Effect of luteinizing hormone (LH), pregnancy-specific protein B (PSPB), or arachidonic acid (AA) on secretion of progesterone and prostaglandins (PG) E (PGE; PGE1 and PGE2) and F2α (PGF2α) by ovine corpora lutea of the estrous cycle or pregnancy in vitro

Review: Maintenance of the ruminant corpus luteum during pregnancy: interferon-tau and beyond

This manuscript reviews the mechanisms that maintain the corpus luteum (CL) of pregnancy in ruminants. In mammals, ovulation and luteinization of the remaining cells in the CL are due to a surge in Luteinizing Hormone (LH). In cattle, continued secretion of pulses of LH is essential for full development and function of the CL during the estrous cycle (LH pulses), however, the few studies on the CL after d20 of pregnancy do not indicate that LH is essential for maintaining the CL of pregnancy. The first essential step in maintaining the CL of pregnancy in ruminants is overcoming the mechanisms that cause regression of the CL in non-pregnant ruminants (d18-25 in cattle; d13-21 in sheep). These mechanisms have a uterine component involving oxytocin-induced prostaglandin F2α (PGF2A) pulses and a luteal component involving decreased progesterone production and luteal cell death. There is a critical role for embryonic interferon-tau (IFNT) in suppressing the uterine secretion of PGF2A during early pregnancy (d13-21 in sheep; d16-25 in cattle) and preventing luteolysis. There are also effects of IFNT on the expression of interferon-stimulated genes in other tissues including the CL but the physiologic role of these interferon-stimulated genes is not yet clear. After the IFNT period, there is another mechanism that maintains the CL of pregnancy in ruminants since embryonic IFNT is inhibited as attachment occurs and trophoblastic binucleate/giant cells begin secretion of pregnancy-associated glycoproteins. The second mechanism for luteal maintenance has not yet been defined but acts in a local manner (ipsilateral to pregnancy), and remains functional from d25 until just before parturition. The most likely mechanisms mediating later maintenance of the CL of pregnancy are increased uterine blood flow or decreased prostaglandin transporter expression in the utero-ovarian vasculature, preventing PGF2A reaching the CL. Finally, implications of these ideas on pregnancy loss in cattle are explored, highlighting the importance of inappropriate regression of the CL of pregnancy as a mechanism for pregnancy loss in cattle.

Bovine embryo elongation is altered due to maternal fatty acid supplementation

The pre-implantation period is prone to embryonic losses in bovine. Embryo-maternal communication is crucial to support embryo development. Thereby, factors of the uterine fluid (UF) are of specific importance. The maternal diet can affect the UF composition. Since omega 3 fatty acids (omega 3 FA) are considered to be beneficial for reproduction, we investigated if dietary omega 3 FA affected factors in the UF related to embryo elongation. Angus heifers (n = 37) were supplemented with either 450 g of rumen-protected fish oil (omega 3 FA) or sunflower oil (omega 6 FA) for a period of 8 weeks. Following cycle synchronization and artificial insemination, the uteri were flushed post mortem to recover the embryos on day 15 of pregnancy. The UF and tissue samples of endometrium and corpus luteum (CL) were collected. Strikingly, the embryo elongation in the omega 3 group was enhanced compared to the omega 6 group. No differences were observed in uterine prostaglandins, even though the endometrial concentration of their precursor arachidonic acid was reduced in omega 3 compared to omega 6 heifers. The dietary FA neither led to differential expression of target genes in endometrium nor CL nor to a differential abundance of low-density lipoprotein cholesterol, cortisol or amino acids in the UF. Interestingly, the omega 3 group displayed a higher plasma progesterone concentration during luteal growth than the omega 6 group, possibly promoting embryo elongation. Further research should include an ovarian perspective to understand the functional link between dietary omega 3 FA and reproductive outcome.

The influence of dietary sunflower oil, rich in n-6 polyunsaturated fatty acids, in combination with vitamin C on ram semen parameters, sperm lipids and fertility

BACKGROUND

Dietary fats, fed to ruminant animals, have been observed to improve reproductive function. Sunflower oil is one of the richest sources of polyunsaturated fatty acids (PUFAs), over 60% of which is linoleic acid (C18:2). With regard to recommendations for increased consumption of PUFAs, special emphasis has been given to the importance of consuming more antioxidants to prevent lipid peroxide formation. This study evaluated the effects of dietary n-6 PUFAs and vitamin C (VC) in rams - in particular, on semen quality, blood metabolites, sperm lipids and overall fertility.

RESULTS

Diets supplemented with SFO and VC increased the proportion of motile sperms and their progressive motility improved (P < 0.01). Rams fed a diet containing SFO had an increased proportion of sperms with normal acrosomes in their semen samples (P < 0.01). The highest levels of lactate dehydrogenase activity (LDH) enzyme were found in control rams (2.60 U mL^-1 ). Feeding SFO significantly affected blood triglyceride and cholesterol concentrations (P < 0.05). Diets containing SFO increased the proportion of C18:2c, C20:4, C20:3 and C22 in the sperm lipid composition (P < 0.05). Semen of SFO and VC-fed rams was more fertile than that of control rams when it was artificially inseminated to ewes.

CONCLUSION

Feeding rams with supplemental SFO and VC increased semen quality and improved fertility rates. © 2019 Society of Chemical Industry.

Associations between pregnancy-associated glycoproteins and pregnancy outcomes, milk yield, parity, and clinical diseases in high-producing dairy cows

Pregnancy-associated glycoproteins (PAG) are produced by the ruminant placenta and secreted into the maternal circulation throughout pregnancy. The extent to which circulating PAG concentrations predict pregnancy outcomes was examined herein. Also, associations between circulating PAG concentrations and various production parameters and clinical diseases were evaluated. Lactating primiparous and multiparous Holstein cows (n=345) were bred via timed artificial insemination using a standard Ovsynch protocol. Pregnancy was diagnosed by transrectal ultrasonography at d 32, 46, and 74 of gestation. Blood was harvested at d 32 to determine plasma concentrations of PAG and progesterone. Cows pregnant at d 32 that subsequently lost their pregnancy at d 46 and 74 had reduced PAG concentrations. Both artificial insemination service number and parity were associated with plasma PAG concentrations. Concentration of PAG in plasma was greater for cows pregnant from their second or later breeding than those pregnant from the first breeding postpartum, and was increased for primiparous compared with multiparous. In addition, cows with greater milk yield had increased plasma PAG concentrations. No association was detected between body condition score and plasma PAG concentrations. Cows that experienced clinical metritis, metabolic problems, or left displacement abomasum in the early postpartum period preceding breeding had greater plasma PAG concentrations than cows not experiencing these clinical diseases. Also, cows with multiple clinical diseases had increased odds of pregnancy loss when compared with cows not experiencing clinical diseases. Odds ratio testing detected a tendency in the relationship between reduced milk yield and increased pregnancy loss. Collectively, these associations illustrate one feature of the early developing placenta that may predict pregnancy outcomes in dairy cattle. It is unclear if plasma PAG are actively involved with mediating pregnancy outcomes, but modifications in circulating PAG concentrations due to pregnancy loss, milk yield, parity, and clinical disease implicate placental PAG production or PAG release as being responsive to various physiological stimuli.

Subspecies differences in early fetal development and plasma pregnancy-associated glycoprotein concentrations in cattle

Inclusion of Bos indicus genetics improves production traits of cattle maintained in hot climates. Limited information exists detailing pregnancy-specific events as influenced by variable amounts of Bos indicus genetics. Three experiments were completed to examine the effect of Bos taurus and Bos indicus genotypes on fetal size and plasma pregnancy-associated glycoprotein (PAG) concentrations. In all experiments, cows were bred by AI after synchronization of ovulation. Fetal measurements were completed by transrectal ultrasonography and plasma PAG concentrations were quantified from plasma harvested the day of each fetal measurement. In Exp. 1, fetal size and plasma PAG concentrations were measured at d 53 of pregnancy in cows composed of various fractions of Angus and Brahman (n = 9 to 21 cows/group). Fetus size was greater in cows containing >80% Angus genetics compared with cows containing <80% Angus influence (3.40 ± 0.28 vs. 2.86 ± 0.28 cm crown-rump length; P < 0.01). Plasma PAG concentrations were reduced (P < 0.01) in cows containing >80% Angus genetics when compared with their contemporaries (6.0 ± 1.5 ng/mL vs. 9.4 ± 1.5 ng/mL). In Exp. 2, fetal measurements and plasma PAG concentrations were determined at d 35 and 62 of pregnancy in Angus and Brangus cows. Breed did not affect fetus size at d 35, but Angus cows contained larger fetuses than Brangus cows at d 62 [3.0 ± 0.03 vs. 2.8 ± 0.03 cm crown-nose length (CNL; P > 0.01)]. Plasma PAG concentrations were not different between breed at d 35 and 62 (P > 0.1). In Exp. 3, fetal measurements and plasma samples were collected at d 33/34, 40/41, 47/48, and 54/55 post-AI in Angus and Brangus cows. Fetus size was not different (P > 0.05) between genotypes on d 33/34, 40/41, and 47/48. Angus fetuses were larger than Brangus fetuses at d 54/55 (2.1 ± 0.03 vs. 1.9 ± 0.03 cm CNL; P = 0.001). Plasma PAG concentrations were less in Angus than Brangus cows at each time point (average 4.9 ± 0.9 vs. 8.2 ± 0.9 ng/mL; P = 0.005). In conclusion, these studies determined that the Bos taurus × Bos indicus genotype impacts fetal size and rate of fetal development by 7 wk of gestation. Plasma PAG concentrations were increased in cattle with Bos indicus genetics in 2 of 3 studies, suggesting that genotype is one of several determinants of PAG production and secretion in cattle.

Leukotrienes are auto-/paracrine factors in the bovine corpus luteum: an in vitro study

The aim of this study was to determine leukotrienes (LTs) functions in the bovine corpus luteum (BCL) during the oestrous cycle. In steroidogenic CL cells we examined the effect of luteotropic [LH, prostaglandin E(2) (PGE(2))] and luteolytic (PGF(2α), cytokines) factors on: the levels of LTB(4) and C(4), the expression of 5-lipoxygenase (LO), LT receptors type I (LTR-I) and LTR-II, and the effects of LTB(4) and C(4) stimulations on the levels of progesterone (P4), PGE(2), F(2α) and nitric oxide (NO) metabolites. Both luteolytic and luteotropic factors stimulated 5-LO expression on days 2-4 and 17-19 of the cycle. Leukotriene receptors type I expression increased after PGE(2) and tumour necrosis factor α with interferon γ (TNF/IFN) stimulation on days 2-4 of the cycle. Leukotriene receptor type II expression increased after PGE(2α) and TNF/IFN stimulation on days 2-4 and 17-19 of the cycle, and LTR-II expression on days 8-10 of the cycle was unchanged after cell stimulation with any factor. Leukotriene B(4) level increased after BSC incubation with luteotropic factors during all examined days of the cycle and after cytokine stimulation at early- and mid-luteal stages, whereas luteolytic factors stimulated LTC(4) secretion over the entire cycle. Leukotriene B(4) stimulated P4 secretion at the mid-luteal stage and stimulated NO secretion during all examined phases. Leukotriene B(4) stimulated PGE(2) secretion at the early- and mid-luteal stage. Leukotriene C(4) inhibited P4 secretion at the mid- and regressing-luteal stage, stimulated NO (entire cycle) and PGF(2α) at mid- and regressing-luteal phases. Leukotrienes modulate steroidogenic cells functions, depending on the stage of the cycle. Leukotriene B(4) plays a luteotropic role stimulating P4 and PGE(2) secretions; LTC(4) stimulates the secretion of luteolytic factors and enhances the luteolytic cascade within BCL.

Effects of prostaglandin E and F receptor agonists in vivo on luteal function in ewes

Loss of progesterone secretion at the end of the estrous cycle is via uterine PGF(2alpha) secretion; however, uterine PGF(2alpha) is not decreased during early pregnancy in ewes to prevent luteolysis. Instead the embryo imparts resistance to PGF(2alpha)-induced luteolysis, which is via the 2-fold increase in prostaglandins E(1) and E(2) (PGE(1), PGE(2); PGE) in the endometrium during early pregnancy. Chronic intrauterine infusion of PGE(1) or PGE(2) prevents spontaneous or an estradiol-17beta, IUD, or PGF(2alpha)-induced luteolysis. Four PGE receptor subtypes (EP(1), EP(2), EP(3), and EP(4)) and an FP receptor specific for PGF(2alpha) have been identified. The objective of this experiment was to determine the effects of EP(1), EP(2), EP(3), or FP receptor agonists in vivo on luteal mRNA for LH receptors, occupied and unoccupied LH receptors, and circulating progesterone in ewes. Ewes received a single treatment of 17-phenyl-tri-Nor-PGE(2) (EP(1), EP(3)), butaprost (EP(2)), 19-(R)-OH-PGE(2) (EP(2)), sulprostone (EP(1), EP(3)), or PGF(2alpha) (FP) receptor agonists into the interstitial tissue of the ovarian vascular pedicle adjacent to the luteal-containing ovary. 17-Phenlyl-tri-Nor-PGE(2) had no effect (P> or =0.05) on any parameter analyzed. Butaprost and 19-(R)-OH-PGE(2) increased (P< or =0.05) mRNA for LH receptors, occupied and unoccupied LH receptors, and circulating progesterone. Both sulprostone and PGF(2alpha) decreased (P< or =0.05) mRNA for LH receptors, occupied and unoccupied LH receptors, and circulating progesterone. It is concluded that both EP(3) and FP receptors may be involved in luteolysis. In addition, EP(2) receptors may mediate prevention of luteolysis via regulation of luteal mRNA for LH receptors to prevent loss of occupied and unoccupied LH receptors and therefore to sustaining luteal function.

Differential regulation of phospholipase A(2) activity and prostaglandin E(2) synthesis in activated and non-activated corpora lutea of lactation by the presence and absence of suckling stimulus in rats

We investigated content of prostaglandin (PG) E(2), a luteotropic eicosanoid, and phospholipase A(2) (PLA(2)) activity in two distinct states of rat corpora lutea of lactation (LCL). Rats subjected to forced weaning on day 0 postpartum (PP0) had a significant attenuation of progesterone synthesis and LCL weight on PP6 and/or PP3 compared with normally lactating rats. Repeated administration of prolactin (10 IU, twice daily) to weaned rats reversed impaired LCL function and structural development beyond the normal level of lactating animals. From PP3 to PP6, PGE(2) level in lactating LCL was increased while it was not altered in non-lactating LCL. In contrast, PLA(2) activity in the cytosol plus microsome fractions was decreased in lactating LCL and was up-regulated in non-lactating LCL as early as on PP3. This study provides the first evidence for differential regulation of PLA(2) activity and PGE(2) synthesis in activation and activation failure of postpartum CL in rats.