Does iodine supplementation of the prepartum dairy cow diet affect serum immunoglobulin G concentration, iodine, and health status of the calf?

Absorption of adequate IgG from colostrum is critical to provide the newborn calf with adequate immunological protection and resistance to disease. Excessive iodine supplementation of the prepartum ewe reduces IgG absorption of her offspring; it is possible that excessive iodine supplementation of the prepartum dairy cow may similarly impair the ability of the calf to acquire immunological protection. The objectives of this study were to determine whether the iodine status, health status, and ability of calves to absorb IgG from colostrum were affected by prepartum iodine supplementation strategies of their dams. Dairy cows (n=127) received one of the following levels of iodine supplementation precalving: 15mg of iodine/kg of dietary dry matter (DM) (HI); no additional iodine supplementation (MI); 5mg/kg of dietary DM (SI); and 15mg of iodine/kg of DM for the first 3.5wk of the precalving period and no additional supplementation for the second 3.5wk (HMI). Calves were assigned to 1 of 6 experimental treatments, based on the prepartum iodine supplementation treatment of their dam and the precalving treatment group of the cows from which the colostrum fed was obtained: (1) HI_HI: born to HI dams, fed HI colostrum (i.e., colostrum produced by cows in the HI group); (2) MI_MI: born to MI dams, fed MI colostrum; (3) SI_SI: born to SI dams, fed SI colostrum; (4) HI_MI: born to HI dams, fed MI colostrum; (5) MI_HI: born to MI dams, fed HI colostrum; and (6) HMI_HMI: born to HMI dams, fed HMI colostrum. Concentration of calf serum IgG and plasma inorganic iodine (PII) was measured at 0 and 24h of age. Apparent efficiency of absorption for IgG was determined. Health scores were assigned to calves twice weekly and all episodes of disease were recorded. Cow experimental treatment group affected calf PII at 0h of age; the PII of calves born to HI dams (987.2µg/L) was greater than that of calves born to MI dams (510.1µg/L), SI (585.2µg/L), and HMI dams (692.9µg/L). Calf experimental treatment group affected calf PII at 24h of age; the PII of HI_HI (1,259.2µg/L) and HI_MI (1,177.8µg/L) calves was greater than MI_MI (240.7µg/L), SI_SI (302.2µg/L), HMI_HMI (320.7µg/L), and MI_HI (216.3µg/L) calves. No effect of experimental treatment was observed on the concentration of IgG measured in calf serum at 24h of age, or on apparent efficiency of absorption. Experimental treatment had no effect on the likelihood of a calf being assigned a worse nasal, eye and ear, cough, or fecal score within the study period, nor did it affect the probability of a calf receiving treatment for a disease a greater number of times. Prepartum iodine supplementation of cows at 15mg/kg of DM increased the iodine levels in their calves at birth and 24h of age, but did not affect their ability to absorb IgG from colostrum. Supplementation with iodine above the minimum requirements established by the National Research Council was unnecessary to ensure appropriate iodine levels in calves at birth.