THE INCLUSION OF HERD-YEAR-SEASON BY SIRE INTERACTION IN THE ESTIMATION OF GENETIC-PARAMETERS IN BONSMARA CATTLE

Weaning weight records of 24 758 Bonsmara calves produced by 503 sires in 30 herds, from 1980 to 1993, were used to examine the importance o f the inclusion of herd-year-season by sire interaction in the estimat ion of genetic parameters. Three separate models were used in the DFRE ML analysis of the data. In the first, permanent maternal environment was included as an additional random factor, while in the second, herd -year-season by sire interaction was included, also as an additional r andom factor. Both these factors were included as additional random fa ctors in the third model. The estimates of the (co)variance components and heritabilities for direct additive (a), maternal additive (m) and additional random factor (c) for the three models analysed, were as f ollows: (sigma(a)(2): 138.04, 65.23, 67.46; (sigma(m)(2): 84.77, 143.8 0, 66.83; (sigma(am): -57.47, -28.24, -21.97; (sigma(perm)(2): 73.72, 71.01; (sigma(HYSxS)(2): 41.79, 41.39; (sigma(e)(2): 251.31, 274.78, 2 65.97; (sigma(p)(2): 490.37, 497.35, 490.74; h(a)(2): 0.28 0.13, 0.14; h(m)(2): 0.17, 0.29, 0.14. The results indicate the importance of bot h permanent maternal environment and herd-year-season by sire interact ion in the estimation of the genetic parameters. The exclusion of herd -year-season by sire interaction could lead to a serious overestimatio n of the direct additive components. The same applies for permanent ma ternal environment. The exclusion of this factor could lead to a serio us overestimation of the maternal components. Both these factors shoul d therefore be included in the across-herd weaning weight analysis of Bonsmara cattle.