ADAPTATION OF RUMINANTS TO BROWSE AND GRASS DIETS - ARE ANATOMICAL-BASED BROWSER-GRAZER INTERPRETATIONS VALID

As a result of pioneering work of Hofmann (1973, 1989), nutritional ec ologists classify ruminants into three feeding-type categories: browse rs (''concentrate'' feeders), grazers, and intermediate or mixed feede rs. Hofmann proposed that these feeding types result from evolutionary adaptations in the anatomy of the digestive system and that one conse quence is shorter retention of the digesta in the rumen of browsers, a nd thus a decreased efficiency of fiber digestion relative to that of grazers. We examined the hypotheses that (1) fiber digestion of browse rs is lower than that of grazers, (2) salivary gland size is larger in all browsers than in grazers, (3) the browser's larger salivary gland s produce larger volumes of thin serous saliva than those of grazers, and (4) thus, browsers have higher liquid passage rates than do grazer s. We found that the extent of fiber digestion is not significantly di fferent between browsers and grazers, although fiber digestion is posi tively related to herbivore size. In general, salivary gland size is a pproximately 4 times larger in browsers than grazers, but some browser s (e.g., greater kudu) have small, grazer-sized salivary glands. Resti ng (non-feeding or ruminating) saliva flow rates of mule deer (browser ) and domestic sheep and cattle (grazers) were not significantly diffe rent from each other. Finally, ruminal liquid flow rates were not diff erent between feeding types. We conclude that many of Hofmann's nutrit ional and physiological interpretations of anatomical differences amon gst ruminants are not supportable.