|
Duncan, P., Foose, T. J., Gordon, I. J., Gakahu, C. G., & Lloyd, M. (1990). Comparative nutrient extraction from forages by grazing bovids and equids: a test of the nutritional model of equid/bovid competition and coexistence. Oecologia, 84(3), 411–418.
Abstract: Ruminants are unevenly distributed across the range of body sizes observed in herbivorous mammals; among extant East African species they predominate, in numbers and species richness, in the medium body sizes (10-600 kg). The small and the large species are all hind-gut fermenters. Some medium-sized hind-gut fermenters, equid perissodactyls, coexist with the grazing ruminants, principally bovid artiodactyls, in grassland ecosystems. These patterns have been explained by two complementary models based on differences between the digestive physiology of ruminants and hind-gut fermenters. The Demment and Van Soest (1985) model accounts for the absence of ruminants among the small and large species, while the Bell/Janis/Foose model accounts both for the predominance of ruminants, and their co-existence with equids among the medium-sized species (Bell 1971; Janis 1976; Foose 1982). The latter model assumes that the rumen is competitively superior to the hind-gut system on medium quality forages, and that hind-gut fermenters persist because of their ability to eat more, and thus to extract more nutrients per day from high fibre, low quality forages. Data presented here demonstrate that compared to similarly sized grazing ruminants (bovids), hind-gut fermenters (equids) have higher rates of food intake which more than compensate for their lesser ability to digest plant material. As a consequence equids extract more nutrients per day than bovids not only from low quality foods, but from the whole range of forages eaten by animals of this size. Neither of the current nutritional models, nor refinements of them satisfactorily explain the preponderance of the bovids among medium-sized ungulates; alternative hypotheses are presented.
|
|
|
Duncan P, C. P. (1980). An unusual choice of habitat helps Camargue horses to avoid blood-sucking horse-flies. Biol Behav, 5, 55–60.
|
|
|
Eisenmann V, G. D. C. (1974). Caractères distinctifs des premières phalanges antérieures et postérieures chez certains équidés actuels et fossiles. Bull Soc g?ol France, 16, 352–361.
|
|
|
Eisenmann V, G. D. C. (1974). Caractères distinctifs entre vrais zèbres et zèbres de Chapman d`après l`étude de 60 têtes osseuses. Mammalia, 38, 509–543.
|
|
|
Eisenmann V, G. C. (1984). Morphologie fonctionelle et environnement chez les périssodactyles. Geobios, Mém sp, 8, 69.
|
|
|
Eisenmann V, T. J. - C. (1978). Sur la taxinomie du genre Equus. Cahiers Analyse Données, 3, 179–201.
|
|
|
Feh, C.., BOLDSUKH, T., & TOURENQ, C. (1994). Are family groups in equids a response to cooperative hunting by predators? The case of Mongolian Kulans (Equus hemionus luteus Matschie). Rev Ecol (Terre Vie), 49, 11–20.
|
|
|
Haughton Sh, C. B. (1931). The fossil Equidae of south Africa. Ann South Afr Mus, 28, 407–427.
|
|
|
Hoyt Df, T. C. (1981). Gait and the energetics of locomotion in horses. Nature, 292, 239–240.
|
|
|
Izraely, H., Choshniak, I., Shkolnik, A., Stevens, C. E., & Demment, M. W. (1989). Factors determining the digestive efficiency of the domesticated donkey.(Equus Asinus Asinus ). Q J Exp Physiol, 74(1), 1–6.
Abstract: Factors determining the digestive efficiency of donkeys were studied in animals fed either a low quality roughage (wheat straw: 77{middle dot}1% neutral detergent fibre, 2{middle dot}8% crude protein) or a high quality forage (alfalfa hay: 47{middle dot}5% neutral detergent fibre, 22{middle dot}7% crude protein). The neutral detergent fibre (NDF) intake when fed wheat straw was 1693 {+/-} 268 g animal-1 day-1, 10% higher than when fed alfalfa hay. Digestive coefficient of NDF and acid detergent fibre (ADF) when fed wheat straw amounted to 50{middle dot}9 {+/-} 4{middle dot}9 and 42{middle dot}0 {+/-} 4{middle dot}1% respectively. NDF and ADF apparent digestibilities and mean retention times (37{middle dot}7 {+/-} 1{middle dot}7 and 36{middle dot}4 {+/-} 3{middle dot}2 h respectively) were not significantly different (P [rang] 0{middle dot}05) between the two diets. The donkey appears to digest cell wall constituents as efficiently as the Bedouin goat when on low quality roughage, but less efficiently when fed alfalfa hay. Its energy digestibility is, however, as high as that reported for the Bedouin goat. The donkey's high energy digestibility is related to its capacity to digest soluble food components more efficiently than the ruminant. The mean retention time in the donkey is shorter than in the Bedouin goat and is consistent with its capacity to compensate for a lower quality diet by increasing its intake rate. Recycling of urea in donkeys maintained on wheat straw amounted to 75{middle dot}5 {+/-} 13{middle dot}0% of the entry rate. A decrease in the rate of renal urea filtration, coupled with an increase in the fraction reabsorbed, increased the retention of nitrogenous waste and permitted recycling of nitrogen into the gut. N1 -
|
|