ORIGINAL ARTICLE Effects of nutrient restriction and melatonin supplementation on maternal and foetal hepatic and small intestinal energy utilization L. D. Prezotto 1 , C. O. Lemley 2 , L. E. Camacho 1 , F. E. Doscher 1 , A. M. Meyer 3 , J. S. Caton 1 , B. J. Awda 4 , K. A. Vonnahme 1 and K. C. Swanson 1 1 Department of Animal Sciences, North Dakota State University, Fargo, ND, USA 2 Department of Animal and Dairy Sciences, Mississippi State University, MS, USA 3 Division of Animal Science, University of Missouri, Columbia, MO, USA, and 4 College of Applied Biotechnology, Al-Nahrain University, Jadriah, Baghdad, Iraq Summary To determine how nutrient restriction and melatonin supplementation influence ewe and foetal hepatic and small intestinal energy use, 32 primiparous ewes on d 50 of gestation were fed 60% (RES) or 100% (ADQ) of NRC recommendations with 0 (CON) or 5 mg/d (MEL) of dietary melatonin. On d 130 of gestation, small intes- tine and liver were weighed and collected. Data were analysed as a completely randomized design with a 2 9 2 factorial arrangement of treatments. Liver weight (g/kg EBW) decreased (p = 0.02) in RES ewes. Jejunum weight (g/kg BW) increased (interaction p = 0.04) in ADQ-MEL ewes compared with all other treatments. Total in vitro O 2 consumption (mol/min/tissue) and total citrate synthase activity (mol/min/tissue and mol/min/kg EBW) in liver decreased (p ≤ 0.03) in RES ewes. Oxygen consumption (mol/min/kg EBW) increased (interaction p = 0.02) in jejunum of ADQ-CON versus RES-MEL and ADQ-CON. Citrate synthase activity (mol/min/kg of EBW) increased (interaction p = 0.03) in jejunum of ADQ-MEL compared with RES-MEL and ADQ-CON. Foetal liver weight (g/kg BW) decreased (p = 0.02) in RES versus ADQ. Foetal small intestine weight (g/kg BW) decreased (interaction p = 0.05) in RES-MEL versus ADQ-MEL. Total O 2 consumption (mol/min/tissue) and total citrate synthase activity (mol/min/kg of BW) in foetal liver decreased (p ≤ 0.05) in RES versus ADQ. Foetal small intestinal O 2 consumption (mol/min/kg of BW) was greater (interaction p = 0.03) in RES-CON and ADQ- MEL than RES-MEL and ADQ-CON. Maternal nutrient restriction had a greater effect than melatonin supple- mentation on liver and jejunum mass and energy utilization in dams and foetuses. Because intestinal mass and energy utilization were more responsive to melatonin supplementation in ewes fed adequate nutrition compared with restricted ewes, melatonin may have limited use as a therapeutic supplement to help overcome potential negative effects of nutrient restriction. Keywords oxygen consumption, citrate synthase, gestation, sheep, nutrition, foetal development Correspondence K. C. Swanson, Department of Animal Sciences, North Dakota State University, Hultz Hall 166, Dept. 7630, PO Box 6050, Fargo, ND 58108-6050, USA. Tel: 701 231 6502; Fax: 701 231 7590; E-mail: kendall.swanson@ndsu.edu Received: 24 April 2013; accepted: 24 September 2013 Introduction The extensive use of grazing systems for ruminant livestock and the high variation in forage quality throughout the year have important impacts on pro- duction. Changes in feed quality and availability alter the nutritional and physiological status of gestating animals (Wu et al., 2006; Caton and Hess, 2010). Maternal homeostatic and homeorhetic adjustments are necessary during pregnancy (Bauman and Currie, 1980) due to the importance that nutrient partitioning between maternal and foetal tissues has on species survival and foetal development. These adjustments have been correlated with an increase in maternal energy use during pregnancy (Ferrell and Jenkins, 1985) and also further adjustments that occur in the dam’s metabolism to provide adequate oxygen (O 2 ), nutrients, and energy reserves for foetal growth and maternal maintenance systems. Alterations in small intestinal and hepatic mass and metabolism, two key tissues influencing total body energy expenditure (Koong et al., 1985; Reynolds et al., 1991), have been Journal of Animal Physiology and Animal Nutrition 98 (2014) 797–807 © 2013 Blackwell Verlag GmbH 797 DOI: 10.1111/jpn.12142