RESEARCH ON THE MEAT PRODUCTION DIFFERENCES DETERMINED BY THE BIRTH MONTH OF THE FATTENED STEERS

The purpose of the paper was to assess the effect of the birth month on some meat production characters such as live weight at the age of 180 days, live weight at the age of 365 days and daily gain during the fattening period in progeny testing for bulls' breeding value estimation in order to correct the biases determined by this environmental factor. In this purpose, the following linear mathematical model was used: xij=m . ai . eij, where xij - the live record of the "j" steer in the month "i" (i=1,2,....12), m- geometrical average of the meat production characters taken into account, ai- the multiplicative effect of the birth month "i" and eij ? the residual multiplicative effect. A number of 1,705 half-brothers belonging to 105 Friesian bulls from Romania was included in this progeny testing. In order to eliminate the biases âi, adequate multiplicative adjusting factors were calculated as 1/âi.. The conclusion was that the effects of birth month on the meat production in terms of live weight at the age of 180 days, live weight at the age of 365 days and daily gain during the fattening period should not be ignored, on the contrary, they should be eliminated by correcting the real data using corresponding adjusting factors. Therefore, adjusting factors are justifed to be used in order to improve the accuracy of the bulls' breeding value estimation for meat production.