Establishing a specific avian egg and embryo necropsy protocol and determining that the cause of embryonic death and initial reproductive failure of the breeding program of the horned guan (Oreophasis derbianus) was due to yolk sac entrapments. Changes in the incubation protocol set thereafter were followed by a sustained success of this breeding program as no additional cases of this yolk sac malformation were noted. Rosas-Rosas AG, et al: Perinatal mortality in a colony of captive horned guans (Oreophasis derbianus). Proc AAZV ARAV Joint Conference 2008, págs 136-7; Juan-Sallés C, et al: Causes of embryonic mortality in an aviary: 72 cases. Proceedings EAZWV 2006, págs. 187-190.