Genetic Assessment of Derived Growth Curve Parameters in Sonadi Sheep Within a Breeding Flock

This study aimed to evaluate the genetic and environmental influences on growth traits in Sonadi sheep by applying Brody and Richards' nonlinear growth models. The dataset included body weight records from birth to 12 months collected over a 15-year period from an organised breeding flock. Significant environmental effects, including year of birth, sex, type of birth, season, parity, and dam's weight at lambing, were observed across most growth traits. Male lambs and those born during favourable seasons exhibited superior birth and yearling weights, while heavier dams produced faster-growing offspring, underscoring the role of maternal nutrition. Heritability estimates indicated moderate to high genetic control for growth parameters such as asymptotic weight (A), maturation rate (k), and degree of maturity at birth (μ₀), with values ranging from 0.229 to 0.716. Yearling body weight (YBW) also exhibited strong heritability (0.448 ± 0.142), establishing it as a dependable trait for selection. Additive genetic correlations revealed significant relationships among growth curve parameters. Notably, negative correlations between k and A reflected a trade-off between rapid early growth and larger mature size. Animals genetically inclined toward higher final weights tended to mature more slowly. The Brody model outperformed the Richards model due to better fit and interpretability. Selecting animals with higher k and moderate A, along with improved maternal and environmental management, can enhance growth efficiency and flock productivity in Sonadi sheep.