Vera Lúcia Cardoso

Variance component estimates applying random regression models for test-day milk yield in Caracu heifers (Bos taurus Artiodactyla, Bovidae)

Random regression models (RRM) were used to estimate covariance functions for 2,155 first-lactation milk yields of native Brazilian Caracu heifers. The models included contemporary group (defined as year-month of test and paddock) fixed effects, and quadratic effect of age of cow at calving. Genetic and permanent environmental effects were fitted by a random regression model and Legendre polynomials of days in milk (DIM). Schwarzs Bayesian information criteria (BIC) indicated that the best RRM assumed a six coefficient function for both random effects and a sixth order variance function for residual structure. Akaikes information criteria suggested a model with the same number of coefficients for both effects and a residual structure fitted by a step function with 15 variances. Phenotypic, additive genetic, permanent environmental and residual variances were higher at the beginning and declined during lactation. The RRM heritability estimates were 0.09 to 0.26 and generally higher at the beginning and end of lactation. Some unexpected negative genetic correlations emerged when higher order covariance functions were used. A model with four coefficients for additive genetic covariance function explains more parsimoniously the changes in genetic variation with DIM since the genetic parameter was more acceptable and BIC was close to that for a six coefficient covariance function.

Influência de fatores de ambiente sobre a contagem de células somáticas e sua relação com perdas na produção de leite de vacas da raça Holandesa

Cumulative milk yield at 305 days (MY-305) and somatic cell count (SCC) from the first to the fifth lactation of Holstein cows were analyzed in this study. Somatic cell count was logarithmically transformed to somatic cell score (SCS) that was then included in the model not only as a dependent but also as an independent variable. Year, season, and parity order all significantly affected the average SCS in this study. Data of the effect of SCS on milk yield showed significant losses on MY-305 because of the observed negative linear relationship between these two variables. Somatic cell score affected differently MY-305 from different parity orders with greater effect after the 3rd parity. Although clinical mastitis seems to cause greater economic losses, prevention and control of sub-clinical mastitis deserve more attention due to its greater prevalence leading to significant reduction on herd productivity.Cumulative milk yield at 305 days (MY-305) and somatic cell count (SCC) from the first to the fifth lactation of Holstein cows were analyzed in this study. Somatic cell count was logarithmically transformed to somatic cell score (SCS) that was then included in the model not only as a dependent but also as an independent variable. Year, season, and parity order all significantly affected the average SCS in this study. Data of the effect of SCS on milk yield showed significant losses on MY-305 because of the observed negative linear relationship between these two variables. Somatic cell score affected differently MY-305 from different parity orders with greater effect after the 3rd parity. Although clinical mastitis seems to cause greater economic losses, prevention and control of sub-clinical mastitis deserve more attention due to its greater prevalence leading to significant reduction on herd productivity.

Objetivos de seleção e valores econômicos de características de importância econômica para um sistema de produção de leite a pasto na Região Sudeste

As part of a preliminary study on the design of a breeding program involving Holstein Friesian and crossbred cattle (Holstein x Zebu) in the Southeast region of Brazil, economic values for milk volume (V), fat (F) and protein (P) production, age at first calving (AFC), mature body weight (MBW) and herd life (HL) were derived for a pasture based milk production system of crossbred cattle (Holstein x Zebu). The feeding regime was based on rotational grazing of elephantgrass during the rainy season and grazing plus maize silage during the dry season. Concentrates were fed when daily individual productions exceed 6-kg milk (1 kg concentrate: 2.5 kg milk). Sensitivity analyses were carried out to evaluate the effect of the change of payment system and milk price variation on economic values of the traits. Economic values were also derived for an alternative source of roughage supplementation based on the mixture of sugar cane plus urea. The economic values (US

Modelo bioeconômico para cálculo de custos e receitas em sistemas de produção de gado de corte visando à obtenção de valores econômicos de características produtivas e reprodutivas

) derived for the current payment system for V, F, P, AFC, MBW and HL were, respectively: 0.15; -0.48; -0.31; -0.11; 0.08 and 0.04. Results of sensitivity analyses are presented and discussed.

Modelos de dimensão finita para a estimação de parâmetros genéticos para a produção de leite de primeiras lactações de vacas da raça Holandesa

A bio-economic model was developed to calculate costs and revenues to obtain economic values (EV) for performance traits of beef cattle in production systems in Brazil. Performance records, economic and biologic parameters were obtained from a Nelore breeding herd. Two production systems: complete breeding cycle (CbcR) and cow-calf (Cc) were simulated using a deterministic and static model. Costs, revenues and the annual profits were calculated using Excel® to obtain the economic values for weaning weight (WW), mature weight (MW), pregnancy rate (PR) and weaning rate (WR) in both systems. The impact of changes in genetic level of traits on annual profits of the production systems were evaluated by increasing the original values of the traits by 1%. This increase resulted in positive changes on profits and the greatest impact was for WR in both systems. EV for WW, MW, PR, WR in CbcR and Cc systems were respectively R

Valores econômicos para as características de produção de leite de búfalas no Estado de São Paulo

0.40/kg, R

Efeitos genéticos e de ambiente sobre a produção de leite e a contagem de células somáticas em vacas holandesas

0.09/kg, R

Short communication: Principal components and factor analytic models for test-day milk yield in Brazilian Holstein cattle.

3.20/1%; R

Parametric correlation functions to model the structure of permanent environmental (co)variances in milk yield random regression models

10.15/1% and R

Genetic association between milk yield, stayability, and mastitis in Holstein cows under tropical conditions

1.31/kg, R