Risk Factors and Treatment of Postpartum Anestrus in Cattle: The Case of Zebu

This literature review reports on risk factors for postpartum anoestrus in zebus and their potential treatments. Prolonged postpartum anestrus is one of the major factors limiting reproductive efficiency in cattle, particularly in Bos indicus cows in tropical regions, as it prevents a calving interval of 365 days from being achieved. During anestrus, ovulation does not occur despite ovarian follicular development, as the growing follicles do not reach maturity. This period is very variable and depends on various factors whose importance is relative or, on the contrary, essential. Some are specific to the animal (breastfeeding or food); others relate more to its social environment, season sanitary conditions. Several hormonal treatments have been used to induce ovulation and cyclicity in postpartum cows. Generally speaking, given the inconsistency of the effects or even their lack of practicability, treatments using a single or repeated injection of a gonadotropin-releasing hormone (GnRH) have been gradually abandoned in favour of progestagens. These are administered for 8 to 12 days on a continuous basis in the form of a subcutaneous implant (Crestar®), a vaginal coil (PRID®) or a CIDR. A prostaglandin injection is given two days before the implant is removed. The addition of an ECG treatment at the time of device removal, which increased plasma progesterone concentrations and pregnancy rates in anestrous postpartum suckled Bos indicus cows, may be useful to improve reproductive performance. This improvement requires a better understanding of the effect of different risk factors on the recovery of postpartum cyclicity.

Plasma progesterone secretion during gestation of the captive short-beaked echidna

This study describes the progesterone profile during pregnancy in sexually mature female captive short-beaked echidnas (Tachyglossus aculeatus aculeatus). Echidnas were monitored daily by video surveillance to confirm key reproductive behaviour. Plasma samples were collected and pouch morphology was assessed three times a week. The pouch of the female echidna only develops during gestation and it was possible to create a four-stage grading system using the most distinguishable characteristics of pouch development. Maximum pouch development was associated with declining progesterone concentrations, with the pouch closing in a drawstring-like manner at oviposition. Control of pouch development in pregnant echidnas is not yet clear but later pouch development is associated with a decrease in progesterone and pouch closure and may be under mechanical influences of the egg or young in the pouch. The length of pregnancy was 16.7 ± 0.2 days with a 15.1 ± 1.0 days luteal phase followed by an incubation period in the pouch. Eggs could be detected in utero at least 4 days before oviposition. Plasma progesterone peaked at 10.5 ± 0.9 ng/mL within 12 days of mating but then declined to basal levels within 1 day of oviposition and remained basal throughout egg incubation, confirming that progesterone is elevated throughout pregnancy and that gestation does not extend beyond the luteal phase. After the loss of an egg or pouch young, most females entered a second oestrous cycle and ovulated, suggesting echidnas are seasonally polyoestrous. The duration of the luteal phase in the echidna corresponds with that observed in other mammals.

Delayed implantation induced by letrozole in mice

Implantation timing is key for a successful pregnancy. Short delay in embryo implantation caused by targeted gene ablation produced a cascading problem in the later stages of the pregnancy. Although several delayed implantation models have been established in wild mice, almost none of them is suitable for investigating the delay on the late events of pregnancy. Here, we report a new delayed implantation model established by the intraperitoneally administration of letrozole at 5 mg/kg body weight on the day 3 of pregnancy. In these mice, initiation of implantation was induced at will by the injection of estradiol (E2). When the estradiol (3 ng) was injected on day 4 of pregnancy (i.e., without delay), the embryo implantation restarted, and the pregnancy continued normally. However, high dose of estrogen (25 ng) caused compromised implantation. We also found that only 67% of the female mice could be pregnant normally and finally gave birth when the injection of estradiol (3 ng) was on day 5 of pregnancy (i.e., one day delay). Most of the failed pregnancies had impaired decidualization, decreased plasma progesterone levels and compromised angiogenesis. Progesterone supplementation could rescue decidualization failure in the mice. Collectively, we established a new model of delayed implantation by letrozole, which can be easily used to study the effect and mechanisms of delay of embryo implantation on the progression of late pregnancy events.

Measurement of progesterone in sheep using a commercial ELISA kit for human plasma

Determination of serum or plasma progesterone (P4) concentrations is important to recognize pregnant and non-pregnant ewes, and also to predict the number of carried lambs. The 2 most common methodologies for the detection of plasma P4 are radioimmunoassay (RIA) and enzyme immunoassay (EIA). RIA is very expensive, and not all laboratories are equipped to perform this test; EIA is commercially available for human use, but only a few companies produce species-specific kits, which are expensive. We verified for ovine plasma a less expensive and easily available ELISA kit (DiaMetra) designed to quantify P4 in humans. Pools of ovine and human plasma were used to compare repeatability, accuracy, sensitivity, and stability of P4 measured by the DiaMetra kit. Repeatability data were within 15%, and accuracy values were ~90% for both plasma matrices. Stability data showed a loss of <20% for freeze–thaw and <30% for 30-d storage. All parameters were acceptable under international guidelines for method validation. The human ELISA kit was used successfully to quantify plasma P4 in 26 ewes during pregnancy until delivery. P4 concentrations were also correlated with the number of carried lambs.

Ovarian dynamics, hormone profiles, and characterization of ovarian and uterine blood flow in cycling Sahiwal cows

The objectives were to investigate the ovarian dynamics and hormonal profiles during the oestrus cycle, and to characterize the ovarian and uterine blood flow (OBF versus UBF) indices on the extent of vascular perfusion towards the dominant follicle (DF) or corpus luteum (CL) during the peri-ovulatory follicular wave in Sahiwal cows. In experiment 1, cyclic cows (n = 21) were selected at their spontaneous oestrus (day 0) and subjected to B-mode ultrasonography throughout the oestrus cycle. In experiment 2, cyclic cows (n = 9) were randomly selected at day 0, and categorized according to the intra-ovarian patterns as ovaries with DF (n = 3), CL (n = 3) or both (DF+CL; n = 3) to characterize the OBF and UBF indices using Doppler ultrasonography. The length of the oestrus cycle (days), number of follicular waves (n) and size (mm) of DF and CL were 20.1 ± 0.9, 2.1 ± 0.2, 14.7 ± 0.7 and 15.9 ± 2.5, respectively. The concentrations (ng/mL) of plasma progesterone increased linearly, and a peak was attained at day 12.2 ± 1.0. However, it reduced linearly with the onset of luteolysis at day 16.4 ± 0.3 of the oestrus cycle. The plasma progesterone (P4) concentrations and the diameter of CL correlated throughout the oestrus cycle. The mean OBF and UBF indices did not differ between intraovarian patterns. Taken together, this information on reproductive physiological parameters could be used to develop synchronization protocols to improve reproductive management in Sahiwal cows.

Assessment of Age Effects on Ovarian Hemodynamics Using Doppler Ultrasound and Progesterone Concentrations in Cycling Spanish Purebred Mares

In equine reproduction, accurate and timely detection of the moment of ovulation is of great importance. Power Doppler ultrasound technology is a non-invasive method that enables to assess the morpho-echogenic features and blood flow changes during the estral cycle in mares. The objective of the present study was to evaluate the influence of age on ultrasonographic parameters (follicular diameter, follicular blood flow—FBF, corpus luteum (CL) area and corpus luteum blood flow—CLBF) and blood plasma progesterone concentrations in cycling Spanish Purebred mares (15 less than 8 years old and 15 equal o higher than 8 years old). The ultrasound images obtained were analyzed with the Image Colour Summarizer software, which allows the quantification of the pixels of each image. Young mares had significantly higher FBF, CLBF and plasma progesterone levels. Moreover, linear regression analysis showed that blood progesterone levels could be predicted in both groups from CLBF with moderate precision and accuracy. In conclusion, Power Doppler was useful to assess ovarian hemodynamics. Our results support that age is a factor that significantly influences FBF and CLBF as well as blood progesterone concentration in mares. More studies would be needed to develop high precision and accuracy predictive models of blood progesterone concentration from CLBF measured by Power Doppler.

Hypothalamic involvement and the role of progesterone in the NGF-induced LH surge pathway

To elucidate the mechanism by which nerve growth factor (NGF) influences the LH secretory pathway in camelids, a series of experiments were done to determine the involvement of the hypothalamus (Experiment 1), the role of GnRH neurons (Experiment 2), and the effect of progesterone (Experiment 3) on the NGF-induced LH surge and ovulation in llamas. In Experiment 1, the declining phase of the NGF-induced LH surge was used to determine if the decline is a result of pituitary depletion or hypothalamic unresponsiveness. Female llamas were treated with NGF and, 7 hours later, assigned to three groups and given a second dose of NGF (n = 5), a dose of GnRH (n = 5), or saline (n = 6). The LH response was attenuated after the second dose of NGF vs. GnRH. In Experiment 2, Fos expression (marker of neuronal activation) in GnRH neurons was examined in the hypothalamus of llamas after NGF or saline treatment (n = 3 per group). Despite an LH surge in the NGF group but not in the saline group, no differences were detected between groups in Fos/GnRH co-expression. In Experiment 3, llamas in low-, medium-, and high-plasma progesterone groups (n = 4 per group) were treated with NGF. The NGF-induced LH surge did not differ among treatment groups. Results from the present study show that the induction of a preovulatory LH surge by NGF may be controlled by a novel pathway involving GnRH neuro-terminals downstream of the hypothalamus and is independent of progesterone influence.