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.

E. Wirth-Dzieciolowska

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 7. Symposia (1), , 44–50, 1982
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