Nutritional Secondary Hyperparathyroidism in the Horse

(:linico-pathologic Determinations 51
a) A diet with a calcium to phosphorus ratio of 1 : 3.68 immedia-
tely caused hyperphosphatemia.
13) Serum calcium first increased slightly and then decreased (NSH
1 and NSH 3) or decreased immediately (NSH 2). Hyperphosphatemia
and hypocalcemia progressed for about 10 weelis.
c) Clinicopathologic evidences of hyperparathyroidism were
manifest at the 11th week (NSH 1 and 3) or at the 13th week (NSH 2).
At week 11 the serum P dropped in NSH 1 and 3. In NSI-I 2 this did
not occur, but the progressing hyperphosphatemia was partly arrested.
As the serum phosphorus started to decrease, a rise in serum calcium
occurred.
During the next phase, covering the period from week 12 to week
23, serum phosphorus increased until it reached maximum and then
decreased rapidly. During the same period serum calcium rose all the
time, although compensation was not complete.
At the end of this period the dietary calcium to phosphorus ratio
was decreased from 1 : 3.68 to 1 : 6.19. Serum phosphorus then
increased from week 23 through week 30, whereas serum calcium
decreased during the same period of time.
At week 30 the serum calcium reached its second minimum. The
hyperparathyroidism now caused decreasing serum phosphorus and
increasing serum calcium levels in all NSH horses.
d) The product of total serum calcium and serum phosphorus
described a triphasic curve over the experiment. The curves of these
products were similar to those of serum phosphorus. The sequence of
events was:
i) Increase; hyperphosphatemia greater in degree than hypo-
calcemia.
ii) Decrease ; hypocalcemia of relatively greater degree than hyper-
phosphatemia, which showed a temporary and partial compensation.
iii) Increase; both phosphorus and calcium increasing; maximum
product reached after 16, 20, and 20 weelis in NSH 1, 2, and 3,
respectively.
iv) Decrease ; hyperphosphatemia compensated for to a greater
degree than hypocalcemia. In the middle of this phase the dietary ratio
of calcium and phosphorus was decreased, resulting in increasing serum
phosphorus levels but in still lower serum calcium levels; net result,
thus, decreased product.
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