Effects of summer heat stress on growth performance, some carcass traits and blood components of New Zealand white rabbits fed different dietary protein-energy levels, under subtropical Egyptian conditions

Eighty male New Zealand White rabbit weanlings, were used in this study. Animals fed normal protein-normal energy level (NP-NE) diet showed reduction in summer than in winter in body weight (14.2\%), daily gain weight (20.3\%), feed intake (22.9\%), feed cost (22.9\%), return from body gain (20.4\%) and final margin (18.5\%). Carcass, most of carcass cuts, kidney fat and liver weights were also lower in summer than in winter. Similarly, concentrations of each total protein, albumin, urea-N, creatinine (as kidney function) and serum transaminase enzymes (as liver function) decreased under summer conditions. Within each of the two seasons, rabbits fed high protein-normal energy (HP-NE) diet recorded higher body weight, gain weight, feed efficiency and final margin, while feed intake was lower when compared with the other groups. Kidney fat weight recorded higher values in rabbits fed high protein-high energy (HP-HE) diet than in those fed normal protein-normal energy (NP-NE), while carcass and carcass cuts weights were not consistently influenced by protein-energy level in rabbit diets. Concentrations of the studied blood components were higher in rabbits fed HP-NE diet than in those fed NP-NE diet. Comparison of summer groups (NP-HE, HP-NE and HP-HE) with NP-NE winter group, showed that rabbits fed HP-NE summer group recorded the highest body weight, daily gain weight and final margin and the lowest feed intake and feed cost, carcass, most of carcass cuts weight, total protein and its fractions and transaminase enzymes. The effects of season and ration type on body, gain, carcass, kidney fat and fore part weights and serum protein, albumin, transaminase enzymes, creatinine and urea-N concentrations were significant (P<0.01). The estimated interactions between season and ration type on the growth traits were not significant, except on body weight at four weeks and on gain weight at 0-4 weeks of the experimental period which were significant (P<0.05).