RELATIONSHIP BETWEEN CARCASS COMPONENTS A ND SLAUGHTER WEIGHT OF HEIFERS FROM COMMERCIAL CROSSING

A dissection was done of carcasses of 111 heifers from commercial cros sing after fathers of the breeds Aberdeen-Angus (Aa - 7 heads), Herefo rd (He - 10 heads), Limousine (Li - 34 heads), Charolais (Ch - 29 head s), Chianina (Ci - 10 heads), Maine-Anjou (Ma - 10 heads), and Blond A quitaine (Pa - 11 heads); the percentage of meat, bones, and fat has b een 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 strai ght 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 we ight. 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 den ote values which are statistically significantly different from zero ( P < 0,0 1), index of determination - R2 evaluates the correspondence o f the values measured with a theoretical model. The quality of estimat ion is mainly affected by the fact that values of net live-weight are distributed unevenly (occurrence of distant observations). It can be s tated that in heifers after Charolais fathers the percentage of meat i ncreases 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 cr ossbreds can be fattened up to the live-weight of 500 to 530 kg. Heife rs 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 perc entage 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 t endencies as crossbreds after Charolais fathers, including fattening a bility to a higher slaughter weight. A group of heifers after Chianina fathers did not show any significant dependences in carcass indexes o bserved.