GENETIC PARAMETERS OF TEST DAY RECORDS IN BRAZILIAN HOLSTEIN CATTLE USING AN AUTOREGRESSIVE MULTIPLE LACTATION ANIMAL MODEL

Abstract Text: Variance components and genetic parameters were estimated for milk (M), fat (F), protein (P) and log-transformed somatic cell count (SCS) of Brazilian Holstein cattle using an autoregressive test day (TD) multiple lactations animal (AR) model. Data consisted of TD records produced by cows calving from 1992 to 2010 in herds under supervised milk recording. Average heritabilities of first three lactations for M, F, Pand SCS equal to 0.,28, 0.29, 0.28 and 0.19 respectively, leaded to genetic gains equal to 40.0, 0.98, 1.0 kg/year and -2,16 units/year for cows born from 1987 to 2008 and 34.9, 0.53, 0.69 kg/year and -4,83 units/year for bulls born from 1977 to 2002, respectively. Heritabilities and genetic gains suggest the AR model as a suitable approach to fit TD records to predict breeding values and to realize genetic gains by selection in Holstein cattle in Brazil.

Keywords: Milk components, selection, variance components