**5. High-risk mares and hormone supplementation**

#### **5.1 Progesterone**

P4 concentrations above 4.0 ng/ml are considered adequate to support early pregnancy. However, when levels are <2.0 ng/ml, P4 supplementation is considered [137]. Several types of P4 products have been used to maintain pregnancies in mares. After oral administration altrenogest is readily absorbed, reaching peak levels after 3–6 h [144]. Altrenogest acts by binding to the P4 receptors but has little effect on endogenous plasma total progestagen concentrations. Specifically, altrenogest is not metabolized to 5α-pregnanes in the horse [128]. For this reason, the only scientific evidence that altrenogest prevents loss pregnancy in mares is during the first trimester, when it prevented abortion induced by repeated administration of PGF2α (cloprostenol) [145]. P4 may exert its effects by interfering with PG production stimulated by proinflammatory cytokines. Daels et al. [146] demonstrated that the rise in endogenous PGF2α concentrations was inhibited by altrenogest treatment. Indeed, when early pregnant mares (21–35 days post-ovulation) were exposed to *Salmonella typhimurium* endotoxin all mares supplemented with altrenogest until day 70 remained pregnant, whereas 6 out of 7 mares aborted when altrenogest therapy was discontinued on day 50 [147].

Mares with suspected luteal insufficiency can be supplemented with altrenogest (0.044 mg/kg per os once or twice daily) or P4 (150 mg/day IM) starting on day

3 after ovulation and continuing until 100–120 days of pregnancy. Long-acting injectable formulations of P4 and altrenogest are available in some countries [148]. Administration of the GnRH analog, buserelin (40 μg), 10 or 11 days after ovulation has been reported to improve luteal function and reduce early pregnancy loss [149]. Panzani et al. [150] showed that the use of altrenogest improved recipient pregnancy rates compared to untreated controls. A recent clinical study showed a positive effect of altrenogest supplementation on embryonic growth rates between 35 and 45 days after ovulation in Warmblood mares older than 8 years [151]. P4 may need to be supplemented generally in early pregnant mares showing estrus signs, with a history of repeated pregnancy loss in case of endotoxemia and of stressful events. In mares under P4 supplementation continuation of pregnancy has to be monitored regularly, since many will lose their pregnancy despite supplementation of P4 and this will prevent those mares return to estrus [152].

The latter sentence has been checked. It has been reported that the administration of a single dose of 20–40 μg of buserelin between day 9 and day 10 after ovulation increases the number of multiple ovulations and gestation up to 5–10% [153]. Buserelin does not increase circulating P4 levels or preventing the luteolysis, acting independently of CL in the mare [154]. These effects preventing pregnancy loss that operating between day 9 to day 10 and day 13 to day 14 of pregnancy.

In a recent study Köhne et al. [155] reported that hCG administration for induction of ovulation in mares increased progestin concentration in plasma of early pregnancy as well as the embryo size at the time of the start of placentation. Periovulatory treatment of mares with hCG may thus be a valuable tool to enhance conceptus growth during early pregnancy by stimulation of endogenous P4 secretion. However, Biermann et al. [156] report that hCG-treatment of mares on day 5 or day 11 post-ovulation influenced peripheral P4 concentrations due to secondary luteal tissue but did not alter ovarian and uterine blood flow or increase pregnancy rates.

#### **5.2 Progestagens**

Several pathological conditions as placentitis, placental separation or fetus as, alteration in umbilical blood flow attributable to a cord pathologic condition stimulates inflammatory and immune responses leading disrupt the endocrine capacity of the FPU and alterations in endocrine profile in plasma maternal attributed to disturbances to the normal synthetic pathway for these pregnanes [126, 157].

Fetal death or imminent fetal expulsión due to uterine torsion, colic, maternal stress, or acute cases of experimentally induced placentitis when the mares abort rapidly (within 7 days of infection) are related with the rapidly declining of P5 and P4 (less than the 95%), consistent with failure of the fetus and feto-placental tissues to produce and metabolize progestagens [158, 159].

In mares with chronic placentitis, placental edema, and placentas with poorly developed or sparse microvilli [159, 160] unusually high concentrations of all the progestagens. This pattern indicates that the fetus and the uteroplacental tissues are metabolically active despite the presence of bacteria or their products. In addition, Shikichi et al. [157] demonstrated that mares with a high concentration of progestins and low concentration of estrogens after day 241 of pregnancy were likely to deliver aborted/dead foals with placentitis. These authors demonstrated elevated and low concentrations of progestins and estrogens in the maternal sera of all cases with placentitis in pregnant mares, respectively.

**19**

*Physiological and Clinical Aspects of the Endocrinology of the Estrous Cycle and Pregnancy…*

corticotropin-releasing hormone (CRH), inhibiting the normal function of the adrenal gland to produce the cortisol surge and associated changes in pregnane metabolism [137]. In mares with fescue toxicosis, prepartum total plasma progestagen concentrations remain low, their foals have low cortisol concentrations, indicat-

antimicrobials, pentoxifylline and nonsteroidal anti-inflammatory (NSAIDs) drugs to mares with placentitis, decreased the incidence of abortion [162]. In these cases, altrenogest counteracts uterine contractility induced by inflammation of the fetal membranes. In the same way, in bacterial placentitis, a combination of trimethoprim sulfamethoxazole, pentoxifylline and a double dose of altrenogest (0.088 mg/kg bwt per os s.i.d.) were successful in maintaining pregnancies to term [163], while that untreated control mares aborted. When mares were treated with trimpethoprim sulfamethoxazole and pentoxifylline without altrenogest, only one live foal was born [163, 164]. Despite this, it is not clear what role, if any, altrenogest plays within this multi-treatment approach. However, the mares can still abort while receiving altrenogest treatment in the last trimester of pregnancy.

Recent studies demonstrated that altrenogest, when given in combination with

In late gestation total estrogen (including E1S, E2, and its metabolites, equilin, and equilenin) may be used for fetal and placental health monitoring. However, it is doubtful that total estrogen concentration can predict fetal death as the fetal gonads

Since the production of estrogens requires both contributions by the fetus and placental, reduced concentrations in maternal circulation may indicate or predict a stressed or hypoxic fetus that is not producing the estrogen precursors [165]. Indeed, E2 [166] and E1S [167] concentrations decreased sharply in mares with placental dysfunction and after the induction of abortion. If the fetus is severely compromised or die in the uterus, maternal plasma E1S are baseline because of the absence of the C19 precursors secreted by the fetal gonads. However, pregnancies compromised by equine herpesvirus-1 infection or severe colic can present normal or transiently decreased E1S concentrations [168]. Compared with the adrenal glands, the gonads are unlikely to respond to fetal stress;

consequently, so it is doubtful that total estrogen concentrations can predict fetal death. Frequent blood sampling of mares induced to abort with PG between 90 and 150 days of pregnancy indicated that E1S levels did not decline until within

In cases of placentitis at gestational ages between 150 and 280 days, Douglas [169] and Shikichi et al. [157] showed hormonal alterations common as elevated progestogens and low estrogens in mares that aborted. Although the decline in E2 associated with placental dysfunction is thought to reflect placental disease per se, Esteller-Vico et al. [170] recommended the estrogen supplementation as a means to reduce the risk of abortion associated with placentitis in mares. Recently, Curcio et al. [171] showed that in addition to basic treatment with trimethoprimsulfamethoxazole and flunixin meglumine, mares with experimentally induced ascending placentitis benefited from E2 cypionate supplementation. Conversely,

After fetal death and stress or fetal weakness, androgens and estrogens levels drop rapidly. For better determination of the health state of the fetus, due to the metabolism of both steroids, it is recommended to monitor androgens and estro-

altrenogest did not appear to make a difference in outcomes.

ing suppression of fetal adrenocortical activity and P5 production [161].

*DOI: http://dx.doi.org/10.5772/intechopen.90387*

are unlikely to respond to fetal stress [157, 165].

**5.3 Estrogens**

5 h of abortion [145].

gens simultaneously [126].

The mare's exposure to ergopeptine alkaloids from the endophyte fungus found on tall fescue grass (fescue toxicosis), ergot alkaloids inhibit fetal *Physiological and Clinical Aspects of the Endocrinology of the Estrous Cycle and Pregnancy… DOI: http://dx.doi.org/10.5772/intechopen.90387*

corticotropin-releasing hormone (CRH), inhibiting the normal function of the adrenal gland to produce the cortisol surge and associated changes in pregnane metabolism [137]. In mares with fescue toxicosis, prepartum total plasma progestagen concentrations remain low, their foals have low cortisol concentrations, indicating suppression of fetal adrenocortical activity and P5 production [161].

Recent studies demonstrated that altrenogest, when given in combination with antimicrobials, pentoxifylline and nonsteroidal anti-inflammatory (NSAIDs) drugs to mares with placentitis, decreased the incidence of abortion [162]. In these cases, altrenogest counteracts uterine contractility induced by inflammation of the fetal membranes. In the same way, in bacterial placentitis, a combination of trimethoprim sulfamethoxazole, pentoxifylline and a double dose of altrenogest (0.088 mg/kg bwt per os s.i.d.) were successful in maintaining pregnancies to term [163], while that untreated control mares aborted. When mares were treated with trimpethoprim sulfamethoxazole and pentoxifylline without altrenogest, only one live foal was born [163, 164]. Despite this, it is not clear what role, if any, altrenogest plays within this multi-treatment approach. However, the mares can still abort while receiving altrenogest treatment in the last trimester of pregnancy.

#### **5.3 Estrogens**

*Animal Reproduction in Veterinary Medicine*

3 after ovulation and continuing until 100–120 days of pregnancy. Long-acting injectable formulations of P4 and altrenogest are available in some countries [148]. Administration of the GnRH analog, buserelin (40 μg), 10 or 11 days after ovulation has been reported to improve luteal function and reduce early pregnancy loss [149]. Panzani et al. [150] showed that the use of altrenogest improved recipient pregnancy rates compared to untreated controls. A recent clinical study showed a positive effect of altrenogest supplementation on embryonic growth rates between 35 and 45 days after ovulation in Warmblood mares older than 8 years [151]. P4 may need to be supplemented generally in early pregnant mares showing estrus signs, with a history of repeated pregnancy loss in case of endotoxemia and of stressful events. In mares under P4 supplementation continuation of pregnancy has to be monitored regularly, since many will lose their pregnancy despite supplementation

The latter sentence has been checked. It has been reported that the administration of a single dose of 20–40 μg of buserelin between day 9 and day 10 after ovulation increases the number of multiple ovulations and gestation up to 5–10% [153]. Buserelin does not increase circulating P4 levels or preventing the luteolysis, acting independently of CL in the mare [154]. These effects preventing pregnancy loss that

In a recent study Köhne et al. [155] reported that hCG administration for induction of ovulation in mares increased progestin concentration in plasma of early pregnancy as well as the embryo size at the time of the start of placentation. Periovulatory treatment of mares with hCG may thus be a valuable tool to enhance conceptus growth during early pregnancy by stimulation of endogenous P4 secretion. However, Biermann et al. [156] report that hCG-treatment of mares on day 5 or day 11 post-ovulation influenced peripheral P4 concentrations due to secondary luteal tissue but did not alter ovarian and uterine blood flow or increase pregnancy

Several pathological conditions as placentitis, placental separation or fetus as, alteration in umbilical blood flow attributable to a cord pathologic condition stimulates inflammatory and immune responses leading disrupt the endocrine capacity of the FPU and alterations in endocrine profile in plasma maternal attributed to disturbances to the normal synthetic pathway for these pregnanes [126, 157].

Fetal death or imminent fetal expulsión due to uterine torsion, colic, maternal stress, or acute cases of experimentally induced placentitis when the mares abort rapidly (within 7 days of infection) are related with the rapidly declining of P5 and P4 (less than the 95%), consistent with failure of the fetus and feto-placental tissues

In mares with chronic placentitis, placental edema, and placentas with poorly developed or sparse microvilli [159, 160] unusually high concentrations of all the progestagens. This pattern indicates that the fetus and the uteroplacental tissues are metabolically active despite the presence of bacteria or their products. In addition, Shikichi et al. [157] demonstrated that mares with a high concentration of progestins and low concentration of estrogens after day 241 of pregnancy were likely to deliver aborted/dead foals with placentitis. These authors demonstrated elevated and low concentrations of progestins and estrogens in the maternal sera of all cases

The mare's exposure to ergopeptine alkaloids from the endophyte fungus found on tall fescue grass (fescue toxicosis), ergot alkaloids inhibit fetal

to produce and metabolize progestagens [158, 159].

with placentitis in pregnant mares, respectively.

of P4 and this will prevent those mares return to estrus [152].

operating between day 9 to day 10 and day 13 to day 14 of pregnancy.

**18**

rates.

**5.2 Progestagens**

In late gestation total estrogen (including E1S, E2, and its metabolites, equilin, and equilenin) may be used for fetal and placental health monitoring. However, it is doubtful that total estrogen concentration can predict fetal death as the fetal gonads are unlikely to respond to fetal stress [157, 165].

Since the production of estrogens requires both contributions by the fetus and placental, reduced concentrations in maternal circulation may indicate or predict a stressed or hypoxic fetus that is not producing the estrogen precursors [165]. Indeed, E2 [166] and E1S [167] concentrations decreased sharply in mares with placental dysfunction and after the induction of abortion. If the fetus is severely compromised or die in the uterus, maternal plasma E1S are baseline because of the absence of the C19 precursors secreted by the fetal gonads. However, pregnancies compromised by equine herpesvirus-1 infection or severe colic can present normal or transiently decreased E1S concentrations [168]. Compared with the adrenal glands, the gonads are unlikely to respond to fetal stress; consequently, so it is doubtful that total estrogen concentrations can predict fetal death. Frequent blood sampling of mares induced to abort with PG between 90 and 150 days of pregnancy indicated that E1S levels did not decline until within 5 h of abortion [145].

In cases of placentitis at gestational ages between 150 and 280 days, Douglas [169] and Shikichi et al. [157] showed hormonal alterations common as elevated progestogens and low estrogens in mares that aborted. Although the decline in E2 associated with placental dysfunction is thought to reflect placental disease per se, Esteller-Vico et al. [170] recommended the estrogen supplementation as a means to reduce the risk of abortion associated with placentitis in mares. Recently, Curcio et al. [171] showed that in addition to basic treatment with trimethoprimsulfamethoxazole and flunixin meglumine, mares with experimentally induced ascending placentitis benefited from E2 cypionate supplementation. Conversely, altrenogest did not appear to make a difference in outcomes.

After fetal death and stress or fetal weakness, androgens and estrogens levels drop rapidly. For better determination of the health state of the fetus, due to the metabolism of both steroids, it is recommended to monitor androgens and estrogens simultaneously [126].
