Serum luteinizing hormone and plasma progesterone levels during the estrous cycle and early pregnancy in cows

The oocyte: the key player in the success of assisted reproduction technologies

The ovulation of a mature oocyte at metaphase II of meiosis, with optimal potential to undergo fertilisation by a sperm cell, complete meiosis and sustain the switch to mitotic division, and support early embryo development, involves a protracted and disrupted/delayed series of processes. Many of these are targeted for exploitation in vivo , or recapitulation in vitro , by the livestock industry. Reproductive technologies, including AI, multiple ovulation embryo transfer, ovum pick-up, in vitro embryo production, and oestrus and ovulation synchronisation, offer practitioners and producers the opportunity to produce offspring from genetically valuable dams in much greater numbers than they would normally have in their lifetime, while in vitro oocyte and follicle culture are important platforms for researchers to interrogate the physiological mechanisms driving fertility. The majority of these technologies target the ovarian follicle and the oocyte within; thus, the quality and capability of the recovered oocyte determine the success of the reproductive intervention. Molecular and microscopical technologies have grown exponentially, providing powerful platforms to interrogate the molecular mechanisms which are integral to or affected by ART. The development of the bovine oocyte from its differentiation in the ovary to ovulation is described in the light of its relevance to key aspects of individual interventions, while highlighting the historical timeline.

Blastocyst Cell Number and Allocation Affect the Developmental Potential and Transcriptome of Bovine Somatic Cell Nuclear Transfer Embryos

Cloning cattle using somatic cell nuclear transfer (SCNT) is inefficient. Although the rate of development of SCNT embryos in vitro is similar to that of fertilized embryos, most fail to develop into healthy calves. In this study, we aimed to identify developmentally competent embryos according to blastocyst cell composition and perform transcriptome analysis of single embryos. Transgenic SCNT embryos expressing nuclear-localized HcRed gene at day 7 of development were imaged by confocal microscopy for cell counting and individually transferred to recipient heifers. Pregnancy rates were determined by ultrasonography. Embryos capable of establishing pregnancy by day 35 had an average of 117 ± 6 total cells, whereas embryos with an average of 128 ± 5 cells did not establish pregnancy (P < 0.05). A lesser average number of 41 ± 3 cells in the inner cell mass (ICM) also resulted in pregnancies (<0.05) than a greater number of 48 ± 2 cells in the ICM. Single embryos were then subjected to RNA sequencing for transcriptome analysis. Using weighted gene coexpression network analysis, we identified clusters of genes in which gene expression correlated with the number of total cells or ICM cells. Gene ontology analysis of these clusters revealed enriched biological processes in coenzyme metabolic process, intracellular signaling cascade, and glucose catabolic process, among others. We concluded that SCNT embryos with fewer total and ICM cell numbers resulted in greater pregnancy establishment rates and that these differences are reflected in the transcriptome of such embryos.

Differences in Microbial Community Composition between Uterine Horns Ipsilateral and Contralateral to the Corpus Luteum in Beef Cows on Day 15 of the Estrous Cycle

This study evaluated differences in uterine microbiota composition between uterine horns ipsilateral and contralateral to the corpus luteum of beef cows on day 15 of the estrous cycle. Cows (n = 23) were exposed to an estrus synchronization protocol to exogenously induce synchronized ovulation. Cows were then euthanized on day 15 of the estrous cycle, and individual swabs were collected from uterine horns ipsilateral and contralateral to the corpus luteum using aseptic techniques. DNA was extracted, and the entire (V1-V9 hypervariable regions) 16s rRNA gene was sequenced. Sequences were analyzed, and amplicon sequence variants (ASVs) were determined. Across all samples, 2 bacterial domains, 24 phyla, and 265 genera were identified. Butyribirio, Cutibacterium, BD7-11, Bacteroidales BS11 gut group, Ruminococcus, Bacteroidales RF16 group, and Clostridia UCG-014 differed in relative abundances between uterine horns. Rikenellaceae RC9 gut group, Bacteroidales UCG-001, Lachnospiraceae AC2044 group, Burkholderia-Caballeronia-Paraburkholderia, Psudobutyribibrio, and an unidentified genus of the family Chitinophagaceae and dgA-11 gut group differed between cows that expressed estrus and those that did not. The composition of the microbial community differed between the ipsilateral and contralateral horns and between cows that expressed estrus and cows that failed to express estrus, indicating that the uterine microbiota might play a role in cow fertility.

History, insights, and future perspectives on studies into luteal function in cattle

The corpus luteum (CL) forms following ovulation from the remnant of the Graafian follicle. This transient tissue produces critical hormones to maintain pregnancy, including the steroid progesterone. In cattle and other ruminants, the presence of an embryo determines if the lifespan of the CL will be prolonged to ensure successful implantation and gestation, or if the tissue will undergo destruction in the process known as luteolysis. Infertility and subfertility in dairy and beef cattle results in substantial economic loss to producers each year. In addition, this has the potential to exacerbate climate change because more animals are needed to produce high-quality protein to feed the growing world population. Successful pregnancies require coordinated regulation of uterine and ovarian function by the developing embryo. These processes are often collectively termed "maternal recognition of pregnancy." Research into the formation, function, and destruction of the bovine CL by the Northeast Multistate Project, one of the oldest continuously funded Hatch projects by the USDA, has produced a large body of evidence increasing our knowledge of the contribution of ovarian processes to fertility in ruminants. This review presents some of the seminal research into the regulation of the ruminant CL, as well as identifying mechanisms that remain to be completely validated in the bovine CL. This review also contains a broad discussion of the roles of prostaglandins, immune cells, as well as mechanisms contributing to steroidogenesis in the ruminant CL. A triadic model of luteolysis is discussed wherein the interactions among immune cells, endothelial cells, and luteal cells dictate the ability of the ruminant CL to respond to a luteolytic stimulus, along with other novel hypotheses for future research.

Using claws to compare reproduction, stress and diet of female bearded and ringed seals in the Bering and Chukchi seas, Alaska, between 1953-1968 and 1998-2014

Rapid climate warming is decreasing sea ice thickness, extent and duration. Marine mammals such as bearded (Erignathus barbatus) and ringed (Pusa hispida) seals, which use sea ice for pupping, molting and resting, may be negatively affected. Claws from bearded and ringed seals store up to 14 and 12 years of sequential analyte data, respectively. These data can be used to compare reproduction, stress and diet across decades. In this study, we compare progesterone, cortisol and carbon and nitrogen stable isotopes in female bearded and ringed seals during 1953-1968 (pre-1968, a period prior to sea ice decline) to 1998-2014 (post-1998, a period during sea ice decline). When comparing these periods, bearded seals had statistically higher cortisol concentrations post-1998, and for both species δ13C was more negative post-1998, while progesterone and δ15N did not change. There was a positive relationship between progesterone and cortisol Z-scores for both species, except for ringed seals post-1998. There was a negative relationship between cortisol Z-scores and δ13C for bearded seals evident in post-1998 indicating that higher cortisol Z-scores are associated with more negative δ13C in bearded seals in recent years. This negative relationship between cortisol and δ13C in bearded seals suggests a shift to higher prey diversity, possibly due to changes in sea ice in the Pacific Arctic evident post 1998. Progesterone Z-scores corresponded to expected differences among non-pregnant, unimplanted, implanted and post-partum individuals. Using these data, pregnancy history was determined for reproductive years for each individual female sampled, which could allow for yearly pregnancy rates to be calculated given a large enough representative sample of the population. These results combine decades of observational studies with hormones and stable isotopes to infer changes in reproduction, stress and diet, as well as the connection between these life history parameters.

Absence of a corpus luteum and relatively lesser concentrations of progesterone during the period of pre-ovulatory follicle emergence results in lesser pregnancy rates in Bos indicus cattle

Concentrations of progesterone before AI have had variable effects on fertility in both Bos indicus and Bos taurus cattle. The aim of this study was to determine if fertility and concentrations of progesterone after AI were affected in Bos indicus females when pre-ovulatory follicles develop in the absence or presence of a corpus luteum (CL). Between 6.5-7.5 days after a synchronised oestrus, all follicles ≥4 mm in diameter were aspirated (Day 0) and cloprostenol was administered on Days 0 and 1 (LP4, n = 36) or on Days 4 and 5 (HP4, n = 40). Animals were inseminated on detection of oestrus until Day 9. Breeding continued using natural mating between Days 9 and 19, AI on detection of oestrus between Day 19 and 29 and natural mating between Days 29-90. Mean concentrations of progesterone were less on Days 2-4 in the LP4 compared to the HP4-treated animals but similar on Days 14 and 20. In the LP4- compared to the HP4-treated animals, the odds of being detected in oestrus and ovulating close to the first AI were similar, but odds of pregnancy to first AI (OR = 0.19, 95% CI 0.07 - 0.52) and after 1, 4 and 13 weeks of breeding were less (P ≤  0.051). Absence of a CL and relatively lesser concentrations of progesterone during emergence of pre-ovulatory follicles resulted in lesser pregnancy rates to AI in Bos indicus cattle but did not affect concentrations of P4 after ovulation.

Differential expression of interferon-gamma, IL-4 and IL-10 in peripheral blood mononuclear cells during early pregnancy of the bovine

Maternal systemic immune response is regulated by conceptus-derived signals through peripheral blood mononuclear cells (PBMCs) via blood circulation during early pregnancy in cattle. In this study, the PBMCs from day 18 in non-pregnant cows and days 14, 18 and 30 in pregnant cows were used to explore the expression of interferon-gamma (IFN-γ), interleukin 4 (IL-4) and IL-10, and the plasma progesterone (P4) concentration was also determined. The results showed that the expression levels of mRNA and the protein of IFN-γ were lower and that IL-4 and IL-10 were higher in the PBMCs from the pregnant cows than in those of non-pregnant cows. From this study, early pregnancy induced a lower Th1 immunity (IFN-γ) and a higher Th2 immunity (IL-4 and IL-10) in the PBMCs, which may be related to interferon-tau and P4, thereby contributing to successful pregnancy in cattle.

Trimethylation of histone 3 at lysine 4 in cryopreserved bovine embryos produced in vivo with sexed semen

The production rates of viable embryos using sexed semen through the conventional methodologies of multiple ovulation and embryo transfer are generally not satisfactory. However, the cryopreservation of these embryos is considered efficient. Knowledge of epigenetics can provide new tools or allow for adapting new protocols that could enhance the efficiency of reproductive biotechnologies. The aim of this study was to characterize the pattern of trimethylation of histone 3 at lysine 4 (H3K4me3) in bovine embryos produced in vivo with sexed semen that were submitted to cryopreservation. Bos taurus × Bos indicus cows (n = 5) were superovulated and inseminated with sexed (two sessions) or conventional (two sessions) semen. A portion of the embryos collected on Day 7 was immediately stored in paraformaldehyde (3%) and another portion was stored in paraformaldehyde after cryopreservation/thawing. All embryos from the four groups (fresh, conventional semen; fresh, sexed semen; cryopreserved, conventional semen; and cryopreserved, sexed semen; 15 embryos per group) were evaluated by immunofluorescence under confocal microscopy to identify and quantify the H3K4me3 status. In total, 190 embryos were recovered, 100 of which were produced with conventional semen and 90 with sexed semen. The use of conventional semen after superovulation yielded 72% (72 of 100) viable embryos, which were mostly (81%; 59 of 72) in advanced stages of development (blastocysts and expanded blastocysts). Embryos produced with sexed semen had a lower viability rate (36.7%; 33 of 90), and most of them were collected at earlier stages of development (morulae and early blastocysts; P < 0.05). The H3K4me3 signal was similar among groups; however, there was a difference between morulae and blastocysts. A high intensity of H3K4me3 was observed in bovine embryos produced in vivo, and this pattern did not vary using sexed semen and the slow cryopreservation process. The lower viability of bovine embryos produced with sexed semen could be not explained by differences in H3K4me. Cryopreservation did not alter the pattern of H3K4me3; in this sense, we suggest that it is a process that exerts minimal damage to the embryos.

Pregnancy rates relative to recipient plasma progesterone levels on the day of nonsurgical transfer of frozen/thawed bovine embryos

A total of 71 synchronized dairy heifers (Holstein Friesian x German Black Pied) were used as recipients of seven-day old frozen/thawed bovine embryos. Plasma progesterone concentrations and corpus luteum quality on the day of nonsurgical transfer (= day 7) were determined and related to pregnancy rates or estrus intervals in nonpregnant recipients. A total of 32 recipients (45.1 %) maintained pregnancy; 39 recipients (54.9 %) did not. No significant differences could be detected between progesterone levels in recipients that remained pregnant (3.14 +/- 0.24 ng/ml; x +/- SEM ) and those that did not maintain pregnancy (3.23 +/- 0.28 ng/ml). Optimal progesterone levels were between 2 and 5 ng/ml coinciding with a pregnancy rate of 51.1 % (24 47 ). Pregnancy rates apparently were decreased when progesterone levels were below 2 ng/ml (35.3 %; 6 17 ) or above 5 ng/ml (28.6 %; 2 7 ). Hence, optimal progesterone levels were identical to those for freshly collected embryos reported previously by Remsen et al. (1). Bovine corpus luteum quality graded by rectal palpation was related to some extent to progesterone levels but not to pregnancy rates. Out of 39 nonpregnant recipients seven animals (17.9 %) with a mean plasma progesterone level of 3.76 +/- 0.72 ng/ml showed an extended estrus interval of more than 55 days, probably indicating early embryonic mortality. Progesterone levels did not significantly differ between nonpregnant recipients with estrus intervals of various length. Plasma progesterone levels at the time of transfer are of limited diagnostic value for screening recipients prior to transfer of frozen/thawed embryos.

Conception rates and serum progesterone concentration in dairy cattle administered gonadotropin releasing hormone 5 days after artificial insemination

The objectives of this study were to determine the effect of administration of exogenous GnRH 5days after artificial insemination (AI) on ovarian structures, serum progesterone concentration, and conception rates in lactating dairy cows. In experiment 1, 23 Holstein cows were synchronized using the Ovsynch protocol. Five days after AI (day 0) cows were assigned randomly to receive either saline (saline; n=11) or 100microg GnRH (GnRH; n=12). To examine ovarian structures, ultrasonography was performed on day 1 and every other day beginning on day 5 until day 13. On days 5 and 13 blood samples were obtained to measure serum progesterone concentrations. All cows in the GnRH-treated group developed an accessory corpus luteum (CL), whereas cows in the saline group did not. Mean serum progesterone concentrations did not differ between GnRH and saline groups on day 5 (1.64+/-0.46ng/ml versus 2.04+/-0.48ng/ml). On day 13 serum progesterone concentrations were greater (P<0.05) in the GnRH group compared with saline (5.22+/-0.46ng/ml versus 3.36+/-0.48ng/ml). In experiment 2, 542 lactating cows, at two different commercial dairies, were used to test the effect of administering GnRH 5 days after AI on conception rates. Cows were synchronized and detected for estrus according to tail chalk removal. Cows detected in estrus received AI within 1h after detection of estrus. Five days after AI, cows were assigned randomly to receive either GnRH (n=266) or saline (n=276). Pregnancy status was determined by palpation per rectum of uterine contents approximately 40 days after AI. There was no effect of farm on conception rate. There was no effect of treatment as conception rates did not differ between GnRH and saline groups (26.7% GnRH versus 24.3% saline). Regardless of treatment, days in milk, parity, milk yield, and number of services had no effect on the odds ratio of pregnancy. In summary, the results of this study indicated that GnRH administered 5 days after AI increased serum progesterone by developing an accessory CL but did not improve conception rates in dairy cattle.

Follicular Size and Response to Ovsynch Versus Detection of Estrus in Anovular and Ovular Lactating Dairy Cows

In a commercial dairy herd, 316 lactating Holsteins were studied to determine the percentage of anovular cows, to examine follicular sizes in anovular cows, and to compare synchronized ovulation (Ovsynch) versus detection of estrus on fertility of ovular and anovular cows. Ultrasonography examinations at 47 to 53 d and at 54 to 60 d postpartum were used to measure follicles and to classify cows as ovular or anovular. Anovular cows were identified as those with no detectable luteal tissue by ultrasonography and by low progesterone in blood samples collected weekly. Anovular cows included 28% of 122 primiparous cows and 15% of 194 multiparous cows. Of 64 anovular cows, 20% had follicles > or = 25 mm that might be considered cystic (4% of total cows), 58% had 15- to 24-mm follicles, and 22% had 9- to 14-mm follicles. Cows identified as ovular and anovular were randomly assigned within cyclic status to one of two artificial insemination (AI) strategies: 1) AI after detected estrus during 21 d, or 2) timed AI after a 10-d Ovsynch protocol. Weekly ultrasonography continued for 21 d to detect ovulations. For the Ovsynch sub-groups, 97% of ovular and 94% of anovular cows ovulated after the second GnRH injection. Within 21 d, spontaneous ovulations for the detection of estrus sub-groups were 42% of anovular cows vs. 89% of ovular cows. Conception rates were greater for ovular cows regardless of treatment, but conception rates between respective Ovsynch and estrus detection groups for ovular (32%, 35%) or anovular (9%, 11%) cows were similar. Although 20% of lactating cows were not cyclic by about 60 d postpartum, nearly all ovulated following Ovsynch. However, anovular cows had lower conception than ovular cows whether inseminated after detected estrous or after Ovsynch.

Estádios de desenvolvimento embrionário de vacas zebuínas superovuladas

O objetivo deste estudo foi relatar o estádio de desenvolvimento de embriões coletados a partir de processos superovulatórios em zebuínos. Foram utilizadas 26 vacas, 16 da raça Nelore Padrão, três da Nelore Mocho, quatro da Gir, duas da Brahman e uma da raça Guzerá. Para o processo de superovulação utilizaram-se 350 UI de FSH em oito doses decrescentes a cada 12 horas, a partir do 10ºdia do ciclo estral (estro = dia 0). Ao sétimo dia após o estro os embriões foram coletados pelo método não cirúrgico e avaliados ao microscópio estereoscópio quanto à qualidade e estádio de desenvolvimento embrionário. Foram coletados 135 embriões viáveis, sendo 68,2% (92/135) Nelore Padrão, 12,6% (17/135) Nelore Mocho, 11,1% (15/135) Gir, 5,2% (7/135) Brahman e 3,0% (4/135) Guzerá. Os embriões foram classificados segundo a qualidade em grau I, 51,1% (69/135), grau II, 43,7% (59/135), grau III, 4,4% (6/135), e grau IV, 0,7% (1/135), e segundo o estádio de desenvolvimento em mórula, 3,7% (5/135), blastocisto inicial, 16,3% (22/135), blastocisto, 37,0% (50/135), blastocisto expandido, 42,2% (57/135), e blastocisto eclodido, 0,7% (1/135). Observou-se predominância de estádios embrionários avançados (blastocisto, blastocisto expandido e blastocisto eclodido) que representaram 80% do total de embriões.

Preliminary observations on the concentrations of serum luteinizing hormone and follicle-stimulating hormone during gestation in bactrian camels (Camelus bactrianus)

The concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in the serum of the Bactrian camel (Camelus bactrianus) throughout pregnancy were analysed by radioimmunoassay. The samples were withdrawn at intervals of half a month. The serum LH concentrations varied significantly between 2.2+/-0.9 and 20.3+/-18.8 ng/ml during the pregnancy, with the highest value on the day of artificial insemination, which indicated that a preovulatory LH peak appeared. Thereafter, the LH concentration tended to fall, reaching a fairly constant low level by the eighth month of pregnancy. The serum FSH concentrations varied between 7.0+/-0.2 and 28.9+/-0.4 ng/ml during gestation, with the peak value being reached at 4.5 months, followed by a marked drop to 7.0+/-0.2 ng/ml at 7.5 months.

Historical perspective of turnover of dominant follicles during the bovine estrous cycle: key concepts, studies, advancements, and terms

This review chronicles the key concepts, studies, advancements and terms that have led to our current understanding of turnover of dominant follicles (growth and atresia) during the bovine estrous cycle. The "two-wave" concept of follicular development was first proposed in 1960, but remained controversial for the next 28 yr. The concept of the "dominant" follicle was adapted to cattle in 1987. By 1988, ultrasound analysis of individual follicles had demonstrated that heifers usually had two or three distinct waves of turnover of dominant follicles during an estrous cycle. From 1992 to 1993, it was established that a transient rise in serum concentrations of FSH initiated each follicular wave, and a decreased episodic secretion of LH was associated with loss of dominance and the end of a nonovulatory follicular wave. In the past decade, numerous intrafollicular growth factors, such as inhibins, activins, and insulin-like growth factors and their binding proteins, have been identified in follicular fluid of individual bovine follicles. In addition, in vitro studies demonstrate that these growth factors could have endocrine, autocrine, or paracrine actions that modify gonadotropin-stimulated follicular growth and differentiation. However, the precise role of intrafollicular growth factors in turnover of dominant follicles has not been defined. We concluded that two or three FSH-stimulated waves of follicular growth usually occur during the bovine estrous cycle, and each follicular wave culminates in development of a single nonovulatory or ovulatory dominant follicle.

Relationship of pregnancy rate to peripheral concentrations of progesterone and estradiol in beef cows

The relationship between pregnancy rate and concentrations of progesterone (P(4)) and estradiol-17beta (E(2)) in serum was examined in inseminated beef cows. Jugular blood was collected twice daily on Days 4 through 7 and Days 14 through 17 after estrus to establish patterns of secretion of P(4) and E(2). Pregnancy rate was determined by palpation per rectum at 45 d. Mean concentrations of each hormone, ratio of E(2):P(4) and regressions of hormone on day were the variables measured for each of the 2 periods. Cows were classified into low (n=26), medium (n=50) and high (n=26) groups for each variable. The relationship of pregnancy rate to each variable was tested using Chi-square analyses. Pregnancy rates to the first service decreased linearly as relative mean concentrations of E(2) increased on Days 14 through 17 (P<0.05) but were not affected by any of the other hormonal variables studied during either period. Pregnancy rates to the second service were not related to concentrations of P(4) or E(2) during the luteal phase before mating (Days 14 through 17). The effects of pregnancy on concentrations of E(2) and P(4) also were tested. On Days 14 through 17, P(4) increased slightly in pregnant cows and declined slightly in nonpregnant cows (P<0.05), but pregnancy did not affect E(2) during either period or P(4) on Days 4 through 7. In summary, pregnancy rate to the first service decreased significantly as concentrations of E(2) increased on Days 14 through 17.

Plasma progesterone and blood metabolite profiles in post-partum small east African zebu cows

Plasma progesterone profiles were used to monitor post-partum reproductive activity in 12 Small East African zebu (Bos indicus) cows allocated to either supplementary or no supplementary feeding (control) with continuous or restricted (twice daily) suckling regimes. Intact bulls were used for breeding. Blood samples were collected 3 times a week for 33 weeks to determine plasma progesterone levels. Weekly blood samples were also used to determine blood metabolite concentrations. Plasma progesterone levels remained below 1 ng/ml in all cows until week 12 post-partum. Only 5 cows showed ovarian activity over the 33 week period. Cows that cycled expressed irregular and short-lived progesterone rises (> 1 ng/ml) lasting 8 to 12 days prior to establishment of normal patterns of progesterone secretion where progesterone levels ranged from 8 to 10 ng/ml in cows with normal cycles. Plasma total protein, albumin, globulin, blood urea nitrogen and glucose levels varied over time without consistent trends, and were not influenced by either supplementary feeding of suckling regimes, nor differed between cyclic and acyclic cows. It was concluded that extended post-partum anoestrus, conception failure and early embryonic mortality were responsible for lowered reproductive efficiency in zebu cows. Blood metabolite concentrations were not good indicators of nutritional status and were not related to post-partum ovarian activity.

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.

Plasma levels of prostaglandin F2 alpha metabolite and progesterone in repeat breeder heifers

A detailed clinical-endocrine investigation was performed in 6 repeat breeder heifers (RBH) with the aim being to ascertain whether endocrine asynchronism exists at luteal regression and during early pregnancy. The heifers were first studied during an open cycle and then after insemination when 3 heifers became pregnant. Circulating plasma levels of PGF2 alpha metabolite were measured every 2nd h, while progesterone (P4) levels were measured every 6th h. The oestrous period and intervals between the onset of oestrus and ovulation were relatively longer, compared with what is normally seen in heifers. Plasma levels of P4 at the onset of oestrus were higher than normal, but it was concluded that the plasma levels of PGF2 alpha metabolite and P4 in RBH at luteal regression and early pregnancy were normal.

Effect of progesterone supplementation in repeat-breeder cattle on conception and plasma progesterone

Reposital-type progesterone (75 mg/d for cows, 40 mg/d for heifers) or saline were administered to 24 Holstein cattle to assess the effects of exogenous progesterone (P) on fertility in repeat-breeders. Treatments were administered daily from day 6 to 10 after fourth, fifth and sixth insemination. Cumulative conception rate (57.1%) for the fourth through sixth insemination was affected by lactation number, service number, plasma P (4.67 ng/ml for pregnant cows vs 4.06 ng/ml for nonpregnant cows) and corpus luteum size on days 5 and 15. Plasma P concentrations were affected by day of cycle and size of corpus luteum on both ovaries on day 15. A treatment by day interaction accounted for higher plasma P in P-treated cattle than saline-treated cattle from day 5 through 15. Administration of exogenous P during early life of the corpus luteum in the repeat-breeder increased plasma P. Higher plasma P was associated with insemination success.

Effect of treatment with progesterone on pregnancy rate and plasma concentrations of progesterone in Holstein cows

Progesterone-releasing intravaginal devices inserted into the vaginas of dairy cows between d 5 to 12 (n = 28) or d 10 to 17 (n = 27) after insemination increased pregnancy rate to 60 over 30% in untreated control cows (n = 30). Plasma progesterone concentrations were increased during both progesterone treatments. Subtraction of the estimated contribution of exogenous progesterone indicated that endogenous, luteal progesterone was reduced during d 10 to 17 but not during d 5 to 12. Supplemental progesterone increased pregnancy rate but suppressed endogenous production of progesterone when administered during d 10 to 17 after insemination.

Use of plasma progesterone profiles for the assessment of reproductive functions in indigenous Nigerian Zebu cattle

The reproductive performance of Zebu cattle is generally low. However, blood concentrations of progesterone may be of practical value in assessing the reproductive status of the Zebu female. This paper reviews recent findings regarding plasma progesterone profiles during different phases of the reproductive cycle of some Nigerian Zebu cattle. The reproductive phases examined include the estrous cycle, early pregnancy and the postpartum periods. Our findings describe variations in plasma progesterone profiles observed under field conditions. The practical implications of these findings in assessing reproductive functions in indigenous Nigerian Zebu cattle are examined.

Effect of exogenous progesterone on prostaglandin F2 alpha release and the interestrous interval in the bovine

The present study was developed to determine if administration of progesterone, early in the estrous cycle of the cow, stimulated an advanced pulsatile release of PGF2 alpha from the uterine endometrium resulting in a decreased interestrous interval. Twenty-three cyclic beef cows were randomly assigned to receive either sesame oil or progesterone (100 mg) on Day 1, 2, 3 and 4 of the estrous cycle. Peripheral plasma concentrations of progesterone and the metabolite of prostaglandin F2 alpha, 15-keto-13,14-dihydro-prostaglandin F2 alpha (PGFM) were measured by radioimmunoassay. Administration of exogenous progesterone increased peripheral plasma concentration of progesterone in treated (3.67 ng/ml) compared to control (1.28 ng/ml) cows from Day 2 through 5 of the estrous cycle. Progesterone administration shortened the interestrous interval (16.7 d) compared to controls (21.6 d). The shortened interestrous intervals in treated cows resulted from an earlier decline in peripheral plasma progesterone. Decline of peripheral plasma progesterone concentrations is coincident with an increased pulsatile release of PGFM in both progesterone treated and control cows. Results indicate that administration of exogenous progesterone stimulates an earlier maturation of endometrial development, causing an advanced release of PGF2 alpha which shortens the interestrous interval of the cow.

Effect of estrous cycle stage at Syncro-Mate B treatment on conception and time to estrus in cattle

Two trials involving 85 heifers and 67 cows were conducted to determine the effect of estrous cycle stage at the time of Syncro-Mate-B((R)) (SMB) treatment on interval to estrus following implant removal and on conception rate at the synchronized estrus. In Trial 1, 57 beef and 28 dairy heifers were treated with SMB on each representative day of a 22-d estrous cycle (estrus = Day 0). Beef heifers were artificially inseminated approximately 48 h after implant removal, whereas dairy heifers were inseminated 0 to 12 h after detection of estrus. Inseminations were scored by the inseminator according to their difficulty. Interval to the onset of estrus was not different between heifers treated early (</= Day 11) in the estrous cycle (31.3 +/- 7.4 h) and heifers treated late (> Day 11) in the cycle (35.2 +/- 7.2 h). Conception rate at the synchronized estrus was slightly higher in early-cycle heifers (22 47 = 47% ) compared to late-cycle heifers (14 38 = 37% , P = 0.2). Heifers that were difficult to inseminate had lower (P < 0.01) conception rates (2 11 = 18% ) at the synchronized estrus than heifers considered normal (21 51 = 41% ) or easier than normal to inseminate (13 23 = 57% ). In Trial 2, of the 131 beef cows synchronized, 67 that were estimated to be either early or late in the estrous cycle by progesterone analysis were utilized. Cows were treated with SMB and inseminated without regard to estrus 48-h after implant removal. Inseminations were scored as in Trial 1. Calves were separated from cows from the time of implant removal to insemination. Conception rate was higher (P < 0.05) in cows treated with SMB early (</= Day 11) in the estrous cycle (20 32 = 62.5% ) compared to cows treated late (> Day 11, 16 35 = 46% ). Cows that were difficult to inseminate had a lower (P < 0.01) conception rate (0 8 = 0% ) than cows that were normal (43 94 = 46% ) or easier than normal to inseminate (13 29 = 45% ).

Effect of estrus synchronization with Syncro-Mate-B® on serum luteinizing hormone, progesterone and conception rate in Brahman heifers

Twenty-two estrous cyclic, 2-yr-old Brahman heifers were randomly assigned to receive either estrus synchronization with Syncro-Mate-B((R)) (SMB; 11) or no treatment (Control; 11). Blood samples were collected via tail vessel puncture at onset of estrus and daily thereafter until Day 11 after estrus. Blood samples were also collected from five SMB and five Control heifers at 0, 4, 8 and 12 h after the onset of estrus. All samples were processed to yield serum and stored at -20 degrees C until radioimmunoassay. Heifers were inseminated by one technician using semen from a single ejaculate of a Brahman bull 12 h after the onset of estrus. All SMB heifers exhibited estrus within 72 h of implant removal. All heifers had corpora lutea (CL) detected by rectal examination 8 to 12 d following estrus. Serum luteinizing hormone (LH) was not affected by treatment, time (4 - h intervals) or an interaction of treatment by time (P > 0.10). Independent analysis with h indicated that at h 12, SMB (2.2 +/- 0.06 ng/ml) had lower LH than did control heifers (8.9 +/- 2.1 ng/ml). Serum progesterone increased from Day 1 through Day 12 in all heifers, which is indicative of functional CL. Serum progesterone was affected by treatment (P < 0.0001) and time (d intervals; P < 0.10). Progesterone elevation was lower (P < 0.05) and area under the progesterone curve was lower (P < 0.03) in SMB (5.6 +/- 0.5 ng/ml, 32.0 +/- 4.5 units, respectively) when compared with control heifers (7.0 +/- 4 ng/ml, 43.7 +/- 2.4 units, respectively). Conception rate was lower (P < 0.01) in SMB heifers (2 of 11) than in control heifers (8 of 11). The lowered conception rate in SMB treated Brahman heifers may be due to altered timing of LH release following estrus, resulting in an altered time of ovulation.

Plasma progesterone levels during the estrous cycle of Holstein and Brahman cows, Carora type and cross-bred heifers

Daily plasma progesterone (P(4)) was determined during one estrous cycle of 19 cows and 18 heifers of four different breeds: Holstein (H), Brahman (B), Carora-type (C) and crossbred (CB) females. Estrus detection was made by visual observation and using a teaser bull with a chin-ball marker. The P(4) profiles showed no differences among groups. In Group 1 (H), P(4) levels ranged from 0.5 ng/ml plasma on the day of estrus (Day 0) to 5.1 ng/ml at the luteal phase peak (Day 13). In Group 2 (B), P(4) levels ranged from 0.5 ng/ml on Day 0 to 9.2 ng/ml on Day 13. In Groups 3 (C) and 4 (CB), P(4) levels ranged from 0.5 ng/ml, on Day 0, to 13.7 ng/ml on Day 12 and 8.8 ng/ml on Day 13. These last two groups were moved to the same location and then compared. It was found that P(4) concentrations were significantly higher (P < 0.025) in Group 3 between Days 7 and 14 of the estrous cycle. In all groups, P(4) levels were lower than 1 ng/ml one day before the next estrus, and levels of 0.4, 0.5, 0.4 and 0.4 ng/ml were obtained the day of estrus in Groups 1 to 4, respectively. Results indicated that the pattern of P(4) for each one of the groups was similar to those reported by other investigators.

The use of progesterone administered intravaginally and pregnant mare serum gonadotrophin given by injection in controlled breeding programs in beef and dairy cattle

Five experiments involving 1,244 cows and heifers were carried out to investigate the factors which might influence the calving performance to fixed-time artificial insemination following intravaginal administration of progesterone (PRID) and intramuscular injection of pregnant mare serum gonadotrophin (PMSG). Factors examined were duration of PRID treatment, time of treatment after calving, time and dose PMSG and lactational status. Experiments 1, 2 and 3 were carried out on milked Friesian cows, experiment 4 on Friesian heifers and experiment 5 on suckled and dry Herefords. All cows were inseminated once with frozen/thawed semen 54 to 58 h or 46 to 50 h after completion of PRID treatment. Overall there was a progressive increase in calving rates with an increase in the duration of treatment from 12 to 14 to 16 days but there was little or no effect of time after calving (4 v 7 weeks) at which treatment was commenced. The poorer calving performance of cows treated for 12 to 14 days was associated with relatively high peripheral levels of plasma progesterone at the time of the PRID removal, suggesting the presence at the end of treatment of residual secretory luteal tissue. There was an effect on calving performance of PMSG given at the time of PRID removal but its effect varied according to the duration of PRID treatment. After 12 days treatments (experiments 1 and 5) PMSG had little effect, whereas after 14 days treatments, 0, 500 and 750 IU PMSG gave calving rates of 27%, 40% and 46% in experiment 2 and 5%, 24% and 38% in experiment 5.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes of luteinizing hormone and progesterone for dairy cows after gonadotropin-releasing hormone at first postpartum breeding

Gonadotropin-releasing hormone administered at breeding enhances fertility of dairy cows, so a study was designed to evaluate the mechanism for enhanced fertility following administration of gonadotropin-releasing hormone at first postpartum breeding. Twenty-four cows were assigned randomly to one of two treatments, 100 micrograms of gonadotropin-releasing hormone intramuscular or saline vehicle intramuscular at insemination. Blood samples for luteinizing hormone assay were taken at 2-h intervals prior to breeding and .5-h intervals for 3 h after insemination. Composite morning milk samples for progesterone assay were collected for 30 days after insemination or until next estrus. Cows given gonadotropin-releasing hormone had higher luteinizing hormone concentrations in blood serum following treatment than cows given saline, 13.2 versus 3.0 ng/ml. There was no relationship between luteinizing hormone and subsequent conception. Progesterone for cows that became pregnant was higher throughout sampling days. Mean progesterone concentrations were 4.6 versus 2.2 ng/ml in pregnant and nonpregnant cows during the first 4 days after insemination. Cows treated with gonadotropin-releasing hormone that conceived had higher progesterone than other cows, and that was evident at the first 4 days postbreeding.

Maternal recognition of pregnancy in cattle

Nature and potential functions of chemical signals involved in the process of pregnancy recognition in cattle are discussed. The array of prostaglandins, steroid metabolites, and proteins produced by the conceptus and endometrium are described and collated with histological and physiological responses of the uterus and ovary that lead toward maintenance of the corpus luteum. Advances during the last 10 yr partially have identified the conceptus-endometrial-ovarian signal sequence that is associated with maternal recognition of pregnancy in cattle. Final evaluation of the control system should permit investigators to improve embryo survival and augment further the impact of embryo manipulation to improve genetic merit of the cattle population.