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PubMed2006

Progesterone plus PMSG Priming in seasonally anovulatory lactating Sarda ewes exposed to the ram effect.

The aim of this trial was to evaluate the effectiveness (fertility and lambing) of priming with a single injection of progesterone plus PMSG in anovulatory lactating Sarda ewes subjected to the ram effect (RE) in spring. Thirty ewes (P4 group) were i.m. injected with 30 mg progesterone and 500 IU PMSG 36 h before ram introduction (d 0). This treatment was compared to a 12-day treatment with fluorogestone acetate intravaginal sponges that was followed by injections of 350 IU PMSG upon sponge withdrawal (FGA group, n=30). All ewes responded to RE, showing plasma progestrone concentrations >1 ng/mL between d 6 and 12 (FGA) or 6 and 9 (P4). Eighty-nine percent of the P4 ewes conceived at first ovulation, and 11% conceived following a short estrus cycle. Lambings occurred on d 150.4 +/- 3.9, and the lambing rate was 100%. The fertility of the FGA ewes was 83% for the induced ovulation and was 7% for the second ovulation after a normal cycle. The FGA ewes lambed on d 149.8 +/- 4.4, and the lambing rate was 83%. Two abortions were recorded for the FGA ewes, which had higher prolificacy than the P4 group (2.2 +/- 0.8 vs. 1.8 +/- 0.4, respectively; P<0.05). Both fertility and the lambing rate were high in both groups, with a high degree of estrus synchronization, and there were no significant differences between the groups. We concluded that priming of lactating Sarda ewes in spring with P4+PMSG before RE is an effective and competitive method (cheaper and more practical than FGA+PMSG) of inducing fertile ovulations in these ewes.

Animals↗
PubMed2001

Effect of long-term and short-term progestagen treatment on follicular development and pregnancy rate in cyclic ewes.

The aim of this study was to evaluate the effect of the length of a progestagen treatment (12 d vs. 6 d) on follicular dynamics, estrus synchronization and pregnancy rate using medroxyprogesterone acetate (MAP) with or without an eCG dose at the end of MAP treatment. One hundred sixty Polwarth ewes were divided into four equal groups: long-term treated (LT, n=40); short-term treated (ST, n=40); long-term treated plus eCG (LTeCG, n=40); and short-term treated plus eCG (STeCG, n=40). Five ewes of each group were separated to undergo daily transrectal ultrasonography, and blood samples were taken for hormone determination. Until 96 h after sponge withdrawal the number of ewes in estrus was higher in both long-term-treated groups than in both short-term-treated groups but at the end of the observational period (144 h) no significant differences were found among groups. The pregnancy rate was higher in the ST group (87%) than in the other groups (LT, 63%; LTeCG, 67%; and STeCG, 58%; P< or =0.03). The ovulatory follicle emerged before sponge withdrawal in long-term-treated ewes (-3.8+/-0.4 d and -2.2+/-0.8 d for LT and LTeCG, respectively), whereas in short-term-treated ewes it emerges around sponge removal (0.4+/-1.1 d and 0.5+/-0.5 d for ST and STeCG, respectively; P< or =0.01). The ovulatory follicle in the LT group had a longer lifespan and attained a larger (P< or =0.05) maximum diameter than in the ST group. We conclude: a) that the lower pregnancy rate observed after long-term progestagen treatment was related to a slower follicular turnover that promoted the ovulation of persistent dominant follicles; (b) that short-term treatment resulted in a higher pregnancy rate probably due to the ovulation of newly recruited growing follicles; and (c) treatment with eCG had no advantage in association with long-term treatment and had a deleterious effect in combination with short-term treatment with MAP.

Administration, Intravaginal↗
PubMed2005

Technical Note: Transcervical deep cornual insemination of goats.

A newly developed technique for trans-cervical deep uterine insemination of goats is described. An experiment was conducted to compare this transcervical method with the laparoscopic intrauterine insemination using frozen-thawed semen. Of the 46 primiparous and 21 multiparous estrus-synchronized Boer goat does inseminated transcervically, 71% (22/31) kidded compared with 53% (19/36) of does inseminated laparoscopically (P < 0.025). The corresponding litter sizes were 2.27 and 1.89 (P < 0.01). In another 34 parous does inseminated transcervically without preceding hormone treatment, kidding rate and litter size were 71% and 1.76, respectively. We conclude that transcervically conducted bilateral deep cornual insemination may be considered a viable alternative to laparoscopic insemination.

Animals↗
PubMed1987

[The exchange of animals in the form of embryos].

The results are given of transplantation work with cattle embryos from Czechoslovakia. The embryos were taken in the stage of morula or blastocyst, frozen and stored for one to ten months. Following thawing they were transplanted via surgical methods to local, estrus-synchronized recipient heifers at the Ruzhevo Konare village, Plovdiv district. A calf was born to each of six of the recipients, while two heifers that were inseminated seven days prior to transplantation yielded twins. It was considered to be the result of both the embryo-transplantation and the fertilization of own ova. Discussed are the opportunities and advantages of long-term storage and shipping of animals in the form of frozen embryos.

Animals↗
PubMed2004

Effect of insemination with doses of 2 or 15 million frozen-thawed spermatozoa and semen deposition site on pregnancy rate in dairy cows.

The effects of low-dose artificial insemination (AI) on pregnancy rates have seldom been studied in lactating dairy cows. We evaluated the pregnancy results after AI with doses of 2 and 15 million frozen-thawed spermatozoa and the effect of semen deposition in lactating dairy cows. A total of 284 first inseminations with 2 million spermatozoa and 312 first inseminations with 15 million spermatozoa were performed on 480 dairy farms. Low-dose inseminations (2 million spermatozoa) under field conditions in commercial dairy herds, without estrus synchronization, generally resulted in significantly reduced pregnancy rates compared with normal doses (15 million spermatozoa). The bull x technician effect on fertility was statistically significant. This finding indicates that there is a high variability in fertility among bulls using 2 million spermatozoa per dose. The semen deposition site did not influence pregnancy rates. It is concluded that a dose of 2 million frozen-thawed spermatozoa is probably too low for most bulls to achieve acceptable pregnancy rates in dairy cows.

Animals↗
PubMed2004

Effect of ram exposure at the end of progestagen treatment on estrus synchronisation and fertility during the breeding season in ewes.

Two experiments were conducted to examine the effects of ram exposure during the breeding season, in combination with progestagen treatment on estrus synchronization, fertility the LH surge and ovulation in ewes. Experiment 1 was subdivided into experiments 1a and 1b. In all experiments cross-bred ewes were treated with an intravaginal sponge for 12-14 days and three days before sponge withdrawal ewes were divided into control (no further treatment; n=191, 103 and 50 for experiments 1a, 1b and 2, respectively) or ram exposed (three mature rams per 50 ewes were introduced; +Ram; n=187, 99 and 49 for experiments 1a, 1b and 2, respectively). At sponge withdrawal ewes in Experiments 1a and 2 received 500 IU eCG and rams were removed from all the +Ram groups. In Experiments 1a and 1b, raddled, entire rams were introduced to ewes 48 h after sponge withdrawal. The timing of mating was recorded and ewes were maintained until lambing. In Experiment 2, estrus behavior was determined every 4 h and the time of the LH surge and ovulation were determined from a subset of 10 ewes per group. In Experiment 1a, less +Ram ewes were bred by 48 h after ram introduction (control 98% versus +Ram 89%, P<0.001) and in Experiments 1a and 1b 14% fewer (P<0.05) of the ewes bred in the first 3 h after ram introduction lambed to that service. In Experiment 1a, ram exposed ewes had a lower litter size than control ewes (1.93+/-0.06 versus 1.70+/-0.06 lambs per ewe; P<0.05). In Experiment 2, rams advanced (P<0.05) estrus, the LH surge and ovulation by 2-6 h compared with control ewes. We speculate that exposure of ewes to rams increased LH secretion and that this in turn increased follicle development and the production of oestradiol that led to a more rapid onset of estrus, the LH surge and ovulation compared to control ewes. Unexpectedly, ewes that were bred had lower fertility in the +Ram groups than control groups.

Animals↗
PubMed1993

Use of prostaglandin products by dairy cattle owners, beef cattle owners, and veterinarians.

Questionnaires regarding the use of prostaglandin F2 alpha and its analogues (hereafter referred to as PG) were sent to 332 Alabama beef cattle owners and to 279 Alabama dairy cattle owners after attempting to contact them by telephone to request their participation in the survey. Questionnaires concerning the use of PG in their clients' herds were likewise sent to 147 food animal and mixed animal practitioners in Alabama after attempting telephone contact. Response among beef cattle owners, dairy cattle owners, and veterinarians to whom questionnaires were mailed was 64.5, 61.6, and 75.5%, respectively. Only 7.4% (13 of 175) of respondent beef cattle owners reported use of PG in their herds, and this use was predominantly for artificial insemination and embryo transfer. In contrast, 66.5% (109 of 164) of respondent dairy cattle owners reported use of PG, generally with satisfactory results, for some of the following conditions: unobserved estrus (n = 77), uterine infections (n = 74), retained placenta (n = 65), cystic ovaries (n = 56), estrus synchronization (n = 45), and induction of parturition (n = 13). Although 94.9% of respondent veterinarians treated cattle with PG, those attending beef herds thought that more important strategies were available for improvement of beef cattle productivity than increased use of PG. Among these strategies were shorter calving seasons, improved nutrition, better record keeping, more frequent herd health visits, improved animal identification, and increased use of bull breeding soundness examinations.(ABSTRACT TRUNCATED AT 250 WORDS)

Agriculture↗
PubMed1992

Sexual performance of rams in serving capacity tests predicts success in pen breeding.

The purpose of this study was to determine the extent to which sexual performance (serving capacity) tests can be used to predict the sexual behavior and reproductive success of rams in the context of pen mating. Standard serving capacity tests were used to select four low (LP) and four high-performing (HP) rams from a population of 94 yearling males. Each selected ram was then exposed to approximately 30 estrus-synchronized ewes for a 9-d period. Ejaculations observed and mounting marks left on ewes confirmed the greater (P less than .001) sexual activity of the HP rams in the field. In addition, ewes exposed to HP rams had a higher lambing percentage, more lambs born, and more live lambs born per ewe. Ram classification was not related (P greater than .60) to the number of lambs born per ewe lambing (prolificacy). It was concluded that serving capacity tests, properly conducted, can be used to predict ram mating performance and thus aid in establishing more efficient ram-to-ewe stocking rates.

Animals↗
PubMed1997

Luteinizing hormone release and reproductive traits in anestrous, estrus-cycling, and ovariectomized cattle after tyrosine supplementation.

The role of rumen-protected L-tyrosine as a nutritional signal altering LH release and other reproductive traits in cattle was studied. In Exp. 1, 28 suckled crossbred cows were assigned randomly to five treatments (0 or 40 g of tyrosine daily in feed for 3 d followed by a single i.v. injection of 200 micrograms of GnRH or 1 mg/kg of naloxone on d 26 +/- 1 postpartum; no tyrosine plus an injection of saline was the control). Peak LH after GnRH was greater (P < .001) in GnRH-treated cows regardless of tyrosine supplementation. Compared to cows receiving saline, days to first postpartum ovulation were reduced (P < .05) by naloxone, tyrosine, and GnRH. In Exp. 2, 47 suckled crossbred cows were assigned randomly to six treatments (0, 20, or 40 g of tyrosine daily for 3 d before GnRH or saline was injected i.m. on d 23 +/- 1 postpartum). Injection of GnRH increased (P < .001) LH. An interaction (P = .08) of tyrosine and GnRH tended to reduce days to first postpartum ovulation. In Exp. 3, tyrosine (40 g) administered once daily for 3 d to ovariectomized cows (six cows per treatment) had no effect on any characteristic of LH before or after estradiol-17 beta. In Exp. 4, suckled cows (n = 136) were allotted randomly to two treatments (0 or 30 g of tyrosine daily for 3 d before a PGF2 alpha-synchronized estrus). Tyrosine increased (P = .05) the percentage of cows in estrus after PGF2 alpha but reduced (P = .05) AI conception rate. These results fail to support the thesis that tyrosine alters LH release in cattle. Supplemental tyrosine increased expression of estrus in suckled cows after PGF2 alpha and tended to reduce intervals to first postpartum ovulation.

Analysis of Variance↗
PubMed1980

In vivo change in the germinal vesicle of the sow oocyte during the follicular phase before the ovulatory LH surge.

This study describes a morphological change in the germinal vesicle (GV) of the sow oocyte during the follicular phase preceding the ovulatory LH surge. Estrus synchronization obtained with methallibure treatment provided a reference point for dating the onset of the follicular phase of each sow in the experiment. The oocyte GV's of preovulatory follicles having a diameter of less than 2 mm (during the first 2 to 3 days of the follicular phase) showed uniformly dispersed chromatin with no condensation, while the GV's of oocytes from preovulatory follicles of more than 2 mm diameter (from days 2 and 3 of the follicular phase to day 5) presented condensed chromatin in the shape of a crown or horseshoe surrounding the nucleolus, and irregular chromatin clusters in the nucleoplasm; these clusters were usually found lying against the nuclear membrane.

Animals↗
PubMed2005

Response of plasma cortisol and progesterone after ACTH challenge in ovariectomized lactating dairy cows.

Shortened and weakened estrous expressions could be one of the causes of poor heat detection rate. Non-specific acute stresses are assumed to depress expression of estrus by an increase of plasma progesterone which may originate from the adrenal cortex. The objective of the present study was to examine whether the adrenal cortex can secrete significant amounts of progesterone in response to exogenous adrenocorticotropic hormone (ACTH) in lactating cows. Four cows had estrus synchronized and were ovariectomized in the luteal phase. The cows were given 25 IU ACTH through an indwelling catheter 5 h after catheterization. Blood samples were collected at an interval of 30 min. In 3 of the 4 cows, plasma progesterone concentrations increased significantly 0.5-1.5 h after the first ACTH challenge with a mean peak value of 4.2 +/- 0.4 (S.D.) ng/ml. A similar response was also observed after the second ACTH challenge. Peak plasma progesterone concentrations in the 3 cows after first ACTH challenge were comparable with the progesterone values in the luteal phase of each cow. The results suggest that lactating cows have the capability to secrete a significant amount of progesterone from the adrenal cortex.

Adrenal Cortex↗
PubMed2004

Ultrasound and endocrine evaluation of the ovarian response to a single dose of 500 IU of eCG following a 12-day treatment with progestogen-releasing intravaginal sponges in the breeding and nonbreeding seasons in ewes.

A standard dose of 500 IU of eCG is commonly given to progestogen pre-treated anestrous ewes for induction of estrus. Twelve seasonally anestrous and 12 cyclic Western White Face ewes were treated for 12 days with intravaginal sponges impregnated with medroxyprogesterone acetate (MAP). In trials in both the breeding and nonbreeding seasons, six randomly selected ewes were given 500 IU of eCG at sponge removal to determine the effects of low dose of eCG on ovarian antral follicular dynamics and ovulation. Ultrasound scanning and blood sampling were done daily. Treatment with eCG did not have marked effects on antral follicular growth. All ewes ovulated, except for five of six control anestrous ewes. Luteal structures and progesterone secretion were confirmed in all but the control anestrous ewes. In the breeding season, peak progesterone concentrations were greater (P<0.05) in eCG-treated compared to control ewes. Daily serum estradiol concentrations were greater in the periovulatory period in eCG-treated compared to control ewes (treatment-by-day interaction; P<0.05), particularly in anestrus. Progestogen-treated ewes ovulated follicles from several follicular waves, in contrast to ovulations of follicles from the final wave of the cycle in untreated, cyclic ewes. Anestrous ewes exhibited more frequent follicular waves and FSH peaks compared to cyclic ewes after a progestogen/eCG treatment. In conclusion, 500 IU of eCG given after 12 days of progestogen treatment had limited effects on the dynamics of ovarian follicular waves. However, eCG treatment increased serum concentrations of estradiol during the periovulatory period, particularly in anestrous ewes; this probably resulted in the synchronous estrus and ovulation in anestrous ewes.

Anestrus↗
PubMed2003

Developmental competence of prepubertal and adult goat oocytes cultured in semi-defined media following laparoscopic recovery.

With an increased interest in transgenic animal production, the caprine species offers many advantages, and the prepubertal goat is a potential source of large numbers of oocytes for in vitro embryo production. The aim of the present study was to evaluate the follicular response and recovery of oocytes from prepubertal and adult goats following ovarian stimulation and laparoscopic recovery, and their developmental competence following culture in semi-defined media. Oocytes were collected over a 15-week period from prepubertal goats (3-7 months old) and adult controls (2-4 years old) that had been subjected to estrus synchronization and ovarian stimulation. Following insemination, zygotes were cultured for 96h in G1.2 followed by an additional 120h in G2.2. Morulae and blastocysts were scored using light microscopy on Days 7 and 9 followed by fluorescent staining for cell counts on Day 9 (216h postinsemination). The mean numbers of follicles aspirated and oocytes recovered were significantly greater for prepubertal than for adult goats (P<0.01). The number of oocytes recovered from prepubertal goats was observed to decline significantly with increasing age of the animals (P<0.05). The proportion of oocytes that matured and cleaved did not differ significantly between prepubertal and adult goats. Furthermore, no significant differences in morulae development (percentage of those cleaved), 5% versus 4%, or blastocyst development, 6% versus 7%, were observed for prepubertal and adult derived oocytes (P>0.1), respectively. Mean cell number per blastocyst also did not differ significantly. In conclusion, higher yields of oocytes were obtained from gonadotrophin-primed, prepubertal does than from adults, while in vitro development was similar.

Animals↗
PubMed1983

[Possibilities of inducing superovulation and obtaining zygotes for transplantation in sheep].

The possibilities were explored of inducing superovulation and obtaining of zygotes from ewes of the Romanov and Tsigai breeds. The pattern used of inducing superovulation included stimulation with the serum gonadotropin preparation Gravohormone applied at the rates of 750 and 1000 IU, estrus synchronization with Estrumate (ICI, England), and ovulation with the use of the choriogonadotropin preparation Gonabion (Jenapharm, DDR). With Romanov sheep both doses of Gravohormone did not affect essentially the ovarian activity--3.4 and 3.7 ovulations were induced, whereupon a total of 5 (20%) and 10 (38%) ova were obtained from all groups of 7 animals each, 3, resp., 2 only of the zygotes being considered of high quality. With Tsigai sheep a differential ovarian response was induced--3.4 and 6.6 ovulations were produced, whereupon 5 (29%) and 15 (35%) ova were obtained, 2, resp., 7 of them being fertilized, but only 2 of the zygotes being considered fit for transplantation from the group treated with 750 IU of the preparation. No substantial differences were established in the blood plasma estradiol-17 beta and progesterone content and dynamics with the two groups of Romanov sheep treated for superovulation. Results showed that the low response of Romanov sheep, the insufficient fertilization of ova, and the low percent of zygotes capable for transplantation should be further discussed.

Animals↗
PubMed1991

Effects of breeding season length and calving season on range beef cow productivity.

A 5-yr study was conducted beginning in 1983 with 460 cows to evaluate the effects of three breeding seasons (30, 45, and 70 d in length) and two times of spring calving, March (early) and April (late), on cattle production under Nebraska Sandhills range conditions. Criteria evaluated included pregnancy and weaning percentages, calving date and distribution, cow weights and body condition at four intervals, calf birth and weaning weights, and cow productivity. The 30-d breeding season included a 10-d estrus synchronization and AI period; in the other breeding seasons only natural breeding was used. The same sires were used over the entire study period. Percentage of cows pregnant and percentage of calves weaned were lower (P less than .01) for cows bred for 30 d than for cows bred for 45 or 70 d. Average calving dates were similar among the breeding groups within the early and late calving herds. Pregnancy rates from AI were higher (P less than .01) for the cows calving in April (64%) than for the cows calving in March (41%). Cows calving in April lost less weight between precalving and prebreeding and were heavier (P less than .05) at prebreeding time than the cows calving in March. Calf weaning weights were not different (P greater than .10) among any of the breeding season groups or between the two calving herds when calves were weaned at a similar age. Cow productivity (calf weaning weight per breeding female) was highest (P less than .05) for the cows bred for 70 d (186 kg), intermediate for the cows bred for 45 d (172 kg), and lowest for cows bred for 30 d (162 kg).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2003

Premature prostaglandin F2alpha secretion causes luteal regression in GnRH-induced short estrous cycles in cyclic dairy heifers.

This study aimed to confirm that the luteolysis in normal-cycling dairy heifers seen during short estrous cycles induced with cloprostenol (Clp) and GnRH administered 24h apart is caused by a premature release of prostaglandin F(2alpha) (PGF(2alpha)). A further aim was to study the PGF(2alpha) release pattern more closely to determine whether it resembles the spontaneous release occurring during normal regression of the corpus luteum (CL) or whether PGF(2alpha) is continuously secreted after the induced ovulations, leading to short estrous cycles. Twenty-four Ayrshire heifers were allotted to four equally sized groups. After estrus synchronization with 0.5mg of Clp, a new luteolysis was induced with 0.5mg of Clp on Day 6 (groups T-d6 and C-d6) or Day 7 (groups T-d7 and C-d7) after ovulation. Gonadorelin (0.1mg i.m.) was given to groups T-d6 and T-d7 to induce premature ovulation 24h later. Groups C-d6 and C-d7 served as controls. Ovaries were examined daily by transrectal ultrasonography, while blood samples (for progesterone and 15-ketodihydro-PGF(2alpha) analyses) were obtained via a jugular catheter every 3h, starting from the second Clp treatment and continuing for 9 days postovulation. Unresponsiveness to Clp or anovulation resulted in 4 C-d6 heifers being excluded. Four heifers in group T-d6 and three in group T-d7 had a short estrous cycle of 8-12 days, while all others had a cycle of normal length. Significant elevations in 15-ketodihydro-PGF(2alpha) concentrations with recurrent high peaks coincided with a decrease in progesterone concentration and were detected in all heifers that showed a short estrous cycle, but not in any heifers with normal estrous cycles in groups T and C. In conclusion, a premature release of PGF(2alpha), which closely resembles its release during spontaneous luteolysis, causes luteal regression in these short cycles.

Animals↗
PubMed2004

Accuracy of transrectal ultrasonography for determination of pregnancy in sheep: effect of fasting and handling of the animals.

The present study was performed to investigate the effect of previous fasting and lifting of the abdomen of the ewes during transrectal ultrasonographic scanning on the results of early pregnancy diagnosis. Ewes of four flocks (A, B, C and D; all Awassi x Merino ewes, n = 1247 ) aged 0.7-10 years were used in this study. These ewes were estrus synchronized and artificially inseminated. From 2 weeks later onwards, fertile rams were kept with the ewes of flocks A, B and C ( n=949 ) for natural breeding, while ewes of flock D ( n=298 ) were re-inseminated 17 days later. Transrectal ultrasonography (5 MHz) was carried out in ewes of flocks A, B and C on four separate occasions but only once in ewes of flock D. For final analysis, animals were divided over two groups: ewes of Group 1 ( n=949 scans) were scanned in a standing position within the milking parlor. Animals of Group 2 ( n=764 scans) were scanned by the same operator and with the same scanning technique, but these ewes were fasted for 12h prior to scanning and the abdominal wall was lifted, just in front of the udder during scanning. The sensitivity of the test for diagnosing pregnancy at Days 18-24, 25-30, 31-40 and 41-50 was 21.8, 32.3, 63.3 and 50% in Group 1, and 46, 92.5, 92.3 and 96.8% in Group 2, respectively. Only within Group 1, the sensitivity of the test was higher in young ewes (0.7-2 years) than in older ones (>2-10 years). Significant differences were observed at scan periods Days 18-24 and Days 41-50 of gestation. It is concluded that, fasting prior to scanning and lifting the abdomen during scanning significantly improve the accuracy of transrectal ultrasonographic pregnancy diagnosis in Awassi x Merino ewes.

Animals↗
PubMed1995

Fate of the dominant follicle, embryonal survival, and pregnancy rates in dairy cattle treated with prostaglandin F2 alpha and progestins in the absence or presence of a functional corpus luteum.

Our objective was to examine the role of progestin type on serum concentrations of progesterone (p4) and estradiol-17 beta (E2), ovarian follicular dynamics, and fertility in cattle in the presence or absence of a corpus luteum (CL) in an estrus synchronization scheme using progestin and PGF2 alpha. In Exp. 1, 325 cows and heifers were given one injection of PGF2 alpha (d 0) and then assigned randomly within parity to five treatments: to receive a second PGF2 alpha injection 14 d later (control); to receive norgestomet (NORG) for 7 d beginning on d 8, with a second PGF2 alpha injection given either 1 d (NORG + no CL) or 6 d (NORG + CL) after insertion; or to receive a P4-releasing intravaginal device (PRID) in lieu of norgestomet at comparable times. Presence or absence of a CL was based on concentrations of serum P4 on d 14. Pregnancy rates after insemination were greater (P < .01) with luteal treatments than with nonluteal treatments. Embryonal survival between two stages of pregnancy was 87.6%. In Exp. 2, ovarian structures in 50 cows were examined daily using ultrasonography and the same five treatments. Diameter of the ovulatory follicle was greater (P < .05) with the nonluteal treatments (NORG and PRID + no CL) than with the control and luteal treatments (PRID and NORG + CL). Replacement of the dominant follicle during progestin treatment was altered by treatment (luteal status) and stage of the estrous cycle. Fertility was not enhanced by exogenous progestins when a CL was present. In the absence of a CL, progestin (P4 less than NORG at the doses used) reduced fertility by increasing E2 and the diameter of the ovulatory follicle and decreasing turnover of dominant follicles.

Administration, Intravaginal↗