Summary
The authors evaluate the effect of crossing three purebred rabbit breeds in a complete 3 × 3 diallel crossbreeding experiment (New Zealand White, V-line and Gabali) on certain immunological traits, including IgG titre. Sheep red blood cells (SRBCs) were administered at 8 weeks of age and boosted at 10 weeks of age. V-line/Gabali crossbreeds gave the highest significant (p<0.05) level of serum total protein at 8 and 12 weeks of age (4.71 and 7.70 g/dl, respectively). Its reciprocal crossbreed Gabali/V-line resulted in the highest estimate of serum globulin at 8 weeks of age (2.07 g/dl). V-line/Gabali crossbreeds showed the highest positive heterosis percentage (H%) of total protein, albumin and globulin at 8 weeks of age (27.98, 30.28 and 25.00, respectively). However, its reciprocal crossbreeds, Gabali/V-line, revealed negative estimates for total protein and albumin at the same age (–4.07 and –29.80). V-line/Gabali crossbreeds gave the highest titre (3.167) and positive H% (0.69) of IgG to the second dose of SRBCs. On the contrary, the highest negative estimate to the second dose was recorded in Gabali/New Zealand White crossbreeds (–2.49). Using the Gabali breed as the female line gave superior results for most immunological parameters.

Keywords
Breed, Breeding, Crossbreed, Egypt, Heterosis, IgG, Immunity, Rabbit.