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.

Cow stayability plays a major role on the overall profitability of the beef cattle industry, as it is directly related to reproductive efficiency and cow's longevity. Stayability (STAY63) is usually defined as the ability of the cow to calve at least three times until 76 months of age. This is a late‐measured and lowly heritable trait, which consequently constrains genetic progress per time unit. Thus, the use of genomic information associated with novel stayability traits measured earlier in life will likely result in higher prediction accuracy and faster genetic progress for cow longevity. In this study, we aimed to compare pedigree‐based and single‐step GBLUP (ssGBLUP) methods as well as to estimate genetic correlations between the proposed stayability traits: STAY42, STAY53 and STAY64, which are measured at 52, 64 and 76 months of cow's age, considering at least 2, 3 and 4 calving, respectively. ssGBLUP yielded the highest prediction accuracy for all traits. The heritability estimates for STAY42, STAY53, STAY63 and STAY64 were 0.090, 0.151, 0.152 and 0.143, respectively. The genetic correlations between traits ranged from 0.899 (STAY42 and STAY53) to 0.985 (STAY53 and STAY63). The high genetic correlation between STAY42 and STAY53 suggests that besides being related to cow longevity, STAY53 is also associated with the early‐stage reproductive efficiency. Thus, STAY53 is recommended as a suitable selection criterion for reproductive efficiency due to its higher heritability, favourable genetic correlation with other traits, and measured earlier in life, compared with the conventional stayability trait, that is STAY63.

Objective:The aim of this study was to estimate genetic parameters for 305-day cumulative milk yield and components, growth, and reproductive traits in Guzerá cattle. Methods:The evaluated traits were 305-day first-lactation cumulative yields (kg) of milk (MY305), fat (FY305), protein (PY305), lactose (LY305), and total solids (SY305); age at first calving (AFC) in days; adjusted scrotal perimeter (cm) at the ages of 365 (SP365) and 450 (SP450) days; and adjusted body weight (kg) at the ages of 210 (W210), 365 (W365) and 450 (W450) days. The (co)variance components were estimated using the restricted maximum likelihood method for single-trait, bi-trait and tri-trait analyses. Contemporary groups and additive genetic effects were included in the general mixed model. Maternal genetic and permanent environmental effects were also included for W210. Results:The direct heritability estimates ranged from 0.16 (W210) to 0.32 (MY305).The maternal heritability estimate for W210 was 0.03. Genetic correlation estimates among milk production traits and growth traits ranged from 0.92 to 0.99 and from 0.92 to 0.99, respectively. For milk production and growth traits, the genetic correlations ranged from 0.33 to 0.56. The genetic correlations among AFC and all other traits were negative (-0.43 to -0.27). Scrotal perimeter traits and body weights showed genetic correlations ranging from 0.41 to 0.46, and scrotal perimeter and milk production traits showed genetic correlations ranging from 0.11 to 0.30. The phenotypic correlations were similar in direction (same sign) and lower than the corresponding genetic correlations. A c c e p t e d A r t i c l e 4 Conclusion: These results suggest the viability and potential of joint selection for dairy and beef traits in Guzerá cattle, taking into account reproductive traits.

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