Estimation of genetic parameters for reproduction traits In sheep

Reproduction traits, known as the most important trait in lamb production, was investigated with respect to the genetic determination of age at first lambing (ELA), lambing interval (ZLZ), total number born, number of born al ive and stillborn lambs These traits were analysed based on multiple-trait as well as repeatability animal models. Finally the genetic parameters of d ifferent breed were compared, The data consisted of 35381 lambings collecte d from 1988 to 1998. Age at the first lambing showed a bimodal distribution and was therefore di vided into two traits. The first trait (ELA1) consisted of ewes, with age a t first lambing of less than or equal to 550 days, the second trait (ELA2) consisted of ewes with age at first lambing of > 550 days. Heritabilities o f both traits were moderate to high (h(2) = 0.31 and h(2) = 0,41) for ELA1 and ELA2, respectively. Genetic correlation between these traits was r(g) = 0,33. Genetic correlation between lambing interval from first to second (Z LZ1, h(2) = 0,18) and from second to third lambing (ZLZ2, h(2) = 0,17) was low (r(g) = -0,09). This shows that the genetic determination of these two traits were different and they should be treated as two different traits. D ifferent genetic determination was also found for number of lambs born aliv e at first parity (LGL1, h(2) = 0,09) and at second and further parities (L GL2, h(2) = 0,10). Their genetic correlation was r(g) = 0,66. The heritabil ity of total number born lambs was only slightly higher as for number of la mbs born alive. The number of stillborn lambs showed the lowest heritabilit ies of h(2) = 0,07, 0,02 and 0,05 for first, second and third parity, respe ctively. There were differences in magnitude of heritabilities between bree ds. Based on the results of this study there was recommended to select on breed ing values for the traits ELA1, ELA2, ZLZ1, ZLZ2, LGL1 and LGL2 in order to improve the reproductive performance in the population.