RELATIONSHIP BETWEEN CARCASS COMPONENTS AND SLAUGHTER WEIGHT OF HEIFERS FROM COMMERCIAL CROSSING

A dissection was done of carcasses of 111 heifers from commercial crossing after fathers of the breeds Aberdeen-Angus (Aa - 7 heads), Hereford (He - 10 heads), Limousine (Li - 34 heads), Charolais (Ch - 29 heads), Chianina (Ci - 10 heads), Maine-Anjou (Ma - 10 heads), and Blond Aquitaine (Pa - 11 heads); the percentage of meat, bones, and fat has been determined and net weight (weight of dressed carcass x coefficient 1,92) calculated. A more detailed description of the initial material is given in our previous works (P o n i z i l et al., 1993a, b). The dependence of the variables observed on net live-weight is represented by Figs. 1 to 5. The values measured were put on the regression straight line with parameters a, b, parameter a being the theoretical value of the investigated variable in net live-weigh of 500 kg, parameter b being the increase of the observed variable per each kg above this weight. With respect to the number of observations, Tab. I gives values only for crossbreds with the Charolais and Limousine breeds. Straight lines in graphs serve only for orientation. Asterisks in the table denote values which are statistically significantly different from zero (P < 0,0 1), index of determination - R2 evaluates the correspondence of the values measured with a theoretical model. The quality of estimation is mainly affected by the fact that values of net live-weight are distributed unevenly (occurrence of distant observations). It can be stated that in heifers after Charolais fathers the percentage of meat increases and the percentage of bones decreases and, at the same time, meat/bone ratio slightly increases with an increasing net live-weight (or weight of the dressed carcass). With regard to these facts and in correspondence with the statement of S a r d i et al. (1986), these crossbreds can be fattened up to the live-weight of 500 to 530 kg. Heifers of the Limousine breed show a higher percentage of fat in the half and a higher meat/fat ratio with increasing live-weight, i.e. the percentage of fat increases at the expense of the percentage of meat with increasing live-weight. We recommend, in correspondence with S a r d i et al. (1986), to fatten these crossbreds up to a live-weight of 400 to 420 kg. In crossbreds after Hereford fathers, similar tendencies as in crossbreds with the Limousine breed were found, that means that it is not appropriate to fatten them to a live-weight exceeding 400 kg. Daughters after Maine-Anjou and Blond Aquitaine breeds show the same tendencies as crossbreds after Charolais fathers, including fattening ability to a higher slaughter weight. A group of heifers after Chianina fathers did not show any significant dependences in carcass indexes observed.