Heritability and repeatability of the number of lambs born and reared estimated using linear and threshold models

The research was conducted on 3 844 Polish Merino lamb dams born in 1991-2001, used in 15 flocks from the Pomerania and Kujawy region in Poland. The assessed parameters were the number of lambs born from a dam after lambing (LSB) (1, 2, 3) and the number of lambs reared (LSW) (0, 1, 2, 3). The genetic parameters LSB and LSW were estimated with the use of two methods: Average Information – REML (AI-REML) and Gibbs sampling (GS). For estimation of components by means of the AI-REML method the animal’s linear model was used, and in the case of the GS method a threshold model was also used alongside the linear one. The LSB heritability estimated using the AI-REML and GS methods in combination with a linear model were similar and their values were respectively 0.025 and 0.029, with similar standard errors for variance components. Applying the GS method combined with a threshold model resulted in a two times higher heritability (0.054) compared to when linear models were used. A similar tendency was found to exist in respect of estimated repeatability. When using linear models, the obtained values were closely matched: 0.064 (AI-REML) and 0.065 (GS). The highest repeatability occurred when a threshold model was used (0.118). The LSW heritability was low and, depending on the model and method (0.016-0.020). Similar values LSW repeatability were obtained with the use of linear models (0.048 – REML and 0.049 – GS), and when a threshold model was used the result was higher – 0.070.