The effect of feeding saltbush and sodium chloride on energy metabolism in sheep

Abstract

ABSTRACTThe effect of consumption of saltbush and sodium chloride on energy metabolism in sheep was investigated. Twenty-four Awassi wethers were fed at maintenance level and allotted to three treatments: saltbush (Atriplex barclayana), salt (NaCl) and control. Daily mineral intakes with these diets were 149, 158 and 57 g, respectively. The saltbush had been irrigated with an equal-part mixture of seawater and fresh water and contained 15 g nitrogen and 310 g ash per kg. Energy and nitrogen balance were conducted using indirect calorimetry. The disappearance of organic matter and nitrogen from saltbush in the rumen was studied by the polyester bag technique.Water intake of animals fed a high salt diet was 2·9 times higher and urine excretion was 3·7 times higher than in the control. Digested energy was proportionately 0·616 of dietary gross energy in the saltbush treatment, and 0·700 and 0·707 in the salt and control treatments respectively. Metabolizable energy (ME) was proportionately 0·795, 0·786 and 0·815 of digested energy, and heat production was 1·135, 1·043 and 0·867 of ME in the saltbush, salt and control treatments, respectively. The calculated values for digestible energy, ME, and net energy for maintenance on the saltbush diet were 5·02, 3·77 and 0·54 MJ/kg dry matter.It is suggested that the low energetic utilization of saltbush is related to its low digestibility and the associated increase in energy expenditure, which are apparently related to mineral metabolism in the rumen. To maintain sheep on saltbush diets efforts should be made to lower the mineral content of this shrub.