A 63-year-old man was also arrested at Peter Boddy Slaughterhouse in West Yorkshire, the other plant where operations were suspended on Tuesday in an investigation by the Food Standards Agency.
Dyfed-Powys Police has confirmed three people are being held on suspicion of offences under the Fraud Act.
They are being detained at Aberystwyth Police Station, where they will be interviewed jointly by the police and the FSA.
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Kirsty Williams successfully defended her Brecon seat, but her party lost four others in a disastrous night.
The body of 75-year-old Iris Owens from Ystrad Mynach was found on Tuesday.