Dietary supplementation with 0.8% L-arginine between days 0 and 25 of gestation reduces litter size in gilts.

In this study, we determined the effects of L-arginine supplementation during early pregnancy on embryonic/fetal survival and growth in gilts. Gilts were housed individually in pens and fed twice daily 1 kg of a corn- and soybean meal-based diet supplemented with 0.0, 0.4, or 0.8% L-arginine (wt:wt) between d 0 and 25 of gestation (10 gilts/treatment). The diets were made isonitrogenous by addition of appropriate amounts of L-alanine. At d 25 of gestation, gilts were fed L-alanine or L-arginine and hysterectomized 30 min later to obtain uteri and conceptuses (embryos and associated fetal membranes and fluids). Dietary supplementation with 0.4 or 0.8% L-arginine enhanced (P < 0.05) its concentrations in maternal plasma (64 and 98%, respectively) as well as the vascularity of chorionic and allantoic membranes, compared with the control group. Reproductive performance [numbers of corpora lutea (CL) and fetuses, placental and fetal weights, and embryonic mortality] did not differ between the 0.4% Arg and control groups. However, supplementation with 0.8% L-arginine decreased (P < 0.05) uterine weight (-20%), total number of fetuses (-24%), CL number (-17%), total fetal weight (-34%), total volume of allantoic and amniotic fluids (-34 to 42%), concentrations of progesterone in maternal plasma (-33%), as well as total amounts of progesterone (-35%), estrone (-40%), and estrone sulfate (-37%) in allantoic fluid, compared with the control group. These results indicate that dietary supplementation with 0.8% L-arginine between d 0 and 25 of gestation, while increasing placental vascularity, adversely affects the reproductive performance of gilts.