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Summary. The gross anatomy of the mammary gland of the red deer is described. A total of 102 milk samples was obtained from six deer (four during a complete lactation). These contained an average of 21\m=.\1 % total solids (8\m=.\5% fat) in early lactation, rising to 27\m=.\1% (13\m=.\1% fat) in late lactation. Milk yieldswere measured by the calf-weighing technique. In well-fed hinds, peak yields of 1400 to 2000 g/day were reached early in lactation. One hind on a restricted food intake gave a maximum of 970 g/day. Lactation continued for 190 to over 280 days. Total yields for the first 150 days were estimated to be 140 to 180 kg in well-fed hinds and 65 kg in the underfed hind.The feed intakes of the hinds rose during late pregnancy, and in early lactation rose again markedly, to a level about 2\ m=. \ 4 to 2\ m=. \ 6 times the maintenance requirement of non-breeding animals.

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At 2--4 monthly intervals during the year blood samples were collected every 15 min for 6 h from 2 intact and 3 castrated red deer stags to study the relationship between season and the secretion of LH and testosterone. In the intact stags plasma LH and testosterone concentrations changed during the year; the LH levels were maximal in August during the phase of testicular redevelopment, while the testosterone levels were maximal from September to November coinciding with the time of peak testicular activity and the mating season. The castrated stags had higher plasma levels of LH than the intact stags at all times of the year, and there was no clear seasonal cycle in LH levels in these animals.

Observations of body weight, testis size, antler status, plasma testosterone and prolactin were made on 12 red deer stags during their first 2 years of life. Six of the stags were fed to appetite throughout the study (Group A) and 6 were fed a 70% restricted diet during each winter (Group B). In addition 6 of the stags , 3 from each group, were studied in more detail; LH and testosterone were measured either after a single injection of LH-RH or in samples taken at frequent intervals over a period of 8 or 24 h. During the study the stags became sexually mature, developed first their pedicles and then antlers and showed at least one complete cycle of casting and regrowth of the antlers . The stags in Group A developed their testes and pedicles about 2 months earlier than did those in Group B. Pedicle initiation was associated with increasing plasma testosterone levels in response to changes in LH secretion, and antler development occurred when testosterone levels were low or decreasing. Cleaning of the velvet was associated with high levels of plasma testosterone. Antler casting occurred when plasma testosterone concentrations were low or undetectable and prolactin levels were high or increasing. The relationship between LH and testosterone varied during the study; in spring when the testes and antlers were growing, relatively high levels of LH were associated with only small peaks of testosterone, yet in summer, when antler growth was complete and the antlers were clean of velvet, low LH concentrations were associated with large peaks of testosterone.