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Summary
The variation of insulin tolerance in normal cattle has been investigated using monozygotic twin Jersey heifers, and Aberdeen Angus bulls of four different sire groups.
Intravenous injections of protamine zinc insulin were made at the rate of 0.8 unit per kilogramme of body weight and the blood-sugar curve was followed over six one-hourly periods following injection.
The variation of insulin tolerance encountered between animals was mainly due to intangible environmental conditions. A small amount of the variation appeared to be due to genetic differences between animals.
It is concluded that the response of an animal to insulin stress is a character of low repeatability and is consequently of little value as a guide to a normal animal's potential rate of gain.