ORIGINAL ARTICLE Impact of energy and protein restriction on energy expenditure of gestation in twin-bearing ewes Alishir KIANI, 1,2 Andre CHWALIBOG, 1 Anne-Helene TAUSON 1 and Mette O. NIELSEN 1 1 Department of Basic Animal and Veterinary Sciences, Faculty of Life Sciences, University of Copenhagen, Denmark; and 2 Animal Science Group, Faculty of Agricultural Sciences, Lorestan University, Khoramabad, Iran ABSTRACT This study aimed to investigate the impact of energy and protein restriction on energy expenditure of gestation (EEgest) in twin-bearing ewes. Multiparous twin-bearing ewes were fed either adequate (A: n = 10) or restricted to 60% of energy and protein requirements (R: n = 10) during the last 6 weeks of gestation. Whole-body energy expenditure (EE) and retained energy (RE) were calculated from respiratory gaseous exchange combined with nitrogen balance at 7, 5 and 2 weeks prepartum. Twin lamb birth weight was lower in the R group compared to those in the A group (7.9  0.31 vs 9.3  0.19 kg, P < 0.01). The EEgest was lower in the R group than the A group (4.6 vs 5.9 MJ/day, SE = 0.30, P < 0.01). Between 5 and 2 weeks prepartum, EEgest contribution to the whole-body EE significantly (P < 0.01) increased from 39% to 45% and from 34% to 40% in the A and R groups, respectively. Based on kg conceptus weight, both EEhomeorhetic (from 292 to 270 kJ/kg/day, SE = 6.2, P < 0.001) and EEconceptus (from 259 to 177 kJ/kg/day, SE = 23.8, P = 0.02) decreased between weeks 5 and 2 prepartum. The EEconceptus tended to be lower (P = 0.06) in the R group than the A group both at 5 weeks (219 vs 298 kJ/kg/day, SE = 32.8) and 2 weeks (from 138 to 217 kJ/kg/day, SE = 30.1) prepartum. In conclusion, energy and protein restriction reduced energy expenditure of gestation calculated per kg conceptus weight. The decrease may be associated with energy expenditure of conceptus growth and maintenance. Key words: heat production, maternal feed restriction, ovine, pregnancy. INTRODUCTION In general, the marked increase in total energy expen- diture during late gestation in sheep (Brody 1945; Graham 1964; Russel et al. 1967; Lodge & Heaney 1970) indicates that gestation (fetal growth) is ener- getically very inefficient in comparison with other physiological process. Approximately 87% of the metabolizable energy (ME) requirement for fetal growth and development is dissipated as heat (Bell et al. 2005) while this value is approximately 35–50% in growing animals. However, the low efficiency of energy utilization for conceptus growth (in animals) varies with nutrient intake (Robinson et al. 1980). The efficiency of utilization of energy (from diet and mobi- lized body reserve) for fetal growth seems to be higher in undernourished dams than in well-nourished dams (Lodge & Heaney 1970; Sykes & Field 1972; Robinson et al. 1980). This might be caused by contribution of body reserves in undernourished dams rather than dietary ME (Robinson et al. 1980). Another explana- tion may be that maternal-fetal metabolism is compro- mised. The latter is supported by the well-documented occurrence of nutritional intrauterine-growth retarda- tion in fetuses in ruminants (Anthony et al. 2003). In the present study, we hypothesized that higher energy efficiency for conceptus growth and development in undernourished dams is associated with alteration in energy expenditure of conceptus development regard- less of the source of available energy. Correspondence: Andre Chwalibog, Department of Basic Animal and Veterinary Sciences, Faculty of Life Sciences, University of Copenhagen, Groennegaardsvej 3, DK-1870 Frederiksberg C, Denmark. (Email: ac@life.ku.dk) Received 17 January 2007; accepted for publication 31 May 2007. Animal Science Journal (2008) 79, 218–225 doi: 10.1111/j.1740-0929.2008.00520.x © 2008 The Authors Journal compilation © 2008 Japanese Society of Animal Science