ABSTRACT
The aim of this Thesis was to estimate the direct response and the correlated responses in litter size and survival rates in an experiment of selection for ovulation rate in rabbits. 
Selection for ovulation rate was performed in a rabbit line during 10 generations. Selection was based on the phenotypic value of ovulation rate estimated at d 12 of second gestation by laparoscopy. A control line was produced recovering embryos from 50 donor females and 18 males, belonging to the base generation of the line selected for ovulation rate. Approximately 470 embryos were vitrified and stored in liquid N2 until transfer at the end of the selection experiment (10th generation of the selected line).
Traits recorded were: litter size (LS), estimated as total number of rabbits born per litter in up to five parities; ovulation rate (OR), estimated as the number of corpora lutea in both ovaries; right and the left ovulation rates (ROR and LOR); the number of implanted embryos (IE), estimated as the number of implantation sites; the number of right and left implanted embryos (RIE and LIE); ovulatory difference (OD), defined as the difference between ROR and LOR, expressed as an absolute value; implantatory difference (ID), defined as the difference between RIE and LIE, expressed as an absolute value; embryonic survival (ES), calculated as IE/OR; fetal survival (FS), calculated as LS/IE; prenatal survival (PS), calculated as LS/OR.
Bayesian methodology was used to analyze the data. The estimated heritabilities of OR, LS, ES, FS and PS were 0.16, 0.09, 0.09, 0.24 and 0.14, respectively. The estimated phenotypic correlations of OR with LS, ES, FS and PS were 0.09, -0.07, -0.26 and -0.28, respectively. The genetic correlation of OR with LS and ES were estimated with low accuracy and nothing can be said about their sign. The estimated genetic correlations of OR with FS and PS were negative (probability of being negative 1.00 and 0.98, respectively). The estimated phenotypic and genetic correlations between LS and survival rates were positive (probability of being positive of 1.00).
Responses to selection were estimated by two methods, genetic trends and differences between the selected and the control line, both estimates being similar for most of the traits. Ovulation rate increased with selection (1.3 ova in 10 generations estimated with genetic trends; 2.1 ova in 10 generations estimated with the control line), but there was no correlated response in litter size, supporting that the genetic correlation between ovulation rate and litter size should be close to zero. No clear changes were observed in ovulatory difference and implantatory difference. A small decrease in embryonic survival expressed as a percentage (around 5% in 10 generations) was observed when comparing the selected and the control lines, but this reduction was not estimated with genetic trends. A decrease in fetal survival expressed as a percentage (around 10% in 10 generations) seemed to be the main responsible for the lack of correlated response observed in litter size.