The objective of this study was to determine the effects of injectable and oral arginine (Arg) supplementation provided 14 d post-breeding on reproductive performance of fall lambing ewes. Upon estrus detection (d 0) ewes were randomly assigned to one of six treatments for a 14-d treatment period: injectable saline (CON; n = 25), injectable alanine (IVALA; n = 20), injectable arginine (IVARG; n = 23), oral rumen-protected Arg (RPARG; n = 20), oral soybean meal (SBM; n = 23), or oral fishmeal (FM; n = 24). Weaning rates were higher (P < 0.05) in Arg supplemented ewes. Plasma progesterone and serum Arg concentrations exhibited a treatment and day effect (P < 0.05), but no treatment × day interaction was observed (P > 0.05). In contrast to previous research, supplemental Arg during the first 14 d of pregnancy did not improve pregnancy or lambing rates, however, IVARG positively impacted weaning rates.