going light or young bird sickness are old terms for a disease called circovirus. loose droppings , not eating .rapid weight loss and in 10% of the cases ..death. it is the same as human aids , its not the circovirus the kills the bird but it lowers the immunity system and the secondary viruses such as ecoli and sam that cause the problem . check it out on the net it will give give you more information on it . ps there is no cure the birds either get over it or die