Digestion experiments were performed on sheep and cattle exposed for prolonged periods to various temperatures in controlled environmental chambers and in field studies on cattle kept outdoors during the winter. Exposure of sheep receiving pelleted hay or a hay–grain mixture to cold (−6.5–−10 C) temperatures as compared to warm (18 C) temperatures resulted in reductions in the apparent digestibilities of dry matter (DM) and nitrogen which could not be explained by changes in feed intake. In sheep, DM digestibility decreased on average by 0.31% per degree C decrease in temperature. Exposure of two cows to −11 C for 4 wk did not influence the apparent digestibilities of DM, energy or nitrogen of a long hay ration compared to values measured at 20 C. In the field studies, beef calves consuming an equal mixture of chopped hay and grain and kept outdoors during winter had apparent digestibilities of DM which were on average 8% lower (P < 0.05) than calves on the same ration kept in a heated barn. The apparent digestibility of nitrogen was also lower (P < 0.05) for the calves kept outdoors. Beef steers kept outdoors during winter and fed an equal mixture of chopped hay and grain had significantly lower apparent digestibilities of DM and acid detergent fiber (P < 0.01) than steers kept indoors. In the steers, low apparent digestibilities tended to be associated with high resting metabolic rates. The effect of temperature on the steers was smaller than that observed for calves although the diets were similar. The decreases in DM digestibility per degree decrease in temperature were: for the calves, 0.21% per degree C and, for the steers, 0.08% per degree C, suggesting that the digestive function in younger, smaller animals my be more markedly influenced by environmental temperature than that of older, larger animals.