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The study was conducted in the conditions of a nucleus herd of sheep Kharkiv  intrabreed type of the Prekos breed. By differentiating the population of ewes of two generations (n=126 mother-daughter pairs) taking into account the deviations of individual indicators from the average values production of wool and reproductive coefficients, 4 groups were distinguished, each of which is characterized by a different reaction in the organism-environment system: AA (increased in both signs), BB (decreased) and their corresponding combinations – AB and BA. In total, in the maternal and daughter generations of sheep, the proportion of animals in subgroups (AA + AB) was approximately the same, and was 46.8% and 45.3%, respectively, which is evidence of deviations close to the norm in the quality of genotypes, respectively – 3.5% and – 4.7%. According to the indicator of the sum of values in subgroups (AA + BA), the pressure of natural selection in the daughter generation is somewhat higher, compared to the maternal one. The deviation from the norm is -9.5% and -17.5%, respectively. Taking into account the peculiarities of the combination of the specified traits in animals of individual groups, in general, the ontogenetic adaptability of the compared generations to environmental conditions turned out to be the same, and was 1.032. This state of adaptation in the generation of daughters was observed against the background of their probable superiority at 12 months of age over mothers in production of wool by 9.4% (p<0.001) and live weight, by 3.9% (p<0.05).

An improbable decrease in reproductive ability was noted against the background of an increase in live weight and especially production of wool in the generation of daughters. At the same time, the values of phenotypic correlations between live weight and reproductive coefficients in the generation of mothers turned out to be significantly lower than in their daughters and amounted to +0.009 and +0.156 (for the first three years of breeding use) and +0.104 and +0.112 (for the entire life), respectively. Production of wool, on the other hand, had negative correlations, which in the compared generations decreased in the corresponding age periods from -0.163 and -0.149 (in mothers) to -0.063 and -0.007 (in daughters). The values of the reproductive coefficients in sheep of this population are characterized by a low level of heritability: 0.011 – for the first three lambings, and 0.003 – for the entire life period of reproductive use of ewes.

It has been proven that new lines are characterized by higher adaptive capacity, and their share in the genealogical structure of the herd is increasing.

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