4 mares were studied over 2 cycles and plasma and urine collected; the diet
remained the same. There were cyclical changes in excretion of electrolytes,
leading to
"large and relatively sudden increases in the volumetric urinary excretion
of sodium, calcium and magnesium .... during the period from 2 days
preceding to 4 days following oestrus compared to the rest of the cycle",
suggesting that
"ovarian steroid hormones may exert an influence on urinary excretion of
electrolytes in the mare. Such an influence could be correlated, in certain
individuals, to a significant effect on electrolyte status, which in turn,
could potentially result in an increased risk" of tying up.
There were some large individual variations - so some mares may be more
likely to lose extra electrolytes than others.
Whether the problem could be overcome in those mares more prone, for example
by the provision of extra electrolytes round the time of their season, I
don't know.
Anne
Western Australia