Abstract
Data from several hundred assays of mare sera for gonadotropic hormone point to the existence of an inverse relationship between body size and hormone content, draft mares usually having a lower concentration than the lighter Thoroughbred mares. This observation led to a study of the concentration in the pony. The sera of grade Welsh ponies were tested according to the method of Cole, Guilbert and Goss. 1 In some instances complete tests were not made, however, if the concentration was lower than 100 R.U. per cc. The results of tests on 10 ponies are shown in Table I. It is clear that a concentration of 200 to 400 R.U. per cc. is not at all uncommon, while we have never found sera testing 200 R.U. per cc. from Thoroughbred or draft mares. The range found is from 12 to 100 R.U. per cc. with a mean of 75 R.U. per cc. in the latter breeds. The data of Catchpole and Lyons 2 indicate that mustangs fall in the upper portion of this range. Thus the concentration in certain ponies is four times greater than has been found in the breeds mentioned. In serum testing 400 R.U. per cc. the rat unit represents approximately 0.25 mg. of dry matter. Thus it would seem that the blood of such ponies would be an excellent starting material for chemical studies.
The data of Table I show further that a variation in concentration occurs from year to year in the same mare. This is particularly well demonstrated in pony 2 in which the concentration in 1937 was 4 times that of 1936 at comparable stages of pregnancy. We have similar observations for mares of other breeds but have not been able to relate this variation to any difference in physiological or nutritional state.
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