The Effects of Dietary Iodine Supplementation on Nursery Pig Growth Performance

Abstract Iodine is an essential trace mineral for thyroid hormone synthesis. Thyroid hormones directly impact key metabolic processes such as cell energy production and consumption, nutrient metabolism, mitochondrial biogenesis, and heat production. Historically, dietary iodine recommendations of 0.14 mg/kg (NRC 2012) for pigs have been based on early research that identified the level needed to prevent deficiency symptoms. Moreover, there has been limited investigation to determine optimal iodine inclusion for swine until recent years. Newer studies have shown that nursery pigs may benefit from iodine supplementation at levels significantly higher than the previously established guidelines. Therefore, an experiment was conducted to evaluate increasing iodine levels from 1.5 to 50 mg/kg to determine the optimal level for growth performance of nursery pigs. A total of 2,426 pigs (PIC 337 × L42, initial BW = 6.12 kg) were used in a 40-d trial. Pens of 34 or 35 mixed-sex pigs were blocked by initial BW and randomly allotted to 1 of 5 dietary treatments with 14 replicates per treatment. Treatments consisted of increasing iodine inclusion rates of 1.5, 8.25, 15, 25 and 50 mg/kg. Iodine was supplemented as ethylenediamine dihydroiodide (EDDI). Experimental diets were fed throughout the nursery period in two phases. From d 0 to 18, nursery diets were fed in pellet form and based on corn, soybean meal, and oats based with 1.38% SID Lys and pharmacological levels of Zn and Cu (3,000 and 200 ppm, respectively). Data was analyzed using the PROC GLIMMIX of SAS (v 9.4) using pen as the experimental unit. From d 18 to 40 diets were fed in mashed form and based on corn, soybean meal, and 10% DDGS diet with 1.30% SID Lys. Pigs and feeders were weighed on d 0, 18, and 40 to calculate ADG, ADFI, and G:F. From d 0 to 18, there was no evidence (P 0.10) for differences in ADG, ADFI or G:F as iodine levels increased from 1.5 to 50 mg/kg. However, from d 18 to 40, there was a linear improvement in ADG (P = 0.028) and G:F (P = 0.017) as the iodine levels increased. Overall (d 0 to 40), there was a tendency for a linear improvement in G:F (P = 0.07). No statistical differences were observed in removals or mortality. Our findings indicate that feeding weaned pigs a diet containing iodine levels up to 50 mg/kg improved gain and feed efficiency.