Objectives: To determine the number of parities sows should be retained in a breed-to-wean system to maximize returns over total cost per weaned pig and net return on investment, and to assess the sensitivity of returns over total cost per weaned pig to feed price and number born alive (NBA).

Materials and methods: Data used to estimate NBA and pre-weaning mortality by parity were collected between 2001 and 2014 at 17 Midwest US farms representing a total of 105,719 sows, accounting for 502,491 total records. Projected budgets were compared for various parity distribution scenarios using a “steady-state” farm model that included both variable and fixed costs associated with the farm and the proportion of sows by parity in the distribution.

Results: The cost of producing a weaned pig was minimized by culling after parities 5 through 9, and culling after late parities (ie, parity 7 through 9) showed greater returns over culling after parities 1 through 4. Culling after parities 5 to 9 showed approximately a 15% net return on investment. When NBA increased, culling after parities 5 through 9 had the highest returns. Culling after parities 6 through 9 showed the greatest returns with low feed prices. With high feed prices, all parity distributions costs exceed returns, though culling after parities 5 and 6 came closest to breaking even.

Implications: Retaining sows in the herd longer has economic benefits that could increase the financial returns of a breed-to-wean system