1. Experiments on three pairs of male identical twin calves have shown that underfeeding at 2.5–6 months of age, i.e. during the critical stage of sexual maturation, considerably delayed the process of puberty, as regards testicular androgen production as well as secretion of fructose and citric acid by the seminal vesicles.
2. There was no marked difference in the blood-plasma content of non-protein nitrogen, vitamin A and carotene at 6 months, as between twins on a normal (N) and low (L) plane of nutrition, although the L-twins were growing and maturing more slowly. However, the blood-plasma content of glucose and of most of the free amino acids, was slightly reduced as a result of underfeeding.
3. When at the age of 6 months two twin-pairs were castrated and injected with either testosterone or androstenedione (50 mg every 3rd day, for 2 months), the L-twins of both pairs and the N-twin of one pair grew at a faster rate. Moreover, the concentration of nitrogen in blood plasma increased, the rise being particularly evident in the content of indispensable amino acids. This effect, however, was more pronounced in the N- than in the L-twins.
4. Testosterone treatment enhanced libido in the N-twin but not in the corresponding L-twin. Androstenedione had no effect on libido in either the N-twin or the L-twin. Thus, although testosterone and androstenedione both effectively promoted growth and nitrogen metabolism, androstenedione, unlike testosterone, was devoid of androgenic activity.