الفهرس 
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Abstract
The objective of this study was to determine the efficiency of five models [Linear with two parameters (L1), Linear with three parameters (L2), second order polynomial (Quadratic), Brody and Richards models] to the growth curves of Farafra and Saidi lambs by using monthly records of live weight from birth to 540 days of age and studying the fixed effect affecting the studied parameters and finally estimate heritabilities for growth curve variables and genetic correlations between these variables.
Data used in the present study were collected from the experimental stations of the Animal Production Research Institute (APRI), Ministry of Agriculture and Land Reclamation, during the years from 1992 to 2005 on two different sheep breeds and locations, Farafra (F) lambs raised in Mallawi experimental station and Saidi (S) lambs raised in Seds experimental station. Farafra data started from year 1992 while Saidi data started from year 1994. A total number of 2559 Farafra and 1539 Saidi lamb records being progeny of 66 and 34 sires, 681 and 318 dams, respectively was available for this study. A Multi Trait Derivative Free Restricted Maximum Likelihood program (MTDFREML; Boldman et al., 1993) was used to estimate the heritability and genetic correlation with Best Linear Unbiased Prediction (BLUP) methodology. The models were evaluated according to coefficient of determination (R2), Akaike’s information criterion (AIC) and Schwarz’s Bayesian information criterion (BIC). In both breeds, all models fitted the data, with high R2 ranged from 98.32 to 99.82 for over all mean, from 98.65 to 99.85 for males and from 98.79 to 99.72 for females. The Brody model gave the best R2 value of 99.85 in Saidi male, while the Quadratic model gave the lowest R2 value of 98.32 in Farafra over all mean. The AIC and BIC values were lower in Quadratic and Richards models for Farafra and Saidi lambs, respectively than other models.
Absolute Growth Rate (AGR) obtained from L1, L2, Quadratic, Brody and Richards models for Farafra was 0.14, 0.13, 0.10, 0.13 and 0.13 respectively, while for Saidi was 0.13, 0.12, 0.10, 0.11 and 0.12 respectively, in the first month and decreased gradually until reach 0.03, 0.04, 0.04, 0.02 and 0.02 for Farafra and 0.03, 0.04, 0.03, 0.02 and 0.02 for Saidi at 540 days of age, respectively.
Sex influenced significantly (P<0.01) all growth curve parameters except parameters A and K in Brody model for Farafra sheep. Type of birth significantly influenced (P<0.01) all growth curve parameters except parameter K in Brody model for Farafra sheep. Age of dam was significant (P<0.01) for most growth curve parameters. Year was the major source of variation (P<0.01) where significantly influenced all growth curve parameters. Season of birth significantly influenced (P<0.01) all growth curve parameters except parameter A in Brody model for Farafra and Saidi sheep and parameters A and M in Richards model for Farafra sheep.
Parameters A, B, C (K) and M were moderately to highly heritable in Farafra lambs (h2=0.24 to 0.74). Genetic correlations between parameters were all positive and ranged from 0.35 to 1.00. In Saidi lambs, parameters had low to moderate heritabilities (0.01 to 0.60). Genetic correlations between parameters ranged from −0.87 to 1.00.
The results of this study suggested that Richards model [Yt = A (1 – Be-kt )m + et] for growth monitoring can be useful in Farafra and Saidi breeds under both station conditions.