INCIDENCE OF NURSING SICKNESS AND BIOCHEMICAL OBSERVATIONS IN LACTATING MINK WITH AND WITHOUT DIETARY SALT SUPPLEMENTATION

The impact of dietary sodium on the incidence of nursing sickness in m ink dams and on the average litter biomass of 28 and 42 day old kits w as studied. One group (n = 115 including 12 barren females) was given a standard feed mixture with a natural content of 0.53 g NaCl/MJ and a nother group (n = 115 including 8 barren females) was given the same f eed mixture supplemented with NaCl to a final content of 1.00 g/MJ. Th e average dam weight at weaning was significantly lower (P < 0.001) an d the incidence of nursing sickness during the last part of the lactat ion period 3 times higher in the nonsupplemented group. The average li tter biomass at weaning did not differ between the 2 experimental grou ps. A number of biochemical markers of preclinical nursing sickness, e .g. plasma aldosterone and osmolality, Na+ and Cl- concentrations in p lasma and urine, were studied during the last part of the lactation pe riod and at weaning in 20 dams of the nonsupplemented group, in 10 dam s of the salt supplemented group and, for comparison, in 5 + 5 barren females on the day corresponding to day 34 after parturition in nursin g mink. The nonsupplemented group had significantly lower concentratio ns of sodium and chloride in plasma and urine and a significantly high er concentration of plasma aldosterone as compared to the salt supplem ented group. Distinct signs of relative salt deficiency and preclinica l nursing sickness thus characterized the nonsupplemented group throug hout this period, while more blurred hints of electrolyte imbalances w ere noticed in the sodium chloride supplemented group at weaning. A be neficial effect of salt supplementation on the incidence of nursing si ckness was shown; however, it remains unclear whether salt deficiency can cause nursing sickness or whether salt acts as an appetite stimula nt preventing inanition and the development of the disorder.