ABSTRACT. The objective of this study was to estimate variance components for oocyte and embryo production traits in Guzerá breed female donors, and investigate their associations with age at first calving (A FC ). The traits analyzed were the number of viable oocytes (N OV ), the number of grade I oocytes (N GI ), the number of cleaved embryos (N CLV ), and viable embryos produced (N EMB ), and the percentages of viable oocytes (P OV ), grade I oocytes (P GI ), cleaved embryos (P CLV ), and viable embryos (P EMB ). Data were obtained from 5173 ovary puncture and in vitro fertilization (IVF) sessions using 1080 Guzerá female donors of different ages, occurred from March 2005 to July 2013. Variables were log-transformed (log e X+1) prior to analysis. (Co)variance components were estimated by restricted maximum likelihood (REML), using one-and two-trait animal models. Permanent environment and IVF sire (father of the embryos) random effects were included. Estimated heritabilities for N OV , N GI , N CLV , N EMB , P OV , P GI , P CLV , and P EMB were 0.19, 0.08, 0.16, 0.14, 0.04, 0.03, 0.01, and 0.07, respectively. Repeatabilities for count traits (N OV , N GI , N CLV , and N EMB ) varied from 0.14 and 0.32, higher than estimated for percentage traits (P OV , P GI , P CLV , and P EMB ), which varied from 0.01 to 0.08. Selection for N OV may be more appropriate in breeding programs than selection for N EMB , because of its strong genetic correlation (0.68) with N EMB and its greater time-and costeffectiveness. A FC was only weakly associated with the oocyte and embryo production traits, which indicates that there would be no effect on A FC when selecting for these traits.
