HERITABILITY AND BREEDING VALUE OF SHEEP FERTILITY ESTIMATED BY MEANS OF THE GIBBS SAMPLING METHOD USING THE LINEAR AND THRESHOLD MODELS ODZIEDZICZALNOŚĆ I WARTOŚĆ HODOWLANA PŁODNOŚCI OWIEC OSZACOWANA METODĄ PRÓBKOWANIA GIBBSA Z WYKORZYSTANIEM MODELI LINIOWEGO I PROGOWEGO

The research was carried out on 4,030 Polish Merino ewes born in the years 19912001, kept in 15 flocks from the Pomorze and Kujawy region. Fertility of ewes in subsequent reproduction seasons was analysed with the use of multiple logistic regression. The research showed that there is a statistical influence of the flock, year of birth, age of dam, flock × year interaction of birth on the ewes’ fertility. In order to estimate the genetic parameters, the Gibbs sampling method was applied, using the univariate animal models, both linear as well as threshold. Estimates of fertility depending on the model equalled 0.067 to 0.104, whereas the estimates of repeatability equalled respectively: 0.076 and 0.139. The obtained genetic parameters were then used to estimate the breeding values of the animals in terms of controlled trait (Best Linear Unbiased Prediction method) using linear and threshold models. The obtained animal breeding values rankings in respect of the same trait with the use of linear and threshold models were strongly correlated with each other (rs = 0.972). Negative genetic trends of fertility (0.01-0.08% per year) were found.