Genetic analysis of oocyte and embryo production traits in Guzerá breed donors and their associations with age at first calving.

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 (AFC). The traits analyzed were the number of viable oocytes (NOV), the number of grade I oocytes (NGI), the number of cleaved embryos (NCLV), and viable embryos produced (NEMB), and the percentages of viable oocytes (POV), grade I oocytes (PGI), cleaved embryos (PCLV), and viable embryos (PEMB). 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 (logeX+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 NOV, NGI, NCLV, NEMB, POV, PGI, PCLV, and PEMB were 0.19, 0.08, 0.16, 0.14, 0.04, 0.03, 0.01, and 0.07, respectively. Repeatabilities for count traits (NOV, NGI, NCLV, and NEMB) varied from 0.14 and 0.32, higher than estimated for percentage traits (POV, PGI, PCLV, and PEMB), which varied from 0.01 to 0.08. Selection for NOV may be more appropriate in breeding programs than selection for NEMB, because of its strong genetic correlation (0.68) with NEMB and its greater time- and cost-effectiveness. AFC was only weakly associated with the oocyte and embryo production traits, which indicates that there would be no effect on AFC when selecting for these traits.