This study investigated whether a 27-day period of nutrition at half-maintenance during early pregnancy (up to Day 14) couldalter maternal endocrine responses. Forty-six ewes were fed all or half of their maintenance requirements and slaughtered on Day14 of the oestrous cycle or pregnancy.We used real time RT-PCR to study gene expression of growth hormone receptor (GHR) andleptin in adipose tissue and GHR, GHR1A and of the insulin-like growth factor I (IGF-I) in the liver. Blood profiles of metabolitesand metabolic hormones were also determined. Throughout the experiment, underfed animals presented lower body weight andbody condition, greater plasma concentrations of non-esterified fatty acids (NEFA), and lower plasma concentrations of leptin,compared to adequately fed animals. Undernutrition affected the patterns of gene expression in adipose and hepatic tissues, andthe responses differed between pregnant and non-pregnant ewes. In adequately fed ewes, pregnancy up-regulated leptin mRNAexpression in adipose tissue, a response that was impaired in underfed ewes. The hepatic expression of IGF-I mRNA was increasedby pregnancy in underfed animals while no effect was observed in adequately fed ewes. It remains to be determined whether thechanges in the endocrine milieu are paralleled by modifications in uterine gene expression that could alter the environment of theembryo during early pregnancy.© 2008 Elsevier Inc. All rights reserved.