273 Effect of dietary iodine supplementation on the growth performance and thyroid hormone concentrations of nursery pigs

Abstract

Abstract Iodine (I) is critical for growth, development, and thyroid hormone circulation. This study examined the impact of dietary iodine concentration on nursery pig growth performance and thyroid hormone concentrations. Weaned piglets (n =180, 21 ± 3 d of age) were blocked by body weight (BW; 5.4 ± 0.8 kg) and sex (2 barrows and 2 gilts/pen). Pens within a block (n = 9) were randomly assigned to dietary treatments (mg/kg I added): 0 (CON), 0.14 (NRC), 1.4 (NRC10), 14 (NRC100), or 140 (NRC1000). Diets were fed in three phases for 35 d (P1, d 0-10; P2, d 11-21; P3, d 22-35). Piglets were weighed and feed intake recorded on d 0, 7, 10, 14, 21, 28, and 35. Blood was collected on d 21 and 35 for analysis of circulating thyroid hormone concentrations. Data were analyzed as a randomized complete block design via the GLM procedure of SAS. Increasing dietary I concentration linearly increased (P < 0.03) piglet BW on d 10, 21, and 35. On d 35 BW were 19.2 kg CON, 19.9 kg NRC, 20.5 kg NRC10, 21.1 kg NRC100 and 20.2 kg NRC1000. Average daily gain was linearly increased by the addition of I to the diet during P1 (P < 0.02), P2 (P < 0.03) and for the entire 35 d feeding period (P < 0.01). From d 0 to 35, average daily gain (ADG) was (g/d) 384 CON, 405 NRC, 420 NRC10, 440 NRC100, and 407 NRC1000. Average daily feed intake was linearly increased dietary treatment during P1 (P < 0.01), P3 (P < 0.04) and from d 0 to 35 (P < 0.01). From d 0 to 35, average daily feed intake (ADFI) was (g/d) 731 CON, 779 NRC, 791 NRC10, 819 NRC100 and 782 NRC1000. No differences were observed for gain to feed ratio (G:F; P > 0.3) at any time during the study. On d 21, T4 concentrations linearly increased in response to dietary I (P < 0.02), On d 35, T4 and the T4:T3 ratio linearly increased (P < 0.01). On d 35 the T4 values were (nmol/L) 48.4 CON, 51.4 NRC, 58.3 NRC10, 59.3 NRC 100, 59.9 NRC 1000 and the T4:T3 ratio was 36.6 CON, 41.3 NRC, 40.0 NRC10, 45.2 NRC100, and 44.6 NRC1000. Based on the present findings, nursery pigs fed iodine levels above NRC recommendations have improved growth and feed intake and positive impacts on thyroid hormone concentrations. The data from this study indicated that dietary I concentrations 100 times the current NRC resulted in the best piglet performance.