THE OMEGA-6: OMEGA-3 FATTY ACID RATIO IN SWINE NUTRITION: LONG-TERM EFFECTS ON PERFORMANCE, MILK FATTY ACID PROFILES, OXIDATIVE STATUS, AND PROTEOMES

The ω3 polyunsaturated fatty acids (PUFAs) are characterized as micronutrients and are usually deficient in animal diets. Frequently excessive animal consumption of ω6 PUFAs from corn and other grains compared to ω3 PUFAs (or high dietary ω6:ω3 ratio) leads to various performance and health problems in animals and can also affect human health – the primary consumers of animal products. In recent years, lowering the ratio between ω6 and ω3 PUFAs in animal diets has gained increasing attention as a nutritional intervention to enhance performance and health. This thesis aimed to improve growth performance and immune system in weaned pigs through early nutritional programs (maternal low ratio of ω6:ω3 (LR) diet during gestation and lactation) combined with later-life nutritional interventions (post-weaned seaweed (SW) diet). Effects of LR in sow diet and SW supplementation in piglet diet on performance, colostrum and milk fatty acids (FA) profiles, and oxidative status, were studied in vivo (Chapter 2). The performance and zootechnical data showed the effects of maternal LR diet during gestation and lactation alone or in combination with the SW supplementation in post-weaned piglets on piglet growth and antioxidant status. Also, the influence of SW supplementation alone on piglet growth was revealed. To discover the fundamental molecular processes that activate biological systems such as reproduction and oxidative status, influenced by gestational and lactational LR diet, sow plasma proteomic pattern changes and related biological pathways associated with LR diet were characterized (Chapter 3). Moreover, the alterations in the serum and ileal proteomes and related pathways induced by the interplay between maternal LR diet and offspring SW diet were studied (Chapters 4 and 5). In the final chapter, the findings of the thesis were summarized, and implications of the results for future feeding regime practices were addressed (Chapter 6). Zootechnical performance: Maternal LR diet during gestation and lactation combined with the SW supplementation in post-weaned piglets did not enhance piglets’ growth or antioxidant status. Nevertheless, the maternal LR diet alone increased total ω3 PUFAs (mainly α-linolenic acid - ALA) in the colostrum and milk, improving the weaning survival rate and suckling piglets’ weight gain. Additionally, SW supplementation enhanced piglets’ growth from sows fed control ratio of ω6:ω3 (CR) diet. Sow plasma proteomics: LR diet altered the plasma levels of several acute phase proteins (APPs) such as HP, SERPINA1, and APCS that might be involved in protective mechanisms against accelerated stresses and, in particular, oxidative stress at later stages of gestation and lactation. Furthermore, significant shifts were found over the late gestation-late lactation period affecting the plasma lipoproteins and the APPs. The end of pregnancy is associated with an acute phase reaction (APR) demonstrated by the increased abundance of positive APPs (i.e., HP and ITIH4 (pig-MAP)) and a decrease in negative APPs, i.e., APOA1, while by the end of lactation, this APR has dissipated and APOA1, APOA2, and APOC3 were all increased. Piglet serum proteomics: Maternal LR diet enhanced piglet host protective response via regulating the expression of C3, SAA, SERPINA3, SERPINC1, and TF and their association with anti-inflammatory activities and innate immunity. Post-weaned piglets’ SW diet enriched C5a and KNG1, stimulating coagulation cascade regulation and the connection between innate and adaptive immunity to enhance the host defence during inflammation conditions. The potential regulator proteins associated with the early development of piglet post-weaning were also underlined, including serum lipoproteins (APOA1, APOB, APOE); pro-coagulation proteins (F2, HRG, ORM1); coagulation regulator (PLG); and APPs (HP, ITIH4, TF, SAA, SERPINA1). These proteins participate in platelet metabolism, haemostasis, and cross-talk between coagulation pathways and inflammation, particularly in the innate immune system. Piglet ileum proteomics: Maternal LR diet positively regulated RPSA regarding protein synthesis process but may induce uncontrolled proliferation and overexpression of cell cycle regulators in the offspring via affecting CCT2. SW supplementation reduced the inflammation severity in post-weaning piglets by regulating ATP5A1 and ATP5B, promoting ileal epithelial growth in piglets fed seaweed from the mother provided a control ratio of ω6:ω3 (CRSW piglets) (HBA, HBB, RPL10A, and RPL24). However, it decreased the fat absorptive capacity in piglets fed seaweed from the mother received a low ratio of ω6:ω3 (LRSW piglets) (FABP6). Overall, the results suggest maternal and offspring nutritional interventions play a vital role in sow reproduction and piglet development. Moreover, potential protein regulators of pig performance and health over sensitive periods were revealed. These can be used as the basis of future studies to understand how nutrition programs can be enhanced to improve the quality and safety of animal products for human consumption.