AM Best Co has affirmed its ratings for the Alterra organisation following its $3.1 billion merger with Markel Corporation.Alterra retains its financial strength rating of A (Excellent) and issuer credit ratings of “a” of Alterra Bermuda Limited (Alterra Bermuda) and its affiliated operating companies.Alterra’s Bermuda’s immediate parent company, Alterra Capital Holdings Limited (Alterra) has retained its “bbb” credit rating.AM Best also has affirmed all debt ratings of Alterra, Alterra USA Holdings Limited, Alterra Finance, LLC (both domiciled in Delaware) and Alterra Capital Trust I.The outlook for all ratings is stable.Markel Corporation acquired specialty-focused underwriter Alterra in May this year and the integration is ongoing.“The ratings for the Alterra organisation take into consideration its recent change in ownership, the future benefits to be derived from its integration into Markel, as well as some of the immediate benefits gained in terms of enhanced scale, reach, the Markel brand, distribution platform and its leadership position in the excess and surplus lines marketplace in the United States,” said AM Best in a press release on Friday.“With integration plans underway, AM Best will continue to maintain a dialogue with management to review and discuss Alterra, its future plans and how the Alterra organisation will ultimately align with Markel and its existing members.“Until that time, the ratings of Alterra are considered as if this were a ‘bolt-on’ acquisition and assume no material changes to business profile, capitalisation, performance as well as inter-company reinsurance.“In addition to the new owner, these ratings also reflect Alterra Bermuda’s solid financial performance through the second quarter of 2013 and its strong risk-adjusted capitalisation. Alterra has platforms and operations in major global underwriting markets, which gives it flexibility to optimise its underwriting portfolio composition.“Being part of Markel, revenue and earnings prospects are likely to be enhanced through synergies, the leveraging of existing business relationships and efficiencies gained.“Partially offsetting these positive rating attributes are the current soft market in casualty classes of business, which represents a significant portion of Alterra’s risk portfolio and the challenging investment climate that places increased pressure on underwriting profitability.”