The objective of this study was to compare the functions of Wilmink and Ali and Schaeffer with Legendre polynomials in random regression models using heterogeneous residual variances for modeling genetic parameters during the

The objective of this study was to identify a nonlinear regression model that better describes the milk production and the percentages of fat and protein curves, and to identify the season and age of calving that result in higher productions

This study aimed to test different genotypic and residual covariance matrix structures in random regression models to model the egg production of Barred Plymouth Rock and

RESUMO Objetivou-se comparar um modelo multicaracterística padrão com modelos de análise de fatores (AF) e de componentes principais (CP) para estimar parâmetros genéticos para a produção de leite no dia do controle (PLDC) de vacas da ABSTRACT The objective was to compare a standard multi-trait (MT) analysis model with factor (FA) and principal components (PC) analyses models to estimated genetic parameters for Holstein cows test day milk production (TD). The data file was composed by 4.616 TD at first lactation registers. The TD was grouped into ten monthly classes of lactation, from the 5th and the 305th day of lactation (TD1 to TD10). Analyses were performed considering 11 different models: standard multi-traits (MT), five reduced rank models to genetic covariance matrix adjusting one (PC1), two (PC2), three (PC3), four (PC4) and five (PD5) principal components and five models using factor analyses (F1, F2, F3, F4 and F5)

This study evaluated the effects of seasons and latitude on tick counting and determined the best model to estimate genetic parameters for tick count and hair coat. Records of animals naturally exposed to ticks on farms in several Brazilian states and in Paraguay were used. The ANOVA was used to verify the effects of seasons and latitude on the tick count trait. Spring was the season with the highest average, followed by summer and autumn, which showed no differences between them. The winter presented the lowest average values. Latitude -11° had the highest mean value followed by latitude -18°. The Bayesian approach was used to evaluate tick count and hair coat and to identify a suitable model for estimating genetic parameters for use in genetic evaluations. The data were analyzed using an animal model with four different specifications for “fixed” purposes. The inference was based on a Markov chain Monte Carlo (MCMC). The criteria for selection of the Bayesian model indicated that the M1 model, which considered the breed composition in the contemporary group, was superior to the other models, both for tick count and hair coat. Heritability estimates for tick count and hair coat obtained using the M1 model were 0.14 and 0.22, respectively. The rank correlations between the models for tick count and hair coat were estimated and reordering was verified for tick count. The estimated genetic correlation between tick count and hair coat traits was negative (-0.12). These findings suggest that different genes regulate tick count and hair coat.

Impact of different numbers of milk test-day records during lactation on the reliability of estimated breeding values

The objective of this study was to evaluate the impact of the reduction in the number of test-day records per lactation on genetic parameters of test-day milk yield (TDMY) and the reliability of estimated breeding values for 305-day milk yield in Holstein cattle. Through the random elimination of milk test-days over the lactation period, seven subpopulations were formed, which differed in number of test-day records/lactation/cow, so that all cows in each subpopulation necessarily contained four to ten records per lactation. Estimates of genetic parameters and breeding values were performed using the animal model of random regression and adjustment of the Legendre polynomial (fourth order). When comparing sires with the same number of daughters, greater reliability was found in the subpopulations with the highest number of milk test-day records/lactation/cow. It was also found that the elimination of at least one test-day affected the reliability of estimated breeding value for 305-day milk yield in the sires, regardless of the class of number of daughters/sires. When selecting the 5% best sires and 20% best cows, the lowest order correlations were observed between the population with 10 test-day records/lactation (complete lactation) and the other subpopulations with incomplete lactations (4, 5, 6, 7, 8, 9 test-day records/lactation). The reduction in the number of milk test-day records per lactation interferes in the reliability of the estimated breeding value for sires and cows, negatively impacting the precision of selecting genetically superior animals.