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The effect of selected factors on the length of gestation period in Silesian mares

Ewa Walkowicz
Wrocław University of Environmental and Life Sciences, Department of Horse Breeding and Equestrian Study Kożuchowska 6, 51-631 Wrocław, Poland
Abstract :
The aim of the study was to determine the average length of gestation and its variation in a population
of Silesian mares bred during a period of 55 years (1945-2000) in national studs and private farms in
southern Poland. Considered was the sex of foals, season, month and year of birth, environmental
conditions (national or private breeding centres), breeding history of a mare (number of foals born)
and influence of the preceding reproductive period.
Gestation period in Silesian mares lasted on average 338.66 days ±13.57 and ranged from 299
(the shortest) to 386 (the longest) days. Gestations lasting from 311 to 356 days were considered
normal for the breed. Gestations resulting in a birth of a colt lasted one day longer (339.23±13.44
days compared to 338.19±13.60 days for fillies). Gestations from the autumn reproductive period
(October–December), when photoperiods become shorter, were the shortest, whereas gestations
from the late spring season (April-June), when photoperiods become longer, were the longest
(329.82±10.25 and 341.14±13.87 days, respectively). Significant differences were also found in the
length of gestations that ended in particular months: the shortest gestations ended in October (327.45
days ±12.24 days), while the longest in May (342.19±14.19 days). The analysis of the years of foaling,
grouped in ten-year periods, showed that the shortest gestations occurred before 1960 (335.41±13.87
days), whereas the longest between 1961 and 1970 (339.64±15.15 days). A slow decrease was observed
in the length of gestation in subsequent ten-year periods.
Mean gestation period in mares from national studs lasted 5 days longer than that in mares from private
breeding centres (334.79±11.21 and 339.60±13.92 days, respectively). The number of foalings did not 
affect the length of gestation significantly; a small difference was found in the case of multiparous
mares (more than eight foals born), whose gestation lasted one day longer compared to remaining
mares (338.71±13.52 and 337.46±12.32 days, respectively). Gestations in mares whose preceding
reproductive period ended with a miscarriage were the shortest, while gestations in mares that were
barren in the previous season were the longest (336.36±13.11 and 340.05±13.71 days, respectively).
Keywords :
reeding / horse / pregnancy / Silesian horse

Date Deposited : 02 Apr 2015 10:35

Last Modified : 02 Apr 2015 10:35

Official URL:

Volume 32, Number 1, - 2013

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