Effect of Increasing Dietary Iodine on Nursery Pig Growth Performance

Iodine is a trace mineral of particular interest due to its central role in the synthesis of thyroid hormones which regulate basal metabolic rate. Little research has been conducted to determine nursery pig’s iodine requirement for maximizing growth performance, but a recent study by Dove et al. (2024) suggested iodine supplementation at 100 times the NRC (2012) requirement estimate improved performance. To confirm this response, a total of 720 weanling pigs (initially BW 6.3 ± 0.09 kg) were used in a 46-d study to evaluate the effects of increasing dietary iodine on growth performance. Pens of pigs were randomly allotted to one of six dietary treatments in a generalized randomized block design with 5 pigs per pen and 24 pens per treatment. Pigs were blocked such that there were 8 replications each of light, medium, and heavy weight pens per treatment. Diets were corn-soybean meal based and consisted of a control diet containing 0.3 mg/kg of added iodine from Ca Iodate provided from the trace mineral premix. Calcium Iodate (63.5% iodine) was added to the control diet to achieve diets containing 6.2, 12.2, 18.1, 24 and 30 mg/kg of added iodine. Treatment diets were fed in three phases from d 0 to 10 (phase 1), d 10 to 24 (phase 2), and d 24 to 39 (phase 3). From d 39 to 46, a common diet was fed which contained 0.3 mg/kg iodine. During the experimental period (d 0 to 39), a cubic response (P < 0.05) was observed for ADG, ADFI, and BW where performance was improved as iodine increased from 0.3 to 12.2 mg/kg, then decreased at 24 mg/kg, followed by another increase at 30 mg/kg. Gain:feed ratio increased (linear, P = 0.021) as iodine increased. Overall (d 0 to 45) there was a cubic response (P < 0.05) for ADG and ADFI resulting in a tendency (P = 0.066) for a cubic final BW response where performance increased from 0.3 to 12.2 mg/kg, decreased at 24 mg/kg, and finally increased at 30 mg/kg. Gain:feed ratio increased (linear, P < 0.05) as dietary iodine increased. In summary, weaned pigs fed 12.2 mg/kg iodine in the diet had increased overall body weight, ADG, ADFI and G:F compared to the basal level of 0.3 mg/kg added iodine.