Seasonal variation in diet, volatile fatty acid production and size of the cecum of rock ptarmigan

Abstract

Abstract 1. Seasonal changes in the chemical and taxonomic character of the diet, the size of the cecum and cecal volatile fatty acid (VFA) production were studied in rock ptarmigan collected in interior Alaska. 2. Ptarmigan fed predominantly on buds and catkins of dwarf birch from late September through April and consumed a significant proportion of berries when available during this period, while seeds predominated in crop contents during July and leaves were preferred during August. 3. Foods selected during July and August were of higher nutritional quality than those selected during other seasons. Crude protein values were highest and lignification of the cell wall lowest in foods selected by ptarmigan during the plant growing season. 4. The length, weight of contents and tissue weight of the cecum were greatest during winter, declined to their shortest, lightest state during summer and early fall and again increased as winter approached. 5. Relative production rates of individual VFA were acetate > propionate > butyrate, whereas relative absorption rates were butyrate > propionate > acetate. 6. The proportion of propionate produced with respect to acetate was highest during summer and early fall suggesting material entering the cecum during these seasons contained the highest proportion of soluble carbohydrates. 7. Seasonal VFA fermentation rates/g of cecal contents differed significantly only during July when the rate was highest. 8. Total VFA production/day did not differ significantly among seasons and metabolizable energy available from VFA averaged 7·1 kcal/day. This energy was equivalent to about 18% of the standard metabolic rate and 7% of estimated free living energy requirements.