The effect of varying levels of mineral and iodine supplementation to ewes during late pregnancy on serum immunoglobulin G concentrations in their progeny

Abstract

Three experiments were carried out to evaluate the effects of varying levels of mineral and iodine supplements when offered to ewes in late pregnancy on lamb serum immunoglobulin G (IgG) concentrations. In experiment 1, 44 individually housed ewes were allocated to one of four treatments (no. = 11) and offered a basal diet of grass silage ad libitum which was supplemented with 500 g/day of a concentrate (190 g/kg of crude protein (CP)), in addition to mineral/vitamin fortification at the rate of 0 g (C), 17.3 g (LM), 34.6 g (MM) or 52.0 g (HM) per day for the final 7 weeks of pregnancy. The mineral/vitamin supplement contained Ca, P, Na, Mg, Mn, Se, I, Co, Mn and vitamin E. The ewes were milked at 1 h, 10 h and 18 h post partum and measured quantities of colostrum, proportional to lamb birth weight, were fed back to the lambs via a stomach tube. Treatment had no effect on total colostrum yield or total IgG yield to 18 h post partum (P > 0.05). There was a linear decrease in serum IgG concentration and IgG absorption efficiency as mineral supplementation increased (P < 0.001). In experiment 2, which was carried out in conjunction with experiment 1, 44 ewes were allocated to four treatments (no. = 11) and offered the same basal silage/concentrate diet as in experiment 1, in addition to receiving one of the following supplements : (C) control, as in experiment 1; (HM), as in experiment 1; (−I), ewes offered the same mineral/vitamin supplement as HM but with iodine excluded; (I0), ewes offered a daily mineral supplement of iodine only at a level of 40 mg per ewe, equivalent to the iodine inclusion in the 52 g of minerals offered in HM. The iodine-supplemented progeny (HM and IO) had lower (P < 0.001) serum IgG concentrations and higher soil scores (P < 0.05) than the C and −I progeny. In experiment 3, the effects of varying levels of iodine supplementation when offered to ewes during the final 6 weeks of pregnancy on lamb serum IgG values were examined. Forty-eight individually housed ewes were allocated to one of four treatments (no. = 12) and offered grass silage ad libitum, which was supplemented initially with 500 g of a concentrate (140 g/kg of CP) from days 99 to 130 of gestation and then replaced with 700 g/day of a concentrate (180 g/kg of CP) from day 131 of gestation until lambing. In addition, the diet of each ewe was supplemented on a daily basis with iodine at the rate of 0 mg (C), 8.9 mg (LI), 17.7 mg (MI) or 26.6 mg (HI). There was a negative linear reduction in serum IgG concentration and IgG absorption efficiency as maternal dietary iodine supplementation increased (P < 0.001). We conclude that supplementation of the ewe's diet in late pregnancy with 17.3 g of a mineral supplement as formulated in the current experiment lowers the lamb's ability to absorb colostral IgG, and offering only the iodine component of this mineral supplement, at a level which approximates to about one third of currently quoted toxicity levels, will result in reduced serum IgG concentration in the lamb. These findings suggest the need to re-examine current toxicity values for iodine.

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

“…The cobalt requirements of sheep are 0.07 mg/kg DM per day (Agricultural Research Council (ARC), 1980) and the concentrations fed in the current study were higher than the requirements of 0.13 mg per ewe per day as outlined by Boland et al (2004). The levels of mineral supplementation offered in this study did not reach the current quoted toxicity levels (ARC, 1980) but the findings of this study and recent work (Boland et al, 2005a(Boland et al, , 2005b(Boland et al, and 2006 show that high levels of iodine inclusion can have negative effects on animal performance even at rates below the quoted toxicity level. 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.…”

“…Recent results have shown that although lambs may appear to receive an adequate supply of colostrum containing sufficient levels of IgG, their serum IgG concentrations can be low, indicating a poor IgG absorption efficiency which leaves the lambs extremely susceptible to infections Crosby et al, 2004;Guinan et al, 2005). A negative linear relationship has been demonstrated between iodine level and serum IgG concentration (Boland et al, 2005b) and these new findings suggest that there may also be a similar relationship between the period of supplementation and serum IgG concentration. Although the serum IgG concentration at 24 h in the I-1 lambs was significantly lower than in the C lambs, it was intermediate between the C and I-3 lambs, indicating that a supplementation period of more than 1 week is required to see the complete negative effects of high levels of iodine supplementation on lamb serum IgG concentration.…”

“…In the current study, there was no effect of treatment on colostrum yield at 1 or 18 h post partum or on total colostrum yield to 18 h. However, colostrum yield at 10 h post partum was significantly lower for ewes in the I-1 v. I-3 treatment. It is unlikely that this lower colostrum yield can be fully attributable to iodine supplementation as a similar level of iodine has been offered previously with no effect on colostrum yield (Boland et al, 2005b). O'Doherty and Crosby (1997b) reported a negative linear correlation between underfeeding in late pregnancy and colostrum production during the first 18 h post partum and data collected on feed intake from day 135 to day 139 of gestation in the current study indicate that I-1 ewes had lower dietary intakes than all other groups (data not shown).…”

“…In addition, iodine has been indicated as the element responsible (Boland et al, 2005a). Furthermore, when iodine was supplemented to pregnant ewes at around one-third of the current published toxicity levels (ARC, 1980), their progeny were still severely compromised, in relation to the acquirement of passive immunity from the colostrum (Boland et al, 2005a and2005b;Guinan et al, 2005).…”

“…--The 26.6 mg level of iodine equates to a mineral intake of 34 g which we have previously shown to have a negative effect on IgG and vitamin E absorption (Boland et al, 2005b). The level of 20 mg of cobalt equates to a mineral intake of 48 g per ewe per day, which has been shown to negatively affect IgG absorption efficiency .…”