Effects of conceptus sex and genetics on circulating thyroid hormones and IGFs in heifers at mid gestation depend on maternal genetic background Stefan Hiendleder1,2*, Entesar S. Shuaib1,2, Julie A. Owens1,3,4, David J. Kennaway1,3, Kathryn L. Gatford1,3, Karen L. Kind1,2. 1Robinson Research Institute, 2Davies Research Centre, 3Adelaide Medical School and 4Office of the Deputy Vice-Chancellor and Vice-President, Research; The University of Adelaide, Australia Pregnancy is characterized by significant changes in maternal metabolism that are essential for adequate fetal growth. These changes are driven by conceptus demand and maternal supply and are also required for lactation. Here we use a purebred and reciprocal cross Bos taurus taurus (Bt, Angus) and Bos taurus indicus (Bi, Brahman) model to demonstrate significant effects of conceptus sex and genetics on maternal endocrine parameters at midgestation that manifest in a dam genetics dependent manner. In Bt and Bi heifers total thyroxine, but not triiodothyronine, concentrations were higher when carrying a male conceptus. However, free thyroxine was higher in Bt heifers carrying females, while Bi heifers showed a tendency for the opposite effect. In Bt heifers, insulin-like growth factor 1 and 2 were not affected by conceptus sex, but in Bi heifers IGF1 tended to be higher with a male conceptus. Furthermore, we found significant effects of conceptus genetics on total thyroxine and reverse triiodothyronine in Bi dams only. Apart from likely impact on heifer and conceptus growth, our data may help explain conflicting results reported for calf sex effects on milk production. Keywords: cattle, maternal circulation, thyroid hormones, IGFs, conceptus sex, genetics

Stefan Hiendleder, Entesar Shuaib, Julie A Owens, David J Kennaway, Kathryn L Gatford, Karen L Kind

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume Biology - Reproduction 1, , 979, 2018
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