547 Journal of Animal and Feed Sciences, 13, Suppl. 1, 2004, 547-550 Phytoestrogen content of subterranean clover related to ewe growth and reproduction * V. Pace 1,3 , K. Carbone 1 , F. Spirito 1 , G. M. Terzano 2 , M. Verna 1 and D. Settineri 1 1 Department of Animal Feeding and Nutrition, 2 Department of Animal Reproduction, Istituto Sperimentale per la Zootecnia Via Salaria, 31-00016, Monterotondo (Roma), Italy ABSTRACT 24 Comisana ewes were fed on subterranean clover (SC, phytoestrogen content = 0.794 mg/g of DM) or Italian ryegrass (IR) for one year to verify the effects of a prolonged ingestion of phytoestrogens on growth rate and reproduction. The animal initial weights were: SC = 25.3 kg ± 2.99 and IR=24.7 kg ± 3.83, respectively. Differences on growth became evident after one month of feeding; after 170 days ewe weights were 47.5 ± 3.43 vs 41.1 ± 4.35 kg (P≤0.01) and ADG was 145.5 g/d vs 107.2 g/d (P≤0.001). No differences were recorded on the onset of puberty and on lamb births: 14 for SC group (LW = 4.83 kg) and 15 for IR (4.36 kg). KEY WORDS: ewes, phytoestrogens, growth, reproduction INTRODUCTION The phytoestrogens detectable in subterranean clover are well-known for their detrimental effects on fertility and reproduction of ruminants due to the presence of a considerable amount of formononetin and its highly oestrogenic rumen metabolite equol. In a previous experiment some new lines of subterranean clover, selected for their very low content of fomononetin (less than the 1% of total phytoestrogens), did not show any influence on fertility and fecundity of sheep fed, for about two months, on fresh subterranean clover, but caused a consistent increase of growth (Pace et al., 2000). * Supported by the Italian Ministry of Agriculture 3 Corresponding author: e-mail: vilma.pace@isz.it