The animals were being kept in appalling conditions.

appalling 是形容词，由动词 appall（使惊骇）加上后缀 -ing 构成。appall 本身来自古法语，原意是"使苍白"，引申为"使震惊、使恐惧"。appalling 表示"令人震惊的、极其恶劣的"，强调程度非常严重。