Physiological development of the equine fetus during late gestation

Abstract

In many species, the pattern of growth and physiological development in utero has an important role in determining not only neonatal viability but also adult phenotype and disease susceptibility. Changes in fetal development induced by a range of environmental factors including maternal nutrition, disease, placental insufficiency and social stresses have all been shown to induce adult cardiovascular and metabolic dysfunction that often lead to ill health in later life. Compared to other precocious animals, much less is known about the physiological development of the fetal horse or the longerterm impacts on its phenotype of altered development in early life because of its inaccessibility in utero, large size and long lifespan. This review summaries the available data on the normal metabolic, cardiovascular and endocrine development of the fetal horse during the second half of gestation. It also examines the responsiveness of these physiological systems to stresses such as hypoglycaemia and hypotension during late gestation. Particular emphasis is placed on the role of the equine placenta and fetal endocrine glands in mediating the changes in fetal development seen towards term and in response to nutritional and other environmental cues. The final part of the review presents the evidence that the early life environment of the horse can alter its subsequent metabolic, cardiovascular and endocrine phenotype as well as its postnatal growth and bone development. It also highlights the immediate neonatal environment as a key window of susceptibility for programming of equine phenotype. Although further studies are needed to identify the cellular and molecular mechanisms involved, developmental programming of physiological phenotype is likely to have important implications for the health and potential athletic performance of horses, particularly if born with abnormal bodyweight, premature or dysmature characteristics or produced by assisted reproductive technologies, indicative of an altered early life environment.

Advances in Thermal Image Analysis for the Detection of Pregnancy in Horses Using Infrared Thermography

“…The high values of Entropy and SumEntrp indicate a high heterogeneity of texture [ 62 ] and may be a detectible feature in the progression of pregnancy. This result is in line with the successive increase of blood flow in the abdominal area, overall metabolic activity, and the proliferation of uterine and foetal tissues that require the pregnant mare to expend a large amount of energy [ 1 , 7 , 63 ]. This additional metabolic energy usage in pregnant mares leads to increases in heat emission from the body surface changing the conventional thermal pattern [ 7 , 8 , 9 ] but also the thermal image texture, as reported here.…”

Thermal features, ambient temperature and hair coat lengths: Limitations of infrared imaging in pregnant primitive breed mares within a year

“…The latter is the most variable and is highly dependent on the ambient temperature. In most of the horses, the longest winter coats (Jørgensen et al., 2020 ) coincide with late pregnancy (Fowden et al., 2020 ), which is also the time when thermography has been proven the most useful (Bowers et al., 2009 ). Therefore, we hypothesized that body surface temperatures are related to the internal conditions of the animal, such as an increased metabolism (Hodgson et al., 1993 ; Witkowska‐Piłaszewicz et al., 2020 ) or changes in blood flow during pregnancy (Bowers et al., 2009 ; Winsor, 1971 ).…”

Collagen and Microvascularization in Placentas From Young and Older Mares

“…In fact, in Thoroughbreds, for each kg of increase in placental weight, there was a raise of 4.5 kg in foal's weight (40). In the mare, the weight of the placenta progressively increases with parity, maternal size, and directly affects the placenta transport surface area and function, as well as fetal endocrine glands that mediate fetal development toward term (42)(43)(44)(45). In addition, equine placental weight increases in the months of April and May deliveries, in comparison to earlier foalings in the year (46).…”