The effect of age on attainment of puberty and on seminal characteristics in yearling and mature rams was studied in German Merino, Persian Blackhead and indigenous Native rams living on Rhodesian highveld.1. Puberty occurred at age and live weight proportional to mature live weight. Well-grown Native lambs ejaculated first at 169 days of age and 46 lb. live weight; Merino lambs when 250 days old and 79 lb. live weight and Persians were intermediate. Onset of sexual maturity was related more closely to live weight than to age, since runts ejaculated first at live weights close to those of well-grown lambs.

Early morning and midday body temperatures of rams and ewes of three breeds of sheep were measured once weekly for a period of 10 months in Northern Rhodesia and 12 months in Southern Rhodesia.1. In all breeds seasonal fluctuations in body temperature were due to concurrent fluctuations in ambient air temperature.2. Mean annual body temperatures were: Merino 102·2° F.; Persian 101·7° F. and Native 101·7° F. Wool and hair breeds differed considerably in their early morning temperatures and in their body temperature increases from 6.30 a.m. to 12.30 p.m. Mean annual values for these measurements were Merino 101·73 and 1·92° F.; Persian 100·81 and 1·83° F.; Native 100·73 and 1–92° F. At all times Merinos showed markedly greater uniformity of body temperature than either hair breed. There was no evidence to show that the thermoregulatory mechanisms of these animals had been stressed unduly.3. Sex had no consistent effect on body temperature or on rise in body temperature.In general, lactating ewes showed a significantly higher initial body temperature than either empty or pregnant ewes, but the respective heat tolerances as measured by body temperature increase did not differ appreciably. Body temperature differed little in empty and pregnant ewes.4. Although the youngest group of ewes in each breed showed the highest early morning temperature, there was no evidence that heat tolerance was less in young than in old animals.5. Black-coated Native ewes had higher initial body temperatures and a smaller body temperature increase during the summer months in Southern Rhodesia than brown or broken-coloured Native ewes. These effects were due to differences in coat density rather than to differences in coat colour or skin pigmentation.6. In all breeds the magnitude of the diurnal and annual variation in body temperature was different in Northern and Southern Rhodesia. Differences were largely of climatic origin but low plane of nutrition in Southern Rhodesia possibly reduced critical body temperature and impaired thermoregulatory ability.

6 5 With text-figure Printed in Great BritainStudies on the adaptability of three breeds of sheep to a tropical environment modified by altitude V. The annual fluctuation in breeding ability of rams maintained on Rhodesian highveld Correct use of highly fertile breeding stock is the Unfortunately, male fertility cannot be assessed basis of successful animal production. In order to completely from microscopic examination of semen, improve sheep husbandry in Rhodesia it is neces-since sperms may look satisfactory and yet have sary to know if fertility fluctuates seasonally in low fertilizing capacity. Conception rate is a truer rams maintained on highveld.criterion of fertility than semen evaluation but Emmens (1959) has discussed the major agencies cannot be obtained simply. In other studies with the which influence breeding ability of rams. In tem-same flock (Symington (1960a) found that absence perate and subtropical areas the fundamental of cyclic activity in ewes did not necessarily indifactor is the photoperiod. In Rhodesia annual cate pregnancy whilst pregnant ewes frequently variation in day-length is small and the photo-exhibited cyclic activity. Birth rate from controlled period may not change sufficiently to play a service is a comparative measure of male fertility dominant role in sexual activity of rams. Neverthe-although many factors other than sperm viability less, since distinct seasonally of rainfall causes must be considered. marked variation in plane of nutrition and ambientIn order to study fertility in Rhodesian rams temperature can be inimical to survival of lambs, seminal characteristics and libido were evaluated an adaptive mechanism may function to induce from April 1956 to January 1959. Birth rate from reproduction at the most appropriate time of year, controlled service between May 1956 and March Male fertility may fluctuate accordingly. Again, 1958 gave additional information on breeding little attention has been paid to libido and its effect ability. on reproductive ability. Good libido is of particular RAMS importance in the tropics because flocks roam over large areas and the duration of oestrus is short.German Merino, Persian Blackhead and indiDesire to seek for ewes on heat and ability to copu-genous 'Native' rams were available as shown in late promptly and effectively are then of major Table 1. The breeds and their management have importance.been described (Symington, 19606).

The application of Johnsen's tannic acid method to the extraction of gonadotrophins from ovine urine was studied using the urine of castrated sheep.Slight modification of the original method increased the efficiency of extraction. Rate of recovery was measured at several levels of added pituitary and urinary gonadotrophins and was similar to recovery rates reported for human urines (30\p=n-\81 %). Reproducibility of the extraction procedure was excellent. Further purification of the final ethanol precipitate without loss in potency was effected by chromatography using diethylaminoethyl cellulose. The daily excretion of total gonadotrophic activity, follicle stimulating hormone and luteinizing hormone by two male and one female castrated sheep was estimated for four periods each of 3 weeks. In all instances excretory levels fluctuated considerably and randomly. Levels of excretion of all types of gonadotrophic activity were much lower than in man.

295Studies on the adaptability of three breeds of sheep to a tropical environment modified by altitude II. Responses in body, skin and coat temperatures, cardio-respiratory frequencies and rate of moisture secretion of ewes to the diurnal fluctuation in ambient temperature during the hottest part of the year