270
ABSTRACTS
[ Vol. XXIV, Part IV
In part 2, the breeding season of six British breeds of sheep kept at Cambridge
from 1948-51 have been discussed. The oestrus percentages were inversely correlat-
ed with the day length and were maximum from November to January. The œstrous
percentage is the total number of heats actually observed per 100 calculated heats
theoretically possible. The duration of the breeding season of the first cross ewes
(Welsh M. X Dorset) was intermediate between the two parents. The breeding
season in ewe lambs was one-fourth to one-third less than those of adults. The
yearling sheep behaved as adults. The first oestrous occurred at 36 weeks (range
29-43 weeks), the live weight being 79 lb. (range 52-113 lb.). Significant differences
exist between breeds in the age at first oestrous. The nutrition of the sheep played
an important role in the duration of the breeding season. The number of 'silent
heats' expressed as percentage of total possible heats was 34-46 ; the conception
rate was lowered. However, this depression was prevented by heavy feeding and
by P.M.S. injection. Annual differences were negligible. If the ewes are not allow-
ed to breed in one season it does not affect the next season. Teasing by a Vasecto-
mised male transforms silent heats into true heat periods.
In part 3, discussion on the breed differences in reaction to light is included.
The studies indicate a possibility to arrange the onset of the breeding season by suit-
able manipulation of the light environment at any desired time of the year.
In part 4 on 'reproduction of the ewe', it was found that the œstrous cycles
were more irregular in ewe lambs than in adults. The frequency of silent heats
was most common in ewe lambs, next in yearlings and lastly in adults. Annual
differences were not observed. The adults and yearlings had a longer œstrum than
ewe lambs. Breed differences were observed. After parturition the heat was
observed after 35 days on the average. It appeared that post-partum heat is a
genetic character.
In part 5, the author has discussed the mating behaviour of ewes which was
not affected by the breed of ram used. Rams, on the other hand, were influenced
by breed, age, colour and appearance of fleece. The sex-desire of the rams was
depressed by rainfall and foot rot. Pregnancy diagnosis by vaginal smears was
studied. The method was 65-79 per cent accurate in the late months of pregnancy.
The paper contains an exhaustive bibliography which enhances its value.
(M.P.J.)
The nature of a yeast-stimulating agent in mammalian spermatozoa. D. GHOSH
and HENRY A. LARDY (1952). J. Anim. Sci. 11, 545
T HE marked difference in the metabolic activity of epididymal and ejaculated
spermatozoa of mammals led the authors to the isolation of a yeast-stimulat-
ing substance (Metabolic regulator) from the spermatozoa. The substance is nor-
mally found in a bound inactive form both in epididymal and ejaculated spermatozoa
and is progressively liberated by them when they come in contact with seminal
fluid. In the present paper the authors have shown that the substance is exclusively
found in spermatozoa. In a zoospermic ejaculate it showed no significant acidity