The relative roles of body size and feeding type on activity time of temperate ruminants

Recently, there has been some critical testing of whether body size or feeding type (CS: concentrate selectors, IF: intermediate feeders, GR: grass-roughage eaters) is the most important determinant of physiological aspects of ruminant ecology, whereas little has been done on behavioral aspects like activity time. Different predictions regarding the relationships between activity time and body weight/feeding type were tested with activity time data from 18 temperate ruminants. Activity time decreased allometrically with increasing body weight, but there was also a tendency for an effect of feeding type. Exclusion of one statistically defined outlier (mountain goat) made the effect of feeding type highly significant. GR and CS were about equally active. Surprisingly, IF were more active than both GR and CS. The hypothesis is put forward that IF are more active than GR/CS due to their opportunistic use of high-quality forage of both types (concentrate and grass-roughage; on average better quality and hence shorter rumination time), though possible confounding effects of observation methods and varied behavior with respect to cover among CS, IF, and GR should also be evaluated. Received: 22 May 1997 / Accepted: 22 September 1997     

The relative roles of phylogeny, body size and feeding style on the activity time of temperate ruminants: a reanalysis

In 1998, A. Mysterud analysed the relationships between a behavioural parameter (activity time, AT) and body mass and feeding style for 18 temperate ruminants. He found a negative allometric relationship between body mass and AT, and also found a significant effect of feeding style on AT after controlling for body mass. We reanalysed this data set taking into account the effect of phylogeny, and found that while body mass and AT were negatively related, feeding style did not have any effect on AT. We discuss the strong effect that phylogeny has on morphophysiological and behavioural features of ruminants that differ in feeding style, and the lack of evidence to support a feeding style effect. Received: 16 November 1998 / Accepted: 20 April 1999     

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 ecologists classify ruminants into three feeding-type categories: browsers (concentrate feeders), grazers, and intermediate or mixed feeders. Hofmann proposed that these feeding types result from evolutionary adaptations in the anatomy of the digestive system and that one consequence is shorter retention of the digesta in the rumen of browsers, and thus a decreased efficiency of fiber digestion relative to that of grazers. We examined the hypotheses that (1) fiber digestion of browsers is lower than that of grazers, (2) salivary gland size is larger in all browsers than in grazers, (3) the browser's larger salivary glands produce larger volumes of thin serous saliva than those of grazers, and (4) thus, browsers have higher liquid passage rates than do grazers. We found that the extent of fiber digestion is not significantly different between browsers and grazers, although fiber digestion is positively related to herbivore size. In general, salivary gland size is approximately 4 times larger in browsers than grazers, but some browsers (e.g., greater kudu) have small, grazer-sized salivary glands. Resting (non-feeding or ruminating) saliva flow rates of mule deer (browser) and domestic sheep and cattle (grazers) were not significantly different from each other. Finally, ruminal liquid flow rates were not different between feeding types. We conclude that many of Hofmann's nutritional and physiological interpretations of anatomical differences amongst ruminants are not supportable.