Structure and genetic progress in the 'CAMDA' and 'Lleyn' group breeding schemes with special reference to sheep improvement in Iran
Two sheep group breeding schemes were considered in this study to examine the genetic progress made over a 20 year period and the success of running such schemes in practice. The data were records of lamb weaning weight in the CAMDA scheme (Welsh Mountain breed) and the Lleyn scheme (Lleyn breed), collected between 1976 and 1996. After the edits, a total of 31,161 records for the CAMDA and 29,090 records for the Lleyn scheme were available for the analyses. The estimates of the heritability of weaning weight for individual flocks were low to moderate. In the CAMDA scheme, the estimates of the direct and maternal heritability values ranged from 0.04 to 0.43, and 0.03 to 0.11, respectively. The ratio of temporary environmental variance over the total variance ranged between 0.13 to 0.35. The estimates of total heritability values in flocks of 12 and 18 weeks of age were in the range of 0.23-0.45 and 0.07-0.18, respectively. In the Lleyn scheme, the estimates of the ratio of temporary environmental variance over the total variance, and the direct and maternal heritability values ranged from 0.15 to 0.39, 0.03 to 0.31, and 0.04 and 0.23, respectively. The estimates of the total heritability values in individual flocks of the scheme ranged from 0.07 to 0.33. The differences in heritability values between the flocks, reflected the differences in the model of analysis fitted, and size and structure of the data available for individual flocks of the scheme. It is concluded that group breeding schemes are a viable means of improving the production of traits of a breed, but that more attention should be paid in the setting up of the schemes, to a scoring system which will accurately reflect the market value of the stock. The application of group breeding schemes in Iran would require taking account of the differences in the social and climatic environments. Much greater attention would be needed to determine the selection objectives and these would need to be properly included in the selection index.