The
interacting effects of temperature and protein level on RBC and Hb were significant (P < 0.05). The
regression equations of RBC, WBC and Hb toward the two factors of interest were established, with the
coefficients of determination being 0.870, 0.836 and 0.881, respectively (P < 0.01). These equations could
be used for prediction in practice. After the challenge, the mortalities for the combinations of 22.1 C/
28.7% and 20.0 C/37.5% were significantly higher than 27.0 C/37.5% (P < 0.05). The optimal temperature/
dietary protein level combination was obtained at 27.9 C/38.1% at which the lowest mortality (13.76%)
was attained. This value was close to the optimal temperature/dietary protein level combination (29.4 C/
41.9%) for the greatest levels of RBC (2.560 106 mL1
), WBC (270.648 103 mL1
) and Hb (92.851 g L1
).
The results of this study indicated that preferred temperature/dietary protein level combination might
strengthen the non-specific immunity and reduce susceptibility to S. iniae.