In addition to all thr comments about meat quality animal health quality would likely suffer as many livestock animals are bred to put on excessive muscle and fat because they are not expected to live long enough for it to seriously affect health.
Letting most meat livestock live longer lives is just means suffering and lower meat quality.
This actually does happen but it is the exception instead of the norm. Cows who calve well will be kept for many years. Eventually, once they are too old or weak to hold a calf, they will be sent to slaughter too. Same thing goes for bulls who’s knees aren’t very good anymore or are shooting blanks. Many times these animals don’t go to auction but straight to the butcher for the farmer’s own freezer. Source: many years of raising cattle.
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