This paper presents a comparison between two genetic evaluations of Sarda dairy sheep breed based upon milk yield corrected for milking length (CMY) and milk yield further on preadjusted for the age class-parity-lambing month interaction (EME). The animal model indexations included 756,522 lactations of rank from 1 to 4. Genetic parameters were estimated with a sire model on a data subset including 127,393 lactations performed from ewes bom up to ‘92. The contemporary grouping (CG) strategies used for the analysis of the two variables were different. In the model for CMY, the CG were defined by the interaction flock-year-age class. In the model for EME, three CG were identified within flock-year: the yearlings, the mature ewes with lambings before the 15 th December and the mature ewes with lambings after the 15th December. The interaction age class-parity-lambing month within year of production was included as a second fixed effect in both the models for CMY and EME. EME showed higher values than CMY of additive genetic variance (402 l2 Vs 357 l2), h2 (0.29 Vs 0.26) and repeatability (0.40 Vs 0.38). The grouping strategy used for the EME analysis also increased the number of compared sires per adult ewe CG. The Spearman correlation coefficient between EBV showed that the EME evaluation modified the rank of the females (r=0.95) and mainly of the natural mating sires (r=0.91), while the AI sires were equally ranked (r=0.99). 

A. Carta, S. R Sanna, S. Casu

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 24: Sheep and goats (fibre); sheep and goats (meat and milk); poultry; horses; buffaloes., , 173–176, 1998
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