POPULATION PARAMETERS FOR BIRTH AND EWE FLEECE WEIGHT AT DIFFERENT PARITIES IN BALUCHI SHEEP

Direct and maternal performance of ewes at different parities were exa mined in Baluchi sheep. The data set was collected during the period 1 966-1989 from two flocks at a sheep breeding station in the north-east of Iran. The animals included in the data set were unselected and ran domly mated. The traits analysed were birth weight of lamb and fleece weight at different parities of the ewe. Variance components were esti mated using Restricted Maximum Likelihood with a bivariate animal mode r including fixed effects of year, sex, type of birth and parity, and random effects of additive genotype of lamb (direct genetic effect), a dditive genotype of ewe (maternal genetic effect) and common environme nt (excluded for ewe fleece weight), and random residual effect. Direc t and maternal genetic correlations between different parities were es timated. There was evidence of increasing phenotypic and genetic varia nces and heritabilities from parity 5 for birth weight of lamb in floc k 1, but only evidence of a slightly increasing age trend for the envi ronmental and phenotypic variance in flock 2. The average heritabiliti es over flocks and parities were 0.12, 0.11 and 0.26 for the direct, m aternal and total heritability, respectively, while the average geneti c correlation between direct and maternal effects for this trait was 0 .42. There were no indications of any age changes in variances oi heri tabilities for ewe fleece weight in flock 1, but indications of slight ly increasing age trends for the environmental and phenotypic variance . The average heritabilities over flocks and parities were 0.19, 0.04 and 0.22 for the direct, maternal and total heritability, respectively , while the average genetic correlation between direct and maternal ef fects was slightly positive in flock 1 but increasingly negative with age of the ewe in flock 2. Direct genetic correlations between paritie s 1-5 were very high for birth weight of lambs (on average 0.96) in co ntrast to the markedly lower correlations of parities 1-5 with parity 6 (on average 0.67) in flock 1 with a similar pattern for the maternal genetic correlations. In flock 2, these correlations were also high b ut without the marked decrease between parities 1-5 with parity 6 that was found in flock 1. Direct genetic correlations between the various parities for ewe fleece weight were similar for the two flocks, rangi ng from 0.73 to 0.92 and without any obvious differences between the v arious combinations of parities. However, the maternal were markedly l ower than the direct genetic correlations, especially for the combinat ions of parity 5 and 6 with the earlier parities, and most pronounced in flock 2 fluctuating from -0.54 to 0.79. To obtain reliable estimate s of breeding values for birth weight of lamb, it is recommended that the prediction should include not only earlier but also later parities (ages) of the ewe.