Kyuuketsu Doutei, Chichi wo Suu.

A fantasy romance about a vampire who can't suck blood and a cow beast-girl. The vampires, who once threatened the lives of people, are now being monitored and managed by the church. One day, Bell, a beast girl cow, is partnered with Yuki, a vampire who can't drink blood. Since Yuki can't drink blood as a source of nourishment, he is so weak that he can't defeat monsters. However, in a desperate situation, he asks Bell for milk...! Instead of blood, breast milk. An unconventional breastfeeding smut begins!