Dietary phenylalanine modulates thyroxine and growth performance in weaned piglets

This experiment evaluates the effect of L-phenylalanine (Phe) on growth performance, thyroxine (T4), dopamine, fecal score, and the correlations among these variables in weaning piglets. A total of 120 piglets (21 ± 1 day old; 6.16 ± 0.23 kg) were randomly allotted to three dietary treatments for 28 days, divided into two phases (phase 1, d 0-14; phase 2, d 15-28). Each treatment included eight replicates of five piglets. The dietary treatments comprised corn–soybean meal basal diets (CN); CN + 0.15% Phe (CP15); CN + 0.3% Phe (CP30). Overall, Phe supplementation had no effect on BW, average daily feed intake, fecal score, dopamine, or gain-to-feed ratio. During phase 1, however, Phe tended to increase (p=0.066) average daily gain (ADG) and serum T4 concentration compared with CN. The coefficient of variation remained unchanged during phase 1 but tended to be higher (p=0.099) in CP15 and CP30 during phase 2. Serum T4 was positively correlated (p<0.05) with BW, ADG, and gain-to-feed ratio. These findings suggest that dietary Phe may improve early post-weaning growth by enhancing T4 levels and supporting metabolic processes in weaned piglets.