The impact of herd age structure on the performance of commercial sow-breeding farms.

Background: The herd age structure, i.e., distribution of sows within a farm based on their parity number, and its management are essential to optimizing farm reproductive efficiency. The objective of this study is to define different types of herd age structure using data from 623 Spanish commercial sow farms. Additionally, this study aims to determine which type of herd age structure can enhance reproductive efficiency at the farm level.

Results: Farms are classified into three groups according to the quadratic function fitted to the percentage of sows by parities. This classification unveils three types of herd structures: type 1 (HS1) exhibits a concave-downward trend, with a higher percentage of sows in intermediate parities (mean of 45.5% sows between the 3rd to 5th parity); type 2 (HS2) presents a trend curve that is close to a straight line, with a gradual decrease in the percentage of sows per parity (approximately 2% loss of sows census per parity); and type 3 (HS3) shows an upward concave trend curve, with an increase in the percentage of sows in later parities (19.0% of sows between 7th and ≥ 8th parity). Parametric tests assess productivity differences between the three types of herd structures (p < 0.01). HS1 farms have the best productive outcomes over a year, with 31.2 piglets weaned per sow and year (PWSY) and a farrowing rate of 87%, surpassing HS2 and HS3 farms (30.1 and 28.7 PWSY; 85.3% and 83.4% farrowing rates, respectively). HS1 also have the lowest percentage of sows returning to oestrus (11.8%) and the highest number of weaned piglets per litter (12.8), compared to HS2 (13.2% and 12.4 piglets weaned) and HS3 (15.1%, 11.9 piglets weaned). These differences show a medium effect size (η² between 0.06 to < 0.14).

Conclusions: This study shows the importance of herd age structure on sow-breeding farms as a factor of reproductive efficiency. The results endorse the proposed classification based on the curvature of the trend parabola obtained with the quadratic function to categorize herd structures into three groups. Additionally, these findings highlight the importance of considering the herd age structure in farm decision-making.