Post said the farms house approximately 5.5 million birds, which represent about 10% of its egg supply.

ST. LOUIS — Post Holdings, Inc. has joined the growing list of companies dealing with avian influenza (A.I.) after an incident at one of its Michael Foods Group segment third-party contracted egg suppliers. The company said it was informed on April 27 that the chickens on a farm in Iowa had tested positive for A.I.

Post said the farms house approximately 5.5 million birds, which represent about 10% of its egg supply. The company said it is in the process of completing an analysis of the financial impact, if any, of the A.I. incident.

“We are working with our suppliers and customers to mitigate the impact of this unfortunate event,” said Rob Vitate, president and chief executive officer of Post. “I have confidence in our team to respond quickly and effectively.”

Post acquired Michael Foods for $2.45 billion last summer.

Avian influenza has affected numerous locations throughout the Midwest this spring. Earlier this month, Austin, Minn.-based Hormel Foods Corp. said federal and state animal health officials confirmed the presence of highly pathogenic H5N2 A.I. at multiple turkey farms that supply turkey to Hormel’s Jennie-O Turkey Store unit. As a result of bird culls and quarantines, the company expects lower supplies of turkey to impact plant operations and cause reduced sales volumes as the year progresses.