Dental enamel hypoplasia as indicators of seasonal environmental and physiological impacts in modern sheep populations: a model for interpreting the zooarchaeological record

Dental enamel hypoplasia is a developmental defect in enamel caused by physiological stress during dental development. Previous analysis of enamel hypoplasia in sheep has demonstrated that variation in its frequency can be linked to nutrition levels, with animals suffering from malnutrition more susceptible to enamel hypoplasia formation. Variation in enamel hypoplasia frequency has also been linked to climatic and ecological factors, leading to variation in the availability of fodder supplies and, consequently, variation in nutritional intake. In this paper, the occurrence of enamel hypoplasia in two modern sheep populations is, for the first time, correlated with known seasonal physiological and nutritional stress events. Using known age-at-death data, the dental development rates for sheep are reconstructed, allowing the position of enamel hypoplasia on the tooth crown to be linked to known periods of malnutrition and physiological stress. Both populations live under identical climatic conditions but with very different diets. Clear differences are observed between the two populations, with peaks of enamel hypoplasia correlating with different seasonal periods of malnutrition as well as common physiological stressors linked to birth and weaning. This is the first time that a clear correlation has been made between seasonal variation in nutrition and the occurrence of hypoplastic enamel defects in caprine populations. As such, this study provides a baseline from which the nutritional impact of caprine foddering and husbandry practices can be determined in future archaeological studies.