РУАЭСТ (RUAEST)
REPRODUCTIVE FUNCTION IN HYBRID POULTRY. II. AN IMPACT OF BREEDING FOR TRAITS OTHER THAN PRODUCTIVITY (review)
Herein, the data are summarized on the impact of such selection criteria as poultry cannibalism, ascites resistance, stress responsiveness, and primary immune response to reproductive function in poultry. The selection for one of these signs changes the productivity and other body functions. High-productive meat crosses differ from slow-growing chicks in a susceptibility to ascites (R. Wideman, 2001). Broilers’ mortality because of ascites makes 5-10 %, and at the lowered temperature of the environment can reach 50 % calculated from world production (H. Pavlidis et al., 2007). Prerequisites to development of the disorder are formed during embryogenesis (E. Decuypere еt al., 2000). In the embryos who are the descendants of ascite resistant poultry (L), a relative heart weight is reliable higher, and pipping shells and a hatching occur earlier, than in Lgenotype lines for which the hypothyroidism and tachycardia are characteristic (D. Luger et al., 2002). An observed increase in egg incubation period in L lines can be caused by lower activity of thyroid gland and an increased pCO2 in egg air camera, and as a result, the embryos suffered from hypoxia. A positive correlation is revealed between the development of lungs and the thyroid gland activity during embryogenesis, i.e. the lungs volume is the larger the higher thyroidal hormone rate, and vice versa (M. Hassanzadeh et al., 2008). In the chickens with better developed lungs, grown up under chronic hypoxia, the mortality from ascites was reliably lower. In Land Lbroilers the mortality was 93.2 and 9.0 %, respectively (S. Druyan, 2009). The heart beating in Land L1-day chickens differed, being on average 435 and 404 beats per minute, respectively, but to the day 17 the difference practically leveled (419 and 417 beats per minute, respectively) due to a decreased rate in L and an increased rate in L. Divergent selection for the feather pecking behavior causes differentiation in reactivity of the neuro-endocrine and immune systems (A. Buitenhuis, 2006). There are the evidences that the optimized incubation protocols for meat hens can prevent broiler chicks from ascites and improve safety of the poultry. Feather pecking reduced in the course of selected is associated with improvements in egg production (number and weight of eggs), but the deterioration in the quality of hatching eggs, the results of incubation, the state of derived chickens and changes of stress responsiveness and(or) immune response. So, the feather pecking rate was reliable lower in Lthan in Lpoultry, and the number and weight of eggs laid during a month are higher (i.e. 0.38 and 2.01 feather pecking per hour, 1223 and 1132 g, 24.4 and 18.3 eggs, respectively). However, the egg quality in Lhens was better compared to L, with the Haugh units of 73.0 and 64.9, shell thickness of 38.1 and 37.0 mm, and yolk ration of 30.6 and 29.5 %, respectively (G. Su, 2006). Selection for humoral immune response causes the metabolic changes and influences on the synthesis of proteins which are key factors for both immune protection and ensuring reproductive function and egg production, so there is an imbalance between a potential of antibody response, growth, development and reproductive function. Under the influence of divergent selection for primary immune response, body weight, time of puberty and egg production were higher in the Llayers compared to Lhens, while the Lhens surpassed them in egg quality, such as height and рН of the egg white, Haugh units, the number of two-yolk eggs. The changes in reproductive function due to poultry targeted selection should be compensated by genotype-specific optimization of feed rations and rearing technologies for adult hens, and by an adjustment of egg incubation conditions.