Reproductive function in hybrid poultry. I. An impact of breeding for productivity traits (review)

In the lines and crosses of modern hybrid poultry bred for high yielding the metabolic disorders are indicated resulting in a number of syndromes, particularly ascites, heart pathology, sudden death, laying termination, disturbances of locomotory functions, declined stress tolerance, more aggressive behavior and cannibalism, etc. The adaptation mechanisms and resistance to external factors are depressed, and as a result, a reduced survivability occurs. The reproduction and the parameters of egg or meat yield are misbalanced. Changes are observed in egg mass, in the rate and composition of egg components and eggshell permeability, and also in the vitelline membrane. Selection for the same type of productivity leads to a significantly heterogenic embryogenesis. Starting from the second or third selected generation, a thermotolerance of embryos differs between the crosses. At that, different thermo tolerance of embryos is characteristic for both the genetic lines selected for definite productive traits and the individuals from free coupling population. In turkeys, the breeding for increased egg production leads to longer egg incubation, whereas the meat production as a selection criterion has no pronounced effect on incubation period. The main peculiarities of embryogenesis in high-yield hybrids when compared to the initial population are as fellows: time to complete embriogenesis differs, the eggshell permeability changes, the metabolic heat production differs, the allometric growth of heart, liver and kidneys occurs, the cordial rhythm and energy exchange in the myocardium are disordered, the neurohumoral functions are modified. It is shown the influence of sex-linked genes and a specific parental effect on reproductive function in the crosses bred for yielding parameters. As a possible ways to correct these negative effects, i) the combination of traits used for breeding should be revised, ii) the rations of parental poultry should be optimized and iii) the technological parameters of egg incubation should be adjusted for different genotypes with respect to their ontogenetic specificity.