| Popis: |
First- (F 1 ) and back-crosses (R 1 ) with Polish Friesian cows of nine (from U.S.A., Canada, Denmark, Great Britain, Sweden, West Germany, Netherlands, Israel and New Zealand) Friesian cattle strains were beef performance tested. The F 1 generation bulls were fattened to either 450 or 550 kg — 280 bulls in total. The R 1 bulls were fattened to 450 kg — 147 bulls in total. In the R 1 generation, significant differences between strains were recorded in kg internal fat (New Zealand cattle had the most and Danish the least) and in lean: bone ratio. The highest growth rate was exhibited in strains from U.S.A., Canada and Israel (Holstein-Friesians) and the lowest in those from New Zealand and Denmark. Holstein-Friesians had the lowest net energy consumption per kg gain. Carcass weight and dressing percentage were highest in European (Dutch, British and Swedish) strains. With the exception of the New Zealand strain no significant differences were found in the percentage of valuable cuts. All the strains produced carcasses of a similar percentage lean. The most fatty carcasses were those of New Zealand and Danish groups. Lowest bone content was found in the carcasses of Polish, British, Dutch and New Zealand strains. Consequently, European strains had a significantly higher lean: bone ratio, while the Holstein-Friesians had the lowest ratio. It was concluded that heterosis might have influenced the growth rate. On the other hand, differences in carcass performance reflect the real pure strain differences. The only significant difference among European strains was found in percentage bone and in lean : bone ratio — the West German strain had more bone and a lower lean: bone ratio than Polish, British and Dutch strains. Thus, three subgroups may be distinguished — Holstein-Friesians, European stock, and New Zealand and Danish strains. |
