HEREDITARY LOAD IN MEAT AND EGG CHICKENS OF VARIOUS ORIGIN
The aim of the study was to determine the spectrum and frequency of hereditary genetic defects of embryo development in meat and egg hens of different genetic origin, obtained during an experiment to study the effectiveness of crossing roosters of imported meat crosses with meat and egg females of domestic selection. All embryos that died during egg incubation were carefully examined to detect morphopathology. The main research method is pathomorphological analysis of genetic defects of dead embryos. The spectrum and frequency of morphological and anatomical hereditary defects of embryos were established during pathological and anatomical examination of incubation waste. During the autopsy of dead embryos, morphological disorders in the structure of the skeleton were determined, as well as various disproportions of its individual parts.
In the meat-egg hens of the original maternal form during three years of monitoring with the highest frequency (2.11–6.06%) revealed such a defect in embryo development as "donald duck". This indicates that the bird is "contaminated" with a "harmful gene" that causes this abnormality. It is worth noting that in groups of chickens that were artificially inseminated with the semen of roosters of meat crosses, this hereditary defect was also recorded. In the descendants of the first and second generations, this anomaly was absent, possibly due to its transition to a heterozygous state. Thus, we can conclude that the allele that expresses this lethal has in its genotype a bird of the local subpopulation "K". Only in meat and egg hens of domestic selection a wide variety of double anomalies was found – four species with a frequency of 1.05–1.12%. Most likely, double abnormalities are the result of homozygosity of dead embryos simultaneously for two lethal genes. Whereas, in chickens of other studied groups, only single anomalies of dead embryos were found, among them "exencephaly", "crossed beak", "shortened beak". Genetic defect of embryos "exencephaly" was found in chickens of most groups. It is obvious that the gene that determines the manifestation of this anomaly is significantly distributed in meat and egg hens of domestic selection and roosters used crosses. And in chickens of the created synthetic population "K-5" only this hereditary defect is revealed. In meat and egg hens of subpopulation "K" (F10) of the original maternal form and in the group of females, which were inseminated with polysperm of meat cocks of the cross "Cobb-500", with a low frequency (0.78–1.12%) a single "crossed beak" anomaly was found among the frozen embryos. This anomaly was not detected in the offspring of the first generation and in groups of chickens inseminated with semen of overripe brood stock. And only in the "cobb" bird of the "K-51" group among the hereditary defects of the dead embryos was this anomaly identified. In meat-egg hens of F10 subpopulation "K" with a low frequency (1.12%) was found a hereditary defect of embryos "shortened beak". Then this anomaly was found only in the "cobb" bird of both the first and second generation. The data show that the hereditary factor that determines this defect, the descendants inherited from the cocks of the cross "Cobb-500". The level of genetic burden in meat and egg hens of the local subpopulation "K", depending on the generation, ranged from 5.26 to 8.99% and was wavy in nature. In the descendants of the first generation it is low – 1.64–4.17%, in the "ross" crossbreeds is much smaller compared to the "cobb". The descendants of the second generation of different origins also had a low hereditary burden – in the range of 4.35–5.88%, which does not exceed the maximum allowable species value of 8.0%.
The results of the research showed that crossing meat-egg hens of domestic selection with roosters of imported meat crosses "Cobb-500" and "Ross-308" did not lead to significant "contamination" of genotypes of F1-F2 offspring with lethal genes. This indicates a low share in the heredity of the used offspring of hidden carriers of "defective" genes. This may be due to the high selection of birds of foreign crosses, which does not contribute to the accumulation in its gene pool of lethal genes that cause embryonic developmental abnormalities. In chickens of the created synthetic population "K-5" the level of genetic burden is low (3.03%), which indicates the relative "purity" of this bird from lethal genes.
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