The incident happened on Saturday afternoon at a farm near Keady.
The man was rushed to Craigavon Area Hospital where he is recovering and in a stable condition.
A Health and Safety Executive spokesperson confirmed it was investigating the incident.
The effects of the poisonous gases released when slurry is mixed can be fatal. A high concentration of hydrogen sulphide disrupts the sense of smell, causing difficulty in breathing, then disorientation. After only a few breaths, collapse and death can follow.
In June, eight year-old Robert Christie tragically died after being overcome by slurry fumes while helping his dad on a Dunloy farm.
In June last year, Ulster Rugby Player Nevin Spence, his father Noel and brother Graham all died as a result of inhaling fumes on their farm in Co Down.
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