Heat treatment of hatching eggs and performance of lines of meat-type chickens

Com o objetivo de se estudar os efeitos do tratamento térmico de ovos incubáveis, para erradicação da Micoplasmose (segundo Yoder, 1970), sobre a Fertilidade, Eclodibilidade, Nascimento e Peso Médio Corporal de Machos e Fêmeas aos 46 dias de idade, em 12 linhagens nacionais de galinhas para corte e 1 linhagem de controle comercial, realizou-se o presente trabalho no Departamento de Genética da ESALO/USP, Piracicaba, SP, Brasil. A referida pesquisa envolveu a manipulação de 18.555 ovos fertilizados oriundos de 786 galinhas para corte em quatro incubações consecutivas com intervalo de 14 dias, as quais originaram 14.209 pintos de um dia. Os pintos foram criados em galpões convencionais de criação até 46 dias de idade, quando foram avaliados individualmente com relação à peso corporal. Do total acima referido, 5.725 ovos foram submetidos ao tratamento térmico segundo Yoder, 1970. O tratamento térmico foi efetuado da seguinte maneira: os ovos retirados da câmara fria (16°C) foram ambientados a 25°C posteriormente aquecidos gradativamente até 46 e num período de 12 horas e resfriados rapidamente até 36°C, sendo então incubados normalmente. Os resultados permitiram as seguintes conclusões: 1) o tratamento térmico dos ovos incubáveis influenciou negativamente os índices reprodutivos; porcentagens de Fertilidade (-4,53%), Eclodibilidade (-15,4%) e Nascimento (-17,8%); 2) com relação ao peso médio corporal aos 46 dias de idade de machos e fêmeas, o tratamento térmico trouxe resultados positivos (+ 84,5 e 42,0 g/ave, respectivamente). Tendo em conta os resultados obtidos, conclui-se que o tratamento térmico é um processo que pode trazer resultados favoráveis conforme indicado por Yoder (1970). Devido a presença de interações Linhagem x Tratamento. para eclodibilidade, fica evidente que algumas linhagens mostraram-se mais resistentes ao tratamento térmico. Entretanto, pesquisa adicional deve ser efetuada em nossas condições de criação, recria e reprodução, posto que os resultados sorológicos não foram conclusivas. possivelmente devido a amostragem insuficiente.This research was conducted in order to study the effects of the heat treatment of hatching eggs (YODER, 1970), on the fertility (Fert), hatchability of fertile eggs (Eclod) hatchability of all eggs set (Hatch) and body weight of males and females at 46 days of age. Data from 12 experimental breeding lines of meat-type chickens and 1 commercial line were utilized. The experiments were carried out in facilities of the Departamento de Genética, Escola Superior de Agricultura "Luiz de Queiroz", Universidade de São Paulo, located in Piracicaba, State of São Paulo, Brazil. The research involved 18.555 fertile eggs from 786 meat-type female chickens in 4 consecutive incubations of eggs stored for 14 days. From these, 5725 eggs were subjected to heat treatment according to YODER, 1970. The heat treatment of the eggs were performed in the following way: the fertilized eggs were removed from the cold storage chamber at 16°C and were kept for several hours until they reached the environmental temperature of 25°C Then, these eggs were incubated, under an initial temperature of 36°C. The temperature of the chamber was than increased by one degree centigrade each hour during 10 hours, until 46°C. The chamber was then kept at 46°C during 2 hours. After the 12 hours peating period, the heater of the incubating chamber was turned off, and the doors of the chamber were wide opened so that the internal temperature would be rapidly decreased; from 46°C to 36°C in 1/2 hours, after what the chamber was turned on and the eggs incubated as usual. The body weights of 3770, chicks which came from heat treated eggs were compared with those of 10439 chicks from eggs not subjected to heat treatment. The body weight data from 14209 chicks which were raised on a conventional broiler house, were evaluated individually. The results indicated: a) Fert, Eclod and Hatch of all lines were negatively influenced by the heat treatment of the hatching eggs; fertility was decreased by 4.53% and hatchability of the fertile eggs by 15.4% on the average. b) the mean body weight at 46 days of age was positively influenced by the heat treatment of the hatching eggs (respectively equal to 42.0g/female and 85g/male). The interaction of lines x treatment was statistically significant, therefore indicating that some lines were more resistant to the heat treatment. This aspect desernes further investigations. c) further research should be carried out since the sorological results were not clearly conclusive possibly due to sampling problems