Multiple Pregnancy in Mares
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MENDELNET 2016 MULTIPLE PREGNANCY IN MARES MARIE IMRICHOVA Department of Animal Breeding Mendel University in Brno Zemedelska 1, 613 00 Brno CZECH REPUBLIC [email protected] Abstract: Mare is in terms of reproduction described as uniparous, it means that she has one foal. More embryos, fetuses or foals represents non – physiological phenomenon and as such it brings a lot of complications. In terms of the etiology is discussed as a predisposing factor mare’s breed, the most common is a higher incidence associated with Thoroughbreds. Although in context of multiple pregnancies often mentioned is mare‘s age. The aim of this study was to evaluate the incidence and results of multiple pregnancy in Thoroughbred and Old Kladruber Horse mares. It was found 323 records of multiple pregnancies in Thoroughbred and 48 in Old Kladruber Horse mares and the result of the multiple pregnancy was in Thoroughbreds in 258 cases twin abortion, in 45 cases parturition of 2 dead foals, 15 records of parturition 1 live and 1 dead foal and in 5 cases it was the parturition of 2 live foals. In Old Kladruber Horse twin abortion was recorded 36 times, in 7 cases 2 dead foals and in 5 cases 2 live foals. Key Words: horse, breeding, reproduction, pregnancy, twins INTRODUCTION The reproduction standard in horse breeding is the fundamental informative factor affecting its success and profitability. One of the factors that can decide about the reproduction outcome is also multiple pregnancy. Multiple pregnancy basically may occur naturally either by spontaneous division of embryos, or by fertilization of two oocytes after multiple ovulation. Specifically horses in the vast majority of cases have dizygotic twins, thus originating from two separate embryos. In terms of double ovulation, which has the potential to result in a multiple pregnancy, can be distinguished according to the localization of an unilateral (two ovulations in the same ovary) and bilateral (one ovulation per each ovary). In the case of the time determination it may be a synchronous (usually during the 24 hours), and asynchronous ovulation. Multiple pregnancy as such can also be classified as unilateral and bilateral, depending on whether at the stage of fixation one embryo is attached in each uterine horn, or both together in one. All these factors, with maternal and environmental influences together, and especially management of selected twins from the breeder’s side affect the outcome of multiple gestation, and thus how its impact is reflected on mare’s reproduction. The incidence of multiple pregnancy in mares generally, for example, as Bílek et al. say (1957) between 2-2.5% of cases, Hutton and Meacham (1986) at 1.1% and Doležel et al. (2000) from 1.5 to 2.5%. As predisposing factors for multiple gestation are most frequently mentioned – breed, mare’s age, reproductive history and heredity. Górecka and Jezierski (2003), Bresińska et al. (2004), McCue (2009), Sheerin (2014) and others state that a breed with the highest incidence of multiple pregnancy is Thoroughbreds. Specifically, in Thoroughbreds Hutton and Meacham (1968) illustrate the incidence of multiple pregnancies at 2.4%, Doležel et al. (2000) at 2.57%, and Bresińska et al. (2004) and Wolc et al. (2006) at 3.5%. Regarding the age Davies Morel (2012) reported that incidence of multiple pregnancy increases in the older mares. Davies Morel and O'Sullivan (2001), Górecka and Jezierski (2003) and McCue (2009) argues that the mares, in which multiple ovulation or pregnancy already occurred once, have a greater likelihood of recurrence than mares in which this phenomenon has not been recorded. With respect to the inheritance factor from the work of Pawlak et al. (2000), Górecka and Jezierski (2003) and Davies Morel (2008) arises that predisposition for the multiple pregnancy is inheritable. 210 | Page MENDELNET 2016 In case of occurrence of multiple pregnancy, the most of the authors are united that only in the low percentage it results in one or two foal births. For example, Larson (2011) says that the chance of a mare having full term of two foals and their successful parturition is 1:10 000. Davies Morel (2008) says that 9% of twin pregnancies survives to full term and the parturition results in the death of both foals in 64.5% cases. The aim of this study was to evaluate characteristics of multiple pregnancy occurrence in the Thoroughbred population and for comparison in the Old Kladruber Horse, to find out in how many cases the result of multiple pregnancy is successful parturition of one or two foals and to evaluate the interrelationships between the result of multiple pregnancy and mare’s breed or age. MATERIAL AND METHODS In the research, selected reproduction characteristics of Thoroughbred and Old Kladruber Horse breed mares were evaluated. Required data were obtained from the Czechoslovak Thoroughbred Studbooks (Volume XI.-XIII.), Czech Thoroughbred Studbooks (Volume 1. to 4.) and the Old Kladruber Horse Studbook. In the Thoroughbred Studbooks records of mares born in the years 1965-2001 and active in breeding in 1985–2008 were found. In the Old Kladruber Horse Studbook they found records of mares born between the years 1978 to 2001 and active in breeding in the years 1981-2009. The Thoroughbred breed was chosen because of increasing incidence of multiple pregnancy within the breed and recorded by many authors and also because of the fact that Thoroughbred can only come of the natural breeding, so the factors like insemination, embryo transport and more cannot influence the evaluation. Moreover, Thoroughbred Studbooks contains exact and comprehensive records about reproduction including evidence of multiple pregnancy for many years. Old Kladruber Horse breed was chosen as a representative of warmblood for comparison with Thoroughbred. Another reason also was that it is possible to find records needed for evaluation in Old Kladruber Horse Studbooks. In the mentioned volumes of Studbooks all the records about reproduction of all the listed mares were reviewed and detailed appraisal was done just in those mares which had the multiple pregnancy during the reproductive life. For evaluating of the founded data and their relationships were used to the statistic programme STATISTICA.12 (© Statsoft, CZ version). The outputs of the programme were rounded to two decimal places or where it was appropriate (eg. an evaluation of the particular year) to integers. Testing took place at a significance level α = 0.05. RESULTS AND DISCUSSION Table 1 Multiple pregnancy in Thoroughbred mares Variable N valid Average Median Mode Frequency Minimum Maximum The age of the multiple 323 10.21 10 Multiple 35 4 20 pregnancy Table 1 states elementary descriptive statistics about the Thoroughbred mare’s age in the multiple pregnancy age. It was recorded in 323 cases of multiple pregnancies. The average age of the mares in the year of such gravidity was 10 years old. The middle value was also 10 years. The most common value was multiple–exactly the 7 and 9 age with the frequency of 35 times. The minimum age of mares in the multiple pregnancy was 4 years, the maximum 20 years. Table 2 Multiple pregnancy in Old Kladruber Horse mares Variable N valid Average Median Mode Frequency Minimum Maximum The age of the multiple 48 10.65 11 11 8 4 20 pregnancy For the characteristics of the age of Old Kladruber Horse mares in the time of multiple pregnancy 48 records were found. The average age was 11 years and also the median. The most common had the 211 | Page MENDELNET 2016 multiple pregnancy mares in the 11 years old with the frequency 8 cases. The lowest age was 4 and the highest 20 years old. The observed data regarding the age of the mares do not correspond with the assertion of Reef (1998), which says that the older mares show a multiple pregnancy more likely, since the oldest mare with such pregnancies recorded were twenty years old in both breeds, it can be assumed that the age of seven and nine-year-old in the Thoroughbreds and eleven-year-old in Old Kladruber Horse does not fall into those categories. On the other hand, Bresińska et al. (2004) are indicated as the most predisposed mares between 5 and 10 years of age and Doležel et al. (2000) say the same thing about mares aged 6- 10 years, which would match the data found in the Thoroughbreds. Figure 1 Repeated occurrence of multiple pregnancy in Thoroughbred mares 300 257 250 200 150 100 29 50 2 0 1 x 2 x 3 x Figure 1 shows the frequency of recurrence of multiple pregnancy. First column shows in how many mares from the observed file of multiple pregnancies occurred once in recorded reproductive history (257 mares), i.e. 89.24% frequency phenomenon. Second column describes which of the number of mares were multiple pregnancies reported in this sense, twice, with 29 mares (10.07%) and similarly in category 3 describes it in 2 mares (0.70%). Figure 2 Repeated occurrence of multiple pregnancy in Old Kladruber Horse mares 36 40 35 30 25 20 15 6 10 5 0 1 x 2 x 212 | Page MENDELNET 2016 As documented in Figure 2, in mares of Old Kladruber Horse breed was found only one variant of repeating multiple pregnancy during the reproductive history of mares, and that in 36 cases (85.71%) and the option of two repetitions in six cases (14.29%). With the results of repeating occurrence of multiple pregnancies in mares generally correspond with McCue’s (2009) assertions that mares which had twins previously have greater probability of their occurrence in future. The phenomenon of recurrence is also confirmed by Bresińska et al.