Assessment of resistance to infectious diseases in birds of line selected against neoplasms
Authors: Livoshenko L. , Livoshenko Y. 
Published: June 2021

As a result of specific selection by CAM-test, two lines of chickens with increased resistance to infection with pathogens of Marek's disease and lymphoid leukemia of the group were created: D-2 - on the basis of Leghorn breed, P-2 - Poltava clay. The D-2 resistance index was 50.5%; P-2 79.3% against control, D-4 - 11.0% and P-37 - 58.8%. Selection by CAM - test helped to increase the bird's resistance to leukemia. When artificially infected with the leukemia virus, subgroups A of the selected lines were probably (at P <0.01) more resistant to leukemia than non-selected. A similar pattern of resistance to leukemia was observed in natural infections.
The bird of line D-2 was more resistant to Marek's disease: the percentage of deaths from this disease in it was 7.0, while in line D-4 (initial, unselected) and 15.5% of the initial population (not vaccinated bird). After vaccination, the number of deaths from Marek's disease decreased to 0.11% and 1.33%, respectively, the named lines. Line P-2 did not show a probable increase in resistance to tumors caused by Marek's disease in comparison with control P-1. Lines P-2 and D-2 during specific selection did not reduce their resistance to the most common bacterial pathogens (E. coli, S. pullorum), did not differ from unselected lines on the sensitivity of the main immunocompetent organs to vaccination (La-sota, smallpox vaccine), as well as the introduction of thymus - and bursa-dependent antigens.
In most cases, both interbreed and interlinear hybrids have an intermediate inheritance of resistance to infection by oncornaviruses, ie hybrids occupied the middle position between more or less resistant baselines.
The hybrid bird, obtained using lines resistant to neoplasms, at the age of 30 weeks had an egg weight of 52-54 g, at the age of 6163 g, and the average for the year - 58-60 g. The egg mass in the best combinations is 14-15 kg. The age of 50% egg production varied significantly depending on the year of the study, the quality of the young and the time of its transfer to poultry houses. Under optimal conditions, the bird reached 50% of egg production at the age of 160-165 days, but the weight of eggs at this age is low - 47.9 - 48.6 g.
As a result of tests of the best laying on the initial and middle laying hens revealed a combination of B-7 x D-2, from which for 72 weeks of life received 230 eggs per initial and 244.2 eggs - on the average laying hen at the weight of eggs at the age of 30 weeks 52.7 g and 52 weeks - 63.1 g. However, the preservation of these hybrid chickens was lower by 2.3%, compared with P-2xD-2. The registered death from neoplasm was 0.9% of the initial population against 0.45% in P-2 x D-2.
At the same time, chickens of the B-7xD-2 hybrid combination received 9.7 more eggs per average laying hen than other hybrids tested in the same poultry house under the same conditions (250.2 eggs vs. 240.5). A characteristic feature of the tested combinations is their reduced susceptibility to neoplasms, the frequency of registered neoplasms did not exceed 1%, while the rest of the chickens of this poultry departure from the neoplasm was 1.75%, ie 2 times more.