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The main objectives of this study was to evaluate the efficiency of crossing between two lines of rabbits under selection programs on the productive performance of cross rabbits. Three genetic groups of rabbits were used in the investigation. Alexandria line (A) as a synthetic paternal line, V line (V) as a synthetic maternal line and crossing between A line males and V line females (AV). The studied traits used to evaluate productive performance in these three genetic groups were individual body weight at weaning and at marketing age (BW4 & BW9), daily weight gain (DWG), daily feed intake (DFI), feed conversion ratio (FCR), viability rate (VR) and economic efficiency (EE). A total number of 493, 1602 and 1123 from V, A and AV rabbits, respectively were used in the investigation. The results showed that AV cross rabbits were heavier than pure line rabbits (AA and VV) for BW at two ages studied and DWG during fattening period. On other words, AV genetic group attained the marketing body weight earlier than other two groups. Also, the value of FCR improved in AV growing rabbits compared with those obtained for AA & VV rabbits. Moreover, the VR during fattening period in AV rabbits was the highest, while the lowest one was recorded in V line rabbits. It is clear apparent from these results that, AV group recorded higher values for EE than the other genetic groups. In conclusion, mating between males of the paternal line A and females of the maternal line V gave a cross that saved time and costs in order to reach marketing.

The purpose of this study was to use nonlinear models (NLN)to characterize the growth pattern and estimate the heritability (h 2 ), the genetic (r g ), and phenotypic(r p ) correlation of the body weight (BW) in two distinct genotypes of chicken raising under Egyptian conditions. A data set of 500 chickens with pedigree information was gathered for this study. For this purpose, the BW was measured at hatching (BW0),4 weeks (BW4), 8 weeks (BW8), and 12 weeks (BW 12) of age. Three NLN models (Logistic, Gompertz, and Von Bertalanffy) were used. Using Wombat software, a multi-trait animal model with a restricted maximum likelihood procedure was used to estimate h 2 , r g, and r p for BW.The results showed that Golden Sabahi (GS) had a significantly higher weight than White Leghorn (WL). The growth curve parameters A (mature body weight), B (biological constant), and K (growth rate) were 3989.9, 0.7853, and 0.0624 for WL and 4332.6,0.7897, and 0.0642 for GS in the von Bertalanffy model, 2152.8, 3.8096, and 0.1322 for WL chickens and 2368, 3.8594, and 0.1350 for GS chickens in the Gompertz model, 1304.5, 19.0421, and 0.3382 for WL chickens and 1455.6, 19.6116, and 0.3411 for GS chickens in the logistic model. Three models represented the growth of the two breeds using goodness-of-fit metrics (R2, MSE, and AIC). Heritability estimates of BW at 0, 4, and 8 were higher in GS than WL, while the estimate of BW at 12 weeks of age was almost similar in the both strains GS and WL (0.1). Between BW0 and BW12, there were strong positive genetic and phenotypic correlations compared by the rest of growth traits. Based on the findings of this investigation, we recommend that the two strains can be utilized for selective breeding between the ages of 4 and 8 weeks to increase the overall genetic improvement of growth traits.