Effects of dietary triiodothyronine or dopamine on small intestinal oxygen consumption in chicks.

This study aimed to investigate the effects of triiodothyronine (T₃)- or dopamine (Dp)-supplemented diets on oxygen consumption by Na⁺, K⁺-ATPase activity in broiler chicks. Five groups, each with twenty-four 6-day-old chicks, randomly received one of the five dietary treatments: (1) Basal diet (commercial broiler rations with 23.0% crude protein and 3,133 kcal metabolizable energy/kg) or CON, (2) basal diet plus 0.7 μmol Dp/kg diet or Dp0.7, (3) basal diet plus 2.4 μmol Dp/kg diet or Dp2.4, (4) basal diet plus 1.9 μmol T₃/kg diet or T1.9, and (5) basal diet plus 3.8 μmol T₃/kg diet or T3.8 from 6 to 14 days of age. There were four replicates per treatment and 120 birds in total. At 14 days of age, three chicks from each replicate of each treatment were pooled into a flock and fed commercial broiler diets until 7 weeks of age. Compared to CON group, birds fed with T3-supplemented diets had lower thyroid, abdominal fat pad, gizzard and pancreas weight, and heavier heart weight adjusted for fasted body weight. Chicks with T1.9 had lower ileal densities at 14 day old compared with those in Dp groups or CON. Chicks with T3.8 exhibited greater duodenal and jejunal O₂ consumptions as well as ouabain-sensitive O₂ consumptions of jejunum and small intestine (duodenum, jejunum, and ileum) by 46.5%, 58.3%, 40.6%, and 26.4% increases, than those in CON. Partial correlation analysis revealed that the weight and length of the small intestine were negatively correlated with body weight gain. Oxygen consumption in the various small intestinal segments was negatively correlated with their respective densities (mg/mm²). In conclusion, a greater oxygen requirement for maintaining ouabain-sensitive respiration (Na⁺-K⁺-ATPase) in the intestine limits energy availability to support gastrointestinal tract growth and, thereby, may result in lower body weight gain.