Electrocardiographic Aspects of Singleton Pregnancy and Neonatal Period in American Miniature Horse Breed

Juliana Almeida Nogueira da Gama, Gabriela Amorim Campos, Raphael Tortorelli Teixeira, Mirian Harumi Tsunemi, Bianca Paola Santarosa, Henrique Barbosa Hooper, Maria Lúcia Gomes Lourenço, Simone Biagio Chiacchio


Background: During pregnancy, cardiovascular adaptations occur in order to meet maternal demands and adequate support for fetal development, but they are still unclear in the equine species, especially in the American Miniature horse breed. The main hemodynamic changes that occur during pregnancy are increased heart rate, cardiac output, and blood volume. It is necessary to use the reference values for the miniature breeds, in addition to the age range and reproductive condition, so the objective of this study was to evaluate the effect of pregnancy on electrocardiographic (ECG) parameters in mares and also of age in newborns foals of American Miniature horse breed. 

Materials, Methods & Results: Ten American Miniature Horse mares, between 7 and 19 years old (12.14 ± 4.05 years), 116.85 ± 24.09 kg of body weight were used in the experiment. All these mares were pluriparous, with 5.9 ± 3.5 of births, minimum of 2, and maximum of 12 foaling times. They were maintained in common social group in an indoor house stable with straw bed, with access to an outdoor paddock for several h per day. Twice a day they were fed with hay. Mineral supplements and water were available ad libitum. The ECG were obtained in 10 pregnant mares and in 10 neonates. All females were examined at a representative time of each trimester of pregnancy, at 30, 210, 300 days before and 21 days after delivery. Neonates were examined on different times: first 24 h after delivery, weekly on the 7th, 14th, 21st, 28th and 35th days of age. The ECG parameters considered were the heart rate and rhythm, duration and intervals (P, PR, QRS, QT, T) and amplitude (P, R, S, T) of ECG waves. The mean of pregnancy duration was 319.4 ± 4.97 days. Heart Rate (HR) varied between 51 to 59 bpm during pregnancy and 56 bpm on the 21st day after delivery. Comparing the clinical parameters of pregnant mares, non-pregnant mares and foal a difference was found for HR, Respiration Rate (RR) and Temperature (P = 0.001). All ECG parameters of pregnant, non-pregnant and foal mares showed a significant difference (P = 0.0001), except for the amplitude of the P1, P2 and R waves, which was similar for the 3 groups. The mean values of HR and amplitude of the positive T wave were higher in foals when compared to pregnant and non-pregnant mares, which in turn did not differ from each other. The mean duration of the P wave, PR segment, QRS complex, QT segment and T wave were the same among mares and greater than in foals. Comparing pregnant and non-pregnant mares, there was a difference in only 3 parameters: duration of the QTc segment, amplitude of the S wave and negative T wave. The non-pregnant mares had a longer duration of the QTc segment and a greater amplitude of the negative T wave, while the foals had a greater amplitude of the S wave.

Discussion: Although this study did not measure HR at delivery time, it is worth to consider the action of the parasympathetic autonomic nervous system close to delivery, which reduces the HR of mares. This is because at delivery, sympathetic-adrenal activation should be avoided since the increase in sympathetic tone can cause uterine atony via B2 receptors. For this reason, it has been shown that, during physiological birth, horses are under parasympathetic control, and stress response mechanisms are not activated. It was conclude that the morphometry of the waves, intervals and ECG complexes, during the evolution of the reproductive state, the electrocardiographic aspects were generally associated with heart rate (PR and QT intervals). As for neonates, there was a discrepancy among the most of ECG parameters when compared to the adult female, regardless of reproductive status, clarifying the importance of ECG patterns not only for the breed, but also for the age group.

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Abbas A.E., Lester S.J. & Connolly H. 2005. Pregnancy and the cardiovascular system. Internacional Journal of Cardiology. 98: 179-189. DOI: 10.1016/j.ijcard.2003.10.028

Adams-Brendemuehl C. & Pipers F.S. 1987. Antepartum evaluations of equine fetus. Journal of Reproduction and Fertility. 35(Supplement): 565-573.

Atherton J.C., Dark J.M., Garland H.O., Morgan M.R., Pidgeon J. & Soni S. 1982. Changes in water and electrolyte balance, plasma volume and composition during pregnancy in the rat. Journal of Physiology. 330: 81-93. DOI: 10.1113/jphysiol.1982.sp014330

Baska-Vincze B., Baska F. & Szenci O. 2015. Fetal Heart Rate and Fetal Heart Rate Variability in Lipizzaner Broodmares. Acta Veterinaria Hungarica. 66: 89-99. DOI: 10.1556/AVet.2015.007

Bazzano M., Giuduce E., Di Pietro S. & Piccione G. 2014. Vital Parameters in Newborn Thoroughbred foals during the first week of life. Internacional Journal of Anesthesiology Research. 2: 27-30. DOI: 10.14205/2310-9394.2014.02.02.1

Buss D.D., Rwalings C.A. & Bisgard G.E. 1975. The normal electrocardiogram of the domestic pony. Journal of Electrocardiology. 8: 167-172. DOI: 10.1016/s0022-0736(75)80025-2

Dantas G.N., Lourenço M.L.G., Santarosa B.P., Ulian C.M.V., Heckler M.C.T., Carvalho L.R. & Chiacchio S.B. 2015. Electrocardiographic methods in equines American Miniature Horse. Ciência Rural. 45: 848-853. DOI: 10.1590/0103-8478cr20140584.

Hunter S. & Robson S.C. 1992. Adaptation of the maternal heart in pregnancy. British Heart Journal. 68: 540-543. DOI: 10.1136/hrt.68.12.540

Klewitz J., Struebing C., Rohn K., Goergens A., Martinsson G., Orgies F., Probst J., Hollinshead F., Bollwein H. & Sieme H. 2015. Effects of age, parity, and pregnancy abnormalities on foal birth weight and uterine blood flow in the mare. Theriogenology. 83: 721-729. DOI: 10.1016/j.theriogenology.2014.11.007

Lombard C.W., Evans M., Martin L. & Tehrani J. 1984. Blood pressure, electrocardiogram and echocardiogram measurements in the growing pony foal. Equine Veterinary Journal. 16: 342-347. DOI: 10.1111/j.2042-3306.1984.tb01939.x.

Lumbers E.R. & Pringle K.G. 2014. Roles of the circulating renin-angiotensina-aldosterone system in human pregnancy. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology. 306: 91-101. DOI: 10.1152/ajpregu.00034.2013.

Matsui K., Sugano S. & Masuyama I. 1985. Changes in the fetal heart rate of Thoroughbred horse through the gestation. The Japanese Journal of Veterinary Science. 47: 597-601. DOI: 10.1292/jvms1939.47.597

Nagel C., Aurich J. & Aurich C. 2010. Determination of heart rate and heart rate variability in the equine fetus by fetus maternal electrocardiography. Theriogenology. 73: 973-983. DOI: 10.1016/j.theriogenology.2009.11.026

Nagel C., Aurich J., Palm F. & Aurich C. 2011. Heart rate and heart rate variability in pregnant Warm blood and Shetland mares as well as their fetuses. Animal Reproduction Science. 127: 183-187. DOI: 10.1016/j.anireprosci.2011.07.021.

Nagel C., Erber R., Bergmaier C., Wulf M., Aurich J., Möstl E. & Aurich C. 2012. Cortisol and progestin release, heart rate and heart rate variability in the pregnant and postpartum mare, fetus and newborn foal. Theriogenology. 78: 759-767. DOI: 10.1016/j.theriogenology.2012.03.023

Nagel C., Erber R., Ille N., von Lewinski M., Aurich J., Möstl E. & Aurich C. 2014. Parturition in horses is dominated by parasympathetic activity of the autonomous nervous system. Theriogenology. 82(1): 160-168. DOI: 10.1016/j.theriogenology.2014.03.015

Nagel C., Trenk L., Aurich J., Wulf M. & Aurich C. 2016. Changes in blood pressure, heart rate, and blood profile in mares during the last 3 months of gestation and the peripartum period. Theriogenology. 86: 1856-1864. DOI: 10.1016/j.theriogenology.2016.06.001.

Neuhauser S., Gösele P. & Handler J. 2018. Clinical signs in late pregnant mares. Tierarztl Prax Ausg G Grosstiere Nutztiere. 46: 164-171. DOI: 10.15653/TPG-180125.

Ohmura H. & Jones J.H. 2017. Changes in heart rate and variability as a function of age in Thoroughbred horses. Journal of Equine Science. 28: 99-103. DOI: 10.1294/jes.28.99

Parraguez V.H., Coloma I., Riquelme R., Llanos A.J. & Escobar C. 2002. Blood and physiological variables in Thoroughbred foals during the first 24 hours of life. Arquivos de Ciências Veterinárias e Zoologia da UNIPAR. 5: 169-176.

Patteson M.W. 1996. Equine Cardiology. Oxford: Blackwell Science, pp.98-135.

Reed S., Bayly W. & Sellon D. 2017. Equine Internal Medicine. 4th edn. St. Louis: Saunders Elsevier; pp. 366-377.

Sanghavi M. & Rutherford J.D. 2014. Cardiovascular Physiology of Pregnancy. Circulation. 130: 1003-1008. DOI: 10.1161/CIRCULATIONAHA.114.009029

Santarosa B.P., Lourenço M.L.G., Dantas G.N., Ulian C.M.V., Heckler M.C.T., Sudano M.J., Gonçalves R.C. & Chiacchio S.B. 2016. Effect of pregnancy and correlation of weight and heart rate with electrocardiographic parameters in the American Miniature Horse. Arquivo Brasileiro de Medicina Veterinária e Zootecnia. 68: 579-586. DOI: 10.1590/1678-4162-8726.

Santarosa B.P., Lourenço M.L.G., Dantas G.N., Ulian C.M.V., Heckler M.C.T., Sudano M.J., Gonçalves R.C. & Chiacchio S.B. 2016. Electrocardiographic parameters of the American Miniature Horse: influence of age and sex. Pesquisa Veterinária Brasileira. 36: 551-558. DOI: 10.1590/S0100-736X2016000600015

Schade J., Schade M.F.S. & Fonteque J.H. 2014. Auscultatory and electrocardiographic characteristcs of Crioulo horses. Pesquisa Veterinária Brasileira. 34 (3): 281-289. DOI: 10.1590/S0100-736X2014000300014

Trautvetter E., Detweiler D.K. & Patterson D.F. 1981. Evolution of the Electrocardiogram in Young Dogs During the First 12 Weeks of Life. Journal of Electrocardiology. 14: 267-274. DOI: 10.1016/s0022-0736(81)80008-8

Wulf M., Erber R., Ille N., Beythien E., Aurich J. & Aurich C. 2017. Effects of foal sex on some perinatal characteristics in the immediate neonatal period in the horse. Journal of Veterinary Behavior. 18: 37-42. DOI: 10.1016/j.jveb.2016.12.010

DOI: https://doi.org/10.22456/1679-9216.111612

Copyright (c) 2021 Juliana Almeida Nogueira Gama, Gabriela Amorim Campos, Raphael Tortorelli Teixeira, Bianca Paola Santarosa, Mirian Harumi Tsunemi, Henrique Barbosa Hooper, Maria Lúcia Gomes Lourenço, Simone Biagio Chiacchio

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