Browsing by Author "Nemutandani, Khetho Ratshilumela"
Now showing 1 - 1 of 1
Results Per Page
Sort Options
- ItemDetermination of variance components for skin traits of ostriches in South Africa(Stellenbosch : Stellenbosch University, 2023-03) Nemutandani, Khetho Ratshilumela; Engelbrecht, Anel ; Cloete, Schalk W. P. ; Dzama, Kennedy; Tada, Obert; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Science.ENGLISH ABSTRACT: In the South African ostrich industry, production of high quality leather is a necessity for sustainability and competitiveness on the world market. However, most skins are downgraded due to poor quality, constraining enterprise revenue. The aim of this study was to identify factors contributing to skin value, to determine genetic and environmental parameters for ostrich skin traits, as well as to evaluate the performance of pure and crossbred ostriches for skin traits. Skin size (SSZ), skin grade (SG) and quill value (QV) were assessed as predictors of skin value, using multiple regression techniques. Pearson’s correlations among independent variables confirmed that SG was the dominant driver of skin value, as indicated by a high negative correlation (r=-0.88) with skin income. Skin traits such as nodule size score (NSZ), nodule shape score (NS), hair follicle score (HF) and pitting score (PIT) mostly failed to reflect the variation in skin value accounted for by QV and SG, respectively. Single-trait heritability estimates, derived on South African Black (SAB) birds, for skin traits such as SSZ, skin weight (SW) and skin thickness (ST) were 0.37±0.06, 0.27±0.06 and 0.20±0.05, respectively. Overall, direct heritability ranged from low (0.08) for pitting scores to high (0.42) for hair follicle scores. Genetic correlations of slaughter weight (SLW) with SSZ, SW and ST were 0.92, 0.48, and 0.15. A positive genetic correlation of 0.33 was found between SLW and NSZ. A high genetic correlation of 0.71 existed between scores for NS and NSZ. For threshold traits, heritability estimates ranged from 0.17 for nodule direction (NDIR) to 0.47 for nodule outliers (OUTL) in the 5- trait threshold model analysis for non-linear and binomial traits. In the 6-trait linear- threshold analysis including SSZ as a linear trait, heritability estimates ranged from 0.20 for NDISTR to 0.39 for OUTL. For both sets of analyses, significant genetic correlations were found between OUTL and PIT (respectively 0.49 and 0.71). Evaluation of purebreds showed that Zimbabwean Blue (ZB) and Kenyan Red (KR) birds outperformed their SAB contemporaries for most size-related traits (P<0.05). Heterosis were found for SLW, SSZ, and NSZ, for SAB and ZB as well as for SAB and KR combinations. The effect of the taller KR dam line was significant for SLW, neckline total length, neckline crown length and neckline width in the middle. However, most of the size dependent genetic group effects were reduced or removed when farm weight was modelled as a covariate across analyses. High scores for HF were observed for all the crosses though. It was concluded that: 1. Skin grading was the dominant force in determining skin value; 2. Genetic variation existed and exploitable levels of variation were found in most quantitative skin characteristics; therefore genetic progress appear feasible through selection; 3. Genetic progress can also be achieved for traits not conforming to the assumptions of normality; 4. ZB and KR birds performed better for size-related traits than their SAB contemporaries, indicating that commercial crossbreeding could improve slaughter weight and size-related traits in hybrids. Overall, this study provides information to the ostrich industry regarding options for the exploitation of additive genetic gains, the choice of breeds, as well as crossbreeding options. This information will provide a sound foundation for genetic improvement of skin traits that is based on scientific principles.