Biomedical subjects

W W Thatcher

Publications and source records attributed to W W Thatcher.

At least 91 records · Page 5Linked to original sources

PubMed1998

Human chorionic gonadotropin-induced alterations in ovarian follicular dynamics during the estrous cycle of heifers.

This experiment was designed to characterize hCG (3,000 IU)-induced alterations in ovarian follicular and corpus luteum (CL) dynamics during the estrous cycle (EC) in heifers. Following synchronization of estrus (norgestomet implant for 7 d with injection of PGF2alpha 1 d before implant removal), 13 heifers were treated with either hCG (n = 6) or saline (control group; n = 7) on d 5 of the EC (d 0 = day of estrus). Blood sampling from the jugular vein and ultrasonography of both ovaries were conducted daily until confirmation of ovulation following a detected estrus. Treatment with hCG at d 5 induced formation of an accessory CL in all hCG-treated heifers. Subsequent plasma progesterone (P4) concentrations were higher (P < .01) between d 9 and 17 for the hCG group than for the control group. More (P < .05) hCG-treated heifers had EC with three waves of follicles than control heifers. The second-wave dominant follicle (DF) emerged earlier in hCG than in control heifers (7.3 vs 10.4 d; P < .01). A group x wave interaction (P < .01) was detected for duration of the second and third wave follicles; hCG treatment decreased duration of the second wave (6.3 vs 9.3 d) and increased duration of the third wave (9.2 vs 5.3 d). The hCG-treated heifers had preovulatory follicles that lasted longer (P < .01) on the ovary than those in control heifers. However, plasma estradiol concentrations did not differ (P > .10) between hCG-treated and control heifers during the preovulatory period. A wave x duration interaction (P < .01) was detected for P4 concentrations, between d 13 and 22, for heifers with two vs three spontaneous-wave EC. Higher P4 concentrations during the luteal phase may contribute to a greater rate of follicular turnover or frequency of three-wave cycles, and lower P4 concentrations were associated with two-wave cycles.

Animals↗

PubMed1998

Mechanisms regulating prostaglandin F2 alpha secretion from the bovine endometrium.

The mechanism that regulates luteolytic PGF2 alpha secretion as stimulated by oxytocin is thought to involve induction of the inositol (1,4,5)-trisphosphate-diacylglycerol second messenger system, which mobilizes intracellular calcium and activates protein kinase C. In Experiment 1, endometrial explants taken from heifers on d 18.5 to 19.5 postestrus had increased PGF2 alpha secretion after treatment with 1 microM calcium ionophore A23187 to increase intracellular calcium, 100 nM phorbol 12-myristate 13-acetate to activate protein kinase C, and 100 nM oxytocin. The stimulatory effects of oxytocin and calcium ionophore A23187 plus phorbol 12-myristate 13-acetate did not differ from each other. In Experiment 2, endometrial explants taken from cows on d 18.5 to 19.5 postestrus had increased PGF2 alpha secretion after treatment with 0.2 and 2 microM thapsigargin to mobilize intracellular calcium that was sensitive to inositol (1,4,5)-trisphosphate. Secretion of PGF2 alpha was also increased by 100 nM oxytocin and was influenced by the interaction of thapsigargin and oxytocin such that 100 nM oxytocin did not further increase the secretion of PGF2 alpha in the presence of 2 microM thapsigargin. In Experiment 3, 100 nM oxytocin stimulated greater production of inositol trisphosphate and total inositol phosphates in the endometrium of cyclic cows than in the endometrium of pregnant cows on d 16.5 to 17.0 postestrus, although luteolysis was not yet initiated in the cyclic cows. These results are consistent with the hypothesis that the activation of the inositol (1,4,5)-trisphosphate-diacylglycerol second messenger system by oxytocin is involved in the stimulation of PGF2 alpha secretion from the endometrium during late diestrus in cows.

Animals↗

PubMed1998

Influence of supplemental fats on reproductive tissues and performance of lactating cows.

Fat supplementation (about 3% of dietary dry matter) has often positively influenced the reproductive status of the dairy cow, including increased size of the ovulatory follicle, increased numbers of ovarian follicles, increased plasma concentration of progesterone, reduced secretion of prostaglandin metabolite, increased lifespan of the corpus luteum, and improved fertility. Supplemental fat may allay partially negative energy status during the early postpartum period, yet often the positive reproductive influence of supplemental fat has been independent of the energy status of the cow. The fatty acid profile of supplemental fats is influential to their impact. Linoleic acid and eicosapentaenoic acid (found in fish meal) are proven inhibitors of cyclooxygenase in endometrial tissue of dairy cows. As a result, endometrial secretion of PGF alpha can be suppressed, thus potentially preventing early embryonic death. This process may be aided by the effect fat has in suppressing estradiol-17 beta secretion, thus reducing uterine PGF2 alpha secretion and decreasing the sensitivity of the corpus luteum to PGF2 alpha. Targeting of dietary fatty acids toward ovarian and uterine function may enhance efficiency of reproductive management and fertility.

Animal Nutritional Physiological Phenomena↗

PubMed1998

Protein degradability and calcium salts of long-chain fatty acids in the diets of lactating dairy cows: productive responses.

Our objective was to evaluate the effect of excessive intake of ruminally degradable crude protein [11.1 and 15.7% of dietary dry matter (DM)] and supplemental fat (Ca salts of long-chain fatty acids at 0 or 2.2% of dietary DM) on the productive performance of lactating Holstein cows (n = 45) during the first 120 d postpartum. The main N sources were soybean meal and urea in the diets with high concentrations of degradable protein versus a combination of vegetable and animal by-product feedstuffs in the diets with less degradable protein. Cows fed the diets with excess degradable protein had slower rates of increase in DM intake (DMI) and milk production, had lower plasma insulin and greater plasma glucose and urea concentrations, and lost more than twice the body weight of cows fed the diets with less degradable protein. Supplemental fat in the highly degradable protein diet reduced the loss of body condition, stimulated DMI, and reduced concentrations of plasma nonesterified fatty acids early postpartum compared with the highly degradable protein diet without added fat. Without affecting DMI, supplemental fat stimulated milk production (2 kg/d) starting at 3 wk postpartum. During early lactation, DMI and milk production were sensitive to the degree of ruminal degradability of protein and energy supplementation in the form of fat.

Ammonia↗

PubMed1998

Protein degradability and calcium salts of long-chain fatty acids in the diets of lactating dairy cows: reproductive responses.

Multiparous Holstein cows (n = 45) were assigned at calving to one of four diets arranged in a 2 x 2 factorial design. The two main factors were dietary concentration (dry matter basis) of 1) degradable intake protein (11.1 or 15.7%) and 2) supplemental fat (Ca salts of long-chain fatty acids; 0 or 2.2%). Soybean meal and urea were replaced with less degradable protein meals (corn gluten meal, meat and bone meal, fish meal, and blood meal). During the first 9 wk postpartum, cows fed diets containing the greater concentration of highly degradable protein demonstrated less follicular development on their ovaries, were delayed in their first luteal activity postpartum (25.2 vs. 38.6 d), accumulated less luteal tissue (< 15 vs. > 70 mm), and had lower plasma progesterone accumulated over time. The supplementation of Ca salts of long-chain fatty acids to the 15.7% degradable protein diet doubled the number of corpora lutea, reduced time to first rise in progesterone by 6 d, doubled the number of normal luteal phases, and restored the pattern of accumulated plasma progesterone concentrations to a pattern that was similar to that induced by other diets. Cows were synchronized to estrus and inseminated at approximately 65 d postpartum. Pregnancy rate was increased from 52.3 to 86.4% when fat was supplemented. Cows fed fat tended to have more corpora lutea and a larger corpus luteum and accumulated more plasma progesterone than did cows not fed fat. Diets containing excess degradable protein or Ca salts of long-chain fatty acids influenced ovarian structures and reproductive performance.

Animals↗

PubMed1997

The dominant follicle exerts an interovarian inhibition on FSH-induced follicular development.

An experiment was conducted to evaluate the role of the dominant follicle (DF) of the first wave in regulating follicular and ovulatory responses and embryonic yield to a superovulation regime with FSH-P. Twenty normally cycling Holstein-Freisian heifers (n = 20) were synchronized with GnRH and pgf(2alpha) and randomly assigned to a control or a treated group (n = 10 each). Treated heifers had the first wave dominant follicle removed via transvaginal, ultrasound-guided aspiration on Day 6 after a synchronized estrus. All heifers received a total of 32 mg FSH-P given in decreasing doses at 12 h intervals from Day 8 to Day 11 plus two injections of pgf(2alpha) (35 mg and 20 mg, respectively) on Day 10. Heifers were inseminated at 6 h and 16 h after onset of estrus. Follicular dynamics were examined daily by transrectal ultrasonography from Day 4 to estrus, once following ovulation, and at the time of embryo collection on Day 7. Blood samples were collected daily during the superovulatory treatment and at embryo collection. Follicles were classified as: small, </= 5 mm; medium, 6-9 mm; or large, >/= 10 mm. Aspiration of the dominant follicle was associated with an immediate decrease in large follicles, and a linear rate increase in small follicles from Day 4 to Day 8 just prior to the FSH-P injections, (treatment > control: +0.33 vs. -0.22, number of small follicles per day; P < 0.10). During FSH-P injections, the increase in number of medium follicles was greater (P < 0.01) for treatment on Day 9-11 (treatment > control: Day 9, 3.2 > 1.8; Day 10, 9.2 > 4.7; Day 11, 13.1 > 8.3; +/- 0.56). Number of large follicles was greater in treatment at Day 11 (5.12 > 1.4 +/-0.21; P < 0.01). Mean number of induced ovulatory follicles (difference between number of follicles at estrus and Day 2 after estrus) was greater in treatment (13.4 > 6.3 +/- 1.82; P < 0.01). Plasma estradiol at Day 11 during FSH-P treatment was greater in treatment (32.5 > 15.8 +/- 2.6; P < 0.01). Plasma progesterone at embryo flushing (Day 7 after ovulation) was greater in treatment (7.4 > 4.9; P < 0.02); technical difficulties at embryo recovery reduced sensitivity of embryonic measurements. No changes in the distribution of unfertilized oocytes and embryo developmental stages were detected between control and treatment groups. Presence of dominant follicle of the first wave inhibited intraovarian follicular responses to exogenous FSH.

Journal Article↗

PubMed1997

Seasonal and acute heat stress effects on steroid production by dominant follicles in cows.

The present study concerned the seasonal and acute effects of heat stress on steroid concentrations in follicular fluid and on steroid production by granulosa and theca interna cells, in bovine dominant follicles. Three groups of cows were studied: summer (n = 5), autumn (n = 5) and winter (n = 9) cows. During the winter season, another group of cows was acutely heat-stressed from days 3 through 5 of the estrous cycle (n = 5). On day 7 of the estrous cycle, follicular fluid from first-wave dominant follicles was aspirated, and dispersed granulosa and theca cells from each seasonal group were incubated for 18 h at normothermic (37.5 degrees C) or high (40.5 degrees C) temperatures. Cells were incubated in media only or in media containing testosterone (300 ng ml-1, for granulosa cells) or forskolin (4 micrograms ml-1, for theca cells). In follicular fluid the 17 beta-estradiol concentration was high (P < 0.05) in winter and low in autumn, and summer, the androstenedione concentration was high in summer (P < 0.05), low in autumn, and intermediate in winter. During the winter season, acute in vivo heat stress increased follicular fluid androstenedione and decreased estradiol to levels comparable with those prevailing in summer. Basal and forskolin-stimulated androstenedione production by theca cells was higher (P < 0.05) in the winter group than in the summer and autumn groups, and also higher than in the cows that were heat-stressed during winter, which suggests that theca cell function is susceptible to chronic (summer), short-term (winter) and delayed (autumn) heat stresses. In vitro incubation at high temperature (40.5 degrees C) reduced the high, forskolin-stimulated androstenedione production in winter (P < 0.05). Estradiol production by granulosa cells was high in winter and autumn, and low in summer (P < 0.05). Acute heat stress in winter did not alter estradiol production relative to winter controls, whereas a high incubation temperature (40.5 degrees C) reduced (P < 0.05) estradiol production only in the autumn, when the highest production rate was recorded. The results indicate a differential effect of heat stress on the functions of granulosa and theca cells. Both concurrent and delayed effects of heat stress on the steroidogenic capacity of ovarian follicles in cattle are presented.

Androstenedione↗

PubMed1997

Oxytocin antagonist [1-D(CH2)5,Tyr(ME)2,Thr4,Tyr-NH2(9)]ornithine vasotocin inhibits oxytocin-induced prostaglandin F2alpha release in late-pregnant cows.

The affinity and specificity of an antagonist of oxytocin, [1-D(CH2)5,Tyr(ME)2,Thr4,Tyr-NH2(9)]ornithine vasotocin (OTA), to oxytocin receptors (OTR) in bovine gestational endometrium was determined in displacement experiments with oxytocin (OT) and vasopressin (AVP) analogues and compared to myometrial OTR. OTA had the highest affinity in both tissues. The effect of OTA on OT-induced increase in plasma concentration of 13,14-dihydro-15-keto-prostaglandin F2alpha metabolite (PGFM) was studied in 24 late-pregnant cows. Treatments consisted of i.v. saline; OT (50 IU); OTA (1200 microg); and OTA (400, 1200, or 4000 microg) injected i.v. 5 min before OT (50 IU) (n = 4 each). Samples were collected from jugular vein at 15-min intervals for 30 min before and 3 h after the injection of OT. Progesterone was measured in once-daily samples taken for 7 days after the experiment. OT caused a twofold increase in plasma PGFM within about 60 min (p < 0.005), with levels returning to baseline at 150-180 min; OTA (1200 microg) caused a gradual lowering of basal plasma PGFM over 180 min (p < 0.05). The 400-microg or 1200-microg dose of OTA did not alter OT-induced PGFM response, whereas the 4000-microg dose inhibited it almost completely (p < 0.005). Plasma progesterone declined after the experiment in all cows, with no differences among groups. Because OTA inhibits OT-induced release of endometrial prostaglandin F2alpha it may be a good tocolytic agent.

Animals↗

PubMed1997

Comparative study between pony mares and ewes evaluating gonadotrophic response to administration of gonadotrophin-releasing hormone.

This study compared equine and ovine LH secretory responses to GnRH treatment. Dioestrous mares and ewes were challenged with continuous GnRH for 15 h. Mares that received constant GnRH (110 micrograms h-1) had sustained LH secretion (P < 0.01), whereas LH concentrations in ewes treated with continuous GnRH (25 micrograms h-1) initially increased, then declined and remained low, suggesting GnRH receptor desensitization or downregulation. In addition, progesterone-primed, ovariectomized mares and ewes were challenged with pulsatile or continuous GnRH for 5 days. Plasma LH concentrations were increased by day 5 in mares treated with pulsatile (25 micrograms pulse-1 h-1) and continuous (110 micrograms h-1) GnRH (P < 0.01). Furthermore, mean LH concentrations and time-response curves were not different. In contrast, ewes treated with continuous GnRH (2.5 micrograms h-1) demonstrated LH secretory patterns indicative of GnRH receptor downregulation on day 1 of treatment. LH concentrations in ewes treated with pulsatile GnRH (250 ng pulse-1 h-1) did not differ from controls. In conclusion, pony mares responded continuously to GnRH treatment (pulsatile and continuous), whereas ewes treated with continuous GnRH experienced reduced LH secretion. These findings suggest a unique hypothalamic-pituitary axis in pony mares.

Animals↗

PubMed1997

Effects of supplemental energy source and amount on forage intake and performance by steers and intake and diet digestibility by sheep.

Two levels of concentrate supplements containing different types of carbohydrates (corn-soybean meal, CSBM; wheat middlings, WM; and soybean hulls, SBH) were evaluated for effects on forage intake and performance in growing steers and total diet digestibility in sheep. In Exp. 1, 63 crossbred yearling cattle (298 and 377 kg initial BW for yr 1 and 2, respectively) were given ad libitum access to chopped bermudagrass (Cynodon dactylon [L.]) hay with no supplementation (CONTROL) or with 25 or 50% of projected total TDN intake from CSBM, WM, or SBH. In Exp. 2, digestibilities of organic matter (OMD) and neutral detergent fiber (NDFD) were determined with sheep fed levels of hay and concentrates similar to those used in the growth trials. Hay intake was 1.99% of BW for steers fed hay alone and averaged 1.93% of BW in steers fed supplements at the low level. At the high level of concentrate supplementation, hay intake was depressed (P < .001) to a similar extent (1.63% of BW) in steers supplemented with CSBM, WM, or SBH. AT the low concentrate level, shrunk ADG was similar (.63 kg/d) among supplements, but at the high concentrate level steers fed SBH had higher (P = .06) shrunk ADG (.95 kg/d) than steers fed CSBM (.76 kg/d). Body condition score (BCS) increased more (P = .06) for CSBM- and SBH- than for WM-supplemented steers. Total tract OMD was lower (P < .001) in sheep fed WM (54.8% for low and 56.9% for high supplementation levels) than in sheep fed CSBM (57.4 and 62.6%) or SBH (57.2 and 62.5%). Total tract NDFD was higher (P < .001) for the SBH (58.9% for low and 63.3% for high levels) diets than for CSBM (54.6 and 51.0%) or WM (54.6 and 51.8%) diets. Supplements containing highly digestible fiber (SBH) produced less negative associative effects than high-starch supplements (CSBM) when fed with bermudagrass hay at the high level (.8 to 1% of BW), but no differences were found at the low feeding level (.4 to .5% of BW).

Animal Feed↗

PubMed1997

Abomasal infusion of glucose and fat--effect on digestion, production, and ovarian and uterine functions of cows.

Four ruminally cannulated lactating dairy cows, arranged in a 4 x 4 Latin square design, were infused abomasally with 1) water (control), 2) 1 kg/d of glucose, 3) 0.45 kg/d of tallow, and 4) 0.45 kg/d of yellow grease. Cows were synchronized for estrus within each 35-d period by injection of a GnRH agonist followed 7 d later by an injection of PGF2 alpha. Dry matter intake was not affected by infusates. Apparent digestibility of total fatty acids was greater for cows receiving the fat infusions relative to those receiving the glucose infusion and tended to increase for cows receiving the yellow grease infusion compared with those receiving the tallow infusion. Energy infusions decreased apparent acid detergent fiber digestibility compared with effects of the control infusion. Fat infusions tended to increase milk fat percentage and decrease the energy status of cows relative to the glucose infusion. The feed efficiency was greater for cows receiving fat infusions than for those receiving the glucose infusion and was greater for cows receiving the yellow grease infusion than for those receiving the tallow infusion. Plasma progesterone concentration peaked higher during the estrous cycle for cows infused with fat than for those infused with glucose. Mean growth rate and maximum size of the first wave dominant follicle were greater with tallow than with yellow grease. During the period of infusion of yellow grease and afterward, release of 13,14-dihydro-15-keto-PGF2 alpha in response to an injection of oxytocin on d 15 of the estrous cycle was attenuated.

Abomasum↗

PubMed1997

Effect of ruminant grade Menhaden fish meal on reproductive and productive performance of lactating dairy cows.

Menhaden fish meal, fed at 0.7 kg/d [2.7% of dietary dry matter (DM)], replaced blood meal and meat and bone meal (2.0% of dietary DM) in the diet fed at dairy A (n = 341) and replaced blood, meat and bone, and corn gluten meals (3.2% of dietary DM) in the diet fed at dairy B (n = 300). Cows consumed the experimental total mixed diets from approximately 24 to 109 d postpartum. Cows were synchronized for estrus using injections of GnRH agonist at 51 d postpartum. PGF2 alpha 7 d later, and artificial insemination at detected estrus. Resynchronization occurred using the same program if estrus was not detected. Diet failed to alter reproductive responses at synchronized artificial insemination. Pregnancy rate at 120 d postpartum was not altered by diet at dairy A (65.4% vs. 60.2%) but was improved by dietary fish meal at dairy B (31.9% vs. 41.3%; interaction of dairy and diet). The dynamics of corpus luteum regression were altered in cows fed fish meal at dairy B. Dietary fish meal did not influence milk production of cows at dairy A but increased production of milk (2.3 kg/d) and protein (0.1 kg/d) of second parity cows at dairy B. When dietary fish meal was fed to cows at dairy B, production of milk fat and 4% FCM was higher for cows in parity 5 or greater than that for cows in fourth parity.

Animal Feed↗

PubMed1996

Effects of administering progesterone at selected intervals after insemination of synchronized heifers on pregnancy rates and resynchronization of returns to service.

In 3 separate trials at 2 locations, dairy heifers (n = 396) were treated with a Controlled Internal Drug Release (CIDR) progesterone device for 9 d. On Day 7 of CIDR treatment, all heifers were injected with PGF(2alpha). Synchronized estruses were detected using a tailpaint and chalk (TPC) scoring system. An animal's tailhead was painted at device insertion, and this strip was covered with a contrasting color of chalk at device removal. Over all trials, 85.1% of the heifers were detected in estrus and were inseminated at 48 or 72 hours after CIDR removal. These synchronized and inseminated heifers were divided into the following treatment groups: 1) untreated controls, receiving no further treatment (n = 138); 2) post-insemination progesterone supplementation with a new (n = 59) or used (n = 29) CIDR device for Days 1 to 8 or 2 to 9, respectively, following insemination; or 3) resynchronization of return to service with a used CIDR device for Days 17 to 22 after insemination (n = 112). The pregnancy rate to first insemination in the control and resynchronized groups (Groups 1 and 3) was 46.4%, but decreased to 18.2% with the post-insemination progesterone supplementation. Resynchronization of returns to service (estrus detected 1 to 4 d following removal of second CIDR) occurred in 58.9% of all nonpregnant heifers in Group 3. In summary, CIDR devices used in conjunction with PGF(2alpha) effectively synchronize estrus in dairy heifers. Progesterone supplementation within 2 d of first insemination for 7 d suppressed fertility. Used CIDR devices inserted for Days 17 to 22 after first insemination resynchronized heifers not pregnant to first insemination.

Journal Article↗

PubMed1996

Control and management of ovarian follicles in cattle to optimize fertility.

Experiments were designed to elucidate the control of ovarian follicle turnover and the impact of follicular dynamics on the subsequent fertility of dairy cattle. An experimental model was established to examine the interrelationships of gene expression for steroid enzymes, the insulin-like growth factor system and inhibin production as associated with follicle selection, dominance and atresia. Follicular dynamics during the postpartum period and the oestrous cycle are shown to be altered markedly by the metabolic demands of lactation. The feeding of ruminally-inert fat stimulated follicular development and improved reproductive performance. The development of persistent follicles during oestrus synchronization causes a reduction in fertility that can be corrected by recruitment and selection of a new ovulatory follicle after the injection of a gonadotrophin-releasing hormone agonist. Present systems of oestrus synchronization need to consider both synchronization of follicular development and corpus luteal regression in order to optimize fertility. With current systems manipulating follicle development, the potential to implement a timed insemination programme to improve reproductive management exists. Ovulation of the first-wave dominant follicle with human chorionic gonadotrophin provides a means to markedly enhance concentrations of plasma progesterone in the luteal phase.

Animals↗

PubMed1996

Intravascular infusion of lipid into ewes stimulates production of progesterone and prostaglandin.

Effects of infusion of a lipid emulsion into ewes during mid-to late diestrus on serum concentrations of total cholesterol (TC), progesterone (P4), prostaglandin (PG) F2 alpha metabolite (PGFM), and PGE2, and on ovulation rate were examined. In experiment 1, ewes received infusions of either saline (S, n = 3) or soybean oil emulsion (SB, n = 3) for 5 h on each of Days 9-13 of the estrous cycle. In experiment 2, ewes received infusions of either S (n = 4), SB (n = 5), or olive oil emulsion (OO, n = 5) for 5 h on each of Days 9 through 15 of the estrous cycle. In both experiment 1 and experiment 2, infusion of lipid increased serum concentrations of TC and P4, which declined with time after infusion was terminated (treatment x hour interaction, experiment 1: TC, p < 0.01, P4, p < 0.01; experiment 2: TC, p < 0.01, P4, p < 0.001). Serum PGFM and PGE2 concentrations were greater in lipid-infused ewes than in controls on Days 13 through 15 (treatment x hour interaction; p < 0.03, p < 0.001, respectively). Duration of the estrous cycle was shortened in OO-infused ewes (16.2 +/- 0.4 days) compared with that of SB- and S-infused ewes (17.2 +/- 0.2 and 18.0 +/- 0.0 days, respectively; p < 0.01). Numbers of corpora lutea and follicles, and diameter of follicles > 4 mm did not differ among treatment groups on Day 14 of the succeeding cycle after infusion. These data indicate that lipid infusion stimulated increases in serum concentrations of TC, P4, and prostaglandins and may shorten the estrous cycle.

Animals↗

PubMed1996

Insulin-like growth factor system in bovine first-wave dominant and subordinate follicles.

Estradiol (E2)-active (Day 5 [D5]), transitional E2-active (D8), atretic (D12 - 1), and E2-sustained dominant follicles (DF, D12 + 1) and associated subordinate follicles (SF) were obtained through use of an experimental model described here. The ovary bearing the DF was surgically removed by colpotomy, and individual follicles were utilized to study changes in concentrations of insulin like growth factor-I (IGF-I) and -II (IGF-II) and changes in amounts and proportions of the different IGF-binding proteins (IGFBP) present in follicular fluid (FF). The ratio of FF E2 to progesterone (EPR) was utilized to classify follicles into E2 active (EPR > 1) and E2 inactive (EPR < 1). The IGF-I and IGF-II concentrations in FF were similar among experimental groups and between DF and SF. Six different molecular mass bands (49, 43, 35, 30, 28, and 22 kDa) were detected by ligand blot in FF of DF and SF. Immunoprecipitation analysis identified four IGFBPs (-2, -3, -4, and -5) in FF. The 35-kDa band corresponded to IGFBP-2, the 49- and 43-kDa bands to IGFBP-3, the 28- and 22-kDa bands to IGFBP-4, and the 30-kDa band to IGFBP-5. No IGFBP-6 was found by immunoprecipitation. Absolute amounts and proportions of low molecular mass IGFBPs (-2, -4, and -5) were increased with atresia of the DF and in SF compared to E2-active DF. Conversely, although absolute amounts of IGFBP-3 remained unchanged, their proportion in FF decreased in SF compared to DF. The ratio of IGF-I to IGFBPs decreased with atresia of the DF, possibly leaving less bioavailable IGF-I to increase FSH action at the level of the follicle.

Animals↗

PubMed1996

Effects of growth hormone and pregnancy on expression of growth hormone receptor, insulin-like growth factor-I, and insulin-like growth factor binding protein-2 and -3 genes in bovine uterus, ovary, and oviduct.

The effects of growth hormone (GH) and pregnancy on insulin-like growth factor (IGF)-I, IGF binding protein (IGFBP)-2, and IGFBP-3 mRNA in reproductive tissues were studied in cattle. Lactating dairy cows were inseminated at estrus and treated with 25 mg/day GH (n = 8) or saline (n = 8) for 16 days. Corpus luteum (CL), ovary (CL removed), oviduct, endometrium, and myometrium were collected at the end of treatment. Messenger RNA for GH receptor, IGF-I, IGFBP-2, IGFBP-3, and actin were measured by nuclease protection assays. The CL contained more GH receptor mRNA than the other reproductive tissues examined. Expression of IGF-I mRNA was highest in myometrium, with lower amounts found in endometrium; the CL expressed the least amount of IGF-I mRNA. The IGFBP-2 mRNA was most abundant in endometrium and least abundant in CL. Expression of IGFBP-3 mRNA was detected in all reproductive tissues examined. However, endometrium, a tissue that expressed the most IGFBP-2 mRNA, had the lowest amount of IGFBP-3 mRNA. The GH receptor mRNA was decreased in cows treated with GH whereas the mRNA for IGF-I, IGFBP-2, or IGFBP-3 was not changed. In the reproductive tissues evaluated, cows that contained a conceptus at tissue collection (pregnant) had higher amounts of IGF-I mRNA than did nonpregnant cows. In summary, the level of mRNA encoding GH receptor, IGF-I, IGFBP-2, and IGFBP-3 varied within the tissues examined, suggesting that these genes may play a variety of roles in the bovine female reproductive tract. Supplemental GH failed to change the expression of IGF-I, IGFBP-2, and IGFBP-3 mRNA, possibly because of low GH receptor mRNA levels in tissues other than CL. A direct action of GH on IGF-I, IGFBP-2, or IGFBP-3 gene expression within cow reproductive tissues was not supported because the amount of IGF-I, IGFBP-2, or IGFBP-3 mRNA was not altered by GH.

Actins↗

PubMed1996

Effect of a gonadotropin-releasing hormone agonist on follicle recruitment and pregnancy rate in cattle.

Two experiments were conducted to determine whether a GnRH agonist eliminated a potentially persistent first-wave dominant follicle (PDF) and recruited a new dominant follicle with improved fertility upon ovulation. In Exp. 1, five nonlactating Holstein cows were treated on d 7 (d 0 = estrus) with a norgestomet implant and PGF2 alpha (25 mg); a GnRH agonist was injected on d 9. On d 16, the norgestomet implant was removed and PGF2 alpha was injected. The corpus luteum (CL) regressed (5/5 cows), and plasma progesterone (P4) decreased (P < .01) from d 7 (P4 = 10.4 +/- .3) to 9 (P4 = 1.0 +/- .3 ng/mL). The GnRH agonist induced ovulation of the first-wave dominant follicle. New dominant follicles emerged by d 12 +/- 1. In all cows, removal of norgestomet implants and injection of PGF2 alpha on d 16 caused regression (P < .01) of the CL induced by the GnRH agonist. The GnRH agonist-recruited dominant follicles were highly estrogenic on d 17 (estradiol = 19.6 +/- .8 pg/mL) and ovulated on d 19.8 +/- .2 (5/5). In Exp. 2, 147 heifers at a synchronized estrus were assigned disproportionally but randomly to two treatments (GnRHa, n = 94; PDF, n = 53). On d 7, a used controlled internal drug releasing (CIDR-B) device was inserted into the vagina and PGF2 alpha was injected. On d 9, heifers in GnRHa were injected with GnRH agonist. The CIDR-B devices were removed and PGF2 alpha was injected into all heifers on d 16. Within 4 d after removal of CIDR-B devices, 96.8 and 94.3% of heifers in GnRHa and PDF were detected in estrus and inseminated. Pregnancy rates were GnRHa = 60.6% > PDF = 43.4% (P < .05). In summary, fertility after ovulation of a persistent first-wave dominant follicle is reduced, whereas induction of a new dominant follicle following injection of a GnRH agonist results in greater fertility.

Animals↗