Histological investigations into the relationship between low birth weight and spontaneous bowel damage in the neonatal piglet.

Experimental models for the study of neonatal necrotizing enterocolitis (NEC) using the small for gestational age (SGA), viable, term-delivered piglet have recently been described. A spontaneous model, especially of the early phases of NEC, has not been reported. Pig litters usually include one or two lethally or sublethally SGA "runted" piglets culled from the litters by breeders. We have examined four groups of piglets: group A, SGA, lethally runted animals who died spontaneously before 12 h postpartum; group B, SGA, sublethally runted animals, showing some signs of vitality and left alive for 24 h before culling; group C, appropriate for gestation age (AGA) animals subjected to hypoxia and hyperviscosity known to induce NEC-like lesions; and group D, AGA control animals. Acute, multiorgan pathology common to pre- and dysmature neonates was seen in groups A and B. Animals in group B also showed evidence of early postnatal complications such as urinary tract infection and diffuse pulmonary damage. All animals of groups A and B showed unequivocal early changes in the distal ileum, with mucosal and submucosal necrosis, suggestive of ischemic injury. One animal in group B had developed mural necrosis involving the whole of the submucosa. No similar changes were seen in control group D animals. The very-SGA, lethally and sublethally runted, spontaneously term-delivered piglet offers sufficient spontaneous early NEC-like changes for studies of the early pathogenesis of this condition.