We offered udh-hiyah (Eid sacrificial animal) for the sake of Allah Almighty. Bad weather conditions and storage caused a large part of its meat to spoil. Have we lost the reward because of this? Are we required to offer another udh-hiyah as compensation during the next ‘Eed?

All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.

You are not required to offer another udh-hiyah in the next Eid as compensation. In fact, your udh-hiyah is valid as long as all the conditions were fulfilled. It was narrated on the authority of Al-Baraa’ that the Messenger of Allah, sallallaahu ‘alayhi wa sallam, said: "Whoever slaughters after the prayer will have completed the rites and followed the Sunnah (way) of the Muslims." [Al-Bukhari and Muslim]

You are not required to do anything regarding the meat that spoiled due to bad storage. Saving a portion of the meat of the udh-hiyah was allowed by the Messenger of Allaah, sallallaahu ‘alayhi wa sallam. Hence, you are blameless for the consequent spoiling. It was narrated on the authority of Buraydah that the Messenger of Allah, sallallaahu ‘alayhi wa sallam, said: "I forbade you to keep the meat of the udh-hiyah for more than three (days), but now you can keep it as you wish…" [Muslim]

‘A’ishah narrated that the Messenger of Allah, sallallaahu ‘alayhi wa sallam, said: "Eat, and do not keep it for more than three days." Later, they (the companions) said: "O Messenger of Allah, people used to benefit from the fat from their sacrificial animals and made water-skins (from their hides)."  The Messenger of Allah, sallallaahu ‘alayhi wa sallam, said: "What is that?" They said: "You forbade us to keep the meat of our sacrificial animals for more than three days." He said: "I forbade you to do that because of the poor who came (asking for meat), but, now, eat some, preserve some, and give some in charity." [Ahmad, An-Nasaa’i and Al-Bayhaqi]

Allah Knows best.