Short- and long-term effects of low estrogenic subterranean clover on ewe reproductive performance

This study examined the short- and long-term effects on the reproductive performance of sheep by subjecting them to varieties of subterranean clover (Trifolium subterraneum), containing a low content of total phytoestrogens and formononetin. In the first trial, 30 ewe lambs of the Sarda breed (initial mean live weight 16.4±1.3 kg) were divided into three groups of 10 animals each and maintained separately on pastures for 60 d, with alfalfa (Medicago sativa L.), oats (Avena sativa), and subterranean clover with a phytoestrogen content ranging from 10.21 mg/g on a dry matter basis (DM) at the onset, to 0.90 mg/g DM at the end of the trial, respectively. All three pastures were integrated to make them isoproteic and isoenergetic. At the end of the grazing period, the animals were pooled into one group and fed the same phytoestrogen-free diet. No differences were recorded between the groups with regard to the development of the reproductive system as monitored by transvaginal ultrasonography, fertility, fecundity, breeding performance of the ewes, or with regard to the birth weight and conformation of the lambs. Puberty was attained earlier by the animals fed on subterranean clover, while the lambs also weighed more. In the second trial, 24 ewe lambs of the Comisana breed (initial mean live weight 25.0±3.4 kg) were divided into two groups of 12 animals each. All animals were fed ad libitum for a 20 months period with fresh-cut or dried subterranean clover (phytoestrogen content of 0.88 and 0.81 mg/g DM, respectively); or a control non-estrogenic diet, based on fresh-cut or dried Italian ryegrass (Lolium multiflorum Lam.). The two diets were integrated so to be isoenergetic and isoproteic. No differences were recorded between the groups with regard to the attainment of puberty, although the animals fed clover were heavier at puberty. The development of the reproductive system, fertility, fecundity and breeding performance in both lambings, the interval between lambings, and body weight and conformation of the lambs did not show differences. In both trials, neither non-degraded phytoestrogens nor equol (metabolite of formononetin) were recorded in the blood of the ewes. The only metabolite present was p-ethylphenol. All animals fed subterranean clover-based diets, showed a significantly higher ADG, compared to those fed the control diets. The results of this study indicate that the levels of total phytoestrogens and formononetin in the new varieties of subterranean clover do not negatively affect the reproduction of sheep and appear to improve the growth rate of the animals