ENERGY-LOSSES IN FOWL AND DUCK EGGS DURING INCUBATION

Energy (gross energy, GE) transfer based on chemical composition was s tudied in 80 layer (White Leghorn, WL) eggs, in 80 broiler (New Hampsh ire, NH) eggs between days 1 and 20 of incubation, and in 40 White Bei jing duck eggs between days 1 and 25. Our data indicate that at the be ginning of incubation, both NH and duck eggs contained substantially m ore energy (450 +/- 18 kJ and 614 +/- 18 kJ, respectively) than WL egg s (359 +/- 15 kJ). In the course of incubation, 30.8% of available ene rgy was utilized by WL, 33.9% by NH, and 19.9% by Beijing ducks. Thus the highest incubation efficiency was found in ducks. This is also ind icated by their incubation power that reached only 45.5 mW. It was hig her in WL and NH (63.9 and 88.3 mW, respectively). Similar results wer e obtained when this power was calculated for the initial and metaboli c egg mass. Also the formation and functioning of the new individual's tissues (including the embryonic membranes and fluids) required the s mallest GE amount in ducks (2.39 kJ.g(-1)), whereas in WL it increased to 3.66 kJ.g(-1), and in NH to 4.12 kJ.g(-1). The transfer of one J o f GE from the eggs into tissues of embryos (without membranes anf meco nium) required 0.95 J in WL, 0.87 J in NH, and only 0.54 J in ducks. T hese energy transfer processes did not become significant until the la st 9 (in fowl) or 10 (in ducks) days of incubation. The almost exclusi ve energy source during incubation were lipids. Protein energy amount did not decrease significantly except for WL. These experimental data confirm the older ones only in part. Some interspecies differences, or iginating also from the fact that incubation of ducks lasts longer, ar e smaller than intraspecies differences, those between layer and broil er type of chicks. These facts show that the incubation energy transfe r in avian species is not only variable but also adaptable.