Data on of 430 performance records (1995-2008) of 127 Holstein Friesian cows reared at Research Farm of Agricultural College at Ataturk University, Erzurum, Turkey was used to investigate the effects of environmental factors on the 305-days milk and milk fat yields. Genetic, phenotypic and environmental trends were also estimated in these traits. The data were analyzed by the least square technique to determine the influence of the environmental factors. Individual animal models were also fitted to 305-days milk and milk fat yields from all lactations to estimate breeding values by Restricted Maximum Likelihood methodology. The least square means for 305-days milk and milk fat yields were 3408.17 +/- 48.54 and 112.05 +/- 2.30 kg, respectively. The influence of the parity and years on the 305-days milk and milk fat yields were significant (P<0.01); while calving season significantly (P<0.05) affected 305-days milk yield. The estimated annual genetic, phenotypic and environmental trends were 3.73 +/- 4.07, -17.73 +/- 9.64 and -21.46 kg for 305-days milk yield and 0.22 +/- 0.15, -2.29 +/- 0.46 and -2.51 kg for milk fat yield, respectively. The genetic trends for 305-days milk and milk fat yields were slightly positive indicating that the sires used during last 14 years had better breeding values. The environmental trends for 305-days milk and milk fat yields depicted deteriorating trends indicating presence of some environmental inadequacies. (C) 2012 Friends Science Publishers
