Energy metabolism and nitrogen balance in the fat jird (Meriones crassus) and the Levant vole (Microtus guentheri)

Abstract

The ability of the fat jird (Meriones crassus) to survive on low quality roughages only, was studied and compared with that of the Levant vole (Microtus guentheri). The ability of the two species to balance their metabolism by lowering requirements for metabolic energy or increasing food digestibility was also studied. Energy intake of the fat jird when fed on alfalfa hay, amounted to 77% of that recorded for the levant vole, whereas energy digestibility was similar in the two species. Metabolic rate (O2 consumption) in the fat jird was 60% that of the levant vole. When fed Panicum grass, the gross and digestible energy intake and metabolic rate dropped only in the Levant vole. This drop (22%) in metabolic rate was not compatible with the decrease (52%) in digestible energy intake. In the fat jird digestible energy and O2 consumption were not significantly different from the value when fed alfalfa hay. Nitrogen metabolism was balanced on a much lower intake than in the Levant vole. The 14C-urea recycling rate was 52·7 ± 5·4% and 89·4 ± 11·6% in the fat jird and the Levant vole respectively when fed the high quality roughage. When fed the low quality roughage, urea recycling rates amounted to 67·3 ± 7.0% and 63·2 ± 6.5% respectively. When the low quality roughage was supplemented with glucose, Levant voles recycled 86·9 ± 7·8% of the urea synthesized in the liver, the same rate as when fed high quality roughage. Low energy metabolism, together with a high capacity for digesting dry plant feed and low nitrogen requirements enables the fat jird to cope with food shortage. Voles were unable to adjust to a low quality diet.