The objective of this study was to evaluate the effect of selection for body weight on the genetic variability and diversity in broiler lines. Two paternal broiler lines (LL and LLc) were used. LL line was selected for 12 generations for growth and carcass and reproduction characteristics. The LLc line was established from LL line in 1985 and mated at random. Blood samples from six chickens per line were collected and used for molecular analysis. Also, a DNA pool was made for each line to compare effects between lines. Data were analyzed considering the collected information on the presence or absence of DNA bands. Band sharing scores were calculated using the DICE coefficient. The pattern of the 21 most representative bands was used. DNA fingerprinting (DFP) showed 90.48 % of polymorphism bands for both lines. Difference between lines was not due to the presence or absence of bands, but to the frequency of such bands in each genotype. Considering that both lines had the same genetic background, changes on band frequency were probably due to selection. Selection for body weight had an effect on the band frequency as evaluated by DFP, and for this reason this technique could be used as a tool in the selection process. Results also suggest that bands 4, 5 and 19 were linked to body weight traits, and bands 9, 10, 12, 13 and 21 were linked to reproductive traits such as egg production.

Aves de quatro linhagens de galinhas para corte foram criadas no sistema semi-intensivo, em 16 boxes, sendo 4 boxes por linhagens, com 4,5 m² de área interna (abrigo) e 35 m² de área de pastejo, com o objetivo de analisar a adaptação dessas linhagens a esse sistema de criação, através de parâmetros ambientais e comportamentais. O período experimental desenvolveu-se entre 35 e 75 dias de idade, durante o qual foram coletados dados relativos à quantidade de aves presentes no pasto, temperatura e umidade relativa nos boxes e no pasto e porcentagem de sombra no pasto. Os parâmetros ambientais monitorados influenciaram o comportamento das aves. A análise bioclimática e a observação do comportamento permitiram diferenciar as linhagens estudadas no que diz respeito à adaptação das linhagens ao sistema semi-intensivo de criação. As aves das linhagens avaliadas mostraram-se adaptadas ao sistema semi-intensivo por demonstrar o comportamento esperado para esse sistema de criação.

Birds of four meat-type chicken lines were reared at the semi-intensive system with the objective of evaluate the adaptation to these breeding systems through environmental and behavioural parameters. The experimental period took place between 35 and 75 days of age during which it was collected data of number of broilers in the pasture, air temperature and relative humidity inside the boxes and in the pasture areas, and percentage of shadow in the pasture areas. Environmental factors influenced the behaviour of the evaluated lines. The bioclimatic analysis and the observation of the chicken behaviour allowed to discriminate the studied lines regarding to the adaptation to the semi-intensive breeding system. The broilers of the evaluated lines showed adaptation to the semi-intensive system, presenting the expected behaviour for this breeding system.