Vaccines against (ER) and porcine parvovirus (PPV) are employed in sow farms worldwide. This study evaluated the impact of administering a bivalent ER/PPV vaccine during lactation. Multiparous sows ( = 83) of two different farms (A (herd size 900 sows) and B (1000 sows)) were allocated in two different groups: 1) sows inoculated with saline solution (non-vaccinated group); 2) sows inoculated with the bivalent vaccine against ER/PPV (vaccinated group). The injections were administered at ∼11 days of lactation. The study was conducted in four different experiments: the first experiment, evaluating the female genital tract (uterus and ovary) and follicle development, was performed in culled sows ( = 19) of Farm A the day after weaning (∼24 days). The remaining experiments, which examined internal temperature, offspring growth, and sow feed intake, were conducted at Farm B ( = 64). The results of follicle populations, showed a greater frequency of large follicles in non-vaccinated compared to vaccinated sows was observed ( < 0.001). The final weight of the piglets and their weight gain were higher in the non-vaccinated group ( ≤ 0.05). A statistical trend was also observed in the average weight gain of piglets. No differences were observed regarding sow´s rectal temperature between groups around the period of injection but the vaccinated group consumed less sow feed on the day of injection ( = 0.016). In conclusion, the administration of this vaccine against ER/PPV during the lactation period had a negative impact on follicle development, sow feed intake, and offspring weight gain and final weight.