The Effect of Mare Age and Reproductive Status on Embryo Recovery Rate and the Quality of Embryos Recovered

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Implications Embryo recovery allows an increase selection intensity and use of fewer breeding horses providing fast assessment of breeding improvements within a breed and across the breeding industry. Despite this limitations in embryo recovery procedure limit its wide spread use within the equine industry. This study supports industry and research based indications that age of the donor mare has an effect on the success of embryo recovery as well as the quality of embryos recovered. Introduction Equine embryo transfer (ET) has become more widespread in the equine breeding industry, but variable success rates averaging 50% (Squires and McCue, 2007) indicate that there are many limiting factors within embryo recovery reducing the application of the technique. Respective studies have shown that intrinsic factors of the donor mare (Lopes et al., 2011) and quality of embryos (Scherzer et al., 2008) recovered pose the main limitations within the embryo recovery process. This study hypothesised that first1) age influences the quality and the recovery rate of embryos and, second reproductive status influences the quality and the recovery rate of embryos. The final aim of this study was to investigate whether a combination of age and reproductive status affects the successful recovery of quality embryos. Material and methods Data was collected from a commercial ET centre, using the records for 156 sport horse mares aging from 2 to 24 years old for the 2007 to 2012 breeding seasons. The mares were allocated a code, and their age, reproductive status, success of embryo recovery and the embryo quality were recorded. Mares were allocated on one of five age groups: 2-5years, 6-9 years, 10-14years, 15-19years and 20 years and older. Reproductive status was grouped into the following four groups: maiden mare, barren mare, foal at foot, flushed in previous season(s). The quality of embryos was graded on a standard industry scale of 1-4 (Camargo et al., 2013), with the alteration of nonfertilised oocytes graded as 5 to keep results nominal. The relationship between embryo recovery and quality and the age and reproductive status were analysed using Spearman’s Correlation Coefficient on SPSS v. 21. The differences between embryo recovery, embryo quality and reproductive status were analysed using Kruskal-Wallis. The data was grouped by reproductive status then the differences between age group, embryo recovery and embryo quality were analysed using Kruskal-Wallis. Results The age of the mare was significantly related to embryo recovery (rs = -.134, P <0.01), and embryo quality, (rs = -.122,P <0.05), showing a weak, but significant negative relationship. No other significant differences between variables were established as part of this study. Conclusion In agreement with other studies, there is significant, but weak negative correlation between mare age and the successful recovery of embryos in older mares. The reproductive status was not shown to have a significant effects, which is likely to be due to a number of variables affecting the reproductive status. These were not explored in this study, but could be investigated in future research. This study does not support findings from other studies (Pycock, 2006) which report that older maiden mares are less likely to conceive successfully compared to younger maiden mares. This may indicate that improved knowledge about age related conditions such as endometritis, resulting in improved and more successful management of these conditions, may counteract some of the age related issues which have previously been identified, resulting in higher conception rates in older mares
Original languageEnglish
Publication statusPublished - 2014
EventBritish Society of Animal Science Conference 2014: Science into Practice - , United Kingdom
Duration: 30 Apr 201430 Apr 2014


ConferenceBritish Society of Animal Science Conference 2014
Abbreviated titleBSAS 2014
Country/TerritoryUnited Kingdom


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