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Home / Equine Research Bank / Can Vet J / Quantifying the occurrence of early embryonic mortality on t...
The Canadian veterinary journal = La revue veterinaire canadienne1991; 32(11); 665-672;

Quantifying the occurrence of early embryonic mortality on three equine breeding farms.

Abstract: This prospective field study was designed to describe the incidence of early embryonic mortality (EEM) and factors associated with the cause of EEM on three equine breeding farms in Ontario during the 1989 breeding season. Early embryonic mortality was defined as the loss of a single embryo during the first 40 days of pregnancy (day 0 = day of ovulation or last breeding). Pregnancy diagnoses and subsequent embryonic losses were observed by serial trans-rectal ultrasonography between days 12-20 (PD1) and 21-30 (PD2), and by trans-rectal ultrasonography or palpation per rectum between days 31-40 (PD3). Information on pregnancy status of a mare (or cycle) at 40 days after the last breeding was recorded when available. Nonpregnancy rates were calculated on a per cycle basis, to account for mares with no ultrasonic evidence of an embryo at the initial pregnancy examination. Embryonic mortality rates per cycle were calculated cumulatively (EMR((40))) for the entire 40 day embryonic period and during the specific time periods when a pregnancy diagnosis took place (EMR((PD1)), EMR((PD2)), EMR((PD3))). Embryonic mortality rates were also calculated on a per mare basis for mares experiencing EEM on either their first (EMR((f))) or any (EMR((a))) breeding cycle. Per cycle mare withdrawal rates were calculated cumulatively for the entire 40 day embryonic period (MWR((40))), and at each specific pregnancy diagnosis time period (MWR((PD1)), MWR((PD2)), MWR((PD3))) to account for those breeding cycles in which mares were not able to be observed for the entire forty days of the embryonic period. Records from a total of 699 mares involving 1014 breeding cycles were examined and analyzed. Per cycle risk rates for nonpregnancy (NP) were 36.4%, 45.0%, and 22.1%, for farms 1,2 and 3, respectively. Per cycle EMR((40)) ranged from 8-17%. Per cycle MWR((40)) ranged from 56.5-98.9%, indicative of a high rate of mare withdrawal from the study for the duration of the "embryonic" period. Significant differences (p < 0.05) in EMR((f)) and EMR((a)) per mare existed between two farms, indicative of a farm effect on EMR. Multivariable forward stepwise logistic regression analyses revealed that mares bred on foal heat were 1.9 times more likely than mares not bred on foal-heat to experience EEM (p = 0.008).
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Publication Date: 1991-11-01 PubMed ID: 17423895PubMed Central: PMC1481100
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Summary

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The research paper discusses a field study conducted to determine the rates of early embryonic mortality (the loss of an embryo during the first 40 days of pregnancy) and the factors contributing to it, in three horse breeding farms in Ontario, Canada, throughout the 1989 breeding season.

Research Methodology

  • The study monitored the pregnancy and embryonic loss statuses from day 12 to day 40 post breeding. Three key observations were made between days 12-20 (PD1), 21-30 (PD2), and 31-40 (PD3) of the pregnancy.
  • Data on mares’ pregnancy status at 40 days after the final breeding were recorded, when accessible.
  • To account for mares with no ultrasonic proof of an embryo during initial pregnancy examination, non-pregnancy rates were calculated on a per-cycle basis.
  • Embryonic mortality rates were computed accumulatively for the whole 40-day embryonic period. Rates were also calculated for each specific time period when a pregnancy diagnosis was carried out.
  • The study also calculates the embryonic mortality rates on a per mare basis for mares experiencing EEM in their first or any breeding cycle.
  • The research noted mare withdrawal rates for the entire 40-day embryonic period and for each specific pregnancy diagnosis time. This was done to account for breeding cycles where observation was not possible for the mares throughout the 40-day embryonic period.

Findings and Analysis

  • A total of 1014 breeding cycles from 699 mares were evaluated and analysed in this study.
  • Risk rates for non-pregnancy ranged from 22.1% to 45.0% between the three farms.
  • Embryonic mortality per cycle ranged from 8-17%, while mare withdrawal rates per cycle ranged from 56.5-98.9%, indicating a high level of mare withdrawal from the study during the embryonic period.
  • There were significant differences in embryonic mortality rates per mare between two farms, hinting at the impact of the farm environment on the prevalence of embryonic mortality.
  • Interestingly, the study found out that mares bred on foal heat (the first heat cycle following the birth of a foal) were 1.9 times more likely to experience EEM compared to mares not bred on foal-heat.

Cite This Article

APA
Meyers PJ, Bonnett BN, McKee SL. (1991). Quantifying the occurrence of early embryonic mortality on three equine breeding farms. Can Vet J, 32(11), 665-672.

Publication

The Canadian veterinary journal = La revue veterinaire canadienne
ISSN: 0008-5286
NlmUniqueID: 0004653
Country: Canada
Language: English
Volume: 32
Issue: 11
Pages: 665-672

Researcher Affiliations

Meyers, P J
    Bonnett, B N
      McKee, S L

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