The aim of this study was to determine basic production indices in the conservation flock of old-type Polish Merino Sheep and to compare them with the production results of the whole sheep flock of this breed kept on the Boguszyn farm belonging to the Lubiana Pedigree Breeding Establishment. Reproduction performance of dams as well as growth and rearing of their offspring in the period 2007–2009 were evaluated. Single born (birth type) dams predominated (56.8–62.9%) in both flocks. The percentage of twin births was approx. 38% for the ewes in the foundation flock and over 44% for those in the conservation flock. In the age structure of sheep from both flocks in the years 2007–2009, young sheep at the age of 2 to 5 years predominated, which could have affected the reproduction results of the dams. The mean body weight of all the evaluated lambs at 2 days of age was 4.14 kg. The lambs born in 2009 were the lightest. Their body weights were 3.55 kg and 3.69 kg in the foundation and conservation flocks, respectively. Statistically significantly heavier (P≤0.01) lambs were born in the conservation flock. Also, lambs from this flock gained significantly higher body weight (21.89–22.33 kg) at 56 days of age in the years 2008–2009, compared with the range of 17.85–21.84 kg for the lambs from the foundation flock in the period 2007–2009. The daily body weight gains in both flocks ranged from 240 g to 333 g and were statistically significantly better (P≤0.01) in the conservation flock. In both flocks, the significant effect of birth type and sex of lambs on their body weight and daily body weight gains was shown.

91-104