An Improved Pigs Weaned per Sow per Year (PSY) Accounting Method Based on Whole-Herd Resource Accounting with Mode-Specific Adaptation for Continuous and Batch Production

Pigs weaned per sow per year (PSY) is the core indicator used to evaluate sow-herd reproductive efficiency and a key factor affecting production profitability in commercial pig farms. The traditional PSY calculation uses the average inventory of mated (or parous) sows as the denominator and ignores the resource consumption of non-productive inventory, such as unserved gilts and weaned sows awaiting culling, leading to overestimated reproductive efficiency, concealed costs, and misleading management decisions. The overestimation range of 8–15% has been indicative estimates on non-productive days of commercial sow herds, and the improved method achieved a robustness of ≤ 3% based on the validation of basic data from pig farming enterprises involved in this paper. In this study, an improved PSY accounting method was developed based on whole-herd resource accounting. Gilts ≥220 days of age and weaned sows not yet culled were incorporated into the basic sow inventory, a dynamic inventory-time-weighting approach was established, and the method was adaptively optimized for continuous and batch production, with mode-specific formulas, validation cases, and an implementation system. It should be noted that traditional PSY and improved whole-herd PSY measure different quantities: the former reflects reproductive efficiency per mated sow, while the latter reflects resource-weighted reproductive efficiency per unit of resource-weighted sow inventory. Case studies on two commercial pig farms showed that the improved method addressed the structural limitations of the traditional formula, produced PSY values of 20–30 piglets per sow per year, and remained robust to parameter variation, with PSY estimates fluctuating by no more than 3% across the feasible range of w (0.60–0.80) in these two cases, and supports refined on-farm cost accounting and standardized cross-farm comparison, although independent multi-farm validation is still required. This study provides a practical tool for reproductive efficiency assessment and refined management in pig farms.