Evaluation of growth curve in domestic guinea fowl (Numida meleagris) embryo through Gompertz and Logistic model

The interest in domestic guinea fowl farming is relevant in some EU countries, particularly in France and Italy. Limited literature on embryo development in domestic guinea fowl is available. To our knowledge, an illustrated and written description of guinea fowl embryo development with its morphological changes is still missing. Therefore, to perform a descriptive chart of the guinea fowl embryo development, an industrial Italian breeding farm provided us hatching eggs from a 56 weeks old genetically controlled flock (Galor ltd, Amboise, France). Eggs were weighted and setted using incubation parameters applied in industrial hatchery (setter: 99.66°F and 57% RH; hatcher: 97.34°F and 82% RH), and then transferred on day 21 of incubation into the hatcher. Starting from hour 12 up to day 8 of incubation, 4 eggs were evaluated every 12 hours; thereafter 4 eggs were analyzed every 24 hours. Soon after removal from the incubating machine, eggs were cooled in a 4% Formaldehyde solution bath at 0°C for half an hour to prevent bleeding, then candled for the location of the embryo and carefully opened to expose it. During analyses embryos were photographed in-ovo and extra-ovo; main embryonic morphological changes were macroscopically evaluated. Blastoderm diameter (from day 0.5 to day 4.5) and embryo weight (from day 5 to the hatch) were recoded. The chronological development of the guinea fowl embryo is illustrated by growth curves and a photographic timetable. The growth curve and its parameters was estimated by Logistic and Gompertz functions. The accuracy of the curve fit was high in both models based on yolk-sacless embryo weights (R2adj=0.9956 and 0.9953, respectively). The position of the inflection point in terms of age resulted at day 21 and 23 of development for the Logistic and Gompertz model, respectively, where embryo achieved its maximum daily weight gain (2.66 g/d and 2.35 g/d, respectively), indicating the conclusion of the auto acceleration phase of the guinea fowl embryonic growth after third week of incubation.