Effect of yolk ratio in hen's eggs on the hatching weight and on the heart and liver ratio in chicks at hatching

The aim of this study was to examine, whether the yolk ratio of hen’s eggs has an effect on the hatching weight and on the heart and liver ratio in chicks at hatching. Altogether 3.500 hen’s eggs – originated from a 24 weeks old TETRA-H parent stock – were involved in the examination. The yolk ratio of these eggs was determined by means of computer tomography in vivo using a SIEMENS Somatom Emotion 6 multislice CT scanner at the Institute of Diagnostic Imaging and Radiation Oncology of the Kaposvár University. Based on the measured values eggs were separated into three groups: eggs with extreme high, eggs with average and eggs with extreme low yolk content (10-10% in each group). All of these eggs (n=350 per group) were incubated thereafter. After hatching 30 chicks per group (15 males and 15 females) were randomly chosen and their liveweight was measured thereafter. After measuring the liveweight chicks were killed and dissected. The weight of the heart and liver was measured and their ratio to the hatching weight was calculated. Based on the results it was established that the hatching weight of the chicks decreased with increasing the yolk ratio in the eggs in both sexes. In spite of the hatching weight the ratio of the heart to the hatching weight was increasing with increasing the yolk ratio in the breeding eggs in the case of the cocks. In the case of the pullets the opposite tendency was observed. The change in the ratio of liver to the hatching weight showed similar tendency in the case of cocks as it was observed in the case of the heart. In the case of the pullets no clear tendency was observed in this trait. Based on the results it was concluded that – according to some former results – the higher albumen content in the eggs results in higher hatching weight and the higher yolk content in the eggs in better body composition in the chicks.