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Abstract
1. Changes in the relative weights of carcase, abdominal fat, breast and leg muscles, and plasma thyroid hormone concentrations occurring during the first 6 weeks of postnatal growth were analysed in males of HG and LG lines divergently selected for high and low relative body weight (BW) gain between 11 and 28 d of age, respectively, and constant adult BW.
2. The second week of postnatal life was a critical age at which the HG males exhibited a relatively faster growth in comparison to their LG counterparts and permanently exceeded LG males in the percentage by weight of carcase, breast and leg muscle. A higher production of muscle tissues was associated with lower accumulation of abdominal fat before sexual maturity.
3. In general, the plasma T3 level of HG quail exceeded that of LG quail. Nevertheless, significant differences were found only at 14, 21 and 28 d of age, that is, in the period during which the highest inter-line differences in relative growth rate were noted. Also the T3/T4 ratio followed a similar trend while plasma T4 level showed no clear and consistent inter-line differences.
4. The results suggest that the selection for the shape of the growth curve, like the selection for body fat, modifies the carcase quality owing to shortening/prolongation of the acceleration growth phase. Individuals with a short acceleration phase of the growth curve are characterised by low carcase quality during the fattening period.
Acknowledgements
This research was supported by grants MZE 0002701401, GAČR 523/99/1262 and AVOZ 50390512. The authors wish to thank Ms E. Gregušová, Ms P. Řezáčová, Mr A. Mohsen, Ms L. Noterdaeme and Mr W. Van Ham for excellent technical assistance, and Dr H. Knížetová for critical revision of the manuscript.