Benefit Plans

Our employees ceased to participate in the Pfizer, Inc. U.S. qualified defined benefit plans and the U.S. retiree medical plan effective December 31, 2012, and liabilities associated with our employees under these plans were retained by Pfizer. Pfizer continued to credit certain employees' service with Zoetis through December 31, 2017 (or termination of employment from Zoetis, if earlier) for certain early retirement benefits with respect to Pfizer's U.S. defined benefit pension and retiree medical plans. Pension and postretirement benefit expense associated with the extended service for certain employees in the U.S. plans totaled approximately $2 million in each three month period ended March 31, 2018, and April 2, 2017.

The following table provides the net periodic benefit cost associated with our international defined benefit pension plans:



	Three Months Ended
	March 31,			April 2,
(MILLIONS OF DOLLARS)	2018			2017
Service cost	$	2		$	2
Interest cost	1			1
Expected return on plan assets	(1		)	(1		)
Curtailment and settlement loss	—			1
Net periodic benefit cost	$	2		$	3

Total company contributions to the international pension plans were $2 million and $3 million for the three months ended March 31, 2018, and April 2, 2017, respectively. We expect to contribute a total of approximately $6 million to these plans in 2018.