Comprehending the patterns of alteration in boar semen quality and identifying effective nutritional interventions are crucial for enhancing the productivity of commercial pig systems. This study aimed to examine the alteration in semen quality in boars, and assess the impact of protocatechuic acid (PCA) on semen quality during the phase of declining semen quality. In Exp. 1, a total of 38 Pig Improvement Company (PIC) boars were selected and their semen quality data were recorded from the age of 9 to 37months. In Exp. 2, 18 PIC boars (28months old) were randomly assigned into three groups (n = 6) and fed a basal diet, a basal diet containing 500 or 1,000mg/kg PCA, respectively. The experiment lasted for 12weeks. The semen volume, concentration, and total number of spermatozoa in boars exhibited an increase from 9 to 19monthsold and showed a significant linear decreased trend in 28, 24, and 22monthsold. Sperm motility displayed an upward trajectory, reaching its peak at 20months of age, and showed a significant linear decreased trend at 20monthsold. Dietary supplementation of PCA demonstrated an effect to mitigate the decrease in semen volume, concentration of spermatozoa, total number of spermatozoa (P > 0.05), and significantlyincreased the sperm motility (P < 0.05). Moreover, supplementation of 1,000mg/kg PCA significantly increased the sperm viability (P < 0.05). Analysis on cellular signaling pathways revealed that PCA restored serum testosterone levels and alleviated oxidative damage by upregulating the expression of HO-1, SOD2, and NQO1 in testicular stromal cells. Notably, PCA can enhance phosphorylation by selectively binding to AMP-activated protein kinase (AMPK) protein, thereby improving sperm mitochondrial function and augmenting sperm motility via PGC-1/Nrf1. These data elucidated the pattern of semen quality variation in boars within the age range of 9 to 37monthsold, and PCA has the potential to be a natural antioxidant to enhance sperm quality through modulation of the AMPK/PGC-1/Nrf1 signaling pathway.