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Biomedical subjects

W W Thatcher

Publications and source records attributed to W W Thatcher.

At least 127 records · Page 7Linked to original sources
PubMed1993

Regulation of dominant follicle turnover during the oestrous cycle in cows.

The effect of progestin and luteinizing hormone (LH) pulse frequency on dynamics of dominant follicle growth during the first follicular wave after oestrus was examined in non-lactating Holstein cows by ultrasonography. On day 8 of the cycle, cows (n = 8) received a luteolytic dose of prostaglandin F2 alpha (PGF2 alpha; 25 mg) and an ear implant of Norgestomet (6 mg). On day 18, cows were assigned to a crossover design in which the implants were retained (T1) or replaced with a new implant (T2). All implants were removed on day 23. After oestrus, cows underwent a normal intervening oestrus cycle. On day 8 of the third cycle, T1 and T2 were reversed among cows. Ultrasonography and blood sampling were performed on alternate days throughout the experiment. On days 10 and 19 of the third cycle, blood was sampled every 15 min for 8 h in concert with an additional control group (n = 3) sampled on day 10 of the cycle. Progesterone concentration on day 8 before PGF2 alpha was 6.5 +/- 0.5 ng ml-1. Dominance of the first wave dominant follicle was extended beyond day 18 in 15 of 16 cows for T1 and T2 periods. The original dominant follicle ovulated in five of eight T1 and none of eight T2 periods (P < 0.01). New dominant follicles were detected on day 24 +/- 1 in T1 (n = 3) and on day 20.6 +/- 1 in T2 (n = 8; P < 0.01) cows.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Effects of induction of low plasma progesterone concentrations with a progesterone-releasing intravaginal device on follicular turnover and fertility in cattle.

The effects of concentration of progesterone in plasma on development and fertility of the first wave dominant follicle were studied in cattle. To identify a source of exogenous progesterone that would permit extension of the first wave dominant follicle, nonlactating Holstein cows (n = 6) received on day 8 of two successive oestrous cycles an injection of PGF2 alpha (25 mg) and a new (1.9 g of progesterone (Period 1)) or used (approximately 1.2 g of progesterone (Period 2)) CIDR-B device that was removed on day 17. Control cows (n = 6) received a new CIDR-B device on day 8 that was removed on day 17 and a PGF2 alpha injection (25 mg) on day 17. Ultrasonography and collection of blood samples were performed on alternate days throughout the experiment. Plasma concentrations of progesterone and oestradiol were different between treatments (P < 0.0001 and P < 0.05, respectively). The dominant follicle was maintained until day 17 and ovulated upon removal of the intravaginal device in 1 of 6, 6 of 6 and 0 of 6 in new CIDR-B, used CIDR-B and control groups, respectively (P < 0.01). The preovulatory dominant follicles were 14.2 +/- 1.6 mm, 20 +/- 1.3 mm and 10 +/- 1.3 mm, respectively (P < 0.001) on day 17. There were fewer 5-9 mm follicles in cows having a persistent dominant follicle (P < 0.01). The interval to onset of oestrus was negatively correlated with size of the dominant follicle on day 17 (P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Intravaginal↗
PubMed1993

Effects of recombinant bovine somatotropin (sometribove) on ovarian function in lactating and nonlactating dairy cows.

Metabolic and ovarian responses of lactating and nonlactating cows to recombinant bST (sometribove) were measured. Eighteen lactating cows (60 to 100 d postpartum) and 6 nonlactating cows (> 400 d postpartum) were injected daily with bST or saline during one of two periods. Concentrations of hormones and metabolites were measured in plasma, and ultrasonography was used to quantify ovarian follicular growth. Concentrations of glucose, insulin, IGF-I, progesterone, and estradiol in plasma were greater in nonlactating cows than in lactating cows. Lactating cows had fewer class 2 (6- to 9-mm) and class 3 (10- to 15-mm) follicles and more class 4 (> 15-mm) follicles than nonlactating cows. Bovine somatotropin increased the numbers of follicles in lactating cows so that the numbers of class 2 and of class 3 follicles were equivalent to those for non-lactating cows. Sizes of the largest follicles were similar for bST-and saline-treated cows. The second largest ovarian follicles, however, were larger in bST-treated cows. Ovarian follicular dynamics were altered by bST and lactation. Bovine somatotropin increased the numbers of follicles (6 to 15 mm) in lactating cows and size of second largest ovarian follicles in both lactating and nonlactating cows. Lactating cows developed dominant follicles that were larger and less estrogenic than those of nonlactating cows.

Animals↗
PubMed1993

Ovarian follicular populations in lactating dairy cows treated with recombinant bovine somatotropin (sometribove) or saline and fed diets differing in fat content and energy.

Interactions of dietary energy and fat with recombinant bST (sometribove) injections were tested for their effects on ovarian function. Lactating dairy cows were fed one of three diets differing in energy concentration (NEL) and percentage of DM of calcium salts of long-chain fatty acids: diet 1, 1.68 Mcal/kg and 0%; diet 2, 1.68 Mcal/kg and 2.2%; and diet 3, 1.78 Mcal/kg and 2.2%. Cows were injected daily with bST or saline during one of two 19-d interestrous periods (crossover design) in which ovarian follicles were measured by ultrasonography. The bST-treated cows produced more FCM and were in lower energy balance than saline-treated cows. Before d 12 (first follicular wave, estrus = d 0), bST-treated cows had more ovarian follicles in classes 1 (3 to 5 mm; cows on diet 3) or 2 (6 to 9 mm; cows on diets 1 and 2) than saline-treated cows. After d 12 (preovulatory follicular wave), numbers of follicles in different size classes were similar for bST-treated and saline-treated cows, but cows fed diet 2 had larger preovulatory follicles. Lower dietary energy and bST treatment were both associated with larger subordinate follicles. Ovarian follicles less than 10 mm were stimulated by bST, and calcium salts of long-chain fatty acids increased diameters of preovulatory follicles.

Animals↗
PubMed1992

Ovariectomy by colpotomy in cows.

For the purpose of collecting active ovarian structures for cell culture, unilateral ovariectomy (n = 34 ovaries) was performed per vagina on 17 dairy cows having normal estrous cycles, bilateral ovariectomy was performed on 9 (n = 18 ovaries) dairy cows, and corpora lutea (n = 13) were removed from 11 beef cows having normal estrous cycles. None of the cows was clinically ill after the operation. Nine of 37 cows developed adhesions of both uterine horns and the body of the uterus. Three instruments were used to perform colpotomy. The described surgical technique for removal of the ovaries or corpora lutea is practical and inexpensive, and has low morbidity associated with it.

Animals↗
PubMed1992

Inhibition of lymphocyte proliferation by bovine trophoblast protein-1 (type I trophoblast interferon) and bovine interferon-alpha I1.

Bovine trophoblast protein-1 (bTP-1) is a Type I interferon secreted by the bovine trophoblast from about Day 15 of pregnancy. It is not known whether bTP-1 has functional properties in common with other interferons. The aim of the present study was to determine whether bTP-1 inhibits proliferation of lymphocytes induced by mitogens, mixed lymphocyte cultures (MLC) and interleukin-2 (IL-2) and, if so, whether this activity is similar to that of a related interferon, bovine interferon-alpha I1 (bIFN-alpha I1). Stimulation of lymphocyte proliferation caused by phytohemagglutinin (PHA), concanavalin A (Con A) and pokeweed mitogen (PWM) was inhibited by bTP-1 and bIFN-alpha I1 without any reduction in cell viability. Maximum or near-maximum inhibition (less than 50%) was achieved at concentrations of 0.5-5.0 nM of bTP-1 and bIFN-alpha I1. Cells stimulated with PWM were less inhibited than cells stimulated with PHA and Con A. Both bTP-1 and bIFN-alpha I1 inhibited MLC to a greater degree than lectin-stimulated cells (maximum inhibition was 78% or greater). Also, bTP-1 and bIFN-alpha I1 slightly inhibited incorporation of [3H]thymidine ([3H]TdR) induced by the combination of phorbol ester, 12-O-tetradecanoylphorbol 13-acetate (TPA), and calcium ionophore A23187. Finally, bTP-1 and bIFN-alpha I1 had bimodal effects on incorporation of [3H]TdR by IL-2-induced lymphocytes. Incorporation of [3H]TdR was increased at 0.005 nM and 0.05 nM concentrations while higher concentrations caused a slight decrease in [3H]TdR incorporation. Results confirm that bTP-1 inhibits lymphocyte proliferation in a manner similar to that caused by the leukocyte-derived interferon, bIFN-alpha I1. Incomplete inhibition of mitogen-induced proliferation and differences in degree of inhibition between various stimulators suggest that bTP-1 and bIFN-alpha I1 preferentially inhibit certain lymphocyte subpopulations. Local inhibition of lymphocyte proliferation caused by bTP-1 may help protect the allogeneic conceptus from immune responses to fetal antigens or regulate the release of cytokines from endometrial lymphocytes.

Animals↗
PubMed1992

Follicular dynamics, plasma metabolites, hormones and insulin-like growth factor I (IGF-I) in lactating cows with positive or negative energy balance during the preovulatory period.

The effect of dietary energy balance (EB) on growth of ovarian follicles was tested. Cows (n = 9) were fed a high energy diet (HE diet; positive EB; n = 4) or switched to a low energy diet (LE diet; negative EB; n = 5) during the preovulatory period. Non-esterified fatty acids (NEFA) were greater in cows fed the LE diet. Concentrations of luteinizing hormone (LH) were similar in HE and LE cows. However, the growth of preovulatory follicles in cows fed the LE diet was 50% that of cows fed the HE diet. Insulin-like growth factor-I (IGF-I) in plasma was less in LE-fed cows compared with HE-fed cows, and plasma IGF-I was positively correlated to estrogen: progesterone ratio in follicular fluid of dominant follicles. In summary, slower follicular growth in cows fed an LE diet occurred despite normal plasma LH and coincided with reduced IGF-I and elevated NEFA in plasma.

Animals↗
PubMed1992

Endocrine and ovarian responses associated with the first-wave dominant follicle in cattle.

To examine endocrine and biochemical differences between dominant and subordinate follicles and how the dominant follicle affects the hypothalamic-pituitary-ovarian axis in Holstein cows, the ovary bearing the dominant follicle was unilaterally removed on Day 5 (n = 8), 8 (n = 8), or 12 (n = 8) of synchronized estrous cycles. Follicular development was followed daily by ultrasonography from the day of detected estrus (Day 0) until 5 days after ovariectomy. Aromatase activity and steroid concentrations in first-wave dominant and subordinate follicles were measured. Intact dominant and subordinate follicles were cultured in 4 ml Minimum Essential Medium supplemented with 100 microCi 3H-leucine to evaluate de novo protein synthesis. Five days after unilateral ovariectomy, cows were resynchronized and the experiment was repeated. Follicular growth was characterized by the development of single large dominant follicles, which was associated with suppression of other follicles. Concentrations of estradiol-17 beta (E2) in follicular fluid and aromatase activity of follicular walls were higher in dominant follicles (438.9 +/- 45.5 ng/ml; 875.4 +/- 68.2 pg E2/follicle) compared to subordinate follicles (40.6 +/- 69.4 ng/ml; 99.4 +/- 104.2 pg E2/follicle). Aromatase activity in first-wave dominant follicles was higher at Days 5 (1147.1 +/- 118.1 pg E2/follicle) and 8 (1028.2 +/- 118.1 pg E2/follicle) compared to Day 12 (450.7 +/- 118.1 pg E2/follicle). Concentrations of E2 and androstenedione in first-wave dominant follicles were higher at Day 5 (983.2 +/- 78.2 and 89.5 +/- 15.7 ng/ml) compared to Days 8 (225.1 +/- 78.6 and 5.9 +/- 14.8 ng/ml) and 12 (108.5 +/- 78.6 and 13.0 +/- 14.8 ng/ml). Concentrations of progesterone in subordinate follicles increased linearly between Days 5 and 12 of the estrous cycle. Plasma concentrations of FSH increased from 17.9 +/- 1.4 to 32.5 +/- 1.4 ng/ml between 0 and 32 h following unilateral removal of the ovary with the first-wave dominant follicle. Increases in plasma FSH were associated with increased numbers of class 1 (3-4 mm) follicles in cows that were ovariectomized at Day 5 or 8 of the cycle. Unilateral ovariectomy had no effects on plasma concentrations of LH when a CL was present on the remaining ovary. First-wave dominant follicles incorporated more 3H-leucine into macromolecules and secreted high (90,000-120,000) and low (20,000-23,000) molecular weight proteins that were not as evident for subordinate follicles at Days 8 and 12.(ABSTRACT TRUNCATED AT 400 WORDS)

Androstenedione↗
PubMed1992

Possible mechanisms for reduction of circulating concentrations of progesterone by interferon-alpha in cows: effects on hyperthermia, luteal cells, metabolism of progesterone and secretion of LH.

Experiments were performed to determine the mechanism by which recombinant bovine interferon-alpha I1 (rbIFN-alpha) causes an acute reduction in plasma concentrations of progesterone. In experiment 1, administration of a prostaglandin synthesis inhibitor blocked rbIFN-alpha-induced hyperthermia but did not prevent the decline in plasma concentrations of progesterone. The decline in progesterone concentrations caused by rbIFN-alpha was, therefore, not a direct consequence of the associated hyperthermia or of pathways mediated through prostaglandin synthesis. It is also unlikely that rbIFN-alpha acts to increase the clearance of progesterone since injection of rbIFN-alpha did not decrease plasma concentrations of progesterone in ovariectomized cows given an intravaginal implant of progesterone (experiment 2). In experiment 3, rbIFN-alpha did not affect basal and LH-induced release of progesterone from cultured luteal slices, indicating that rbIFN-alpha is unlikely to affect luteal function directly. Injection of rbIFN-alpha did, however, cause a decrease in plasma concentrations of LH in ovariectomized cows (experiment 4) that coincided temporally with the decrease in progesterone concentrations seen in cows having a functional corpus luteum. The present results strongly suggest that rbIFN-alpha acts to reduce secretion of progesterone by interfering with pituitary support for luteal synthesis of progesterone. The finding that rbIFN-alpha can inhibit LH secretion implies that interferon-alpha molecules should be considered among the cytokines that can regulate hypothalamic or pituitary function.

Animals↗
PubMed1992

Factors that affect ovarian follicular dynamics in cattle.

Studies of ovarian follicular dynamics in cattle may lead to methods for improving fertility, for synchronizing estrus with more precision, and for enhancing superovulatory responses. Within an estrous cycle, two or three large (> 10 mm) follicles develop during consecutive waves of follicular growth. The last wave provides the ovulatory follicle, whereas preceding wave(s) provide follicles that undergo atresia. The life span of large follicles seems to depend on the pulsatile secretion of LH; decreased frequency of LH pulses results in atresia of large follicles. Aromatase activity in the walls of the largest follicles is greatest during the first 8 d of the estrous cycle and decreases by d 12. Steroidogenesis of the largest and second-largest ovarian follicles differs on d 5, 8, and 12 of the estrous cycle. Follicular dynamics are altered by negative energy balance and lactation. The number of large follicles and concentration of estradiol during the preovulatory period differs between postpartum lactating and nonlactating cows. Dietary fats stimulate follicular growth when they are fed to increase energy balance. Administration of bovine somatotropin decreases energy balance and has a differential effect on ovarian follicular responses; growth of the largest follicle does not change, but growth of the second-largest follicle is stimulated by somatotropin. Studies of follicular dynamics in lactating cows demonstrate changes in ovarian function associated with energy balance that may be related to inefficient reproductive performance of cows producing high yields of milk.

Animals↗
PubMed1992

The effect of bovine interferon-alpha I1 on pregnancy rate in heifers.

Bovine interferon-alpha I1 (bIFN-alpha) may be useful for enhancing fertility in sheep and cattle because it has extensive sequence homology with ovine and bovine trophoblast protein-1 and, like those proteins, extends corpus luteum lifespan. To test the effectiveness of bIFN-alpha to enhance fertility, several experiments were performed in which inseminated heifers were given i.m. injections of bIFN-alpha approximately at the time of embryo-mediated signals that result in maintenance of the corpus luteum. In Exp. 1, heifers given 20 mg of bIFN-alpha daily from d 14 to 17 tended (P less than .07) to have lower pregnancy rates at d 110 to 112 of gestation (36/75; 48% vs 43/72; 60%). Similar results were obtained in Exp. 2 when heifers received a single injection of 40 mg of bIFN-alpha or placebo at d 13 after estrus; pregnancy rates at d 42 were 39/104 (38%) for bIFN-alpha and 47/98 (48%) for placebo. In Exp. 3, heifers were given gradually increasing doses of bIFN-alpha or placebo from d 11 to 19, because such a regimen had been shown to reduce the number of heifers experiencing hyperthermia after bIFN-alpha injection. Pregnancy rates were 42/95 (44%) for bIFN-alpha and 62/111 (56%) for placebo. Across all three experiments, pregnancy rates were lower (P less than .01) for heifers treated with bIFN-alpha (117/274; 43%) than for heifers treated with placebo (152/281; 54%). In conclusion, these results demonstrate that, under the administration systems used, bIFN-alpha does not increase pregnancy rate, but rather tends to reduce it.

Animals↗
PubMed1992

Factors affecting days open, gestation length, and calving interval in Florida dairy cattle.

Effects of several factors on reproductive performance were evaluated. Mean performance and number of observations were for days from parturition to first service, 93 and 7730; days from first to successful service, 35 and 11,751; days open, 123 and 8571; gestation length, 280 and 13,612; and calving interval, 400 and 8524. Data covered 52 yr during which no detectable trends in calving interval occurred; other variables changed slightly. Jerseys had 8 fewer d from parturition to first service, 16 fewer d from first service to conception, 8 fewer d open, and 8-d shorter calving intervals than did Guernseys and Holsteins, which did not differ. Cows freshening in warm rather than cool weather suffered by 7, 7, 12, and 13 d for these variables. Repeatabilities ranged from .05 to .12; heritabilities were .05 and .06. Nonmaternal estimate of heritability of gestation length was .22. Phenotypic and genetic correlations between days from parturition to first service and calving interval were .48 and .87; for days open and calving interval, they were .97 and .96. Although days from first to successful service were essentially uncorrelated with days open and calving interval phenotypically (.05), genetic correlations were greater than 1.0 and estimated as unity. Results show no discrepancy between estimates for measures of reproductive performance in a subtropical environment and numerous studies in temperate areas. Large studies from subtropical areas are sparse; essentially none concerns long-term trends.

Animals↗
PubMed1992

Postpartum performance of dairy heifers freshening at young ages.

Records from Florida Agricultural Experiment Station dairy herd for 1144 heifers freshening from 1959 to 1979 were studied to evaluate effects of age and problems at parturition on subsequent yield and reproduction. Statistical analysis was by method of ordinary least squares analysis of variance; five measures of reproduction, survival to second lactation, and 15 measures of yield were studied. Mean first parturition age was 25.8 mo with 40% of individuals less than or equal to 23 mo; survival to second parturition was 67%. No effects of age at first parturition were detected on survival, postpartum reproductive performance, or milk composition other than lactose-mineral, chloride, and acidity percentages; effects on yield were similar to previous reports. Stillbirth did not affect subsequent reproductive performance but was associated with decreased milk yield: 181 kg or 5.2% of overall mean. Milk yield was depressed by 239 kg for retained fetal membrane, 173 kg for dystocia, and 98 kg for metritis; milk composition essentially was unaltered. Heritability of postpartum days to first estrus was .14; estimates were 0 for days to first service, days open, and calving interval. Additional research is needed on interrelationships of gestation length with subsequent yield and reproduction and in alleviating detrimental effects of problems at parturition.

Age Factors↗
PubMed1991

Follicular dynamics and superovulatory response in Holstein cows treated with FSH-P in different endocrine states.

The effect of follicular and/or endocrine environments on superovulatory response was tested. Eighteen nonlactating Holstein cows were superovulated with 32 mg FSH-P given in decreasing doses at 12-h intervals plus two injections of prostaglandin F2-alpha (25 mg each) on the third day of treatment. Cows were assigned randomly to treatments: T1, superovulatory treatment initiated on estrous cycle Day 10.5; T2, CIDR (intravaginal device containing 1.9 g of progesterone) inserted from Days 3 to 9 and superovulation initiated on Day 6.5; T3, identical to T2 but Buserelin (GnRH agonist) was injected (8 microg, i.m.) on Day 3 at the time of CIDR insertion. Embryos were recovered on Day 7 after the superovulatory estrus. Cows were examined daily by ultrasonography and blood was collected for progesterone and estradiol determinations. Mean diameter of the dominant follicle (frequency of first-wave dominant follicle) at the beginning of FSH injections was 13.7 mm (4/6), 11.2 mm (6/6) and 8.7 mm (6/6) (P<0.01) for T1, T2 and T3, respectively. Following initiation of superovulation, follicles moved into larger follicle classes (Class I, <3 mm; Class II, 3 to 4 mm; Class III, 5 to 9 mm; Class IV >9 mm) earliest in T1 (P<0.01). Cumulative follicular diameter and plasma concentrations of estradiol at Day 4 of superovulation were higher (P<0.01) in T1 (200 mm, 82 pg/ml) compared with T2 (123 mm, 24 pg/ml) and T3 (130 mm, 18 pg/ml). Proportion of cows in estrus prior to 12 h vs 12 to 24 h differed (P<0.05) between groups (T1: 5 vs 1; T2: 2 vs 4; T3: 1 vs 5). Mean number of follicles on the last day of superovulation treatment, number of CL and number of embryos plus unfertilized ova recovered were 17.5, 12.2 and 13.3; 13.8, 10 and 8.2 (P<0.1) and 8.7, 4.5 and 2.3 (P<0.05) for T1, T2 and T3, respectively. The developmental stage of the dominant follicle was associated with not only the number of ovulations, but also the size and periestrous concentrations of plasma estradiol associated with the recruited follicles.

Journal Article↗
PubMed1991

Effects of postinsemination progesterone supplementation on fertility and subsequent estrous responses of dairy heifers.

The objective of Experiment I, replicated twice, was to evaluate whether fertility of estrus-synchronized dairy heifers could be improved by postinsemination progesterone supplementation. Estrous cycles were synchronized using two injections of prostaglandin (PG) F(2alpha) adiministered 11 days apart. Heifers displaying estrus were inseminated and assigned to control (n = 155) and treated (n = 159) groups. Treatment consisted of intravaginal insertion of controlled internal drug release (CIDR) devices for Days 7 to 13 (Day 0 = day of estrus). The conception rate for CIDR-treated heifers (57.9%) did not differ significantly from that of the controls (53.6%). The return-to-estrus rate and pattern of return estruses were not affected by treatment, but indicated that early embryonic mortality may have occurred in some of the heifers diagnosed nonpregnant. The objective of Experiment II was to evaluate if used CIDR devices were effective in resynchronizing returns to estrus in previously synchronized inseminated but nonpregnant and noninseminated heifers. Estrous cycles of dairy heifers of breeding age were synchronized with PGF(2alpha). Heifers displaying estrus were assigned to be inseminated (n = 117) or not inseminated (n = 35). All heifers were treated with 9-day used CIDR devices for Days 17 to 22 after synchronized estrus in order to resynchronize returns to estrus. Of the inseminated but nonpregnant heifers (n = 41), 78.1% were detected in estrus after CIDR removal (versus 94.3% of noninseminated heifers [n = 35]; P < 0.05) and 61.0% of the estruses occurred within 4 days of CIDR removal (versus 91.4% of noninseminated; P < 0.05). Estruses of synchronized inseminated nonpregnant heifers occurred over a longer period compared with those of noninseminated heifers (P < 0.025). The results indicate that response to the resynchronization protocol was altered by the outcome (early embryo death or failed fertilization) of the previous unsuccessful insemination, and support the hypothesis that delayed returns to estrus can be attributable to a pregnancy which was initiated but failed to establish itself. Such factors should be considered when evaluating responses of cattle to treatments designed to enhance fertility.

Journal Article↗
PubMed1991

Dynamics of ovarian follicular development in cattle during the estrous cycle, early pregnancy and in response to PMSG.

Ovarian follicular dynamics of cattle were examined during the estrous cycle, early pregnancy and in response to PMSG. Number and size of follicles were monitored by ultrasonographic examinations. During the estrous cycle, distinct periods of follicular dominance (measured by the increase in difference in size between the largest and second largest follicle) occurred in both the luteal (Days 6-8) and proestrus (18-22) phases of the estrous cycle (two follicular waves). Associated with the well timed development of the first dominant follicle was a change in distribution of follicle numbers in small (less than 5 mm; increased on Days 2-4), medium (6-8 mm; increased on Days 3-5) and large (greater than or equal to 9 mm; increased on Days 6-9) follicular size classes. Follicular development was greater on the ovary bearing the CL for the period that the CL was present. The dominant follicle formed during the first follicular wave was capable of ovulating (6 of 8 heifers) following an injection of a synthetic analogue of prostaglandin F-2 alpha on Day 9 of the estrous cycle. During early pregnancy (Days 6-34), follicular development (size of largest follicle, number of follicles and total accumulated size of all follicles) on the ovary bearing the CL was suppressed between Days 24 and 34 of pregnancy. This was a local effect in that follicular development was sustained on the contralateral ovary. Therefore, the CL or conceptus may be regulating follicular development in a manner to help prevent luteolysis. Associated with the injection of PMSG was an initial increase in the number of small follicles followed by their recruitment into medium and large size classes leading to ovulation. Number of follicles greater than 5 mm on the Day of estrus was related (r = .97) to the number of subsequent embryos and oocytes collected. Ultrasonography is a valuable technique to monitor ovarian follicular dynamics in cattle, and can thereby be used to infer changes in physiological and endocrine states.

Animals↗
PubMed1991

Dynamics of ovarian follicular development in cattle following hysterectomy and during early pregnancy.

Three experiments were conducted to evaluate ovarian follicular dynamics and functional activity during pregnancy in cattle. In 11 pregnant Charolais cows of Experiment I, size of largest follicle, number of follicles and accumulated follicle size were reduced by day 27 of pregnancy on the ovary bearing the corpus luteum (CL) but not on the non-CL bearing ovary. In experiment II, local attenuation of ovarian follicular development on the CL bearing ovary of seven pregnant heifers was evident compared to the contralateral ovary without the CL. However, in four hysterectomized heifers, follicular development was sustained on both the CL- and non-CL bearing ovaries when CL maintenance was achieved without presence of the uterus or conceptus. In Experiment III, steroidogenic characteristics of the largest and second largest follicles at 17 d postestrus were evaluated for seven pregnant and six cyclic cattle. Follicle by physiological status interactions were detected for both aromatase activity of the follicle and follicular fluid concentrations of estradiol and progesterone. In cyclic cows, the largest follicle had appreciably more aromatase activity than did the second largest follicle; whereas, aromatase activity of the largest follicle from pregnant cows was less than that of cyclic cows. However, in pregnant cows the second largest follicle became the estrogen-active follicle, and this follicle occurred with a higher frequency on the ovary contralateral to the CL-bearing ovary. These changes in aromatase activity were reflected by parallel changes in estrogen concentrations of follicular fluid. The higher progesterone concentration in follicular fluid of the largest follicle in pregnant cows provided further confirmation of their atretic status. In conclusion, during early pregnancy the conceptus and/or uterus ipsilateral to the conceptus appear to secrete compounds which alter local follicular steroidogenic activity and attenuate subsequent follicular growth between 17 to 34 d of pregnancy on the CL-bearing ovary. This local mechanism acting within the ovary may contribute to the antiluteolytic effects of early pregnancy in cattle.

Animals↗