Agriculturae Conspectus Scientificus, Vol 76, No 4 (2011)

Estimation of Variance Components for Litter Size in the First and Later Parities in Improved Jezersko-Solcava Sheep

Dubravko ŠKORPUT, Ante KASAP, Gregor GORJANC

Pages: 337-340


Aim of this study was to estimate variance components for litter size in Improved Jezersko-Solcava sheep. Analysis involved 66,082 records from 12,969 animals, for the number of lambs born in all parities (BA), the first parity (B1), and later parities (B2+). Fixed part of model contained the effects of season and age at lambing within parity. Random part of model contained the effects of herd, permanent effect (for repeatability models), and additive genetic effect. Variance components were estimated using the restricted maximum likelihood method. The average number of lambs born was 1.36 in the first parity, while the average in later parities was 1.59 leading also to about 20% higher variance. Several models were tested in order to accommodate markedly different variability in litter size between the first and later parities: single trait model (for BA, B1, and B2+), two-trait model (for B1 and B2+), and single trait model with heterogeneous residual variance (for BA). Comparison of variance components between models showed largest differences for the residual variance, resulting in parsimonious fit for a single trait model for BA with heterogeneous residual variance. Correlations among breeding values from different models were high and showed remarkable performance of the standard single trait repeatability model for BA.


sheep; litter size; variance components; heterogeneity

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