Predicting Genetic Trend by Uni- and Multitrait Models

Abstract

The effects of evaluating milk yield in the first three lactations by a single-trait animal model or by a repeatability animal model instead of by the true multitrait animal model were investigated using stochastic simulation. The models were compared both in terms of how accurately they predicted genetic trend when applied to the same dataset and regarding difference in true genetic progress when selecting on breeding values predicted by these models. A breeding structure resembling the Icelandic dairy cattle population was used for the simulation.

The single-trait model underpredicted the true genetic trend in second and third lactations quite heavily but only by 2.3% in the first lactation, while the repeatability model overpredicted the true genetic trend in the first three lactations by 9.4% on average. The multitrait animal model, however, estimated genetic trends with a high degree of accuracy.

When selection was made on all three lactations with equal economic weights, the multitrait model was only about 2.5% superior to the repeatability model in terms of true genetic trend.

The multitrait animal model was applied to estimate genetic trend regarding milk production using real data from the Icelandic dairy cattle population. A total of 61 621 animals were included, of which 38 014 were cows with production records. The genetic trend for milk yield was estimated at 10.4, 10.0 and 9.3 (kg per year) in each of the three first lactations respectively.

Key Words:

• animal model
• dairy cattle
• Iceland
• stochastic simulation