Genetic parameters of multiple ovulation traits in Nellore females

Variability in superovulatory response is a limiting factor for animal breeding programs using Multiple Ovulation and Embryo Transfer (MOET) nucleus schemes. To evaluate genetic factors affecting superovulory response, 1036 multiple ovulation records from 475 Brazilian Nellore embryo donors (daughters of 139 sires), 2.2-20.5-year olds, were analyzed. Traits used to evaluate superovulatory response included the number of palpable corpora lutea (CL), the total number of recovered structures (RS), and the number of viable embryos (VE). Two data sets were used: data from the first flush only or data from the first three flushes. Genetic parameter estimations were carried out using Restricted Maximum Likelihood (REML) methodology, with single- and multiple-trait animal models. According to the data set used, heritability estimates ranged from 0.47 to 0.57 for CL, from 0.20 to 0.65 for VE, and from 0 to 0.34 for RS, and were higher for the data set that used only the first flushing only. For the first flush, genetic correlations were 0.43 between CL and SF, 0.01 between CL and VE, and 0.73 between SF and VE. Repeatability estimates ranged from 0.47 to 0.51. In conclusion, the use of data from the first flush only might result in better estimates of genetic parameters for MOET traits in Nellore females. Furthermore, moderate to high values for repeatability suggested that selection for a high response to superovulation could be made after the first flush. (c) 2004 Elsevier Inc. All rights reserved.