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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The Met Office has issued a Yellow 'Be Aware' warning for strong winds and gusts of 60-70mph on exposed coastal areas
Breezy with further showers, locally heavy, spreading in from the west at times.
Breezy, but winds gradually easing overnight. There will be clear spells and isolated showers through the evening.