title: Serum total iodine concentrations in pasture-fed pregnant ewes and newborn lambs challenged by iodine supplementation and goitrogenic kale.
abstract: Iodine deficiency can impair the reproductive performance of livestock and affect perinatal mortality of offspring, yet diagnosis of deficiency is complicated and guidelines for I supplementation are imprecise. We challenged pasture-grazing pregnant ewes with a long-acting I supplement and a goitrogenic forage, then monitored their I status during gestation and lactation and in their lambs from birth to weaning. Approximately 46 d into gestation, 376 ewes were assigned to 6 groups comprising 3 supplementation levels × 2 diet regimens. On d 0 the groups received an intramuscular injection of iodized oil providing 0, 300, or 400 mg of I. They grazed until d 23, then half of each supplementation group were fed brassica kale until d 85, then all groups returned to pasture for lambing (parturition approximately d 99) and remained there until weaning (d 192). Serum total I concentration (STIC) was measured repeatedly in 8 'monitor' ewes per group and in their lambs and in milk sampled postpartum. Severity of goiter was determined as the thyroid-weight:birth-weight (TW:BW) ratio in 82 newborn dead lambs. Mean ± SE STIC for all ewes was initially 42 ± 2 (range 24 to 105) µg/L. Diet did not affect I concentrations in ewe serum or milk. Responses to iodized oil were proportional to dose level; STIC increased to approximately 150 and 240 µg/L for the 300- and 400-mg I groups and remained greater than 0-mg I groups for 161 d (P < 0.05). Milk contained 26, 271, and 425 µg I/L for the 0-, 300-, and 400-mg I groups, respectively. Mean STIC of lambs from supplemented ewes did not differ by diet; concentrations for the 300- and 400-mg I groups were 237 and 287 µg I/L at birth, and by weaning all groups were similar (62 ± 3 µg/L). Lamb STIC measured at birth correlated with exposure to I in utero (R(2) = 0.59), which was estimated from the area under the curve (AUC) of ewe STIC measured during the last 99 d of gestation. Thyroid enlargement in lambs affecting the TW:BW ratio was a sensitive indicator of maternal nutrition, being greater with kale feeding (1.27 vs. 0.51 g/kg) and lesser with I supplementation (0.35 vs. 1.44 g/kg). Results support the use of STIC as a biochemical criterion. It was sensitive to the effects of I supplementation with responses in ewes and lambs proportional to dose level and it reflected the relationship between ewe and lamb I metabolism. However STIC did not discriminate between groups of ewes fed pasture vs. goitrogenic forage during pregnancy.
authors.affiliation: Food Nutrition and Health Team, Food and Bio-based Products Group, AgResearch Limited, Grasslands Research Centre, Private Bag 11008, Palmerston North 4442, New Zealand scott.knowles@agresearch.co.nz.
authors.forename: S O
authors.initials: SO
authors.lastname: Knowles
authors.affiliation: 26 Williams Road, RD 4, Palmerston North 4474, New Zealand.
authors.forename: N D
authors.initials: ND
authors.lastname: Grace
mesh_terms: D000818:Animals; D001724:Birth Weight; D001835:Body Weight / Q000502:physiology; D001937:Brassica / Q000737:chemistry*; D004032:Diet / Q000009:adverse effects / Q000662:veterinary*; D019587:Dietary Supplements; D005260:Female; D006042:Goiter / Q000139:chemically induced / Q000662:veterinary*; D007455:Iodine / Q000097:blood / Q000494:pharmacology*; D007774:Lactation / Q000502:physiology; D039382:Maternal Nutritional Physiological Phenomena; D008892:Milk; D049590:Postpartum Period; D011247:Pregnancy; D011248:Pregnancy Complications / Q000139:chemically induced / Q000662:veterinary; D012756:Sheep; D012757:Sheep Diseases / Q000139:chemically induced* / Q000473:pathology; D014886:Weaning
chemical_list: D007455:Iodine
keywords: ewe; goiter; iodized oil; lamb; milk iodine; serum total iodine