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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It's hoped more people will consider using their local service amid concerns over the future of the bus industry.
Dry across the country this evening with broken cloud and some late sunshine. Scattered showers expected tomorrow.
40,000 people are expected at the motorbike event in the capital this weekend.