Selection indices for improvement in body weights and fleece yield of chokla sheep

Data on 3714 Chokla sheep, maintained at ICAR-Central Sheep and Wool Research Institute (CSWRI), Avikanagar, Rajasthan, collected for a period of 18 years (1994 to 2011) were used in the study. Traits analyzed were body weights at birth (BWT), 3 months (3WT), 6 months (6WT), 9 months (9WT), 12 months (12WT) of age and first six monthly greasy fleece yield (GFY1). Genetic and phenotypic covariance between body weights increased with advancing age. The covariance among body weights at different ages and GFY1 also showed similar trends. A total of 59 selection indices was constructed by incorporating these traits in different combinations. The index I₅₈ (0.0008 BWT + 0.0033 3WT + 0.2348 9WT +0.2257 12WT + 0.1803 GFYI) was considered most useful for its reliability (r IH = 0.4181) and genetic gain (ΔH = 2.3295). However, due to complexity of index I₅₈, Index (I₄) with single trait based on 9 months was considered as a best selection index (I₄), due to its accuracy (r_IH = 0.4289), positive b values and genetic gain (ΔH =0.8920). Preliminary selection at 9 months, followed by direct selection at 12 months age based on (9WT) was recommended as selection criteria. Usually breeding rams are used for breeding after 12 months age, so preliminary selection of ram at 9WT was recommended as selection criteria.