Two-dimensional polyacrylamide gel electrophoresis of proteins synthesized and released by conceptuses and endometria from pony mares

Conceptuses were obtained from pony mares on each day of pregnancy between Days 12 and 28, and on Days 39, 45, 65 and 100. Endometrium was obtained from mares at Days 12, 14, 16, 18, 39, 45, 65 and 100 of pregnancy, and from non-pregnant mares during anoestrus, during transition into the breeding season, at oestrus, or during dioestrus. Tissues were incubated in vitro for 24 h with L-[3H]leucine. Proteins synthesized and released into the culture medium were analysed by two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) and fluorography. Conceptuses obtained before Day 14 after ovulation released a characteristic pattern of labelled proteins. These included two groups of apparent isoelectric variants of relative molecular weights (Mr) 30,000-40,000 (pI values 4.5-5.5 and 6-7), one group of Mr approximately 22,000 (pI 6.5-7), and large protein(s) that did not enter the 10% polyacrylamide gel. After Day 14 the array of labelled proteins had changed and resembled that produced by isolated yolk sac at the later stages of pregnancy studied. Included amongst these were several acidic polypeptides with Mr 20,000 (pI 5-6). The endometrial samples released an array of non-dialysable polypeptides into the culture medium. Fluorograms could be assigned to one of three general groups, with endometrium from mares within each group producing similar patterns of labelled proteins. The first group consisted of anoestrous, transitional and ovariectomized mares, and mares at oestrus or Day 1 or Day 18 after ovulation. The second group was comprised of mares at Days 12-16 of dioestrus or Days 12-18 of pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)     

Characterization of the uterine environment during early conceptus expansion in the bovine

Fifty-three Angus and Hereford beef cows were utilized to investigate the effect of the conceptus on uterine environment during the period of pregnancy recognition. Blood samples were collected on Days 10, 12, 14, 16 and 18. Cows were randomly assigned to be either mated on the subsequent oestrus or serve as cyclic controls. Blood samples were then collected daily from Day 10 until slaughter on Day 15, 16 or 17 from the initiation of oestrus. Uteri were flushed with physiological saline and flushings analyzed for quantitative and qualitative protein changes, calcium, oestradiol-17β and prostaglandin F content. Endometrial explants of caruncular and intercaruncular tissue, and conceptus tissue recovered from pregnant cows were cultured with [³H]-leucine to determine quantitative and qualitative polypeptide synthesis and release. Plasma progesterone concentrations were similar between pregnant and cyclic cows from Day 10 through 17. Only the uterine content of prostaglandin F significantly increased in the ipsilateral horn of pregnant cows on Days 16 and 17. This increase in prostaglandin content was related to the increase in conceptus length from 25 to 40–80 mm. Conceptus production of bovine trophoblastic protein-1 was also first clearly detectable in fluorographs of medium from conceptuses measuring 25 mm. The complexity of the polypeptides present in the medium increased with conceptus development. Polypeptide synthesis by the endometrium was similar between tissues and days; however, production of two groups of low molecular weight basic polypeptides continued to be intensified on fluorographs from the pregnant horn on Day 17 compared to cyclic cows.     

Effectiveness of administration of gonadotropin-releasing hormone at Days 11, 14 or 15 after anticipated ovulation for increasing fertility of lactating dairy cows and non-lactating heifers

One strategy for improving fertility in cattle is mid-cycle administration of GnRH to increase progesterone secretion and delay luteolysis. This strategy might be especially useful during hot weather because heat stress increases uterine prostaglandin release and reduces development of the elongating embryo. A series of experiments was conducted to test the efficacy of GnRH for increasing fertility. There was no effect of administration of 100 microg GnRH at Day 11 after anticipated ovulation on pregnancy rates in virgin heifers subjected to timed artificial insemination (TAI) during the summer. Similarly, there was no beneficial effect of administration of GnRH at Day 11 after anticipated ovulation on pregnancy rates of lactating cows subjected to TAI in summer and winter. Three experiments tested effects of injection of GnRH at Days 14 or 15 after anticipated ovulation on pregnancy rates of lactating cows. The first experiment used 477 lactating cows subjected to TAI. Cows receiving GnRH at Day 14 had higher pregnancy rates in both summer and winter than cows receiving vehicle (20.3 versus 12.7%, P<0.02). When this experiment was repeated during summer with 137 cows, there was a negative effect of GnRH treatment at Day 14 on pregnancy rate. In the third experiment, lactating cows during summer were inseminated at detected estrus and cows were assigned to treatment with either GnRH or vehicle at Days 14 or 15 after insemination. Pregnancy rates were 25.6% (32/125) for cows receiving vehicle, 20.7% (19/92) for cows receiving GnRH at Day 14, and 20.3% (16/79) for cows receiving GnRH at Day 15. In conclusion, GnRH administration at Days 11-15 after anticipated ovulation or estrus did not consistently increase pregnancy rates in either cool or warm seasons.     

Ovarian function in Nelore (Bos taurus indicus) cows after post-ovulation hormonal treatments

Maternal recognition of pregnancy in the cow requires successful signaling by the conceptus to block luteolysis. Conceptus growth and function depend on an optimal uterine environment, regulated by luteal progesterone. The objective of this study was to test strategies to optimize luteal function, as well as prevent a dominant follicle from initiating luteolysis. Nelore (Bos taurus indicus) beef cows (n=40) were submitted to a GnRH/PGF(2alpha)/GnRH protocol. Cows that ovulated from a dominant ovarian follicle (ovulation=Day 0) were allocated to receive: no additional treatment (G(C); n=7); 3000IU of hCG on Day 5 (G(hCG); n=5); 5mg of estradiol-17beta on Day 12 (G(E2); n=6); or 3000IU of hCG on Day 5 and 5mg of estradiol-17beta on Day 12 (G(hCG/E2); n=5). Ultrasonographic imaging of the ovaries, assessment of plasma progesterone concentration, and detection of estrus were done daily from Day 5 to the day of subsequent ovulation. Treatment with hCG induced an accessory CL, increased CL volume, and plasma progesterone concentration throughout the luteal phase (P<0.01). Estradiol-17beta induced atresia and recruitment of a new wave of follicular growth; it eliminated a potentially estrogen-active, growing ovarian follicle within the critical period for maternal recognition of pregnancy, but it also hastened luteolysis (Days 16 or 17 vs. Days 18 or 19 in non-treated cows). In conclusion, the approaches tested enhanced luteal function (hCG) and altered ovarian follicular dynamics (estradiol-17beta), but were unable to extend the life-span of the CL in Nelore cows.     

Interrelationships between progesterone, 13,14-dihydro-15-keto PGF-2 alpha (PGFM) and LH in cyclic and early pregnant cows

Plasma progesterone and LH secretion patterns were examined in 18 mature dairy cows during the oestrous cycle and after insemination. Blood samples were collected every 15 min for 8 h per day on Days 3, 5, 6, 7, 8, 9, 10, 12, 14, 16, 17, 18, 19, 20 and 21 of the oestrous cycle, then, in the same cows, at the same times during early pregnancy. PGF-2 alpha secretion rates (as determined by plasma PGFM concentrations) were also monitored on Days 14, 16 and the day of, or equivalent to, luteal regression. Mean daily plasma progesterone concentrations were similar until Day 16 in cyclic and pregnant cows, after which values in non-pregnant animals declined. Regression analysis indicated that progesterone concentrations were best described by a quadratic expression with fitted maximum values on Day 13 in non-pregnant animals but values increased linearly over the whole period to Day 21 in pregnant cows. The frequency, amplitude and area under the curve of LH episodes showed no significant differences between cyclic and pregnant animals. In pregnant cows, the amplitude and area under the curve of progesterone episodes increased linearly between Days 8 and 21, although no such increase occurred in cyclic cows. Low-level PGFM episodes were present in cyclic and pregnant cows on Days 14 and 16 after oestrus, and high amplitude episodes occurred in non-pregnant cows during luteal regression. Pregnant cows showed a significant depression of the amplitude, but not the frequency of episodes at the expected time of luteal regression. These results confirm that the corpus luteum of pregnancy secretes an increasing amount of progesterone per se and per unit of LH until at least Day 21 after mating. They further suggest that the corpus luteum of the cyclic cow may experience small episodes of PGF-2 alpha and be subjected to initial degenerative changes by Day 14 after oestrus, some time before the onset of definitive luteolysis.     

Effect of human chorionic gonadotropin administered at specific times following breeding on milk progesterone and pregnancy in cows

Two trials were conducted to investigate the efficiency of human chorionic gonadotropin (hCG) following breeding to increase progesterone (P(4)) secretion and pregnancy rates in cows. In Trial 1, 79 lactating Holstein cows were randomly allocated to four groups to receive hCG either at breeding (Day 0, n=20), Day 7 (n=20) or Day 14 (n=20), or to receive no hCG treatment (control n=19). Whole milk samples were collected every other day from breeding until Day 21 and, thereafter, at weekly intervals until Day 42 or until the return to estrus for determination of P(4) concentrations. Similar treatments were employed in Trial 2, and 121 lactating Holstein cows were randomly assigned to treatment at Day 0 (n=29), Day 7 (n=32), or Day 14 (n=29), or to receive no treatment and serve as a control group (n=31). Milk samples were obtained at weekly intervals from breeding until Day 42, or the return to estrus for determination of P(4) concentrations. Pregnancy diagnosis was made by palpation per rectum at approximately 60 days post breeding. Significant increases in P(4) concentrations were observed in Day-7 and Day-14 treated cows from Days 18 to 42 after breeding compared with the Day 0 or the control cows. A slight decrease in P(4) concentration throughout the sampling period was observed in the Day-0 treated cows. Significant increases in pregnancy rates were observed in hCG-treated cows compared with that of the controls, with the highest rate observed in the Day-7 treated group. The overall pregnancy rates were 47, 62, 55 and 40% for the Day 0, 7 and 14 groups and for the control groups, respectively. In nonpregnant cows the mean (+/- SEM) numbers of days to basal P(4) concentrations were 21.6 +/- 1.3, 24.1 +/- 1.6, 24.6 +/- 1.3 and 23.2 +/- 1.3 for cows treated on Days 0, 7 and 14 and for the control group, respectively. It is concluded that the administration of hCG at Day 7 or Day 14 after insemination could be used as a management tool to improve pregnancy rates in postpartum cows.     

Fetal survival in the cow after pregnancy diagnosis by palpation per rectum

It is desirable to determine wheter a cow has failed to become pregnant as early as possible, preferably prior to 50 d after insemination. Although palpation per rectum has been the generally accepted method of pregnancy diagnosis in cattle, the procedure may be a significant iatrogenic cause of fetal attrition. In a study conducted at a North Florida dairy from January through June 1982, pregnancy was determined in 192 Holstein-Friesian cows by measuring low milk progesterone (P4) content on day of insemination (Day 0) and elevated P4 on Days 21 and 24. Pregnant cows were randomly assigned to a treatment and a control group. Cows in the treatment group (n = 85) were palpated per rectum twice between Days 42 and 46 after insemination. Cows in the control group (n = 107) were not palpated until both groups were palpated at Day 90. Palpation, done by two experienced clinicians, consisted of palpation of fetal fluid fluctuation, identification of the amniotic vesicle, and slipping of the chorioallantoic membranes. In both groups of cows fetal viability was monitored by milk P4 content. Last milk (5 to 15 ml) was collected from one front quarter on Days 0, 21, and 24 and twice weekly thereafter through Day 63. Milk was defatted by centrifugation and the fat-free milk progesterone content measured by a radioimmunoassay without extraction. The milk P4 test was 80.0% accurate in determining pregnancy in the palpated and nonpalpated cows. In the cows palpated on Days 42 to 46, pregnancy rates declined by 7.5% as determined by palpation at Day 90, or by 11.4% as determined by milk P4 content through Day 63 (both values P < 0.05). Cows that were not palpated on Days 42 to 46 showed a 1.9% increase or a 4.3% decline in pregnancy rates as determined by the same criteria. Before palpation, at Days 42 to 46, pregnancy rates were better in cows that were inseminated in winter (January to March) than in spring (April to June) (82.3% vs 61.6%; P < 0.05); P4 content was higher (winter > spring = 2.13 ng/ml vs 1.38 ng/ml; P < 0.05). First-lactation cows had higher P4 values on Days 21 and 24 than older cows (P < 0.01).     

Pregnancy rates in lactating dairy cattle following supplementation of progesterone after artificial insemination

Poor conception rates in highly productive lactating cattle is especially prevalent in large, intensively-managed commercial herds. One of the causative factors is sub-optimal pre-implantation embryonic development which appears to result from inadequate circulating concentrations of progesterone. In the present study, the efficacy of very modest progesterone supplementation, between Days 3.5 and 10 post-AI, on pregnancy rates was determined in a commercial herd where bovine somatotropin (bST) was used as a management tool. All lactating cattle that were deemed to be in estrus and inseminated over a 4-week period were randomly assigned to either a control group (no treatment) or CIDR-1.9g (previously used for estrous synchronization) treatment from Day 3.5 to Day 10 post-AI. Milk samples were collected four times: on the day of AI, at Day 2 or 3, at Day 4 and at Day 22 post-AI and were analyzed for progesterone content. Data from a total of 130 breedings were used in the final analysis. The CIDR treatment increased circulating concentrations of progesterone in treated animals over those of control animals on Day 4 by 0.7ng/ml (P<0.05) and increased pregnancy rate from 35% (22/63) to 48% (32/67) (P=0.068). The effect of treatment was greater in first and second lactation cows, where pregnancy rates were 33% (18/55) in controls and 51% (31/61) in treated animals (P=0.03). The results of this study indicate that the timing of onset of the progesterone influence is important for successful pregnancy outcome, particularly in first and second lactation cows.     

Plasma progesterone profiles and fertility status of anestrus Zebu cattle treated with norgestomet-estradiol-eCG regimen

Zebu cattle are notorious for poor fertility characterized by late maturity and long intercalving intervals attributed to a variety of factors, including genetic, nutritional and climatic. The aim of the present investigation, therefore, was to induce fertile estrus in acyclic pubertal heifers and postpartum anestrous Zebu cows by hormonal intervention. Pubertal Hariana and Sahiwal anestrous heifers (n=51) and postpartum cows (n=55) were either assigned a placebo (controls, N=6 for each breed and parity) or treated with 10-d norgestomet (3 mg) subcutaneous ear implants, with an initial injection of 3 mg, im norgestomet + 5 mg estradiol valerate, followed by 500 IU eCG at implant withdrawal (NOR-treated groups). Jugular venous plasma samples were obtained from a total of 28 animals (controls : 4 heifers and 4 cows; NOR-treated : 12 heifers and 8 cows) on Days 0 (implant insertion), 3, 7, 9 and Day 10 (implant withdrawal), every 12 h on Days 11 and 12, and then once daily on Days 17, 24 and 31. All the samples were assayed for progesterone. Almost all (97%) heifers and 81% cows were induced to estrus, the majority (92% heifers and 79% cows) within 120 h of implant removal. Synchrony of the induced estrus was better in cows, but interval to estrus and estrus duration were significantly longer in heifers (P<0.05). Post-treatment fertility, based on Day 28 nonretum rate, first service, and overall conception rates, was better in heifers (78.9, 60.5 and 73.7%, respectively) than cows (77.1, 48.6 and 62.9%, respectively), but the differences were significant only for the overall pregnancy rate (71.8% for heifers and 51.2% for cows; P<0.05). Low pre-treatment plasma progesterone values (<0.5ng/mL) were consistent with ovarian inactivity, confirming the true anestrus status of experimental animals. Controls failed to exhibit estrus and maintained low progesterone concentrations throughout the study. In treated animals, high progesterone values from Day 17 onwards suggested ovulatory estrus. These early luteal phase progesterone concentrations in nonpregnant (P=0.06) and nonpregnant, nonretum (P<0.05) animals were low in comparison with those of pregnant animals. Good fertility resulting from breeding according to estrus, inspite of variable intervals to estrus and estrus duration, advocates its advantage over fixed-time insemination in norgestomet-treated anestrous Zebu cattle.     

Effectiveness of prostaglandin F2alpha in the initial treatment of bovine ovarian cysts

This study was conducted to evaluate the use of prostaglandin F2alpha (PGF2alpha) in the initial treatment of ovarian cysts in dairy cattle. Two hundred and sixty three cows diagnosed cystic on palpation per rectum were randomly assigned to one of three treatment groups (A, B or C). Cows in Groups A and B were treated with 25 mg i.m.of PGF2alpha at the time of diagnosis (Day 0), while cows in Group C received 100 mug of GnRH. Seven days following initial treatment (Day 7), cows from Group A that were not observed in estrus were treated with GnRH. Cows from Groups B and C were not treated. On Day 14, all cows that had not been inseminated received PGF2alpha. A blood sample was obtained from all cows on Days 0, 7 and 14 and was analyzed for progesterone (P4) using radioimmunoassay. Incidences of estrus were recorded and cows that were more than 60 d in milk at the time of diagnosis were bred when observed in estrus. The incidence of follicular cysts on Day 0 (as defined as P4 <0.5 ng/ml) was similar between groups and constituted about 40% of all cysts. There were significantly more cows pregnant to insemination within 7 d of initial treatment in Group B than in Groups A and C (P<0.05). After Day 14, the pregnancy rate was not statistically different between Group B and C, but Groups B and C had a statistically higher pregnancy rate than Group A from Day 21 to Day 35. At the end of the study, there was no statistical difference for the pregnancy rate between groups. We concluded that treatment of ovarian cysts diagnosed by per rectum examination with prostaglandin (at time of diagnosis and 14 d later for cows that were not inseminated) was as effective as initial treatment with GnRH followed by prostaglandins 14 d later for cows that were not inseminated previously. Cows that were initially treated with prostaglandins also tended to become pregnant sooner.     

Alterations in embryo development in progestogen-supplemented cows administered prostaglandin F2alpha

The objective was to examine effects of elevated prostaglandin F2alpha (PGF) on embryo development in cows supplemented with exogenous progestogen. Cows were artificially inseminated at estrus (Day 0) and a synthetic progestogen supplemented in the feed from Days 3 to 8. Cows were allotted randomly to receive either 15 mg PGF (TRT) or saline (CON) at 06:00, 14:00 and 22:00 h from Days 5 to 8. Blood samples were collected at 06:00 and 22:00 h from Days 5 to 8 for determination of progesterone and 13,14-dihydro-15-keto-PGF2alpha (PGFM). Single embryos were recovered on Day 8, assigned a quality score, and stage of development recorded. Progesterone was lower from Days 5 to 8 in TRT versus CON cows (P = 0.0001). Concentrations of PGFM from Days 5 to 8 were elevated in TRT compared to CON cows (P = 0.0001). Embryo quality was reduced in TRT cows compared to CON cows (P = 0.059). Percentage of embryos considered transferable was decreased by administration of PGF (P = 0.003). Sixty-four percent of TRT embryos were retarded in development at Day 8, whereas 80% of CON embryos had developed to expanded blastocysts (P = 0.003). In conclusion, treatment of progestogen-supplemented cows with PGF reduced quality and retarded development of embryos. Decreased fertility in conditions causing elevated concentrations of PGF may result from altered embryo development and quality.     

Early pregnancy diagnosis in cattle by means of linear-array real-time ultrasound scanning of the uterus and a qualitative and quantitative milk progesterone test

We compared three methods for diagnosing early pregnancy in cattle: 1) a trans-rectal ultrasound scan of the uterus, 2) a cow-side enzymeimmunoassay (EIA) milk progesterone test 3) a radioimmunoassay (RIA) milk progesterone test. Scanning of the uterus was performed in 148 cows. These cows were not detected in estrus before scanning, which took place between Days 21 and 33 after insemination (AI). A considerable difference was noted between the reliability of the scannings performed at an early stage (Days 21 to 25) and those performed at a later stage (Days 26 to 33). The sensitivity and specificity of the ultrasound examination between Days 21 and 25 were only 44.8% and 82.3%, respectively, but were 97.7% and 87.8% between Days 26 and 33, respectively. Milk samples were collected on the day of AI. (Day 0) and 21 days later. Samples that were positive in the EIA test always contained more than 1 ng/ml progesterone (P4); however, 20% of the negative EIA samples contained also more than 1 ng/ml P4. Only 59% of the animals showing a negative EIA test on Day 0 and a positive test on Day 21, indicating pregnancy, calved, while 16% of the cows with a negative test on Day 0 and Day 21, indicating nonpregnancy, turned out to be pregnant. Of the 82 animals with P4 levels lower than 1 ng/ml on Day 0 and higher than 1 ng/ml on Day 21, only 61.0% calved. All 14 cows with low levels both on Day 0 and Day 21, indicating nonpregnancy, were found to be not pregnant. The influence of both early embryonic death and the accumulation of intrauterine fluids on the accuracy of these tests are discussed.     

The use of a deslorelin implant (GnRH agonist) during the late embryonic period to reduce pregnancy loss

Embryonic and fetal mortality reduce reproductive performance of lactating dairy cows. The objectives of this study were to reduce pregnancy loss by administering a deslorelin implant (GnRH agonist) during the late embryonic period, to reduce follicular growth, induce accessory corpora lutea, and increase plasma progesterone concentrations. Lactating dairy cows received an implant containing 2.1 mg of deslorelin (Deslorelin group; n = 89) or no treatment (Control group; n = 92) on Day 27 of pregnancy. Pregnancy, ovarian structures and plasma progesterone concentrations were determined on Days 27 and 45, and pregnancy was re-confirmed on Day 90. On Day 45, mean +/- S.E.M. numbers of class 2 (6-9 mm; 0.72+/-0.19) and class 3 (> or = 10 mm; 0.86 +/- 0.12) follicles for cows in the Deslorelin group were lower (P < 0.01) than the numbers of class 2 (1.90 +/- 0.18) and class 3 (1.92 +/- 0.12) follicles for cows in the Control group. On Day 45, the number of accessory corpora lutea for cows in the Deslorelin group (1.80 +/- 0.07) were greater (P < 0.01) than for cows in the Control group (1.31 +/- 0.07). On Day 45, plasma progesterone concentration was increased (P < 0.01) for cows in the Deslorelin group (8.03 +/- 0.33 ng/mL) compared to cows in the Control group (6.40 +/- 0.31 ng/mL). Pregnancy losses did not differ between Days 27 and 45 and Days 45 and 90 for cows in the Control (15.2 and 11.0%, respectively) and Deslorelin groups (20.2 and 10.5%, respectively). However, in the Deslorelin group, pregnancy loss between Days 45 and 90 was lower (P < 0.05) for cows that formed an accessory CL (0%) compared to cows that did not form an accessory CL (16.1%).     

Changes in ovine conceptus and endometrial function following asynchronous embryo transfer or administration of progesterone

The secretory protein profile from conceptuses collected from naturally mated ewes on Days 10, 12, 14, and 16 was characterized by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and fluorography. The presence of the anti-luteolysin ovine trophoblast protein-1 (oTP-1) in culture medium from Day 10 conceptuses was confirmed by fluorography, Western blotting, and radioimmunoassay (RIA). On each of the days studied, oTP-1 was the dominant secretory protein, and was secreted in increasing quantities as pregnancy progressed. In a second experiment, Day 6 embryos were transferred to either Day 6 (SR) or Day 4 (AR) recipients. Three mated ewes (P) received daily injections of 50 mg progesterone on Days 4-9. Controls consisted of 2 groups of pregnant ewes (D8 and D10). Conceptuses and ipsilateral endometrium were collected 4 days following transfer of conceptuses to SR and AR ewes, on Day 10 in P and D10 ewes, and on Day 8 in D8 ewes. Conceptus volume was estimated upon recovery from the uterus. Tissues were cultured with 35S-methionine, and the medium was analyzed for total and trichloroacetic acid-precipitable radiolabeled proteins. Levels of specific endometrial secretory proteins were determined after protein separation by 2D-PAGE and estimation of the radioactivity associated with discrete radiolabeled proteins on fluorographs. The concentration of oTP-1 in conceptus culture medium was estimated by RIA. Thirty endometrial proteins were investigated. All 30 proteins were present in endometrial cultures from SR, AR, D10, and P ewes, but 13 proteins were absent from D8 ewes. Levels of three proteins were higher in AR compared to D8 (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of resynchronization with GnRH on day 21 after artificial insemination on pregnancy rate and pregnancy loss in lactating dairy cows

The objectives of the present study were to determine the effects of resynchronization with GnRH on Day 21 after artificial insemination (AI) on pregnancy rate and losses of pregnancy in lactating dairy cows. Holstein cows (n=585) on two dairy farms were assigned to one of two treatments in a randomized complete block design. On Day 21 after a pre-enrollment AI, animals assigned to the resynchronization (RES) group received 100 microg of GnRH i.m., whereas animals in the control (CON) group received no treatment. All animals were examined ultrasonographically on Days 21 and 28 after AI, and blood samples were taken for progesterone measurement on Day 21. Pregnancy was diagnosed on Day 28 and reconfirmed 14 days later. Nonpregnant cows on Day 28 were inseminated using timed AI after the completion of the Ovsynch protocol 10 and 17 days after enrollment in the study for RES and CON groups, respectively. Progesterone concentration > or =2.35 ng/ml was used as an indicator of pregnancy on Day 21. For RES and CON cows, pregnancy rate at Days 21 (70.9% versus 73.0%, P<0.56), 28 (33.1% versus 33.6%; P<0.80) and 42 (27.0% versus 26.8%; P<0.98) after the pre-enrollment AI did not differ. Administration of GnRH on Day 21 after AI had no effect on pregnancy loss in RES and CON groups from days 21 to 28 (53.2% versus 53.5%; P<0.94) and days 28 to 42 (17.9%; P<0.74) after AI. Pregnancy rate after the resynchronization period was similar for both treatment groups. Resynchronization with GnRH given on Day 21 after AI for initiation of a timed AI protocol prior to pregnancy diagnosis does not affect pregnancy rate and pregnancy loss in lactating dairy cows.     

Conception rate and reproductive function of dairy cows fed different fat sources

The objective of the experiment was to determine the effects of fat supplementation on cyclicity, progesterone concentration, follicular development, conception rate, embryo mortality, and plasma concentrations of prostalglandin F metabolite (PGFM) in cattle. The hypothesis of this experiment was that feeding flaxseed, which is a source rich in C18:3, would increase conception rate of dairy cows due to decreased plasma PGFM concentrations. A total of 138 lactating Holstein cows were allotted at calving to three groups of 46 cows, blocked for similar calving dates. Cows within each block were assigned to one of three isonitrogenous, isoenergetic, and isolipidic supplements based on either whole flaxseed (FLA), Megalac (MEG) or micronized soybeans (SOY). The diets were fed from calving to Day 50 of pregnancy for pregnant cows, or 120 day postpartum for those not diagnosed pregnant after AI. Detailed measurements of PGFM and follicle dynamics were only made on four cows for FLA and five cows for both MEG and SOY. The response in PGFM concentration following the oxytocin challenge administered around Week 11 of lactation was similar over time among treatments. Plasma progesterone concentrations from Days 17 to 21 of the estrous cycle starting around Week 9 of lactation and determined on a subsample of cows (n=for FLA and n=5 for both MEG and SOY) were higher for cows fed FLA than for those fed SOY (P=0.04) or MEG (P=0.06). Conception rates were similar among treatments. Total embryo mortality was lower (P=0.07) for cows fed FLA (0%) compared to those fed either MEG (15.4%) or SOY (8.0%). The mean size of the CL measured during a complete estrous cycle from Week 9 of lactation was smaller for cows fed SOY (16.3 mm) compared to those fed either FLA (19.1 mm) or MEG (18.3 mm). We inferred that pregnancy losses could be reduced by feeding whole flaxseed as a result of its effects on different factors such as modulation in concentration of progesterone and size of the CL.     

Steroid metabolism by endometrial and conceptus tissues during early pregnancy and pseudopregnancy in gilts

Endometrial and conceptus tissues were obtained on Days 10.5, 11, 12, 16 and 25 of pregnancy and Day 25 of pseudopregnancy of gilts and incubated for 6 h in Minimal Essential Medium (5 ml) containing 35 ng [3H]progesterone. Metabolism of [3H]progesterone to oestrone, oestradiol and oestriol was determined by gas and high-pressure liquid chromatography and successive recrystallizations with unlabelled standards. Conceptuses collected between Days 10.5 and 12 were spherical, tubular or filamentous and incubated with 500 mg endometrium and [3H]progesterone. Production of oestrone by spherical conceptuses was not detected, but was 44-47 pg/tubular conceptus and 21 pg/filamentous conceptus. A similar trend was observed for oestradiol. Conceptus tissues from Days 16 and 25 (chorion) were most active in producing oestrone (123 and 520 pg/mg tissue, respectively) and oestradiol (277 and 876 pg/mg tissue, respectively). Endometrial oestrogen production was less than that for conceptus tissue for oestrone and oestradiol on Days 16 and 25 of gestation. Coincubations of endometrium and conceptus tissues had lower oestrogen production than conceptus alone. Endometrium from Day 25 of pseudopregnancy metabolized [3H]progesterone to several non-polar metabolites, but no oestrogens were detected. An unidentified phenolic metabolite of [3H]progesterone was detected in higher quantities than either oestrone or oestradiol; 445 to 461 pg/conceptus at the tubular stage. These results indicate temporal changes in the conversion of [3H]progesterone to oestrogens by conceptus and endometrial tissue from pregnant gilts, but not endometrium from pseudopregnant gilts.     

The effect of prostaglandin administration to Holstein-Friesian cows at Day 26 postpartum on clinical findings, and histological and bacteriological results of endometrial biopsies at Day 40

Ninety-two cows that calved between April and August 1984 in a commercial dairy herd were studied. The cows were randomly assigned to receive either cloprostenol (500 mug) or saline placebo on Day 26 postpartum. In addition, each cow was examined per rectum, had three endometrial biopsies taken and milk progesterone level determined. Double-blind techniques were used in administering treatments and in assessing response to treatment. The results of histological and bacteriological assessment of endometrial biopsies and clinical findings at Day 40 were compared between the cows that received prostaglandin at Day 26 and those that did not. Each Day 40 variable which was significantly associated with prostaglandin treatment at Day 26 was regressed against the treatment variable and progesterone level at Day 26 as well as a prostaglandin progesterone interaction term. Prostaglandin-treated cows had less vaginal discharge, smaller diameter uterine horns, less inflammation and fibrosis in the endometrium, and were less likely to have Actinomyces pyogenes isolated from a biopsy at Day 40 than untreated cows. These effects were independent of progesterone level at the time of treatment.     

Synchronization and resynchronization of inseminations in lactating dairy cows with the CIDR insert and the Ovsynch protocol

Pregnancy per artificial insemination (AI) was evaluated in dairy cows (Bos taurus) subjected to synchronization and resynchronization for timed AI (TAI). Cows (n = 718) received prostaglandin F_2α (PGF) on Days –38 and –24 (Days 39 and 53 postpartum), gonadotropin-releasing hormone (GnRH) on Day –10, PGF on Day –3, and GnRH and TAI on Day 0. Between Days –10 and –3, cows received a progesterone intravaginal insert (CIDR group) or no CIDR (Control group). Between Days 14 and 23, cows received a CIDR (Resynch CIDR group) or no CIDR (Resynch control group), GnRH on Day 23, with pregnancy diagnosis on Day 30. Cows in estrus (between Days 0 and 30) were re-inseminated at detected estrus (RIDE). Nonpregnant cows received PGF on Day 30 and GnRH and TAI on Day 33. Plasma progesterone was determined to be low or high on Days –24 and –10. Pregnancy rates were evaluated 30 and 55 d after AI. The CIDR insert included in the Presynch-Ovsynch protocol did not increase overall pregnancy per AI for first service (36.1% and 33.6% for CIDR; 34.1% and 28.8% for Control) but did decrease pregnancy loss (7.0% for CIDR and 15.6% for Control). The CIDR insert increased pregnancy per AI in cows with high progesterone at the time the CIDR insert was applied. Administration of a CIDR insert between Days 14 and 23 of the estrous cycle after first service did not increase overall pregnancy per AI to second service (24.7% and 22.7% for Resynch CIDR; 28.6% and 25.3% for Resynch control). For second service, RIDE cows had lower pregnancy rates in the Resynch CIDR group than in the Resynch control group. Cows with a CL (corpus luteum) at Day 30 had higher pregnancy rates in the Resynch CIDR group than those in the Resynch control group.     

The use of progestins in regimens for fixed-time artificial insemination in beef cattle

Four experiments were conducted to investigate modifications to gonadotropin releasing hormone (GnRH)-based fixed-time Al protocols in beef cattle. In Experiment 1, the effect of reducing the interval from GnRH treatment to prostaglandin (PGF) was examined. Lactating beef cows (n = 111) were given 100 mg gonadorelin (GnRH) on Day 0 (start of treatment) and either 500 microg cloprostenol (PGF) on Day 6 with Al and 100 microg GnRH 60 h later, or PGF on Day 7 with Al and GnRH 48 h later (6- or 7-day Co-Synch regimens). Pregnancy rates were 32/61 (53.3%) versus 26/50 (52.0%), respectively (P = 0.96). In Experiment 2. cattle (n = 196) were synchronized with a 7-day Co-Synch regimen and received either no further treatment or a CIDR-B device (Days 0-7). Pregnancy rates were 32/71 (45.1%) versus 33/77 (42.9%) in cows (P < 0.8), and 9/23 (39.1 %) versus 17/25 (68.0%) in heifers (P < 0.05). In Experiment 3, 49 beef heifers were randomly assigned to receive 12.5 mg pLH on Day 0, PGF on Day 7 and 12.5 mg of pLH on Day 9 with Al 12 h later (pLH Ovsynch), or similar treatment plus a CIDR-B device from Days 0 to 7 (pLH Ovsynch + CIDR-B), or 1 mg estradiol benzoate (EB) and 100 mg progesterone on Day 0, a CIDR-B device from Days 0 to 7 (EB/ P4 + CIDR-B), PGF on Day 7 (at the time of CIDR-B removal) and 1 mg i.m. EB on Day 8 with AI on Day 9 (52 h after PGF). Pregnancy rate in the EB/P4 + CIDR-B group (75.0%) was higher (P < 0.04) than in the pLH Ovsynch group (37.5%): the pLH Ovsynch + CIDR-B group was intermediate (64.7%). In Experiment 4, 266 non-lactating cows were allocated to a 7-day Co-Synch protocol (Co-Synch), a 7-day Co-Synch plus 0.6 mg per head per day melengestrol acetate (MGA) from Days 0 to 6 inclusive (Co-Synch + MGA) or MGA (Days 0-6) plus 2 mg EB and 50 mg progesterone on Day 0. 500 microg PGF on Day 7, 1 mg EB on Day 8 and fixed-time Al 28 h later (EB/ P4 + MGA). Pregnancy rates (P < 0.25) were 44.8% (39/87: Co-Synch), 47.8% (43/90; Co-Synch + MGA), and 60.7% (54/89: EB/P4 + MGA). In conclusion, a 6- or 7-day interval from GnRH to PGF in a Co-Synch regimen resulted in similar pregnancy rates in cows. The addition of a progestin to a Co-Synch or Ovsynch regimen significantly improved pregnancy rates in heifers but not in cows. Progestin-based regimens that included EB consistently resulted in high pregnancy rates to fixed-time Al.