4.1. Treatment and Litter Performance Traits
Piglet performance traits are intricately linked to the animals’ performance and physiology throughout the lactation period. Therefore, parameters such as PS, PO, and ADG are commonly assessed to characterize the efficiency of the production system. In the present study, the overall data revealed an average PWM of 17.8%. This PWM value falls below the 25% figure reported by Marchant et al. (2001) [
3], in a study on PWM attributed to crushing in sows housed in free pens during the initial week of lactation. Conversely, it exceeds the mean PWM reported by Heidinger et al. (2022) [
19], at 13.7%, who examined various periods of sow confinement in farrowing pens.
The expectation was that adjustments to the farrowing pen layout, relocating sows away from the heat source, and providing an alternative free resting area for piglets could enhance their performance. Thermal distribution within the farrowing pen (
Figure 4) illustrates that, in the standard treatment, the sow area experiences the most impact from the heat lamp, elevating the temperature to levels exceeding 32.0 °C, beyond the optimal thermal comfort range for sows (12.0 to 22.0 °C) [
23]. In this study, when analyzing overall data, no significant differences were observed in PO, and ADG between the treatments. The only piglet performance trait exhibiting a statistical difference was PS, where the offset treatment displayed a lower PS compared to the standard treatment. This difference may be attributed to the altered layout promoting a more comfortable microclimate for the sows, potentially influencing the farrowing process.
Wegner et al. (2016) [
24], conducted a study on the influence of temperature and the Temperature and Humidity Index on the reproductive performance of sows during the Summer months. Their findings revealed that as climatic variables increased, there was a corresponding decrease in the number of piglets born alive and an increase in the number of stillborns. Notably, these observations were made in an experiment conducted in a moderate climate, with the authors recording an average temperature consistently below or equal to 16 °C throughout all three evaluated summers. In the current study, the average temperature across all seasons ranged from 23.2 °C (Winter) to 24.6 °C (Summer) (
Table 2). However, it is crucial to highlight that the physiological or behavioral parameters of the sows, which could validate this observed trend, were not investigated in this study. Future research focusing on these aspects among various proposed alternative pens may provide insights into the identified effects. Despite the difference in layouts, examined in this study maintained an equal yet expanded size compared to a traditional farrowing pen. Additionally, exploring these same treatments in a traditional, smaller-sized farrowing pen would be valuable to assess whether relocating the sow from the heating source has an impact on production traits.
In the evaluation of sows with high mortality (2 piglets), the results showed that the offset treatment had lower PO than the standard. This observation may be attributed to the fact that the selected sows in this category had notably larger litters, averaging 16.2 piglets per sow, in contrast to the general data with an average of 14.0 piglets per sow. The presence of a larger litter tends to intensify competition for nursing space and occupies more resting areas, thereby posing an increased risk of crushing for the animals involved. This indicates that as litters become larger, alternative farrowing pen designs such as the offset design become increasingly more important.
Leonard et al. (2021) [
20], investigated the impact of the farrowing pen size and the number of heat lamps on piglet performance. Their investigation compared traditional farrowing pens, pens with expanded piglet rest areas, and pens with expanded areas for sows and piglets. The authors reported no differences between treatments in percent of mortality, percent of overlays, number of piglets born alive, or the total number of piglets weaned per sow. Similar to the current study, the authors identified statistical differences in the percent of stillborns among different pen layouts. The authors highlighted the importance not only of the amount of space but also of its usability. Nevertheless, in the present study, when considering this space quality, no significant differences were found in the litter performance traits across treatments using general data. Conversely, when focusing on high-mortality sows (>2 piglets), the offset treatment had a lower PO compared to the standard pen layout. This suggests that, particularly for sows with larger litters, a simple modification of the farrowing pen layout and the provision of a wider piglet resting area on one side of the sow could contribute to mitigating mortalities caused by overlays.
Moustsen et al. (2013) [
21], evaluated four distinct periods of sow confinement: sows released throughout the entire lactation period, sows confined in crates from day 0 to 4 postpartum, sows confined from day 0 to 7 postpartum, and sows crated from introduction to the pen until day 7. The findings indicated a lower piglet mortality rate when sows were confined, as opposed to sows without any movement restraint. However, there were no significant differences in piglet mortality observed among the other confinement periods that were evaluated.
In addition to the aforementioned investigations, other studies have reported a reduction in piglet mortality with the confinement of sows [
4,
25]. Despite the increasing consideration for adopting systems without the confinement of sows, it enables the assessment of diverse physiological and environmental aspects in productive parameters. Individual systems of this nature incorporate standardized protocols conducive to individual animal monitoring. While a consensus on the optimal type or management strategy has yet to emerge, research involving sows in crates is pivotal for acquiring insights to enhance system management. Positive effects on piglet performance have been observed when sows are housed in farrowing crates compared to free farrowing. Furthermore, studies highlight that most mortalities occur within the initial week after farrowing. Combining this information with the current study’s findings suggests that the adoption of larger farrowing pens, with the crate further away from the heating source and, potentially, for a shorter duration, could present a more sustainable alternative compared to conventional farrowing pen systems. As previously mentioned, additional studies exploring the interplay between animal behavior and productive parameters can contribute to a more comprehensive investigation of the proposed systems. Moreover, investigations considering environmental perspectives and seasonal variations can offer pertinent insights into both systems and animal welfare.
4.2. Season and Parity Affecting Litter Performance Traits
Sow parity and the season of the year were also investigated as factors influencing piglet performance traits, as existing studies suggest a direct correlation between high parity and elevated temperatures with diminished piglet performance [
10,
11,
24,
26]. In the present study, parity did not exhibit a significant impact on PS or PO, but it did influence ADG, with first-parity sows having piglets with lower ADG compared to sows with higher parities (
Table 4). Leonard et al. (2021) [
20], explored piglet performance across different farrowing pen treatments and noted that parity not only affected ADG but also influenced the percent of mortality and the percent of overlays. The authors reported that fourth-parity sows had a higher percent of overlays than first-parity and a higher percent of mortality than first- and second-parities. Additionally, concerning ADG, piglets from first-parity sows displayed lower ADG than those from higher-parity sows.
Li et al. (2023) [
27], studied the effect of maternal behaviors (postural, nursing, defense, and sow-piglet communication) of primiparous and multiparous sows on litter weight and number of piglets crushed. The study revealed that multiparous sows exhibited good maternal behavior in terms of time spent in a specific posture, feeding arrangement, care for lying down, and response to the “piglets’ request for help”. No discernible effects were noted on litter weight and the number of crushed piglets, as these traits displayed no significant variations between primiparous and multiparous sows. Although the aforementioned study did not show any differences in production parameters, the better maternal ability of multiparous sows may explain the difference observed in ADG between first-parity and higher-parity sows in this study. Additionally, considering their youth and ongoing growth and development, primiparous sows may allocate less time for nursing or utilize part of the energy that could be directed toward milk production for their own development.
In this study, even within a controlled environment, the influence of the season on the PO and ADG was observed (
Table 4). Autumn and Summer presented higher PO values than Spring and Winter, while Summer demonstrated lower ADG compared to the other seasons. During the Summer, one explanation for these differences could be the elevated RH resulting from the activation of evaporative cooling pads to mitigate the high air temperature (
Table 2). Increased RH limits the sow’s capacity to dissipate heat through evaporation in environments with elevated temperatures [
28]. Consequently, an increase in RH may induce thermal discomfort in sows and alter their behavior, thereby potentially influencing piglet performance. Milk production and feed intake exhibit a close relationship and are susceptible to the effects of hyperthermia given their direct connection to the nutritional well-being of sows [
13]. In thermal discomfort, sows tend to reduce food and water intake. A meta-analysis of literature data conducted by Dourmad et al. (2022) [
29] revealed that lactating sows experienced a 36% reduction in feed intake and a 20% decrease in milk production when temperatures ranged between 22 °C and 32 °C. Additionally, hyperthermia can impact the frequency and duration of postural changes in sows [
11], a factor directly linked to their availability for nursing and the PO.
An additional justification for elevated PO values observed during Autumn lies in the manual management of the air inlets, a factor directly influencing the heat flow in the facility. In the Midwest of the USA, in the Autumn, the temperature fluctuations require continuous adjustments to the inlets. For example, during the study, on 7 September, the highest temperature was 35.5 °C (ranging from 16.2 °C to 22 °C indoors) and in two days (9 September), the highest temperature was only 7.8 °C (ranging from 11.5 °C to 20.3 °C indoors). Thus, making it difficult to manually adjust the ventilation from summertime tunnel ventilation to wintertime ceiling-type ventilation. Therefore, resulting in improper air inlet regulation, and plausible sow and piglets’ thermal stress. In colder periods, the piglets tried to warm themselves closer to the sows. The options available to piglets include artificial heating sources or seeking warmth in the vicinity of the sow [
30]. In addition, it is part of their natural behavior to stay close to the sow in the first few days after birth [
31,
32]. Inadequate management of these systems can adversely affect piglet performance, prompting them to seek warmth near the sow and increasing the risk of crushing. On the other hand, in warmer periods, supplemental heat lamps are switched off and, in this situation, there is no difference between lying next to the sow and under the heating lamp. Therefore, the piglets’ behavior may have changed, causing them to lie down closer to the sow, increasing the risk of overlays.
Studying the behavior of sows, piglet location, and assessing stress are important and complementary information that should be investigated in future studies.