Reproductive rate in many species of farming animals is much
lower than their theoretical potencielity. That is a result of
prenatal loss, especially significant in multiple young bearing
species. Such factors as mother’s age, body weight at mating
time, nutrition level both before and during pregnancy affect
the ovulation rate and the litter size at birth. At the same
time the litter size is the resultant of the ovulation rate and
the embryonic survival rate. According to Bowman /1958/ the
amount of losses of the fertilized aggs is the bigger as the
higher is the ovulation rate on a uterus horn. Barr et al. /1970/
have also stated that there are some places in an uterus horn
where the embryo losses are much higher. Me Laren and Miclcie
/1959/, Dzigciolowslca /1973/ and Bruce /198O/ have observed that
the embryo losses are connected with different periods of pregnancy.
According to some authors most losses are observed during the
firtst period - before implantation, some others connect the
losses in the litter size with the late pregnancy, for example
Bruce /198O/ reports about 30'jo embryo losses during that period.
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 7. Symposia (1), , 44–50, 1982
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