Effects of sodium intake during two parities on Na status in Blackface sheep

Abstract

1.A low-sodium diet was given to Blackface ewes over two reproductive seasons. This diet provided a total of 3-7 mmol/d except during lactation when the intake was about 11 mmol/d. Control ewes were given the same diet supplemented with sodium chloride to provide recommended levels which were about tenfold that of the experimental diet.2. The output of Na in urine and faeces from ewes given the low-Na diet was very low, about 3 mmol/d, from early in the experiment and continued at about this level throughout.3. Lambs born to low-Na ewes and given a low-Na diet similar to that of their dams during lactation, grew, after weaning, more slowly than corresponding lambs from control ewes, but at 6 months of age when six from each group were killed, tissue Na contents were only slightly lower in experimental than control lambs.4. Fluids and tissues obtained at the end of the second lactation from four ewes of each group that had suckled twin lambs, were analysed for Na and potassium. The Na concentration in saliva and rumen fluid of low-Na ewes was about half that of control ewes and there were corresponding increases in K: the differences were significant. Although Na concentrations for experimental ewes were generally lower than those for control ewes in the tissues analysed (liver, kidney, heart, brain and bone), the difference was significant only for the heart (P < 0.05). Haemoglobin and packed cell volume were significantly elevated in low-Na ewes (P < 0.01), indicating decreased body fluid volume. Enlargement of the adrenal glands in low-Na ewes (P < 0.01) and specifically in the zona glomerulosa (P < 0.001), showed the marked hormonal response to Na status of experimental ewes given a very-low-Na diet over two reproductive cycles.An experiment was carried out over two reproductive cycles to determine the effects of a low sodium intake on productive performance and health in Blackface ewes and their lambs. The efficiency of reproduction of these experimental ewes and of corresponding control ewes has been described recently (Vincent et al. 19863): no significant difference was observed in any aspect of reproduction between these two groups of ewes. Furthermore, there were no differences in milk yield and growth of the lambs (Vincent et al. 1986a). The experiment provided an opportunity to determine Na and potassium levels in excreta from the ewes, and in tissues and fluids from small groups of first-year lambs, and of ewes killed at the end of the second lactation.These three sets of values, the Na and K contents of excreta of ewes, tissues of lambs and tissues of ewes are described in the present paper. They provide information on the Na status of these animals, particularly the ewes. MATERIALS A N D METHODS Animals and dietsForty-two mature Blackface ewes were divided into two groups of similar mean live weight, one group was given a control diet (C) providing adequate Na, the other group a low-Na diet (T). They were housed on wooden slats throughout the two seasons, except when the lambs were small. From abou...