The optimum length of roaster cock fattening

Performance including dressing percentage was studied in cocks of ROSS 208 hybrid of roaster type fattened at different dietary protein levels by 6, 8 , 10 and 12 weeks of age. Three groups were housed on litter, each consisti ng of 64 cocks. All groups received loose feed mix by 3 weeks of age which contained 23.31% proteins and 11.379 MI ME per 1 kg. Granular feed mixes we re used when cocks were older than 3 weeks of age. Wheat grain at an amount of 20% was used as additional feed in group 1 from 8 weeks of age, at an a mount of 20% from 6 weeks in group 2, and at an amount of 20% from 3 to 8 w eeks and 30% from 8 weeks in group 3. Protein and metabolizable energy cont ents in feeds used in different periods of chicken age are given for the pa rticular groups in the section Material and Methods. Table I shows average live weight of cocks at 6, 8, 10 and 12 weeks of age. Data in the table doc ument a weak trend of lower growth rate in cocks receiving the highest amou nt of fodder wheat grain. Basic statistical data on live weight of cocks we re determined at 10 weeks of age (Tab. II). Variation-statistical data proc essing by means of analysis of variance did not demonstrate any statistical ly significant difference (P > 0.05). Table III shows feed consumption per I kg live weight from hatching to the age of 6, 8, 10 and 12 weeks. Similar ly like in live weight, feed conversion was worse in group 3 receiving a hi gher proportion of wheal, but the differences were not large. Examination o f cock health showed that about 20% of roaster cocks had weak legs when old er than 6 weeks, and scarse symptoms of edema disease were observed in dead cocks. Mortality by 6 weeks of age was 4.7% in groups 1 and 2, 6.2% in gro up 3, at the age of 6-12 weeks 6.6% in group 1, 4.9% in group 2 and 3.3% in group 3. Table IV shows the results of carcass analyses at 6, 8, 10 and 12 weeks of cock age. Data clearly document increasing dressing percentage du ring fattening, and a substantially higher proportion of abdominal fat in r elation to live weight at the age of 10 and 12 weeks. Economic evaluation w as used to determine optimum fattening length, which is however largely var iable due to continually varying prices of feed components, straight run ch ickens, technical power, etc. Given the price relations effective in the Cz ech Republic in 1997, the lowest production cost per 1 kg of live weight wa s achieved at the age of 8 weeks (23.86 KC) and per 1 kg of carcass with gi blets at the 10th week - 31.45 Kc without processing cost. Additional feedi ng of fodder wheat from the 3rd and/or Gth week in cocks fattened to 12 wee ks of age decreased the live weight of cocks by 0.9-1.9% and feed conversio n by 1.0-2.2%. Total production cost per 1 kg of live weight decreased when less costly feeds were used.