## 2 Materials and Methods  
### Animals and Diets  
The investigation used 50 carcasses of fatteners from the following four genetic groups: ZS--Zlotnicka Spotted \(\times\) Zlotnicka Spotted (\(n\) = 20)--purebreed fatteners, ZS \(\times\) PLW--Zlotnicka Spotted \(\times\) Polish Large White (\(n\) = 10), ZS \(\times\) D--Zlotnicka Spotted \(\times\) Duroc (\(n\) = 10) and (ZS \(\times\) ZS) \(\times\) D--Zlotnicka Spotted \(\times\) Zlotnicka Spotted/Duroc (\(n\) = 10). The animals were divided into four experimental groups keeping the sex ratio at 1:1. All the animals were tattooed and ear-marked. Experimental animals with the average weight of 20 kg were selected and the experiment was terminated when the animals attained the slaughter weight of approximately 120 kg (113.0-123.6 kg). The experiment was divided into the starter (20-30 kg), grower (30-80 kg) and finisher (over 80 kg) periods. Table 1 shows the approximate composition of diets. The rations in all of the three stages were similar for all of the four crosses. The fatteners were kept in collective pens of 10 animals per pen on shallow bedding. They were fed _ad libitum_ with total mixed rations and they had constant access to water. After the final fattening, the animals were transported from the farm to the abattoi located at a distance of approximately 50 km. The slaughter of animals was conducted after two hours' rest. Fatteners were shocked with a current using the Polish apparatus STZ 6 KTM 29.53.16.50 SWW 0782-11, year of production 2015 (P.P.U.H.\"KOMA\" Sp. z o.o. Wilkanowo) of the following parameters: an intensity of approximately 1.5 A, a frequency of 50 Hz, a voltage of 250 V, the time of the was shock 8 s and the time from the shock to the pricking was 20 s. About 30 min after the slaughter, carcasses were weighed with a 100 g accuracy; meat content was estimated with the help of the optical-needle apparatus CGM; and, backfat in the following five measuring points was also assessed: over the shoulder, on the back and on the cross in point I, II and III [38]. Later, half-carcasses were cooled using a mono-gradual system at the temperature of approximately 4 \({}^{\circ}\)C.  
\begin{table}
\begin{tabular}{l c c c} \hline \hline \multirow{2}{*}{**Items**} & \multicolumn{3}{c}{**Diets**} \\ \cline{2-4}  & **Starter** & **Grower** & **Finisher** \\ \hline Spring barley (\%) & 26.00 & 20.00 & 21.00 \\ Triticale (\%) & - & 20.00 & 39.80 \\ Winter wheat (\%) & 30.40 & 16.10 & - \\ Maize (\%) & 20.00 & 13.00 & 12.00 \\ Soybean meal 46 (\%) & 16.00 & 13.00 & 7.40 \\ Rapeseed meal “00” 34 (\%) & - & 5.00 & 2.00 \\ Wheat bran (\%) & - & 10.00 & 15.00 \\ \({}^{1}\) Ekonomix T (\%) & 2.40 & 1.50 & 1.30 \\ Fodder chalk (\%) & 1.10 & 1.40 & 1.50 \\ \({}^{2}\) Zintertal (\%) & 0.10 & - & - \\ \({}^{3}\) Substimed 950 (\%) & 4.00 & - & - \\ Dry matter (\%) & 90.29 & 90.28 & 90.56 \\ Energy (M)/kg) & 13.46 & 12.63 & 12.46 \\ Crude protein (\%) & 16.26 & 17.31 & 14.79 \\ Digestible protein (\%) & 13.65 & 14.65 & 12.65 \\ Lysine (\%) & 1.11 & 0.99 & 0.79 \\ \hline \hline \end{tabular} \({}^{\ddagger}\) Mineral feeding stuff, \({}^{2}\) Additive of Zn, \({}^{3}\) Additive of whe.  
\end{table}
Table 1: Proximate composition of diets.