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Summary
Twelve pairs of identical-twin heifer calves were divided into 3 groups. For 12 consecutive weeks daily injections were carried out as follows: Group 1 Growth hormone 5 mg/100 lb body weight Group 2 L-thyroxine 0.5 mg/100 lb body weight Group 3 Normal saline 1 cm3
During the injection period the growth-hormone group gained in live weight by approximately 14 lb more than the control group, whereas the weight gain of the l-thyroxine group was some 12 lb less than that of the control group.
The extra gain in height made by the growth hormone and l-thyroxine groups compared with that made by the control group amounted to 20 mm and 14 mm respectively.
L-thyroxine increased blood-sugar levels by some 20–30%. The increase in blood sugar recorded in the growth-hormone group was slightly less than this and was probably due to the contamination of the growth hormone with thyrotrophic hormone. Non-protein nitrogen levels in the blood were unaffected by either growth hormone or l-thyroxine.