The use of nitrogen isotopic fractionation as a biomarker for feed conversion efficiency in pigs using blood and hair samples

This study aimed to 1) Establish relationships between feed conversion efficiency (FCE; live weight gain/intake) and several biomarkers in pigs using blood and hair samples, and 2) Investigate the relative FCE performance of pigs from maternal vs. terminal genetic lines fed high vs. low energy diets. 80 male pigs (Large White x Landrace) were fed for 56 days. The terminal genetic line and pigs fed the high energy diet had 5% and 15% higher FCE than the maternal genetic line and pigs fed the low energy diet, respectively. Blood nitrogen isotopic fractionation (Δ¹⁵N; animal δ¹⁵N–feed δ¹⁵N) explained 34% more variation of FCE, compared with the blood insulin‑like growth factor‑1 (IGF‑1). The turnover rate of δ¹⁵N in plasma was faster than δ¹⁵N in blood, suggesting that blood and plasma δ¹⁵N can predict long‑term versus short‑term FCE changes. Pigs fed the high energy diets showed 13% higher live weight gain, 16% greater high standard carcass weight, and 38% higher carcass backfat than those on low‑energy diets. In conclusion, Δ¹⁵N is a more effective FCE biomarker for pigs compared to IGF‑1. Hair samples were less predictive of FCE than blood‑derived biomarkers, suggesting further refinement in the methodology of harvesting hair samples.