Pregnancy Loss in Mares
The reasons concerning losses during the first months of pregnancy has special importance in equine reproduction. Most of these losses occur early in pregnancy and around 15-20% of mares that conceive will lose the embryo before day 50. Early pregnancy loss is generally characterized by the sudden disappearance of the embryonic vesicle and is due to different reasons. Several etiologies factors involving both the mother and the embryo as, inflammatory and non-inflammatory endometrial disease, progesterone insufficiency, maternal age, lactation, site of intrauterine fixation of the embryonic vesicle, stress, plane of nutrition, season or climate, chromosome abnormalities or oocyte quality are some of the factor listed. Abortion occurs from the first month of pregnancy to full term and may be have an infectious or not origin. Causes of abortion include viral or bacterial infections, ingestion of mycotoxins, stress, gene mutations, Mare Reproductive Loss Syndrome, lack of sufficient nutrients and umbilical cord abnormalities. Some mares will show signs of impending abortion but other mares will abort without warning. Premature labor, discomfort, unusual activity or having a vulvar discharge of the mare require immediate attention. Pregnancy failure in mares represents a serious economic damages, expectations, and potential genetic improvement. Therefore is absolutely important that all losses are assessed for giving an appropriate treatment, and for preventing current and future losses.
Part of the book: Genital Infections and Infertility
Infection and Infertility in Mares
In cyclic mares, the uterine environment can easily disturbed due to inflammatory processes that occur secondary to microbial invasion. Different aerobic and anaerobic bacteria can enter the uterus during natural mating, artificial insemination, reproductive examination or parturition. The postpartum period is a critical phase since due to relaxation of the uterus and cervix may favor recurrent infections air intake (pneumovagina) or urine collection in mares with poor perineal conformation. Infections are mainly caused by opportunistic or commensal microorganisms, such as Streptococcus zooepidemicus, hemolytic Escherichia coli and Staphylococcus aureus. Other microorganisms like Taylorella equigenitalis, Klebsiella pneumoniae and Pseudomona aeruginosa are transmitted through venereal route. Regarding to the fungal endometritis, the most common fungi include Candida and Aspergillus. These microorganisms cause infertility as a result of repeated inseminations during the breeding season and proliferate when the natural immune system is weakened in mares with advanced age and multiparous, or after repeated use of antibiotics. Indeed, in susceptible mare to endometritis, uterine defense mechanisms involving phagocytosis and opsonization by neutrophils, local synthesis of antibodies, mucociliary activity, vascular and myoelectric activity permeability are compromised, leading to fluid accumulation in response to inflammation and infertility.
Part of the book: Genital Infections and Infertility
Action Mechanisms and Pathophysiological Characteristics of Cortisol in Horses
Cortisol (CORT), also known as stress hormone, plays a vital role in physiological processes such as electrolyte and fluid balance, cardiovascular homeostasis, carbohydrate, protein and lipid metabolism, immune and inflammatory responses, and sexual development and reproduction. Cortisol levels are influenced by various physiological factors such as race, age, circadian rhythm, seasonality, exercise and pregnancy. Also, some stressful conditions including isolation or transport, among others, modify levels of this hormone in the body. Excesses or deficiencies of cortisol cause important clinical problems such as Cushing’s and Addison’s syndromes, which contribute substantially to morbidity in equine medicine. Thus, in this review, we will develop the mechanisms of synthesis and regulation, as well as the physiological factors involved and the most important diseases related to the alteration of cortisol secretion in horses and foals.
Part of the book: Corticosteroids
Clinical Aspects Related to Plasma Serotonin in the Horse
Serotonin (5-HT) is a neurotransmitter that has important functions such as the physiological regulation of hemostasis, blood clotting, bone metabolism, cardiovascular growth, contractile activity and gastrointestinal motility, renal function, and stress and sexual behavior, among others. In this review, we consider the potential of 5-HT to contribute to the development of various pathological conditions, including metabolic, vascular, and nervous disorders in horses. The values of 5-HT in circulation are modified under common pathological conditions. Thus, laminitis, endotoxemia, surgical cramps, recurrent airway obstruction, Cushing’s syndrome, central fatigue, and certain behavioral alterations such as stereotypes and other acute or chronic conditions can cause increased levels of 5-HT.
Part of the book: Serotonin
Physiology and Metabolic Anomalies of Dopamine in Horses: A Review
Dopamine (DA) is an important endogenous catecholamine that exerts generalized effects on both neuronal (as a neurotransmitter) and non-neuronal tissues (as an autocrine or paracrine agent). In the central nervous system (CNS), DA binds to specific membrane receptors present in neurons and plays a key role in the control of motor activity, learning, cognition, affectivity and attention. Horses can also present with hyper- and hypo-dopaminergic conditions, including stereotypic behaviors and pituitary pars intermedia dysfunction and Parkinsonian’s syndrome, respectively. DA biosynthesis also occurs in peripheral tissues, and receptors in various organs such as the kidney, pancreas, lungs and blood vessels outside the CNS have been detected. DA emulates the actions related to the sympathetic nervous system (SNS), promoting the increase in heart rate, blood pressure, electrolyte balance and gastrointestinal (GI) motility. In fact, GI alterations in dopaminergic transmission have been directly or indirectly related to hypomotility and/or postoperative ileus (POI). On the other hand, there are physiological factors, such as breed, age, exercise and reproductive status that modify DA concentrations. In reproduction, the administration of DA antagonists in the middle/end of the spring and anestrus transition period advances the first ovulation of the year in mares. This chapter offers a brief description of the importance of DA as a neurotransmitter and peripheral hormone. Special attention is paid to: (1) functional alterations that occur in the brain and GI tract in various diseases and (2) current therapy to correct alterations in DA systems.
Part of the book: Dopamine
Scientific Evidences Supporting the Activation of the Renin-Angiotensin-Aldosterone System during Estral Cycle and Pregnancy in Mares
In women and laboratory animals, local and circulating components of the renin-angiotensin-aldosterone system (RAAS) are related to specific reproductive functions that occur during the estrous cycle, such as folliculogenesis, ovulation, corpus luteum development, and steroidogenesis. Also, in pregnant females of these species, maternal cardiovascular and renal systems undergo intense modifications, with the aim of matching the increased energy requirements of the fetus and fetoplacental unit. Some of these changes can be the origin, and others the consequence of a new endocrine environment. The fetus and the placenta induce endocrine changes, with modifications in the protein, lipid, carbohydrate, and mineral metabolism, together with simultaneous cardiovascular changes derived from the uterine growth and its content. The participation of RAAS during this period is of vital importance to regulate these cardiovascular, hemodynamic, hematological, and metabolic adjustments imposed by pregnancy because they will have a direct influence on the correct development and viability of the fetus. In mares, our research team has been investigating the changes of RAAS in mares during the estral cycle and during pregnancy, and these results are presented in the current chapter, comparing with the data previously reported for women and laboratory animals.
Part of the book: Selected Chapters from the Renin-Angiotensin System
Physiological and Clinical Aspects of the Endocrinology of the Estrous Cycle and Pregnancy in MaresView all chapters
The use of advanced reproductive endocrinology can generate important economic benefits for equine breeding farms. Pregnancy in the mare involves considerable endocrine changes, which can be explained in part by the development of different structures such as embryonic vesicles, primary and secondary CL, endometrial cups and development of fetoplacental units. Both the pregnant mare and the fetus adapt to this development with unique mechanisms, such as alterations in the maternal endocrine metabolism and hormonal feedback. Since the ability to produce a viable foal is critical for the broodmare, the maintenance of the gestation implies almost a year of physiological effort. Therefore, the joint knowledge of basic reproductive science and current clinical endocrinology allows veterinarians and breeders to be better positioned to achieve their objectives. This chapter reviews normal and abnormal endocrine patterns during the equine estrual cycle, pregnancy. We also consider hormonal evaluation related to placentitis, abortions, recurrent pregnancy loss, and premature deliveries. Also, several aspects associated with endocrinological control of the reproductive cycle, ovulation, parturition, high-risk mare, and hormone supplementation will be developed.
Part of the book: Animal Reproduction in Veterinary Medicine