Endocrine changes associated with a dietary-induced increase in ovulation rate (flushing) in gilts

Effects of an increased level of dietary energy (flushing) on plasma concentrations of FSH, LH, insulin, progesterone and estradiol-17 beta and ovulation rate were studied in 16 gilts. Gilts received 5,400 kcal ME/d for one estrous cycle and the first 7 d of a second. On d 8 of the second estrous cycle, gilts received either 5,400 kcal ME/d (control [C], n = 8) or 11,000 kcal ME/d (flushed [F], n = 8) for the remainder of the estrous cycle. Blood was collected daily at 15-min intervals for 6 h from d 8 through estrus. Gilts were examined by laparotomy 6 d after estrus. Ovulation rate was greater (P less than .05) in F than C gilts (16.0 vs 9.4). Mean daily concentrations of FSH were greater (P less than .05) in F gilts at 5 d, 4 d and 3 d prior to estrus compared with C females. In both C and F gilts, FSH decreased (P less than .05) prior to estrus. Mean daily concentrations of LH and LH pulse amplitude were not different (P greater than .05) between treatments. Mean number of LH pulses/6 h at 4 d, 3 d and 2 d prior to estrus were greater (P less than .05) in F than in C gilts. In both treatments, LH pulse amplitude decreased (P less than .05) and pulse frequency increased (P less than .07) prior to estrus. Mean plasma concentrations of insulin tended to be higher (P less than .07) in F than in C females during the 7-d period before estrus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Characterization of gonadotropic and ovarian steroid hormones during the periovulatory period in high ovulating select and control line gilts

Cyclic gilts from Control (C, randomly selected, n = 11) and Relax Select (RS, nine generations of selection for increased ovulation rate followed by seven generations of relaxed or random selection, n = 9) lines of the University of Nebraska Gene Pool population (derived from 14 different breeds) were utilized to characterize differences in gonadotropic and ovarian steroid hormones during preovulatory and postovulatory phases of the estrous cycle. Blood samples were collected during four periods (0500, 1100, 1700 and 2300) daily beginning 2 d prior to anticipated estrus (d -2, d 18 of a 20-d estrous cycle), and continuing through d 4 postestrus (d 0 = 1st of standing estrus). Sampling within a period consisted of five blood samples at 15-min intervals. All plasma samples were analyzed for concentrations of follicle stimulating hormone (FSH) and luteinizing hormone (LH). Neither mean LH nor peak concentration of LH during the preovulatory surge differed between genetic lines (P greater than .10). Concentrations of FSH increased faster (line X period, P less than .05) and tended (P less than .1) to peak at a higher concentration in RS (.88 ng/ml) than in C (.54 ng/ml) gilts (P less than .05) during the 12 h preceding the FSH and LH preovulatory peaks. The second FSH surge began approximately 24 h after the preovulatory FSH peak. Peak FSH concentrations were observed at 42 h in both lines (1.46 vs 1.74 ng/ml for C and RS gilts, respectively). The higher FSH concentration in RS gilts established during the preovulatory surge was maintained through the second FSH surge (P less than .01). No line differences were detected in plasma concentrations of estradiol-17 beta and progesterone.     

Follicular development and maturation in gilts selected for an index of high ovulation rate and high prenatal survival

Seventy-one 10th-generation gilts from White Line-1 (WL-1 = randomly selected control line) and White Line-2 (WL-2 = selected for an index of ovulation rate and prenatal survival rate) were used to compare the pattern of follicular development and atresia during the follicular phase of the estrous cycle. Gilts were treated with PGF(2alpha)on d 13 of the estrous cycle (d 0 of induced follicular development) to induce luteolysis and assigned randomly within line and sire for ovary recovery on d 0, 2, 3, 4, 5, and the day after estrus. Ovaries were evaluated for numbers of corpora albicantia and small (2 to 2.9 mm), medium (M1 = 3 to 4.9 mm; M2 = 5 to 6.9 mm), and large (>or=7 mm) follicles. The concentration of estradiol-17beta in follicular fluid was used to classify individual M2 and large follicles as estrogen-active (>or=100 ng of estradiol-17beta/mL) or inactive (<100 ng of estradiol-17beta/mL). The WL-2 gilts had a greater ovulation rate than WL-1 gilts at their pre-treatment estrus (20.4 vs. 13.8 corpora albicantia; P < 0.001). The small and M1 follicle populations decreased rapidly in both lines over time (P < 0.001). The M2 follicle population increased in both lines between d 0 to 4 and then decreased. Mean estradiol concentration of M2 follicles increased in both genetic lines over time (P < 0.02). All large follicles were estrogen-active in both lines; the number of large follicles increased with day (P < 0.001) and was similar in both lines. The number of estrogen-active M2 follicles was similar in both lines, increasing to d 3 and 4 and then decreasing (P < 0.01) thereafter. However, the total number of estrogen-active follicles (sum of estrogen-active M2 and large follicles) was greater in WL-2 than in WL-1 gilts (P < 0.04), increasing to the ovulatory potential by d 3 in WL-1 gilts, but continuing to increase through d 4 in WL-2 gilts. Selection of an additional six ovulatory follicles from the estrogen-active M2 follicle pool after d 5 was required in both lines to achieve the projected ovulation rate, and after estrus, the number of large follicles remained insufficient to attain the ovulatory potential of each line.     

Endocrine patterns in the postpartum beef cow associated with weaning: a comparison of the short and subsequent normal cycles

Levels of luteinizing hormone (LH), follicle stimulating hormone (FSH), progesterone and estradiol-17 beta were measured in five Polled Hereford cows. Blood samples were collected once or twice daily for 5 d, then every 6 h from 1 d before weaning (d 28 to 38 postpartum) until 10 d after the second postweaning estrus. Blood samples were again collected at daily intervals until the third postweaning estrus. All cows exhibited estrus within 4 d after weaning, a second estrus 8 to 10 d after the first and a third estrus 16 to 23 d after the second. All cows had peaks in serum concentrations of LH during the first (22.6 to 81.7 ng/ml) and second (4.4 to 149.0 ng/ml) postweaning estrus. Mean levels of LH in serum during the peak and the area under the LH curve during the first and second postweaning estrus did not differ. Serum levels of LH and FSH during the first 4 d of the short cycle did not differ from LH and FSH levels the first 4 d of the subsequent normal cycle. Levels of LH in serum for 4 d before the first LH surge, associated with the first postweaning estrus, did not differ from levels of LH found 4 d before the second Lh surge, associated with the second postweaning estrus. However, serum levels of FSH during the 4 d before the first ovulatory LH surge were lower (P = .05) than those observed during the 4-d period before the second ovulatory surge of LH. Progesterone levels were similar the first 6 d after the first and second estrous periods, but were lower after d 6 of the first (short) cycle than after d 6 of the second (normal) cycle. Estradiol peaks of 1.2 to 2.8 pg/ml were detected during the first postweaning estrus and 1.4 to 12.5 pg/ml during the second postweaning estrus, but due to the variability among cows mean levels of estradiol during first estrus did not differ from second estrus. These data agree with previous reports that postpartum anestrous cows had short cycles if they exhibit estrus in response to weaning. The early decline of progesterone after the first estrus apparently did not stem from lack of LH in serum, but the lower levels of FSH observed before this first ovulation may have been an important factor contributing to the reduced life span of the subsequent corpus luteum.     

Ovarian function and hormone secretion of gilts actively immunized against androstenedione

Fifty crossbred gilts immunized against bovine serum albumin (BSA) or androstenedione conjugated to BSA (AD) were used in three experiments. Primary immunizations were given at 120 d of age and boosters at 148 and 176 d. Gilts were moved to pens containing four to five animals each and exposed to boars beginning at 180 d of age. Immunization against AD did not affect age at puberty, percentage of gilts exhibiting estrus or duration of first estrous cycle. Over the three experiments, ovulation rate was 24% greater for AD-immunized gilts than for controls, and the number of corpora lutea was related positively (r = .82) to the log of the antibody titer. Number of ovulations decreased as interval from booster immunization to onset of estrus increased. During diestrus of the first estrous cycle, gilts immunized against AD had more follicles 5 to 10 mm in diameter, more total ovarian follicles and more total ovarian structures (corpora lutea plus follicles) than controls. Immunization against AD increased the frequency of LH pulses on d 16 but not on d 17 or 18, of the estrous cycle. However, average serum concentrations of LH, FSH and estradiol from 5 d before until 2 d after expected estrus were not different between treatment groups. Concentrations of AD in follicles 4 to 6 and greater than 7 mm in diameter were greater in gilts immunized against AD. Mean serum progesterone was higher on d 9 and 12 after mating in AD immunized gilts than in controls. Immunization against AD had no effect on maintenance of pregnancy or embryo survival rate.     

Relationship of fertility to ovarian follicular waves before breeding in dairy cows

Cows with two waves of follicular growth during the estrous cycle yield follicles that are older and larger at ovulation compared with cows having three waves. The objectives of the current research were 1) to compare fertility in cows with two or three follicular waves and 2) to examine associations between luteal function, follicular development, and fertility after breeding. Follicular waves were monitored by ultrasonography during the estrous cycle before insemination in 106 dairy cows. Fewer cows had three follicular waves before next estrus and ovulation than two waves (P < 0.01; 30% vs 68%, respectively), but pregnancy rate was higher (P = 0.058; 81 vs 63%, respectively). Cows with two waves had shorter estrous cycles (P < 0.01), with the ovulatory follicle being both larger (P < 0.05) and older (P < 0.01). In cows with three waves, luteal function was extended (P < 0.05) and the peak in plasma progesterone occurred later (P < 0.05) in the estrous cycle compared to two wave cows. Considering cows that became pregnant, luteal phase length was shorter (P < 0.05) during the estrous cycle preceding insemination than for nonpregnant cows. In conclusion, fertility was greater in lactating cows inseminated after ovulation of the third-wave follicle that had developed for fewer days of the estrous cycle as compared with two-wave cows.     

Follicle stimulating hormone pattern and luteal function in ewes receiving bovine follicular fluid during three stages of the estrous cycle

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 different patterns of feed restriction and insulin treatment during the luteal phase on reproductive, metabolic, and endocrine parameters in cyclic gilts

The objectives of the present study were 1) to study potential effects of previous nutritional treatment on developmental competence of early fertilized oocytes in vitro; 2) to study responses to insulin treatment during the period of feed restriction in the late luteal phase which has deleterious effects on subsequent fertility; and 3) to establish the metabolic and endocrine status of gilts during treatment and the subsequent periestrous period. Nineteen trios of littermate gilts were subjected to feed restriction during the first (RH) or second (HR) week of the estrous cycle. A second group of HR gilts received injections of long-acting insulin during their period of feed restriction (HR+I). Intensive sampling was performed in a subgroup of 23 animals on d 15 and 16 of the cycle for analyses of endocrine (gonadotropins and steroid hormones) and metabolic (insulin, IGF-I, leptin, total triiodothyronine [T3], and free T3) variables. Gilts were checked for estrus every 6 h, and time of ovulation was monitored by transcutaneous ultrasonography. Surgeries were performed 12 to 20 h after ovulation, and the early-fertilized oocytes recovered were cultured in vitro under standardized conditions. There was no treatment effect on the developmental competence of fertilized oocytes in vitro; however, ovulation rate was increased in HR+I gilts. No effect of treatment was observed on plasma leptin and IGF-I concentrations on d 15 and 16. However, HR+I gilts had higher (P < 0.05) postprandial insulin and lower (P < 0.05) postprandial total and free T3 on d 15. Plasma concentrations of LH, FSH, and progesterone on d 15 and 16 and plasma estradiol concentrations on d 16 were not affected by previous nutritional or insulin treatment. In the periestrous period, plasma concentrations of LH, FSH, and estradiol were higher (P < 0.05) in RH and HR+I, and the rise in plasma progesterone after the LH surge was lower (P < 0.05), than in HR gilts. No effect of treatment was observed on plasma concentrations of metabolic hormones, except on plasma leptin concentrations, which were higher (P < 0.05) at the time of the LH surge in RH gilts. These results suggest that feed restriction during the late luteal phase may have deleterious effects on ovarian function in the periestrous period, which may be counteracted by insulin.     

Changes in plasma follicle-stimulating hormone, luteinizing hormone, estrogen and progesterone during growth of ovulatory follicles in the pig

This experiment was conducted to determine the changes in secretion of LH, FSH, estrogen and progesterone during follicle maturation. Ovaries were recovered from 11 non-treated (control) gilts, three on day 13, four on day 16, and four on day 19 of the estrous cycle, and from four altrenogest-treated gilts on day 19. Altrenogest, a progesterone agonist, was fed at a dose of 20 mg once daily from days 13 to 18 to block spontaneous follicle maturation. Gilts were bled daily from day 12 until slaughter. For control gilts, the number of follicles/gilt 1-6 mm in diameter decreased (P less than .05) from 93.5 on day 13 to 21.5 on day 19, and the number of large (greater than 6 mm) follicles increased (P less than .05) from 5.3 to 13.2. Altrenogest treatment blocked loss of small follicles and growth of large follicles between days 13 and 19. Plasma progesterone decreased (P less than .001) between days 12 and 16 in both control and altrenogest-treated gilts. Plasma FSH decreased (P less than .05) between days 12 and 16 only in control gilts. Plasma LH was not significantly affected by day or altrenogest treatment. Plasma estrogen increased (P less than .05) between days 15 and 19 only in control gilts. These results indicate that 1) no increased LH secretion was detected in conjunction with emergence of ovulatory follicles, and 2) atresia of nonovulatory follicles was associated with decreased secretion of FSH. Both atresia and decreasing FSH secretion began before estrogen concentration increased in the systemic circulation.     

Lack of an association between plasma follicle-stimulating hormone concentrations and ovarian weight in prepubertal gilts

Selection for increased number of corpora lutea in gilts is associated with increased plasma FSH concentrations during pubertal development. In the current study, 270 gilts from a control (CO) line and a line selected for increased ovulation rate (OR) were unilaterally ovariectomized at 85 d of age, and this ovarian weight was related to FSH concentrations at 65, 75, and 85 d of age. Gilts were produced during two farrowing seasons, spring and fall, and the age at first estrus was monitored from 160 to 250 d. Plasma FSH was greater in OR than in CO gilts at 65 (P < 0.01) and 75 d (difference in spring greater than in fall, P < 0.01), but FSH at these ages was not correlated with ovarian weight at 85 d. At 85 d, FSH did not differ in gilts of these lines; however, FSH was negatively correlated (r = -0.27, P < 0.01) with ovarian weight. The proportion of gilts detected in estrus was less for spring-born CO gilts than for spring-born OR or for fall-born CO and OR gilts (78 vs. 92%, season x line, P < 0.02). The age at first estrus was similar in the two lines but was earlier (P < 0.01) for spring-born than for fall-born gilts (194 vs. 204 d). Concentrations of FSH at each of the ages examined were not correlated with the age at first estrus. These observations support the conclusion that selection for a greater number of corpora lutea produces a correlated increase in plasma FSH during early pubertal development. This increase in FSH most likely reflects differences in FSH synthesis and release and not differences in the stage of pubertal development.     

Endocrine changes and ultrasonography of ovaries in suckled beef cows during resumption of postpartum estrous cycles

Changes in follicular and luteal structures were assessed and concentrations of estradiol and progesterone were measured in 13 Hereford X Angus suckled beef cows during resumption of estrous cycles. Transrectal ultrasonography was used to monitor follicular size, ovulation, and formation and regression of the corpus luteum (CL). The interval from parturition to first postpartum ovulation (FO) was 82 +/- 4.7 d. Serum progesterone remained low before FO. One cow exhibited standing estrus, two cows showed other signs of estrus, and 10 displayed no signs of behavioral estrus preceding FO. All cows exhibited standing estrus before the second postpartum ovulation (SO). All cows had a short luteal phase after FO, with an average interval of 8.5 +/- .2 d between FO and SO. Concentrations of estradiol in serum during the 8 d preceding ovulation were similar before FO and SO. Maximal diameter of the preovulatory follicle was similar before FO and SO. However, the ovulatory follicle was larger in diameter at 2 d (P = .02) and 3 to 8 d (P less than .005) before FO than before SO. The time from detection until ovulation was less (P = .005) for the ovulatory follicle preceding SO than for the follicle associated with FO (8.5 vs 10.2 d, respectively, SE = .4). The second-largest follicle was larger (P less than .005) in diameter during the 8 d preceding the FO than before the SO. The difference in size between the ovulatory follicle and the second-largest follicle on the day before ovulation was greater (P less than .005) preceding SO than preceding FO (8.7 vs 6.6 mm, respectively, SE = .4).(ABSTRACT TRUNCATED AT 250 WORDS)     

Ovarian follicular growth, function and turnover in cattle: a review

Studies in cattle assessing changes in number and size of antral follicles, concentrations of estradiol, androgens and progesterone in serum and follicular fluid, and numbers of gonadotropin receptors per follicle during repetitive estrous cycles and postpartum anestrus are reviewed. The rate of growth of small follicles (1 to 3 mm) into larger follicles increases as the estrous cycle progresses from d 1 to 18 (d 0 = estrus). Size of the largest antral follicle present on the ovary also increases with advancement of the estrous cycle. Most large follicles (greater than 10 mm) persist on the ovarian surface for 5 d or more between d 3 and 13 of the bovine estrous cycle. After d 13, most of these large follicles are replaced more frequently by new growing follicles (turnover) with an increased probability for recruitment of the ovulatory follicle after d 18. More research is needed to determine the time required for growth of bovine follicles from small to large antral size and evoke recruitment of the ovulatory follicle. Factors that regulate selection of the ovulatory follicle are unknown but may involve increased frequency of LH pulses in blood, altered blood flow and(or) changes in intrafollicular steroids and proteins. Quantitative evaluation of ovarian follicles indicated occurrence of consistent short-term changes in fluid estradiol and numbers of luteinizing hormone receptors in cells of large follicles only during the pre-ovulatory period. Presumably, low concentrations of follicular estradiol found during most of the estrous cycle are not due to a lack of aromatizable precursor or follicle-stimulating hormone receptors. Follicular fluid concentrations of progesterone increase only near the time of ovulation. Little is known about changes in follicular growth, turnover and function during postpartum anestrus in cattle. However, preliminary data suggest that the steroidogenic capacity of large follicles changes markedly during the postpartum period.     

Effects of charcoal-extracted, bovine follicular fluid on gonadotropin concentrations, the onset of estrus and luteal function in heifers

A study was conducted to determine the effect of charcoal-extracted, bovine follicular fluid (CFF) on plasma follicle stimulating hormone (FSH) and luteinizing hormone (LH) concentrations, the interval from luteolysis to estrus, and subsequent luteal function in heifers. Fifteen Angus, Simmental and Hereford heifers were allotted by age, weight and breed to a control (C, n = 8) or a CFF (n = 7) group. Heifers received injections of saline or CFF (iv, 8 ml/injection) every 12 h from d 1 (d 0 estrus) through d 5 of the estrous cycle. On d 6, each heifer was injected (im) with 25 mg of prostaglandin F2 alpha (PGF2 alpha). Blood samples were collected every 12 h by venipuncture starting just before the first saline or CFF injection and continuing until estrus. Thereafter, blood samples were collected every other day during the subsequent estrous cycle and assayed for FSH, LH, estradiol-17 beta and progesterone by radioimmunoassay. Injections of CFF had no effect (P greater than .05) on circulating FSH or LH concentrations from d 1 to 5 relative to the C group; however, there was a transient rise (P less than .05) in FSH concentrations 24 h following cessation of CFF injections. This transient rise in FSH was not immediately followed by an increase in plasma estradiol-17 beta concentrations. Although CFF injections did not interfere with PGF2 alpha-induced luteolysis, the interval from PGF2 alpha injection to estrus was delayed (P less than .05) by 5 d in the CFF group compared with the C group.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pituitary-ovarian relationships during the estrous cycle and the influence of parity in an inbred strain of miniature swine

Pituitary-ovarian function was analyzed in a strain of miniature swine previously shown to produce a low ovulation rate resulting in the formation of only 8.6 corpora lutea (CL)/animal. Five multiparous (M) and four nulliparous (N) miniature pigs with a mean inbreeding coefficient of .39 were monitored for estrous behavior through four consecutive estrous cycles. Daily blood samples were collected from 5 d before to 5 d after the onset of the second, third and fourth estrus and at 48-h intervals during the remainder of the second and third estrous cycle. Laparoscopy was used to examine the ovaries 1 and 5 d after onset of the third estrus and 2 d after the beginning of the fourth estrus. For the entire group, temporal fluctuations among serum estradiol-17 beta, luteinizing hormone (LH) and progesterone concentrations and sexual behavior were similar to previously published data in standard swine breeds. Although the mean lengths of the estrous cycle were not different (P greater than .05) between parity subgroups (M, 23 +/- 1.3 vs N, 22 +/- .7 d), multiparous pigs were in estrus longer (P less than .05) than nulliparous females (M, 3.7 +/- .2 vs N, 2.2 +/- .4 d). Parity subgroups were similar with respect to the mean number of follicles forming CL (M, 8.8 +/- .7 vs N, 9.2 +/- .2). Although an average of 6.2 +/- 2.1 CL had formed by 24-h after onset of estrus in the nulliparous subgroup, no CL were detected in the multiparous subgroup at this time.(ABSTRACT TRUNCATED AT 250 WORDS)     

Use of a small dose of estradiol benzoate during diestrus to synchronize development of the ovulatory follicle in cattle

We tested the hypothesis that a small dose of estradiol benzoate (EB) at the midstage of the estrous cycle in cattle would synchronize the subsequent pattern of ovarian follicular development, estrus, and ovulation. Nonlactating Friesian cows received either 1 mg of EB i.m. on d 13 of the estrous cycle (T; n = 12; estrus = d0) or served as untreated controls (C; n = 12). Their ovaries were examined daily with transrectal ultrasonography from d 7, and blood samples were collected 0, 2, 4, 8, 24, and 48 h after treatment on d 13. Plasma concentrations of estradiol-17beta were elevated to 12 pg/mL during the initial 24 h following treatment, compared with a baseline of 1 pg/mL in untreated controls (P < .001). Progesterone concentrations in cows of the T group declined between 24 and 48 h after treatment (-3.2 +/- .5 ng/mL) compared with little change in concentrations of progesterone in cows of the C group at this time (P < .01). This difference was coincident with an earlier time to regression of the corpus luteum in cows of the T group. Disregarding treatment groups, the second dominant follicle of the estrous cycle (DF2) emerged on d 10.6 +/- .3 and was 9.4 +/- .4 mm in diameter on d 13. Further growth of the DF2 was halted by EB treatment on d 13. Cessation of growth occurred irrespective of whether the DF2 was in the early or late growth phase, and a new follicular wave emerged 4.5 +/- .2 d later. The dominant follicle from this wave (DF3) ovulated 5 d after emergence in most cases. During the estrous cycle of every cow in the T group, there were three waves of follicular development (3-wave), whereas the ratio of 2:3 waves of follicular development in cows of the C group was 1:3. Consequently, the interval from emergence to ovulation of the ovulatory dominant follicle in cows of the C group ranged from 3 to 11 d. The dynamics of ovarian follicular wave development during the estrous cycle can be strategically manipulated by treating with a small dose of EB to synchronize proestrous development of the ovulatory follicle.     

Changes in hormonal profiles during the estrous cycle in old lactating beef cows

Patterns of concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH), progesterone (P4) and estradiol-17 beta (E2) during an estrous cycle were compared between 15 lactating beef cows 5 to 7 years of age (young) and 15 cows greater than or equal to 12 years of age (old). Length of estrous cycle did not differ between young and old cows (P = .06). No differences due to age were found for LH. Patterns of concentrations of P4 during the first 15 days of the cycle, of FSH during days 6 through 12 and of E2 during the follicular phase differed with age (P less than .05). An earlier (P less than .025) midcycle elevation of FSH was associated with an earlier rise and greater concentration of E2 (P less than .05) during the follicular phase in old than in young cows. Differences in FSH and P4, although subtle, were consistent with an earlier or more advanced follicular development in old cows, leading to greater secretion of E2 from the preovulatory follicle.     

Characterization of ovine follicles destined to form subfunctional corpora lutea

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.     

Nutritionally induced anovulation in beef heifers: ovarian and endocrine function preceding cessation of ovulation.

Angus x Hereford heifers were used to determine endocrine and ovarian function preceding nutritionally induced anovulation. Six heifers were fed to maintain body condition score (M), and 12 heifers were fed a restricted diet (R) until they became anovulatory. Starting on d 13 of an estrous cycle, heifers were given PGF2alpha every 16 d thereafter to synchronize and maintain 16 d estrous cycles. Ovarian structures of M and R heifers were monitored by ultrasonography daily from d 8 to ovulation (d 1 of the subsequent cycle) until R heifers became anovulatory. Concentrations of LH and FSH were quantified in serum samples collected every 10 min for 8 h on d 2 and 15 (48 h after PGF2alpha), and estradiol and IGF-I were quantified in daily plasma samples from d 8 to 16 during the last ovulatory cycle (Cycle -2) and the subsequent anovulatory cycle (Cycle -1). During the last two cycles before anovulation, M heifers had 50% larger (P < .0001) ovulatory follicles than R heifers and 61% greater (P < .0001) growth rate of the ovulatory follicles. There was a treatment x cycle x day effect (P < .001) for concentrations of estradiol. The preovulatory increase in estradiol occurred in the R and M heifers during Cycle -2 but only in M heifers during Cycle -1. A treatment x cycle x day effect (P < .05) influenced LH concentrations. During Cycle -2, LH concentrations were similar for M and R heifers, but during Cycle -1, M heifers had greater LH concentrations than did R heifers. Concentrations of FSH were greater (P < .05) in R than M heifers after induced luteolysis when R heifers failed to ovulate. There was a treatment x cycle interaction (P < .05) for IGF-I concentrations, and M heifers had 4.7- and 8.6-fold greater IGF-I concentrations than did R heifers during Cycle -2 and -1, respectively. We conclude that growth rate and diameter of the ovulatory follicle, and concentrations of LH, estradiol, and IGF-I are reduced before the onset of nutritionally induced anovulation in beef heifers.     

Dynamics of the Equine Preovulatory Follicle and Periovulatory Hormones: What's New?

Recent studies (2005–2008) on the interrelationships among the preovulatory follicle and periovulatory circulating hormones are reviewed. Close temporal and mechanistic relationships occur between estradiol/inhibin and follicle-stimulating hormone (FSH), between estradiol and luteinizing hormone (LH), and between progesterone and LH. Estradiol from the dominant follicle forms a surge that reaches a peak 2 days before ovulation. Estradiol, as well as inhibin, has a negative effect on FSH, and estradiol has a negative effect on LH. When estradiol decreases, the negative effect diminishes and accounts for the beginning of an FSH increase and a transition from a slow to rapid increase in LH on the day of the estradiol peak. The decrease in estradiol and the reduction or cessation in the growth of the preovulatory follicle beginning 2 days before ovulation are attributable to the development of a reciprocal negative effect of LH on follicle estradiol production when LH reaches a critical concentration. The LH decrease after the peak of the LH surge on the day after ovulation is related to a negative effect of a postovulatory increase in progesterone. Measurable repeatability within mares between consecutive estrous cycles occurs during the preovulatory period in diameter of the ovulatory follicle and concentrations of LH and FSH. Hormone-laden follicular fluid passes into the peritoneal cavity at ovulation and transiently alters the circulating concentrations of LH and FSH. Double ovulations are associated with greater estradiol concentrations and reduced concentrations of FSH.     

Ovarian follicular dynamics and hormones throughout the estrous cycle in Thai native (Bos indicus) heifers

Relatively few studies have been reported regarding the reproductive physiology of female Thai native cattle. Therefore, the objective of the present study was to evaluate the follicular dynamics and concentrations of follicle stimulating hormone (FSH), estradiol (E2) and progesterone (P4) during the estrous cycle in Thai native heifers (TNH) and to compare obtained results with those of European and Indian cattle breeds previously reported. For the detection of estrus, ovaries of all 20 heifers were examined twice daily (12 h intervals) by ultrasonography for three consecutive estrous cycles. From data of 60 estrous cycles (n = 60 estrous cycles from 20 heifers), it was found that 14 (70%) and 6 heifers (30%) had two (42 estrous cycles collected from 14 heifers) and three follicular waves (18 estrous cycles collected from 6 heifers), respectively. The days when estrus was detected, interovulatory intervals, life‐spans of corpus lutea (CL), and days for growing and regression of CLs were shorter in the two follicular waves than those in the three follicular waves (P < 0.05). In both two and thre follicular waves, larger maximum diameters and higher growth rates of the dominant follicle (DF) in an ovulatory wave were observed than those of the preceding waves without ovulation (P < 0.05). There was a progressive increase in follicular size and FSH and E2 production during follicular growth in each follicular wave. In addition, the FSH and E2 peak concentrations during the ovulatory wave were higher than those of the anovulation waves (P < 0.05). Moreover, although the ovarian follicular dynamic patterns in Thai native heifers were similar to those previously reported for European and Indian cattle breeds, the diameter of the largest preovulatory follicle (OF), subordinate follicles (SF) and CLs were smaller than those in European and Indian cattle breeds. In conclusion, when compared with European and some breeds of Indian cattle, the length of interovulatory intervals was shorter, and the sizes of dominant SF and CLs were smaller in Thai native heifers.