In a grass-based production system with seasonal calving, fertility is of major economic importance (Esslemont and Peeler, 1993). For breeding value estimation, currently intervals between successive calvings (CIV) are the only readily available fertility records in Ireland. However, animals with the worst fertility have no CIV in a seasonal calving system. For this reason, a simultaneous analysis of CIV and survival was proposed (Olori et al., 2002). Animals that appear in the data have a CIV and animals that do not re-appear are identified as being culled (for many reasons, including fertility). Hence, breeding values for survival (probability of surviving to the next lactation) and calving interval estimated simultaneously are expected to cover most of the genetic variation in fertility that can be recovered from calving dates. Survival was defined as involuntary culling, and therefore survival scores were pre-adjusted for milk yield within herd-year-season. However, milk yield might also play an important role in censoring of data and insemination decisions of the farmer. Therefore milk yield was included as a third trait in the analysis (Olori et al., 2002). Survival adjusted for milk yield (SURV) and CIV now form part of the national index for selecting of dairy bulls in Ireland (Veerkamp et al., 2002). The objective of this research project was to improve the accuracy and availability of these proofs by expanding the existing evaluation model from a multi trait evaluation of first lactation SURV, CIV and milk yield (Olori et al., 2002) into a simultaneous evaluation of 13 traits: First, second and third lactations for SURV, CIV and milk yield, and three linear type traits and body condition score as predictors of SURV and CIV. Here we present some of the choices made and some of the results for the improvements to the method.
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 2002. Session 1, , 1.23, 2002
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