Effects of diverse developmental environments on neuronal morphology in domestic pigs (Sus scrofa)

Potential effects of environmental rearing conditions on the brains of farm animals have not been examined experimentally, with the exception of one report for pig somatosensory cortex. The goal of the present experiment was to determine whether different developmental environments in use in agricultural production units affect neuronal morphology in the pig cerebral cortex. Littermate female pigs (gilts) were cross-fostered at birth and reared in either an indoor (n = 6) or outdoor (n = 6) production unit for 8 weeks. Additional littermates (n = 6) were sacrificed at 3 days of age to provide a developmental reference point. Brains were fixed by perfusion and stained by the Golgi-Cox method. The primary somatosensory, auditory and visual cortices were sectioned at 170 microns, and layer IV stellate neurons (n = 492) were digitized and 3-dimensionally reconstructed. Measurements of dendritic length, membrane surface area, total number of segments, number of 1st- through 7th-order dendrites, spine density, soma area, and soma form factor were taken. In auditory cortex neurons, outdoor pigs compared to indoor pigs had (a) significantly more primary dendrites, (b) significantly greater spine density, and (c) trends of increases both in number of 2nd- and 3rd-order dendrites and in total dendritic length. In visual cortex neurons, indoor pigs had significantly more 7th-order dendrites, whereas in all three cortical areas, the indoor animals had more 5th-order dendrites. Multiple morphological differences occurred in stellate cell populations between the three sensory areas of the Week 8 pigs. Also, within different cortical areas, dendritic morphology changed substantially from 3 days to 8 weeks of age. Further investigations are needed to determine which environmental factors are critical in producing the observed changes in brain morphology and whether other brain effects may be produced by varying developmental environments.