An investigation into the effects of maternal supplementation with excess iodine on the mechanisms and impacts of reduced IgG absorption in the lamb postpartum.

An experiment was conducted to determine: (1) the effect of excess maternal I supplementation on the thyroid hormone status of the ewe and her progeny; (2) potential mechanisms underpinning the failure of passive transfer associated with excess I and (3) the growing lambs' response to natural gastrointestinal infection. Twin-bearing ewes received one of two treatments (n 32/treatment group): basal diet (C) or C plus 26·6 mg of iodine/ewe per d (I), supplied as calcium iodate. Ewes were individually fed from day 119 of gestation to parturition. Progeny of I ewes had lower (P<0·01) serum IgG concentrations from 24 h to 28 d postpartum but higher serum IgG concentrations at day 70 postpartum (P<0·05). I supplementation increased the relative expression of Fc receptor, IgA, IgM high affinity and polymeric Ig receptor in the ileum of the lamb at 24 h postpartum; however, thyroid hormone receptor-ß (THRB) and ß-2-microglobulin (B2M) expression declined (P<0·05). Progeny of I ewes had higher growth rates to weaning (P<0·05) and lower faecal egg count (FEC) for Nematodirus battus (P<0·05) between weeks 6 and 10 postpartum. In conclusion, excess maternal I supplementation negatively affected the thyroid hormone status, serum IgG concentration, ileal morphology and the gene expression of THRB and B2M in the ileum and ras-related protein (RAB) RAB25 and the mucin gene (MUC) MUC1 in the duodenum of the lamb postpartum. These effects were followed by an enhancement of average daily gain and lower N. battus FEC in the pre-weaning period of I-supplemented lambs.

Association between variation in faecal egg count for a mixed field-challenge of nematode parasites and ovine MHC-DQA2 polymorphism.

The selection of sheep that are resistant to gastrointestinal parasites and have lower faecal egg counts (FECs) has been the subject of extensive research. This has led to the speculation that the Major Histocompatibility Complex (MHC) genes could be used as markers to reduce FEC. In this study, associations between variation in ovine MHC-DQA2 and various measures of FEC recorded at two times (approximately 4 and 9 months of age) were investigated in a large group of New Zealand lambs (n=4676), derived from 185 different sire-lines, of a variety of breeds and raised on 25 separate farms. Pair-sample t-tests revealed that FEC for Nematodirus spp., Strongyle spp. and total FEC differed significantly between the two assessments. A total of twenty one DQA2 alleles or DQA2-DQA2-like haplotypes were identified, with allele/haplotype presence and frequency varying significantly between farms. For example, allele *0103 was observed on all farms, ranging in frequency from 0.2 to 60.9%, while haplotype *0101-*1601 was only present on one farm, in two lambs. A number of associations between the presence/absence of these alleles and egg counts were observed, but nearly all the allelic/haplotypic associations were age and parasite specific, suggesting that immune response is both age and challenge (parasite species mix) dependent. The exception was allele *1201 which was associated with increased total FECs at both 4 and 9 months of age; with it either being, or tending toward being, significantly associated with both increased Strongyle spp. and Nematodirus spp. counts as well. However, the observed increases in egg counts were small and ranged between 5 and 32 eggs per gram. In conclusion, we believe that the MHC plays an important role in parasite resistance, but that the MHC-nematode interaction is complex and thus the development of a single gene-marker based on the "MHC effect" is unlikely.