In our studies, the phenotypic manifestation of the additive form of inheritance of breeding value by milk yield (intermediate and parental dominance) was in 334 (82.2%) bulls, and non-additive form (over-dominance and regression) – in 72 (17.8%) including: over-dominance in 55 (13.5%) and regression in 17 heads (4.2%).
In the population assessment, for all forms of inheritance, there was a clear quantitative shift of the breeding value of sons of milk yield to positive (+) values, compared with the breeding value of their parents. This confirms that sons, selected after their evaluation, and recognized as milk yield improvers.
The variability of the breeding value of sons by milking depending on the forms of its inheritance has been established.
According to the group of bulls by intermediate type of inheritance, milk yield sign were found in 291 (71.7%) sons, whose pedigree value was 606.4 ± 11.6 kg and was higher than the half-sum of both parents (554 kg), which deviates from the action of intermediate inheritance at 52 kg (109%). After all, the recognition of the intermediate nature of inheritance involves obtaining in the offspring of animals with the same set of chromosomes as their parents, and hence with the same phenotype. Therefore, from a theoretical point of view, genetic progress in the population should be not expected from this group of animals. However, in this case, the increase in breeding value was 9%, which is statistically significant (P > 0.99).
A rather high variability of the breeding value of sons from its level in their parents with an intermediate form of inheritance has been established. Thus, of the 159 bulls-breeders in which the breeding value was inherited by intermediate form, only 30 sons (7.3% of the total population) of the bull Duster 2147488 (BV +579 kg and mothers with an average BV +632 kg, half the amount of the BV of both parents was +605 kg), was +605.5 ± 30.8 kg and was equal to the half-sum of the BV of both parents, and 9 (2.2%) sons of the bull Manfred 2183007, whose breeding value was, on average, at the population level +856.3 ± 37.6 kg and was equal to the half-sum of the indicator of the parents' BV (+851 kg).
The inheritance of breeding value of bulls on quantitative signs of milk productivity in highly consolidated breeds on these signs, at intra-breeding selection occurs by a combination of phenotypic display of action of additive and non-additive (super-dominance) forms of inheritance. The frequency of these forms of inheritance probably is determined by the number and quality of chromosome pairs in the karyotype of animals on the probable basis of their manifestation in the population [15].
The relative variability of breeding value by milk yield along the line "father – son" and "mother – son" depends on the form of its inheritance. The coefficient of phenotypic correlation between the breeding value of parents and sons in the intermediate form of inheritance is +0.524 – +0.560 and increases with parental dominance to +0.907 ± 0.040 and +0.985 ± 0.006, and over-dominance to +0.887 ± 0.044 and +0.905 ± 0.033, at high statistical significant.
Inheritance by non-additive form (over-dominance of both parents) is more effectively associated with increasing of breeding value by milk yield their sons than by the additive form.
Genetic and non-genetic parameters for growth traits and Kleiber ratios in Dorper x indigenous sheep
