Greenhouse gas emissions, net energy, and nitrogen balance are not impacted by inclusion of hybrid rye in diets for growing pigs, but ileal digestibility of amino acids and acid-hydrolyzed ether extract is reduced if hybrid rye replaces corn

Two experiments were conducted to test the hypothesis that greenhouse gas emissions, nitrogen balance, net energy (NE), and ileal digestibility of amino acids (AA) and acid-hydrolyzed ether extract (AEE) are not affected by inclusion of hybrid rye in diets fed to growing pigs. Three diets were prepared and fed to pigs in both Exp. 1 and 2. The control diet contained corn and soybean meal as energy sources and 2 additional diets were formulated by replacing half or all of the corn in the control diet with hybrid rye. In Exp. 1, 24 pigs (initial body weight: 52.38 ± 2.52 kg) were assigned to 6 calorimeter chambers with 4 pigs per chamber. Chambers were allotted to a replicated 3 × 3 Latin square design with the 3 diets and three 15-day periods for 6 replicates per diet. After a 7-day adaptation period, oxygen consumption and carbon dioxide and methane production were measured for 6 days to determine total heat production, and feces and urine were also collected. In Exp. 2, twelve ileal cannulated pigs (average body weight = 47.78 ± 4.40 kg) were allotted to 2-period switchback design with 3 diets and 2 periods for a total of 8 replicates per diet. Results from Exp. 1 indicated that consumption of oxygen and production of carbon dioxide and methane, NE, and nitrogen balance were not affected by dietary treatment. However, the respiratory quotient of pigs in the fed state was reduced (linear; P = 0.047) by increasing hybrid rye in diets. Results from Exp. 2 indicated that the ileal digestibility of AEE and indispensable AA was reduced (P < 0.05) by increasing hybrid rye in diets. In conclusion, replacing corn with hybrid rye in the diets for growing pigs did not impact greenhouse gas emissions, NE, or nitrogen balance, but the respiratory quotient and the ileal digestibility of AEE and AA were reduced. Therefore, hybrid rye can be used as an alternative to corn without negatively impacting the environmental footprint of pig production systems. • Hybrid rye did not increase CO₂ or CH₄ emissions in growing pig diets. • Respiratory quotient decreased with more hybrid rye, indicating metabolic shift. • Digestibility of amino acids and lipids was reduced as hybrid rye replaced corn. • Net energy and nitrogen retention were not impacted by hybrid rye inclusion.