One of the methods of evaluation of carcasses is the measuring of electrical impedance which is a modification of the measuring of human body composition by means of the apparatus BIA 101 or BIA 103 (Body Impedance Analyser) of the firm RJL Systems Detroit, Michigan, USA. For this way of impedance measuring, an instrument for measuring the tissue impedance MTI was to be constructed using tetrapolar electrodes with a frequency of 50 kHz and a current of 800 muA. The electrodes have been modified so as to inject the bovine carcass - scalpels have been used. Impedance Z is the relationship between resistance and reactance Z=square-root R2 + X(c)2. According to D v o r a k (1990), there are regression relationships between the weight of the tissue of the bovine half to be analysed and the impedance function. When evaluating carcass halves, three parts must be distinguished. the lean muscle tissue, the fat tissue, and the bone tissue. Through impedance measuring, only the lean muscle tissue can be assessed as it contains water and electrolytes and is thus conductor of the electric current. After weighing and classifying carcass halves in quality classes and after measuring the length of carcass halves, impedance measuring has been conducted. The measuring was done on 131 bulls I, 12 bulls II, 43 cows I, 50 cows II, 32 cows III, 12 cows 3 and on 20 heifers. Impedance measuring on bovine carcass halves was conducted by means of the method NN (groups of muscles of the pelvic and thoracic extremity) and the method NK (groups of muscles of die pelvic extremity and in the neck region). In Tab. I and II, basic characteristics of the sets observed of dressed bovine carcass halves are given which were classified in individual classes according to the norm CSN 46 6120: average weight of dressed bovine halves, average length of dressed halves, and average impedance values Z(NN) and Z(NK) measured. Average impedance values (Z(NN)) and (Z(NK)) gradually decreased with increasing weight. When comparing the both measuring methods (NN and NK), the difference in impedance values of dressed halves of cows was 41 to 46 ohms, while it was only 29 ohms (Tab. ED in the dressed halves of heifers. For individual quality classes, linear models of regression dependence have been calculated between the weight of dressed halves (X) and dependent variables (Y) - the value of impedance NN, the value of impedance NK, ratio between the weight of dressed half and the value of impedance NN, as well as ratio between the weight of dressed half and the measured value of impedance NK. The calculated parameters of this relationship, i.e. the correlation coefficient and the index of determination, are given in Tab. III. Dressed halves of cows classified in quality class III showed the highest value of impedance measured, and dressed halves of cows classified in quality classes I and 3 showed lower values of impedance with an approximately equal dispersion which indicates that impedance value measured decreases with increasing weight of dressed halves of cows. If we consider the value of impedance measured to be dependent on the proportion meat : fat : bones, as mentioned by K e m p s t e r (1983), it means that this method can be used for evaluating the composition of dressed carcasses. For the time being, the great dispersion of impedance values measured represents a big trouble. The causes of this great dispersion can be partially due to temperature in die course of measuring, nutrition before slaughtering, electrolytes content in the feed ration, and weight of the dressed half (Tab. III). In dressed halves of bulls in the quality class I, an average impedance value od 231.5 has been assessed by means of the method NN. Dispersion of the values measured was similar to the values of dressed halves of cows which means that the value of impedance measured was significantly lower than in approximately equally heavy dressed halves of cows. The effect of weight upon the value of impedance was, however, contrary - with increasing weight of the dressed halves of bulls the value of impedance increased. The values of impedance were in our case affected by the sex. Similarly to the dressed halves of cows, temperature in die dressed halves should be observed; also other factors, e.g. the place of injection, could probably play a certain role. It is quite possible that also the distance between injected electrodes could affect results of impedance measurement. Summarized results of measuring show that the method does not provide immediate results for classifying dressed halves to quality classes but the results indicate that, under the presupposition of a materialization of measuring and calculation of correction factors for different effects, the method could probably be used.
