Kinship, understood as biogenetic proximity, between a chosen animal model and a human patient counterpart, is considered essential to the process of ‘translating’ research from the experimental animal laboratory to the human clinic. In the Danish research centre, NEOMUNE, premature piglets are fed a novel milk diet (bovine colostrum) to model the effects of this new diet in premature infants. Our ethnographic fieldwork in an experimental pig laboratory and a neonatal intensive care unit (NICU) in 2013–2014 shows that regardless of biogenetics, daily practices of feeding, housing, and clinical care hold the potential for stimulating and eroding kinship relations between human and nonhuman actors. In the laboratory, piglets and researchers form ‘interspecies-milk-kinships’ that entail the intimate care crucial to keeping the compromised piglets alive during the experiments, thereby enhancing what the researchers refer to as the ‘translatability’ of the results. In the NICU, parents of premature infants likewise imagine a kind of interspecies kinship when presented with the option to supplement mother's own milk with bovine colostrum for the first weeks after birth. However, in this setting the NICU parents may perceive the animality of bovine colostrum, and the background information obtained in piglets, as a threat to the infants' connection to their biological parents as well as the larger human collective. Our study argues that the ‘species flexibility’ of premature beings profoundly shapes the translational processes in the field of neonatology research.