Global pork production has shown steady growth in recent years, reaching approximately 124.5 million tonnes in 2023 – an increase of 1.4 % compared with 2022 (FAO, 2024). Sustaining these volumes under intensive production systems requires optimizing sow reproductive performance, as maternal-type females are the cornerstone of herd productivity and profitability. Sow lifetime reproductive efficiency strongly influences production economics, with key indicators including total piglets born; live-born counts; stillborn counts; litter birth weight; number of weaned piglets; and, during lactation, total and average piglet weaning weights (Segura-Correa et al., 2023). Monitoring these traits allows early detection of reproductive bottlenecks and supports both management adjustments and genetic selection programs.

Genetic improvement programs have targeted high-prolificacy sows; however, the low heritability of most reproductive traits remains a constraint to genetic progress (Tummaruk et al., 2023). Studies in maternal breeds such as Landrace, Large White, and Yorkshire have documented gains in prolificacy, enabling estimation of breeding values and more precise selection (Ehlers et al., 2005). Nevertheless, reproductive performance is also shaped by non-genetic factors, including parity, insemination season, farrowing year, housing type, and management practices, which can substantially influence litter size and weight (Chakurkar et al., 2021; Ek-Mex et al., 2024).

The existing body of research on sow reproductive performance provides a substantial foundation, documenting the complex interplay of genetic and non-genetic factors that shape farrowing and lactation outcomes. Genetic studies consistently report low to moderate heritability estimates for key reproductive traits, underscoring the challenge of achieving rapid genetic progress. For instance, heritability for litter size traits like total number born (TNB) and number born alive (NBA) is typically low (0.10–0.20), while birth weight (BW) often shows moderate heritability (approximately 0.20–0.41) (Boonkum et al., 2025; Rocha et al., 2025). Concurrently, extensive research has characterized major non-genetic influences. Sow parity is a critical factor, with performance generally peaking between parities 2–5 and declining in gilts and aged sows (Koketsu and Iida, 2017). Seasonal effects, particularly high summer temperatures, are reliably linked to reduced fertility and prolificacy (Koketsu and Iida, 2017). Furthermore, detailed investigations into piglet mortality identify risk factors such as increased litter size, low birth weight, extreme gestation length, and high birth order, all contributing to stillbirth and pre-weaning losses (Nam and Sukon, 2021; Kramarenko et al., 2024). While these genetic and environmental factors are often studied separately, there is a recognized need for more integrated models that simultaneously account for both sets of effects to identify robust genetic lines capable of sustaining high performance under variable commercial conditions (Boonkum et al., 2025).

Additionally, there is limited integration of these effects into analytical models that allow for the accurate discrimination of reproductive performance according to genetic lineage under environmental conditions. This limitation hinders the identification of new genotypes capable of maintaining high reproductive performance throughout their lifespan in production systems (Knap et al., 2023). Therefore, it is necessary to characterize the sow's prolificacy and maternal capacity to evaluate performance during farrowing and lactation, integrating indicators that reflect reproductive efficiency, such as piglet survival and growth (Dekkers, 2021). Furthermore, this study will provide applicable information for decision-making in genetic improvement and reproductive management programs in order to contribute to the more efficient allocation of genetic resources and the reduction of losses associated with pre-weaning mortality and low-birth-weight litters (Zotti et al., 2017).

A combined assessment of genetic and non-genetic influences on farrowing and lactation performance is therefore essential for improving reproductive management strategies in commercial herds. The objective of the present study was to quantify these effects on key farrowing and lactation traits in multiparous sows under intensive production and identify genetic lines that sustain high performance under variable conditions. The hypothesis of the assessment was that findings will confirm the multifactorial nature of sow productivity in commercial conditions, suggesting the most important factors to consider for management.

In this study, FY had a significant influence on all reproductive and performance traits, corroborating earlier reports (Niyazov et al., 2020) that annual variation in sow productivity reflects changes in farm management, seasonal environmental conditions (photoperiod, temperature, humidity), and staff turnover. Between 2020 and 2023, TPBs peaked at 12.14 piglets per litter, surpassing the 11.8 reported by Lavery et al. (2019), under intensive management with dry and wet feeding during gestation. SP values were the lowest in the early years (0.25 piglets) but increased after 2019 (0.82 piglets), likely due to increased workload and herd size; these stillbirth rates remain lower than the 2.0 and 1.11 reported by Tani et al. (2016) for Landrace × Large White sows (one to six parities) and by Rangstrup-Christensen et al. (2017) for Landrace × Yorkshire sows evaluated year round (∼ 6000 females), respectively.

TLBW rose steadily from ∼ 14 kg in 2018–2021 to >17 kg in 2022–2023, reflecting improvements in gestation feeding and sow comfort. Although Lavery et al. (2019) reported 17.7 kg in Ireland (2005–2015) under intensive systems with multiple feeding strategies and Yang et al. (2019) recorded 14.6 kg in intensively housed Yorkshire × Landrace sows (one to nine parities), our data show a progressive increase in AWPB to 1.58 kg by 2022, exceeding the 1.50 kg reported by Lavery et al. (2019) and 1.37 kg by Adi et al. (2024). NPDLs fell below one piglet in 2021–2022 but reached 1.5 piglets in 2019, consistent with Torres Novoa and Hurtado Nery (2007). LWW21 consistently exceeded 60 kg in 2018–2021, aligning with Klimas et al. (2020) (∼ 61 kg for pure large White and Landrace sows at 21 d lactation) and outperforming the results of García-Munguía et al. (2014), who recorded 40.3 kg at 16 d in a technologically advanced system with early litter homogenization and creep feeding from day five. These gains likely reflect enhanced feeding and management protocols for both sows and piglets.

PN significantly affected most traits, in line with Lee et al. (2015), who noted that uterine capacity and physiological maturity peak in mid-parities. In our herd, parities three and four yielded the highest TPBs (11.86 and 12.01 piglets, respectively), exceeding the TPB values of Hernández et al. (2002) but falling below those of Klimas et al. (2020), who reported 12.1 piglets at parity four. First-parity sows had only 11.07 PBAs, lower than the 14.9 reported by Yang et al. (2019), under temperate conditions – likely due to our policy of culling after four parities. Litter birth weight and AWPB peaked in parities two and three, consistent with Petrocelli et al. (2021) and Tummaruk et al. (2023), who observed >20 kg in hyperprolific sows at these parities due to improved embryo implantation and placental development. LWW21 was also the highest in parities two and three (64.7–62.6 kg), matching that of Klimas et al. (2020) (61.8 kg) and exceeding that of Yang et al. (2019) (58.4 kg), reflecting increased lactation capacity with age and experience. In gilts, mammary development and milk yield are still immature.

AWPW averaged ∼ 6 kg in first parities, declining by ∼ 0.5 kg by parity seven, consistent with the results of Zotti et al. (2017) and Klimas et al. (2020) for 22 d lactations, though longer lactations (>28 d) can yield >7.5 kg per piglet (Lavery et al., 2019). NPWs peaked in parity two (10.62 piglets) (Nowak et al., 2020), underscoring the importance of parity-based management. Housing and supervision remain critical for piglet survival: farrowing crates reduce crushing risk (Koketsu and Iida, 2017), while free-range systems promote natural behaviors but can increase neonatal losses.

IS significantly influenced SPs, with the lowest values in spring (0.47 piglets) and the highest in winter (0.73 piglets), similar to the results of Tani et al. (2016), who associated cold stress with delayed farrowing and increased stillbirths. Spring–autumn farrowing produced heavier piglets at birth and weaning, likely due to milder conditions; however Kramarenko et al. (2024) and Suescún-Ospina and Ocampo-Duran (2015) reported that high spring–summer temperatures can reduce fetal growth by impairing sow feed intake and nutrient transfer to fetuses.

Cross-fostering (CF) emerged as a key management tool. Homogenizing litters within 48 h saved surplus piglets (>15 piglets per litter) and low-weight piglets, especially when matched to good milk-producing sows with small litters. In donor sows, CF reduced mortality and improved survival of low-birth-weight piglets, in line with García-Munguía et al. (2014). Recipient sows gained in LWW21 and NPWs, but the trade-off between litter size and individual piglet weight was evident.

GG significantly affected TPBs, PBAs, and AWPB. The L5 line averaged 12.07 total piglets born per litter – exceeding pure Yorkshire (10.1 piglets; Ogawa et al., 2019) and comparable to Large White crosses (12.5 piglets; Hagan and Etim, 2019). Although Duroc × Large White crosses can reach 14.2 piglets under climate-controlled conditions (Chakurkar et al., 2021), L5 sows here were naturally mated and housed in individual pens. L1 sows achieved the highest AWPB (1.67 kg), benefiting from higher daily feed allocation (4 kg d⁻¹) and improved late-gestation housing conditions (Hoving et al., 2010; Ogawa et al., 2019).

Heritability estimates for farrowing traits were low (h2=0.00–0.07), indicating strong environmental influences, consistent with Freyer (2018) (h2=0.07–0.11). Repeatability for weight traits (0.19–0.34) was higher, matching Chansomboon et al. (2010) and Lee et al. (2015) and supporting the need for multiple records per sow to improve genetic evaluation. The heritability of TPBs (0.06) was lower than the value of 0.14 reported by Ehlers et al. (2005), likely due to a smaller dataset size and narrower genetic base. Notably, preweaning mortality exhibited repeatability (0.09), driven almost entirely by a permanent environmental maternal effect (pe2 = 0.90 ± 0.035). This suggests that a sow's behavior (e.g., aggression, crushing) is a consistent, major determinant of piglet survival across parities (Nguyen et al., 2021). Complementarily, as an opportunity for further management, a more complete data recording for better data number and genealogical structure analysis for genetic parameter estimation might improve future assessments focused on administration of genetic selection.

Overall, these findings highlight the multifactorial nature of sow productivity and demonstrate that optimizing reproductive outcomes requires coordinated management of environmental conditions, parity structure, genetic selection, and targeted interventions such as cross-fostering. The significant influence of year and season highlights the critical need for environmental control and consistent protocols to mitigate stressors like extreme temperature. Furthermore, the low heritability but notable repeatability of traits like preweaning mortality emphasizes that management practices, such as optimized feeding, parity-targeted care, and strategic cross-fostering, are more impactful for immediate improvement than genetic selection alone. Ultimately, sustained gains in litter size, piglet weight, and survival require an integrated, data-driven approach that simultaneously addresses housing, nutrition, staff training, and genetic potential.

Farrowing year, parity number, and genetic group consistently and significantly influenced sow prolificacy and piglet weights at birth and weaning. Insemination season mainly affected stillbirth rates, whereas weaning period had a marked impact on average piglet weaning weight. Sow body weight at farrowing and gestation length also played important roles, emphasizing the need for precise body-condition management and optimized breeding schedules to enhance productive efficiency. Litter homogenization within the first 48 h after farrowing significantly improved both sow and litter performance, reinforcing its value as a routine management practice to extend sow productive lifespan and increase profitability.

Heritability estimates were low for most traits, except for moderate values for total litter weaning weight and mean piglet weaning weight, confirming the predominance of environmental and management influences. Consequently, the integration of targeted genetic-selection programs, prioritizing lines with higher reproductive potential, with optimized nutritional, environmental, and health management protocols is essential for maximizing reproductive efficiency and economic returns in commercial swine production systems.