Effects of increased water loss on growth and water content of the chick embryo

Domestic chicken eggs that lost 25.1% of their initial mass during incubation produced embryos with smaller wet masses than control eggs that lost 12.5% of their initial mass. However, water-stressed embryos did not differ from control embryos in dry body mass, indicating that water-stressed embryos were dehydrated. Yolk, albumen, heart, and gizzard wet and dry masses were not different between water-stressed and control groups during the last week of incubation. However, wet mass of the liver was significantly greater and that of the right leg significantly less in water-stressed embryos. Tarsometatarsal length, dry mass of the liver and right leg, and daily rates of oxygen consumption were not different between groups. Hatching success was 20.5% for water-stressed eggs and 85% for control eggs. These results show that increased egg water loss during the last week of incubation results in embryos that weigh less because they have a lower water content, not because they grow more slowly. The reduction in water content, with respect to the individual organs and body parts examined, is due primarily to a difference in leg tissue water content. We conclude that embryos do not alter their growth in response to a change in the amount of water available in the egg.