 46 ± 6 ng/ml 6 days afterwards.     

Endocrine profiles during the estrous cycle and pregnancy in the Baird's tapir (Tapirus bairdii)

Serum samples were collected 1–3 times weekly from two Baird's tapirs (Tapirus bairdii) for 6 months in 1987–1988, and for more than 3 consecutive years beginning in 1989 to characterize hormone patterns during the estrous cycle and pregnancy. Based on serum progesterone concentrations, mean (±SEM) duration of the estrous cycle (n = 20) was 30.8 ± 2.6 days (range, 25–38 days) with a luteal phase length of 18.1 ± 0.4 days (range, 15–20 days). Mean peak serum progesterone concentrations during the luteal phase were 1.35 ± 0.16 ng/ml, and nadir concentrations were 0.19 ± 0.03 ng/ml during the interluteal period. Distinct surges of estradiol preceded luteal phase progesterone increases in most (14/20) cycles. Gestation length was 392 ± 4 days for three complete pregnancies. Mean serum progesterone concentrations increased throughout gestation and were 1.83 ± 0.13, 2.73 ± 0.13, and 4.30 ± 0.16 ng/ml during early, mid- and late gestation, respectively. Serum estradiol concentrations began to rise during mid-gestation, increasing dramatically during the last week of pregnancy. Patterns of serum estriol and estrone secretion during pregnancy were similar to that observed for estradiol. In contrast to progesterone and estrogens, serum cortisol concentrations were unchanged during pregnancy or parturition. Females resumed cycling 16.2 ± 2.0 days after parturition (n = 4) and, on two occasions, females became pregnant during the first postpartum estrus. These data suggest that the tapir cycles at approximately monthly intervals and that increases in serum progesterone are indicative of luteal activity. The interluteal period is relatively long, comprising approximately 40% of the estrous cycle. During gestation, progesterone concentrations are increased above luteal phase levels, and there is evidence of increased estrogen production during late gestation. The absence of increased cortisol secretion at the end of gestation suggests that this steroid does not play a major role in initiating parturition in this species. © 1994 Wiley-Liss, Inc.     

Influence of GnRH infusion on endocrine parameters and duration of postpartum anestrus in beef cows

The effect of an intravenous infusion of gonadotrophin releasing hormone (GnRH) on the duration of postpartum anestrus in suckled beef cows was studied. Twenty-eight, mature, suckled beef cows were assigned in equal numbers to one of four treatment groups which were based on infusion with saline or GnRH (15ug/hour for 12 hours) and stage postpartum (pp) (20 or 35 days). Serum LH and progesterone were determined by radioimmunoassay for the period which began 5 days pre-infusion and ended at 55 days postpartum (ie: 35 or 20 days post-infusion). Serum LH remained below 5ng/ml during infusion in all control cows. Peak serum LH values, times of LH peaks, and duration of LH responses (means +/- SE) during infusion were 49 +/- 12 ng/ml, 162 +/- 42 minutes and 7.8 +/- 1.3 hours for the 20 day group and 44 +/- ng/ml, 144 +/- 6 minutes, and 8.2 +/- 1.1 hours for the 35 day group respectively. Serum progesterone levels indicated that the proportion of cows showing the onset of estrous cycles within 10 days of infusion was greater in the 20 day pp GnRH group (4/7) than the 20 day pp saline group (0/7) (p < .05) but was not significantly different between the 35 day pp GnRH (4/7) and 35 day pp saline (2/6) groups. The incidence of estrus was not affected by GnRH treatment and was 37% in all cows prior to 55 days pp. It was concluded that infusions of GnRH for 12 hours at a rate of 15 ug/hour could induce estrous cycles in suckled beef cows treated at 20 days postpartum.     

Estrus and ovulation in beef cows following use of progesterone-releasing devices, progesterone and estradiol valerate

Two hundred nonsuckling beef cows were treated with either 1) a progesterone-releasing intravaginal device (PRID) for 12 days; 2) PRID plus an IM injection of 200 mg progesterone (PRID-P); 3) PRID plus 5-mg IM injection of estradiol valerate (PRID-EV); or 4) PRID-EV-P. Cows were started on treatment on one of the first eight days of the estrous cycle. The number of cows which had P levels above 1 ng/ml one day after PRID removal was 12 to 50% lower in PRID-EV and PRID-EV-P groups than in PRID and PRID-P groups (P < 0.05). The proportion of cows showing estrus by 96 hours after PRID removal was 38, 36, 77, and 88% (P < 0.05) for the PRID, PRID-P, PRID-EV and PRID-EV-P groups, respectively. Thirty-one percent fewer cows treated with PRID on days 5 through 8 of the estrous cycle showed estrus by four days after PRID removal than those treated on days 1 through 4. In addition, 18 to 22% more cows had P levels above 1 ng/ml among cows treated with PRID or PRID-P on days 5 through 8 than among cows treated similarly on days 1 through 4. It was concluded that effective synchronization of estrus is achieved only when estrogen is used in conjunction with PRID in cows treated for twelve days during the first eight days of an estrous cycle.     

Progesterone concentrations during estrous cycle of dairy cows exposed to electric and magnetic fields

Sixteen multiparous nonpregnant lactating Holstein cows (each weighing 662 ± 65 kg in 150.4 ±40 day of lactation) were confined to wooden metabolic cages with 12:12 h light:dark cycle during the experiment. The cows were divided into two sequences of eight cows each and exposed to electric and magnetic fields (EMF) in an exposure chamber. This chamber produced a vertical electric field of 10 kV/m and a uniform horizontal magnetic field of 30 μT at 60 Hz. One sequence was exposed for three estrous cycles of 24 to 27 days. During the first estrous cycle, the electric and magnetic fields were off; during the second estrous cycle, they were on; and during the third estrous cycle, they were off. The second sequence was also exposed for three 24 to 26 days estrous cycles, but the exposure to the fields was reversed (first estrous cycle, on; second estrous cycle, off; third estrous cycle, on). The length of each exposure period (21 to 27 days) varied according to the estrous cycle length. No differences were detected in plasma progesterone concentrations and area under the progesterone curve during estrous cycles between EMF nonexposed and exposed periods (2.28 ±0.17 and 2.25 ± 0.17; and 24.5 ± 1.9 vs. 26.4 ± 1.9 ng/ml, respectively). However, estrous cycle length, determined by the presence of a functional corpus luteum detected by concentrations of progesterone equal to or more than 1 ng/ml plasma, was shorter in nonexposed cows than when they were exposed to EMF (22.0 ± 0.9 vs. 25.3 ± 1.4 days). Bioelectromagnetics 19:438–443, 1998. © 1998 Wiley-Liss, Inc.     

Effect of repeated laparoscopic surgery on the bovine estrous cycle

The effects of repeated laparoscopic surgery on the length of the bovine estrous cycle, estrus, ovulation and corpus luteum function were determined after one estrous cycle of normal duration (18 to 24 days). Five, Angus x Hereford cows were subjected to laparoscopy on days 5, 13, 18 and 20 (estrus = day 0) of the subsequent cycle. Blood was collected daily during the cycle in which laparoscopy was performed (surgical cycle) and during the next cycle (postsurgical cycle). Lengths of the surgical and postsurgical cycles (22.3 +/- .5 days and 21.5 +/- .6 days, respectively) did not differ (P>.05) from that of the presurgical cycle (21.8 +/- .2 days). Average concentrations (ng/ml) of LH and progesterone in serum were similar during the surgical and postsurgical cycles (1.2 +/- .1, 2.2 +/- .2 vs 1.3 +/- .2 and 2.3 +/- .1). Progesterone concentrations remained above 1 ng/ml for 17 and 16 days during the surgical and postsurgical cycles, respectively. A pre-ovulatory rise in LH, along with estrus and ovulation was confirmed in all animals. Follicular development, characterized by follicular volume, increased progressively from days 5 to 20, with the largest increase occurring between days 13 and 18. These results indicate that laparoscopy, used at the times and frequency specified, does not alter reproductive function of cyclic cows and can provide information on ovarian activity.     

Difference in luteinizing hormone response to an opioid antagonist in beef heifers and cows

In three experiments, we examined endogenous opioid inhibition of luteinizing hormone (LH) secretion during the bovine estrous cycle. An increase in serum LH in response to the opioid antagonist naloxone (Na; 1 mg/kg i.v.) was the criterion for opioid inhibition. Estrous cycles were synchronized via prostaglandin administration. In Experiment 1, mean serum LH was not different during the luteal phase in yearling heifers (n = 6/group) at Hour 1 after Nal (2.1 ng/ml) compared to controls (1.8 ng/ml). However, LH peak amplitude was increased (p less than 0.05) in the Nal compared to the control group. Serum LH was increased (p less than 0.01) during the follicular phase in heifers at Hour 1 post-Nal compared to controls (4.7 and 3.5 ng/ml, respectively). Again, Nal administration was followed by increased (p less than 0.05) LH pulse amplitude compared to control. In Experiment 2, no effect of Nal upon serum LH was detected in cows (n = 9) during proestrus, metestrus, midluteal and late luteal portions of the estrous cycle. In Experiment 3, the LH response to Nal was examined simultaneously in yearling heifers and cows (n = 5/group) during the luteal and follicular phases. Serum LH increased (p less than 0.001) during Hour 1 post-Nal in heifers compared to cows during the follicular (3.4 vs. 1.7 ng/ml) but not during the luteal phase. LH pulse amplitude also increased (p less than 0.05) during Hour 1 post-Nal in heifers compared to cows during the luteal (2.5 vs. 1.1 ng/nl and follicular (2.5 vs. 1.3 ng/ml) phases.(ABSTRACT TRUNCATED AT 250 WORDS)     

Temporal changes in serum prostaglandin F2alpha and oxytocin in dairy cows with short luteal phases after the first postpartum ovulation

Luteolysis in the cow depends upon an interaction between prostaglandin F(2alpha) (PGF(2alpha)) and oxytocin. The objectives of our study were 1) to determine oxytocin concentrations in postpartum dairy cows and 2) to identify the temporal relationship between oxytocin and PGF(2alpha) release patterns during luteolysis in normal and abbreviated estrous cycles in the postpartum period. Serum oxytocin and PGF(2alpha) metabolite (PGFM) concentrations from nine cows which had short estrous cycles (< 17 d) were compared with those of six cows which had normal estrous cycles. Serum basal oxytocin concentrations in short estrous cycle cows (23.7 to 31.1 pg/ml) were higher (P<0.05) than those of normal estrous cycle cows (14.6 to 19.8 pg/ml). Oxytocin concentrations increased to peak values in both short and normal cycle cows, during luteolysis. Basal PGFM concentrations (112.2 to 137.4 pg/ml) were higher in cows with short cycle (P<0.05) than in cows with normal cycles (62.9 to 87.5 pg/ml). The increase in PGFM concentrations during luteolysis was significant in both normal cycle and short cycle cows (P<0.05). Increases in serum PGFM concentrations were always associated with increases in serum oxytocin concentrations in normal cycle and short cycle cows and the levels decreased simultaneously before the subsequent estrus. Results support the idea of a positive relationship between PGF(2alpha) and oxytocin concentration during the estrous cycle as well as a possible synergistic action of these hormones in the induction of luteolysis in dairy cattle.     

Evaluation of steroid microspheres for control of estrus in cows and induction of puberty in heifers

Two trials were designed to test whether a single treatment with a microsphere formulation of progesterone (P) could simulate the luteal phase of the estrous cycle and lead to estrus and subsequent luteal development. The first experiment was to characterize the pattern of serum P concentrations and estrus in cows treated with a microsphere formulation (P + E) that contained 625 mg P and 50 mg estradiol (E). Four cows with palpable corpora lutea were treated with 25 mg prostaglandin F2 m. Each cow was given P + E (i.m.) 12 h later. Tail vein blood samples were taken on Days 1 and 2 following P + E treatment and then three times weekly for 24 days. Serum P increased from 0.8 +/- 0.1 ng/ml at P + E treatment to 4.7 +/- 0.6 ng/ml on Day 1, declined gradually to 4.1 +/- 0.3 ng/ml on Day 7 and then declined more rapidly to 0.6 +/- 0.1 ng/ml on Day 13. Treated cows showed estrus 16.25 +/- 0.7 days after P + E treatment. Thereafter, serum P increased beginning on Day 20 after P + E treatment, as expected following estrus. In Experiment 2, Angus and Simmental heifers (10.5-11.5 months of age) were administered i.m. either the vehicle (controls), E (50 mg), P (625 mg) or P + E (n = 13 per group). While treatment with E resulted in behavioral estrus (1-2 days after treatment) in each treated heifer, it did not (P > 0.5) initiate estrous cycles as indicated by subsequent increased serum P. In contrast, the P and P + E treatments increased (P < 0.05) the proportion (11/13) of heifers that showed estrus by 21 days after treatment followed by elevated serum P. We conclude that the microsphere formulation of P simulated the pattern of serum P concentrations during the luteal phase of the estrous cycle and initiated estrous cycles in peripubertal heifers with or without E.     

Relationships between insulin and glucose metabolism and pituitary-ovarian functions in fasted heifers

The effects of fasting between Days 8 and 16 of the estrous cycle on plasma concentrations of luteinizing hormone (LH), progesterone, cortisol, glucose and insulin were determined in 4 fasted and 4 control heifers during an estrous cycle of fasting and in the subsequent cycle after fasting. Cortisol levels were unaffected by fasting. Concentrations of insulin and glucose, however, were decreased (p less than 0.05) by 12 and 36 h, respectively, after fasting was begun and did not return to control values until 12 h (insulin) and 4 to 7 days (glucose) after fasting ended. Concentrations of progesterone were greater (p less than 0.05) in fasted than in control heifers from Day 10 to 15 of the estrous cycle during fasting, while LH levels were lower (p less than 0.01) in fasted than in control heifers during the last 24 h of fasting. Concentrations of LH increased (p less than 0.01) abruptly in fasted heifers in the first 4 h after they were refed on Day 16 of the fasted cycle. Concentrations (means +/- SEM) of LH also were greater (p less than 0.05) in fasted (11.2 +/- 2.6 ng/ml) than in control (4.7 +/- 1.2 ng/ml) heifers during estrus of the cycle after fasting; this elevated LH was preceded by a rebound response in insulin levels in the fasted-refed heifers, with insulin increasing from 176 +/- 35 pg/ml to 1302 +/- 280 pg/ml between refeeding and estrus of the cycle after fasting. Concentrations of LH, glucose and insulin were similar in both groups after Day 2 of the postfasting cycle. Concentrations of progesterone in two fasted heifers and controls were similar during the cycle after fasting, whereas concentrations in the other fasted heifers were less than 1 ng/ml until Day 10, indicating delayed ovulation and (or) reduced luteal function. Thus, aberrant pituitary and luteal functions in fasted heifers were associated with concurrent fasting-induced changes in insulin and glucose metabolism.     

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.     

Serum LH,FSH, estradiol-17β and progesterone profiles of native and crossbred goats in a tropical semiarid zone of Venezuela during the estrous cycle

The patterns of serum luteinizing hormone (LH), follicle stimulating hormone (FSH), progesterone and estradiol-17β during the estrous cycle of six crossbred (Alpine × Nubian × Native) and six native goats showing a 21 day estrous cycle in a semiarid zone of Venezuela are presented. In the crossbred goats, FSH had two significant peaks on Days 19 and 0 (33 ± 8.6 ng ml⁻¹ and 25 ± 6 ng ml⁻¹, respectively); in contrast, native goats only had one significant peak on the day of estrus (22 ± 2 ng ml⁻¹), with the increase beginning on Day 17. During the follicular phase of crossbred goats, estradiol-17β and LH increased to 28 ± 6 pg ml⁻¹ and 23 ± 6.9 ng ml⁻¹, respectively, on Day 0. Prior to Day 0, LH increased to 10.0 ± 4.9 ng ml⁻¹ on Day 18, decreasing to 1.5 ng ml⁻¹ on Day 19, while estradiol-17β was increasing. This relationship between estradiol-17β and LH was not found to exist in native does, which presented a LH peak on Day 0 (30 ± 8 ng ml⁻¹ and 35 ± 10 ng ml⁻¹ in first and second estrus, respectively). LH basal levels were notably higher in native does. The highest concentrations of progesterone (10 and 12 ng ml⁻¹) were detected on Days 12 and 15 in crossbred and native females, respectively. In conclusion, the relationship between estradiol-17β and gonadotropins during the follicular phase in crossbred goats suggests negative and positive feedback effects on both LH and FSH. Serum concentrations of LH were higher in native than in crossbred goats, whereas concentrations of FSH were higher in crossbred does. Thus, genetic factors need to be taken into account when comparing blood levels of gonadotropins in goats raised in tropical semiarid zones.     

Peripheral plasma levels of lh in the cow throughout the estrous cycle.

Peripheral plasma levels of LH during the bovine estrous cycle were measured in 5 cows and one heifer by using double antibody radioimmunoassay. The sources of variability of basal LH-levels were analyzed in detail. The range of basal levels of LH WAS 0.3--3.5 Ng/ml. Between days 11 and 14 of the cycle the mean daily levels were lower in all cows by about 28% as compared with the remaining parts of the cycle. This did not seem to be directly influenced by changes in progesterone levels. A single peak of LH was observed around estrus. The magnitude of that preovulatory peak varied from 6.7 to 16.0 mg/ml, and lasted only a few hours.     

Levels of lutenizing hormone, estradiol and progesterone in serum during the estrous cycle and pregnancy in the beagle bitch (38491).

Levels of luteinizing hormone (LH), estradiol-17 beta and progesterone were determined by specific radioimmunoassays in sera obtained from Beagle bitches during proestrus, estrus and diestrus. Concentrations of LH (expressed as NIH-LH-SI equivalents) were 2.8 plus or minus 0.1 ng/ml in proestrus, 35.5 plus or minus 10.0 ng/ml during early estrus and 2.2 plus or minus 0.1 ng/ml in early diestrus. Peak levels of estradiol-17beta (68.9 plus or minus 11.0 ng/ml) were detected 24 hr prior to the LH peak, declined rapidly and reached basal levels (17.8 plus or minus 6.3 ng/ml) by five days following the LH peak. Levels of progesterone were 1.7 plus or minus 0.3 ng/ml during proestrus, 3.5 plus or minus 0.3 ng/ml during early estrus and 23.3 plus or minus 2.8 ng/ml on day 5 after the LH peak . Progesterone levels remained elevated through day 28 of diestrus and pregnancy. A significant decrease (p smaller than 0.05) in levels of prosgesterone occurred between day 28 of pregnancy and one day prior to shelping (3.3 plus or minus 1.2 ng/ml, with a further decrease on the day of whelping (1.1 plus or minus 0.2 ng/ml). Levels of estradiol-17beta and LH did not change significantly (p smaller than 0.0k) during diestrus or pregnancy.     

Induction of estrus and ovulation in non-cyclic buffalo (Bubalusbubalis) heifers with progesterone-releasing intravaginal device and pregnant mare serum gonadotrophin and their gonadotrophin profile

A study was undertaken to induce estrus among 15 non-cyclic Murrah buffalo heifers at a relatively early age of 2.5 to 3 yr by progesterone releasing intravaginal device (PRID) application. On Day 13, the PRID was removed and the animals were divided into two groups (A and B). Group B received 1000 IU of pregnant mare serum gonadotrophin (PMSG) intramuscularly (i.m.) immediately after removal of the PRID, whereas Group A was given no further treatment. Circulating gonadotrophin profiles (luteinizing hormone (LH) and follicle stimulating hormone (FSH) were quantified during and after the PRID treatment, as well as during the induced estrous cycle. LH and FSH levels before, during, and after PRID treatment were in the range of 0.5 to 3.0 ng/ml and 10 to 45 ng/ml, respectively, and could be considered basal levels. The peak FSH levels of Group B (PRID + PMSG) during estrus ranged from 69.44 to 337.06 ng/ml, much higher than the levels recorded in Group A (PRID). None of the animals in Group A showed peak LH levels during estrus, whereas two animals in Group B had peak LH levels of 15.84 and 16.93 ng/ml at 0 h and 12 h after detection of estrus. The higher LH and FSH levels obtained in Group B animals compared with Group A animals was possibly due to the superimposed effect of PMSG over PRID. All of the 14 animals exhibited estrus. None of the animals in Group A conceived whereas three out of seven animals in Group B conceived, indicating that PMSG following PRID resulted in ovulatory estrus.     

Repeatability of blood serum progesterone levels in dairy heifers on day 7 of the estrous cycle

Thirty normally cycling dairy heifers were used to determine the repeatability of blood serum progesterone levels on Day 7 ± 0.25 d of the estrous cycle. The experimental group consisted of 16 Holsteins and 14 dairy crossbreds ranging in age from 18 to 24 months. Day of the estrous cycle was determined from twice daily observations for standing heat (Day 0). Serum progesterone levels for Day 7 ± 0.25 d were determined by radioimmunoassay from blood samples collected by jugular venipuncture over three to four consecutive estrous cycles. Levels of blood serum progesterone for Day 7 ± 0.25 d ranged from 0.57 to 6.03 ng/ml. Least square means for the Holstein (2.74 ng/ml) and dairy crossbred (3.38 ng/ml) groups were different (P<0.006). The repeatability for levels of blood serum progesterone on Day 7 of the estrous cycle was low (0.0115).     

Effects of phyto-estrogenic alfalfa consumption on plasma LH levels in cycling ewes

Plasma luteinizing hormone (LH) concentrations were determined in five Dorset ewes fed orchard grass hay (Dactylus glomerata) and five ewes fed alfalfa (Medicago sativa). Total phyto-estrogen content ($\text{X}\text{±}\text{SEM}$ genistein equivalents) of the orchard grass hay and alfalfa was 16.9 ± 2.9 and 118 ± 12.3 ppm respectively. LH was determined at regular intervals during the estrous cycles synchronized with progesterone impregnated pessaries and characterized by marker ram and vaginal cytology.Peak LH levels in control ewes (40.1 ± 5.5 ng/ml) were lower (P<0.05) than in ewes fed phyto-estrogenic alfalfa (66.0 ± 16.8 ng/ml). Results also indicate that the LH peak may occur later (P<0.05) in the estrus period of ewes fed phyto-estrogenic alfalfa (15.4 ±4.5 h). These experiments may suggest that peak LH concentrations are elevated and delayed further into the estrus period in ewes fed phyto-estrogenic alfalfa.     

Pulsatile infusion of luteinizing hormone-releasing hormone: Effects on luteinizing hormone secretion and ovarian function in prepuberal gilts

Ten intact and hypophysial stalk-transected (HST), prepuberal Yorkshire gilts, 112–160 days old, were subjected to a pulsatile infusion regimen of luteinizing hormone-releasing hormone (LHRH) to investigate secretion profiles of luteinizing hormone (LH) and ovarian function. A catheter was implanted in a common carotid artery and connected to an infusion pump and recycling timer, whereas an indwelling external jugular catheter allowed collection of sequential blood samples for radioimmunoassay of LH and progesterone. In a dose response study, intracarotid injection of 5 μg LHRH induced peak LH release (5.9 ± 0.65 ng/ml; mean ± SE) within 20 min, which was greater (P < 0.001) than during the preinjection period (0.7 ± 0.65 ng/ml). After HST, 5 μg LHRH elicited LH release in only one of three prepuberal gilts. Four intact animals were infused with 5 μg LHRH (in 0.1% gel phosphate buffer saline, PBS) in 0.5-ml pulses (0.1 ml/min) at 1.5-h intervals continuously during 12 days. Daily blood samples were obtained at 20-min intervals 1 h before and 5, 10, 20, 40, 60 and 80 min after one LHRH infusion. Plasma LH release occurred in response to pulsatile LHRH infusion during the 12-day period; circulating LH during 60 min before onset of LHRH infusion was 0.7 ± 0.16 ng/ml compared with 1.3 ± 0.16 ng/ml during 60 min after onset of infusion (P < 0.001). Only one of four intact gilts ovulated, however, in response to LHRH infusion. This animal was 159 days old, and successive estrous cycles did not recur after LHRH infusion was discontinued. Puberal estrus occurred at 252 ± 7 days in these gilts and was confirmed by plasma progesterone levels. These results indicate that intracarotid infusion of 5 μg LHRH elicits LH release in the intact prepuberal gilt, but this dosage is insufficient to cause a consistent response after HST.     

Luteinizing hormone secretion and corpus luteum function in cows receiving two levels of progesterone

The objectives of this experiment were to determine if subnormal levels of progesterone (P4) indicative of luteal insufficiency influence (1) pulsatile release of luteinizing hormone (LH), (2) the interval to the preovulatory surge of LH after removal of P4, and (3) the secretion of P4 during the estrous cycle subsequent to administration of subnormal levels of P4. On Day 5 (Day = 0 day of estrus) of the estrous cycle, cows received P4-releasing intravaginal devices (PRID) to produce normal (2 PRIDs; n = 7) or subnormal (0.5 PRID; n = 6) concentrations of P4. Five cows served as controls. On Day 10, serial blood samples were collected from all cows. Collection of blood samples was again initiated on Day 17 in cows receiving PRIDs. The PRIDs were removed and blood collection continued for 78 h. Daily blood samples were collected from all animals for 42 days subsequent to estrus (estrous cycles 1 and 2, respectively). During estrous cycle 1, mean concentration of P4 was lower (p less than 0.05) and frequency of pulses of LH was higher (p less than 0.05) in cows receiving subnormal P4 than in cows receiving normal P4 and control cows. Plasma concentrations of estradiol (E2) were higher (p less than 0.05) on Days 9-16 of estrous cycle 1 in cows receiving subnormal P4 than in cows receiving normal P4 or in control cows. Concentrations of E2 were greater (p less than 0.05) at 6, 18, and 30 h following removal of PRIDs in cows receiving subnormal P4 than in cows receiving normal P4.(ABSTRACT TRUNCATED AT 250 WORDS)     

Changes in ovarian function in mature beef cows grazing endophyte infected tall fescue

The objective was to examine follicular and luteal development and function in mature, lactating beef cows grazing endophyte free (E-) or endophyte infected (E+) tall fescue during the early postpartum period. Angus, Hereford, and Angus x Hereford cows were exposed to pasture for 37-39 days before synchronized estrus. Serum concentrations of prolactin were evaluated during the luteal phase before the synchronized estrus. Every Monday, Wednesday, and Friday for one estrous cycle ovaries were monitored by transrectal ultrasonography and blood was collected for determination of serum concentrations of progesterone and estradiol in cows that responded to synchronization. Signs of fescue toxicosis in E+ cows included decreased serum concentrations of prolactin (84.9+/-13.6 pg/ml versus 32.3+/-12.0 pg/ml; P < 0.009) measured during the luteal phase (day 37 of grazing) and decreased body condition of cows and weight of cows and calves (P < 0.001). Neither serum concentrations of progesterone or estradiol, nor diameter of the CL differed between treatments. Diameter of the largest follicle tended to be smaller for cows grazing E+ fescue, especially between days 8 and 12 of the estrous cycle (P < 0.08). Numbers of class 1 (3-5 mm) and class 3 (>10 mm) follicles were similar (P > 0.05) between treatments, but number of class 2 (6-9 mm) follicles was reduced in E+ cows for most of the cycle (days 10 through 20; P < 0.03). Length of synchronized estrous cycle, days open, calving interval, and pregnancy rate at 30, 45, 60, and 90 days post-breeding was similar (P > 0.05) among treatment groups. Even though follicular dynamics (diameter of the largest follicle and number of class 2 follicles) were altered in cows grazing E+ tall fescue, follicular function was apparently not affected by ergot alkaloids.