The effects of cobalt and iodine supplementation of the pregnant ewe diet on immunoglobulin G, vitamin E, T3 and T4 levels in the progeny

Abstract

Sixty twin-bearing ewes were allocated to one of four dietary treatments investigating the effects of supplementary iodine or cobalt during late pregnancy on lamb serum immunoglobulin G (IgG), triiodothyronine (T 3 ), thyroxine (T 4 ) and vitamin E concentrations, and lamb IgG absorption efficiency. Ewes were offered grass silage ad libitum supplemented with 800 g per ewe per day of a 190 g/kg crude protein (CP) concentrate from day 126 of gestation until parturition plus one of the following supplements (n 5 15 per treatment); no supplement (C); 26.6 mg iodine per day for final 3 weeks pre partum (I-3); 26.6 mg iodine/day for final week pre partum (I-1); 20 mg cobalt/day for final 3 weeks pre partum (Co-3). Lambs were blood sampled at 24 and 72 h post partum for serum IgG and vitamin E concentrations. Ten lambs from C and I-3 were blood sampled at 1 h post partum for serum IgG, vitamin E, T 3 and T 4 concentrations. There were no differences in serum IgG, vitamin E or T 4 values (P . 0.05) at 1 h post partum between lambs born to the C and I-3 ewes. T 3 levels were lower in I-3 compared with C progeny (P , 0.05). Supplemental iodine reduced colostral IgG absorption efficiency (P , 0.001) and lamb serum IgG concentrations at 24 and 72 h post partum (P , 0.001). Serum vitamin E concentration in I-3 and I-1 lambs was lower than in Co-3 lambs at 24 h post partum, while at 72 h post partum I-3, I-1 and Co-3 lambs had significantly lower concentrations than C lambs (P , 0.001). Supplementing the ewe's diet with 26.6 mg/day of iodine for the final week of pregnancy reduced lamb serum IgG concentration at 24 and 72 h post partum. The lower total and free T 3 values in the progeny of I-3-treated ewes suggest interference in the synthesis and metabolism of thyroid hormones when ewes receive excessive dietary iodine for 3 weeks immediately pre partum. Based on these findings, the indications are that the toxicity level for iodine in the diet of the pregnant ewe should be lowered to 20 mg per ewe per day, equivalent to 40% of its current level. The finding that high-level cobalt supplementation during the final 3 weeks of pregnancy will have a negative effect on serum vitamin E concentration at 72 h post partum is a new and significant finding and previously has not been reported in the literature.

Iodine supplementation of the pregnant dam alters intestinal gene expression and immunoglobulin uptake in the newborn lamb

“…Ewes received either the basal diet with no supplementary iodine (Control) or the basal diet plus 26.6 mg/day of iodine supplied as either CaIO 3 or KI (Table 1). This level of supplementary iodine equates to the level offered to ewes in a previously reported study (Boland et al, 2008) and is reflective of the level of intake achieved when ewes are offered free access mineral supplements indoors . In accordance with a previous study, carried out at this institute, the dietary intake of iodine on the control diet can be estimated at~0.57 mg iodine per ewe per day (Boland et al, 2008).…”

“…In specific livestock species, low immunoglobulin levels in the newborn have been associated with impaired health in later life, thus emphasising the importance of colostrum for the growth and well-being of the newborn (Speikermann et al, 2002). Previous studies have, however, recently demonstrated a negative relationship between iodine supplementation of the pregnant ewe in late gestation and the serum IgG concentration of her progeny at 24 h postpartum (Boland et al, 2006 and2008;Rose et al, 2007).…”

“…The iodine supplement was manually mixed into the concentrate on the day before feeding. Before mixing, the daily iodine allowance was first added to 20 g (fresh weight) of the concentrate which was used as a carrier for (Boland et al, 2008).…”

“…These results were then multiplied by 0.91 to provide the IgG only content of the serum (Larson et al, 1974;Boland et al, 2005c). Plasma free T 3 and total T 4 concentrations were determined by solid phase timeresolved fluoroimmunoassay using AutoDelfia kits (Wallac Oy, Turku, Finland), as described previously (Boland et al, 2008).…”

“…In ruminants, the neonate is born hypoimmunocompetent (O'Dohert and Crosby, 1997;Boland et al, 2008) due to the presence of a placental barrier which prevents the in utero transfer of immunoglobulins from mother to offspring (Brambell, 1970). Neonatal lambs are therefore dependent upon passively acquiring maternal immunoglobulins from colostrum to confer disease resistance in early life.…”