Improving dietary amino acid (AA) and energy efficiency in lactating sows is a potential nutritional approach to mitigate impacts of swine production on the environment. In addition, greater metabolic rate during lactation renders sows prone to heat stress (HS), therefore strategies to lessen metabolic heat production will improve sow welfare in particular given the foreseeable increase in global warming. The main hypothesis of this dissertation was that feeding a reduced protein diet with near ideal AA profile (NIAA) and a leucine:lysine of 1.14 improves the dietary essential AA (EAA) and energy utilization efficiency for lactation, and reduces the metabolic heat associated with lactation, compared to feeding diets containing leucine:lysine of 1.63. To test the hypothesis, three diets were formulated iso-calorically (2,580 kcal/kg net energy), including 1) control diet with a 1.63 leucine:lysine (CON; 18.75% CP), 2) reduced CP diet with 1.14 leucine:lysine referred to as optimal (OPT; 13.75% CP) and formulated to contain a NIAA by supplementation with the limiting AA in their crystalline form to meet their minimum requirements (i.e., L-Lysine (Lys), L-Valine (Val), L-Threonine (Thr), L-Phenylalanine (Phe), DL-Methionine (Met), L-Isoleucine (Ile), L-Histidine (His), and L-Tryptophan (Trp); and 3) OPT diet with L-Leucine (Leu) supplementation to achieve CON Leu:Lys of 1.63 (OPTLEU; 14.25% CP). The overall objective was to determine the efficiency of individual EAA and energy for lactation in sows fed CON, OPT and OPTLEU, and quantify the metabolic heat production of lactating sows fed CON and OPT. Three studies were conducted to address the following aims: 1) to estimate maximal biological efficiency value (MBEV) of EAA in lactating sows fed CON, OPT and OPTLEU diets; 2) to estimate dietary energetic efficiency, energy partitioning and heat production in lactating sows fed CON, OPT and OPTLEU diets; and 3) to measure heat production in lactating sows fed CON and OPT diets and exposed to thermal neutral and HS environments. The first study showed that feeding OPT diet improved utilization efficiency of nitrogen (N) (79.1%), arginine (61.1%), His (78.3%), Ile (65.4%), Leu (75.1%), Met + Cys (78.2%), Phe (53.4%), Phe + Tyr (69.5%) and Trp (70.1%) and maximized the efficiency of Lys (63.2%), Met (67.9%), Thr (71.0%) and Val (57.0%) for milk production over a 21-day lactation period. Leucine reduced Met utilization but did not affect that of N and other EAA. The second experiment demonstrated that feeding OPT led to greater energy utilization for lactation due to less urinary energy and metabolic heat loss, and triggered dietary energy deposition into milk at the expense of maternal lipid mobilization. A Leu:Lys of 1.63 compared to 1.14 reduced dietary energy utilization for lactation by directing dietary energy away from the mammary gland and towards maternal pool, in part explaining the efficacy of a NIAA diet over CON. Sows fed OPT diet produced less metabolic heat and had lower body temperature when exposed to HS conditions compared to CON fed sows. In conclusion, feeding a diet with NIAA profile containing Leu:Lys of 1.14 improves dietary EAA and energy utilization efficiency for lactation, and reduces the metabolic heat associated with lactation compared to feeding a diet with Leu:Lys of 1.63 and meeting SID Lys requirement with feed ingredients as the sole source of Lys. This improvement is in part due to a lower dietary Leu:Lys. Feeding lactating sows with reduced CP diets with crystalline AA supplementation to attain NIAA profile is a feasible strategy to improve efficiency of N and energy utilization, and to mitigate the impacts of HS on lactating sows and of swine production on the environment.
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