Production capacity in the swine industry has increased over the past 60 years through improved sow longevity, increased litter sizes, and increased offspring growth rate. However, these improvements to efficiency are associated with decreased birth weight and increased total mortality. Currently, increased litter size in commercial production is estimated to place 10 to 30% of all offspring at risk of intra-uterine growth restriction (IUGR) during gestation. Consequently, offspring that experience IUGR exhibit hindered growth, reduced survivability, and decreased carcass quality; leading to compromised system efficiency.

Growth restriction phenomena can be observed across species and is commonly due to reduced nutrient availability to the offspring during gestation. In pig production, dietary protein and energy requirements for the sow during gestation are based on dated work with less prolific sows. While total protein quantity during gestation has been observed to influence birth weight, appropriate balance of amino acids (AA) within the diet is known to impose a greater benefit to nutritional efficiency in the pig. Arginine (Arg) has been implicated as beneficial to litter size, placental and fetal muscle development, and birth weight. Due to these benefits, Arg is suggested to be a possible solution for gestating offspring at risk of IUGR. These benefits, however, remain unclear under commercial production conditions. Therefore, the objectives of this dissertation are to evaluate the effect of Arg supplementation during gestation on gilt reproductive performance and offspring performance in a commercial swine production system. Additionally, litter characteristics were analyzed to understand the role of litter size and birth weight on post-weaning pig performance within commercial data. Finally, two experiments were conducted to evaluate the effects of Arg supplementation during gestation on uterine and fetal tissues prior at d 44 of gestation and on piglet characteristics at birth.

The results obtained from investigating these objectives found that supplementation with 1% synthetic L-Arg offered limited benefits to reproductive performance, offspring growth, or fetal development under commercial conditions. Gestational supplementation of Arg in the current work reduced variation in birth weight across litters of varying sizes (P < 0.01), and tended to improve pre-wean offspring growth performance with gestational supplementation of Arg during late gestation (P = 0.06). However, because Arg supplementation did not affect birth weight (P > 0.10), lasting effects were not observed in offspring growth to 100 kg. Analysis of the impact of litter characteristics on post-weaning growth performance found that birth weight (P ≤ 0.05) was more influential than litter size (P > 0.10) on growth performance to 100 kg, independent of maternal gestation diet. Further, fetal, placental, and endometrial tissue development was not influenced by Arg supplementation during gestation (P > 0.10).

These data combined suggest that maternal supplementation of Arg during gestation does not provide a physiological benefit to offspring in commercial production. Influence of maternal supplementation of Arg during late gestation may be limited to mammary tissue and lactation, as benefits observed in pre-wean pig growth performance did not persist in post-weaning growth. Overall, this work suggests increased litter sizes and increased pre-wean growth do not necessarily impact performance to market. However, more research is needed to improve knowledge on the nutritional needs of the developing litter, to continue improving production efficiency of highly prolific sows of modern pig production.