ABSTRACTS
Female aspects of relative fertility in sheep. R. B.
KELLY (1939). Aust. vet. J. 15, 184
KNOWLEDGE concerning the fundamental principles of the
physiology of reproduction owes much to the painstaking
observations of laboratory animals such as rabbits and guinea¬
pigs, but relatively recently a few attempts have been made
to obtain that information concerning the larger farm ani-
mals. It has been inferred commonly that what has been
observed in small animals also occurs in other species. The
anterior lobe of the pituitary gland activates the gonads alike
in birds and man and therefore in broad principles the above
inference is justified. Although in the rabbit ovulation is
induced by coitus and even by mechanical irritation of a
like nature it would be quite incorrect to infer that this is
so for the ewe in which ovulation is quite independent of
such a stimulus. In the ewe oestrus is the first phase of the
reproductive function.
Oestrus by itself is not a sign of
fertility though it is a necessary preliminary to conception.
There is little interbreed variation in the duration of dioes-
trus in domestic ewes. The normal period is 17 days. A
range 16-18 is common, however 15 or 19 days
interval must also be regarded as normal. The so-called
'silent heat' occurs most frequently in Merino ewes. In these
cases oestrus usually reappears after a period which is a
multiple of the normal. During silent heat no odoriferous
substances attractive to the ram are produced. Recurrent
intervals of sexual excitement alternating with a period of
dioestrus constitute a breeding season. The long break
between these seasons is known as the period of anoestrus
or sexual inactivity.
According to Marshall, sexual periodicity is primarily a
function of the gonads. In England most breeds of sheep
have an extended breeding season during late summer,
autumn and winter. In Scotland it is later. While the
breeding season is more limited in countries further north
than Scotland, a continual activity is approached within the
tropics. Marshall also observed that Dorset Horned and
Merino breeds of sheep are peculiar in that they come on heat
throughout the year. The author's observations on three
groups of Merino ewes and a group of Border Leicester x
Merino cross-bred ewes showed a well-defined periodicity
in the percentage of ewes coming into oestrus. In these
four groups there was a decrease in the incidence of oestrus
during the spring followed by an increase in the summer
months and higher levels maintained during late summer,
autumn and winter.
The importance of periodicity in sexual activity cannot
be over-estimated in Australia where the statements of Mar-
shall and others are accepted, since, if there is a definite pe-
riodicity as observed above then brief paddock matings will
give unsatisfactory results. Again genetic factors play an
important part in the periodicity. Some wild types and
domestic breeds of sheep (the Scottish Blackface) are either
monoestrus or nearly so; and others (Merinos) approximate
a completely polyoestrus condition. The long wool breeds
have a marked autumnal periodicity in sexual activity
and this is accepted as due to hereditary make up. It is
further suggested that the observed periodicity of sexual
activity within the Australian Merinos is the result of out-
crossing with long wool sheep during the foundation of the
breed.
Marshall attributes the reproductive rhythm to three
things (1) Metabolical (2) general environment and (3) exter-
oceptive stimuli. The observations of the author do not
support the first two points of Marshall and other workers.
It has been observed that light has a marked, if indirect,
effect upon the gonads and that the essential stimulation is
of the anterior lobe of the pituitary. The effect of daylight
on sexual activity is discussed and according to the obser-
vations of the author, increased sexual activity in ewes was
observed during decreasing hours of daylight. The funda-
mental phenomenon of reproduction is discussed showing
its complexity and indicating that reduced fertility results
from a number of causes. Fertility is defined as the ability
of a male or female to beget or bear progeny. Fertility may
be high or low and it is determined by the number of off-springs
they produce during their breeding life. (The breeding life
of a Merino ewe is divisible into three periods, youth,
maturity and old age. The age factor on fertility indicates
a range of 40 per cent between youth and early maturity
(three years) and this is maintained up to the age of eight and
then the level falls.) Normally fertile Merino ewes can ex-
perience 95 parturitions per centum of ewes adequately mated.
Twinning is more characteristic of British breeds than of
Merinos. British breeds have borne at least 70 per cent twins
while for Merinos of all ages it was only 8 per cent. The
breeding records of 89 ewes, each born in a twin pair, showed
that only 20 of these bore twins and 69 did not. Some workers
are of opinion that twinning is capable of being inherited
as a recessive unit character. On the other hand the ex-
perience of the author and few others shows that the incidence
of twinning is highest when the ewes are either naturally or
artificially 'flushed' prior to or during mating and also
that the age of the ewe is important. The ages when most
twinning occurs were from 7-10 years and during this period
the incidence was 33 per cent higher than the general average.
Factors affecting low lamb markings and the methods to
be adopted to prevent these are also discussed. [M. K. S.]
Sulphanilamide in animals: dosage and tolerence.
A. W. STABLEFORTH and S. L. HIGNET (1942).
Vet. Rec. 54, 525
HORSES, cows and dogs were given varying doses of sul-
phanilamide either single or repeated via the subcutaneous
or oral routes and estimations of the concentrations in blood
and milk were made at varying intervals. Detailed obser-
vations of symptoms and any toxic effects exhibited by
experimental animals were recorded.
Single doses given varied from 1 gm. per 5 lb. body weight
to 1 gm. per 20 lb. weight, while in others continued dosage
was maintained to give a concentration of about 10 milligrams
per cent in blood and milk respectively. In cows serious
toxic symptoms developed if the drug administration was
continued over seven days. The most common symptoms
of sulphanilamide overdosing in animals were lack of muscle
coordination, anorexia and sleepiness. The drop in milk
yield reached a miximum of 40 per cent in cows receiving an
initial dose of 1 gm. per 5 lb. weight and maintenance doses
totalling 1 gm. per 10 lb. daily for five to seven days.
From the results of many experiments carried out it was
concluded that for therapeutic purposes it is desirable to
maintain a concentration of about 10 mg. per cent. On
this basis the doses recommended for different animals are,