Nonlinear Modeling of Growth in Lambs by Sex, Breed, and Genotype: A One-Year Deterministic Projection​

This study aimed to estimate the growth curves of five different sheep breeds raised in Türkiye (Akkaraman, Morkaraman, İvesi, Karayaka, and Şavak Akkaraman) using five nonlinear models; to determine the differences in growth performance among sex, breed, and the rs427117280 genotype; and to predict the live weights of lambs up to one year of age through deterministic simulation. The study used live-weight data measured at specific intervals from birth to 150 days of age from a total of 2,089 lambs. The growth curves were compared using the Gompertz, Logistic, Richards, Brody, and Von Bertalanffy models; model fit was evaluated based on R², AIC, and BIC criteria. The Gompertz model was found to best describe the growth process (R²=0.8233). In terms of asymptotic weight, the Akkaraman breed (45.44 kg) and male lambs (40.25 kg) attained the highest live weight values. Genotypic analyses revealed that the TG genotype at the rs427117280 locus provided an advantage in early growth rate (peaking at day 40), the GG genotype was advantageous in long-term fattening, while the TT genotype showed the lowest performance. Simulation results indicated that the Male-Akkaraman-TG combination would attain the highest live weight after 365 days (one year of age). In conclusion, the Gompertz model best predicted the growth performance of indigenous sheep breeds in Türkiye. It is suggested that the Akkaraman breed and the TG genotype, in particular, should be prioritized in breeding programs for dam selection aimed at increasing red meat production.