RESUMEN
The timing and magnitude of a coccidian infection, judged by the numbers of oocysts of Eimeria present in the litter, were affected by the duration of medication. In birds medicated for 6 wk and infected at 35 d of age, fewer oocysts were produced than in birds medicated for 4 or 5 wk whether infected at 18 or 35 d of age. Feed conversion at 6, 7, and 8 wk of birds infected at 18 d and medicated for 6 wk was less than that of birds medicated for 4 or 5 wk. Birds infected at 35 d and medicated for 6 wk had a lower feed conversion than birds medicated for 5 wk. Immunity to Eimeria tenella had developed by 8 wk in birds medicated for 4, 5, or 6 wk if infected at 18 d of age. Immunity did not develop in those birds medicated for 6 wk when infected at 35 d.
Asunto(s)
Coccidiosis/veterinaria , Coccidiostáticos/administración & dosificación , Eimeria tenella , Enfermedades de las Aves de Corral/parasitología , Piranos/administración & dosificación , Roxarsona/administración & dosificación , Animales , Pollos , Coccidiosis/tratamiento farmacológico , Coccidiosis/inmunología , Eimeria tenella/inmunología , Masculino , Enfermedades de las Aves de Corral/tratamiento farmacológico , Factores de TiempoRESUMEN
Three generations of divergent selection for 21-day growth response to a diet deficient in selenium (-Se) were bred using a meat-type chicken. The Athens-Canadian Randombred (AC) population of chickens served as the base population for this study. Mass selection was used to establish a -Se refractory line (SDR) and a -Se susceptible line (SDS). A genetic control line was maintained during the selection process to facilitate evaluation of the responses of the selected lines. The SDR males and females had an average of 17% increase in weight gain at 21 days of age when fed the -Se diet compared with the control line males and females fed the same diet for the three generations of selection. The SDS line had an average reduction in weight gain of 27% during the same period of selection. A difference of 25 g was observed between the mean body weights of SDR males and females and between the SDS males and females after one generation of selection. By the third generation of selection, the difference between SDR and SDS males had increased to 31 g, whereas the SDR and SDS females differed by 41 g. Early response to selection was asymmetrical because the response was greater in the SDS than in the SDR line. Response to selection, however, generally declined after the first generation. Realized heritability estimates for individual generations for this trait were variable (ranging from -.26 to .95), but cumulative estimates (.15 to .39) for growth through three generations were similar to those reported for chickens and quail.(ABSTRACT TRUNCATED AT 250 WORDS)
Asunto(s)
Pollos/crecimiento & desarrollo , Selección Genética , Selenio/deficiencia , Animales , Dieta , Femenino , MasculinoRESUMEN
Experiments were conducted to determine whether a hereditary factor accounted for part of the variation observed in the growth responses of young chicks to uncomplicated selenium (Se) deficiency. Results showed that such a factor influenced the growth of chicks fed a Se-deficient diet. Those chicks most susceptible (SUS) to the growth depressing effects of Se-deficiency oxidized 14CH3-methionine to 14CO2 at a greater rate when fed the Se-deficient diet than did chicks that appeared refractory (REF) (i.e., grew at near normal rates) to Se-deficiency. When diets were supplemented with Se, both lines exhibited equivalent rates of 14CH3-methionine oxidation. The SUS chicks appeared to have lower levels of free homocystine and cystathionine in plasma compared to REF chicks or to Se-supplemented chicks of both lines. These results provide evidence for an impairment in sulfur-amino acid metabolism as the basis of the hereditary effect.