Reproductive and Developmental Behaviour in Sheep. An Anthology from “Applied Animal Ethology'”

422 Pages·1985·8.62 MB·English

by  A.F. Fraser (Eds.)

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Developments in Animal and Veterinary Sciences, 18
Reproductive
and developmental
behaviour in sheep
An anthology from " Applied Animal Ethology "
Edited by
A.F. Fraser
Professor of Comparative Physiology
Memorial University of Newfoundland
St. John's, Newfound/and, Canada
ELSEVIER
Amsterdam — Oxford — New York — Tokyo 1985
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This volume consists of a selection of articles
reprinted from the journal "Applied Animal Ethology" (Vols. 1-11).
ISBN 0444-42444-x (Vol. 18)
ISBN 0-44441703-6 (Series)
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ix
Introduction
Of all the farm animals, the sheep is the one which remains closest to the
natural condition in traditional husbandry. Although intensive husbandry
is increasingly being applied to sheep, most sheep production around the
world is still based on the extensive system. Under these conditions, there-
fore, attempts to improve productivity require to take particular account
of reproductive and developmental behaviour. Successful sheep production
depends heavily on optimal reproduction and development. These topics
are presented here in related sections which make up this anthology of
selected publications on sheep behaviour. They have been taken from 10
years of "Applied Animal Ethology", from its inception in December 1974
to the end of its publication under that title in 1984.
During the first decade of "Applied Animal Ethology", a great many
papers were published on sheep behaviour. Of these, 39 have been drawn
together in four sections which deal with sexual behaviour, fetal and peri-
natal behaviour, ewe—lamb recognition and development. In order to be pro-
ductive and to perpetuate themselves successfully, sheep clearly need profi-
ciency in mating, birth and nursing. While other aspects of sheep behaviour
will deserve due attention in the future, the topic of each section, as men-
tioned, has clearly represented an area of special interest in applied ethology;
these topics undoubtedly relate to the realities of sheep breeding and to
biologically critical features of sheep behaviour.
The sheep is a seasonal-breeding animal. Although some breeds have breed-
ing seasons which can extend over much of the year, most breeds only mate
around the time when there is less light than dark per day and when daily
light is diminishing. Those breeds which have had their origins in mountain-
ous regions or where climatic conditions are most severe in the winter have
the most restricted breeding season. Such restriction results in a very sudden
emergence of reproductive activity among the males. This activity tends to
be of limited duration and, as a result, sheep libido comes close to resembling
the rut which occurs in many boreal forms of ungulate life (Fraser, 1968).
The strength of the breeding drive is obviously critical to optimum flock
reproduction.
Since it is critical that the newborn lamb has maximum viability at birth,
it is essential for it to survive the parturient experience without difficulty.
χ
This calls for fetal vitality and the ability of the fetus to adopt an appropriate
posture for expulsion at birth. Awareness of fetal activity improves our
appreciation of fetal needs and obstetrical requirements in sheep birth.
Although there may be frequent lying down and rising before birth, most
ewes remain recumbent until the fetus is partially or completely expelled.
In cases of twin and multiple births, the neonates usually follow each other
within a matter of minutes. Birth is a short process, averaging 80 minutes in
duration. Most newborn lambs are able to stand within the first half-hour
following birth and nearly all are able to stand within the first two hours.
The lamb's first attempts to suck are usually unsuccessful; it often seeks out
the teat by nosing between the forelegs of the dam or any nearby object
which the lamb may feel has maternal properties. If, at this point, the new-
born fails to find the teat or is prevented from doing so by the behaviour of
the mother, its drive to suck may become inhibited.
One of the most noticeable behavioural aspects of sheep in relation to a
newborn lamb is the strong maternal relationship which quickly develops.
A ewe nearly always vigorously rejects any attempts by other lambs to en-
gage in sucking and will look after her own young exclusively. The nature of
the vital bond between ewe and lamb has been given particularly keen study.
Such scientific attention to the phenomenon is justified since this is the
fulcrum on which sheep production is balanced.
Once the newborn lamb is able to stand, it sucks and nibbles at any object
which is at hand; this may be the fleece of the ewe. While the ewe is removing
the placenta from the lamb, the latter finds its way to the region of the teats
and udder. Sometimes the lamb is prevented from undertaking sucking by
diligent efforts of the mother to remove the placenta. If the udder is too
large, the newborn may find the teat difficult to grasp. However, once the
newborn has sucked successfully its survival is largely assured. Within about
one hour of birth, approximately 60% of newborn lambs have begun to suck
and, in normal cases, nearly all lambs have sought out the udder within the
first two hours.
For the first few weeks of life, lambs stay in close proximity to their ewes.
By one month of age, young lambs spend two-thirds of their time in the
company of other lambs and play within such groups is a notable feature
of behaviour. Play becomes reduced as lambs grow and is of only occasional
occurrence as nursing terminates with weaning.
The behavioural life-cycle of sheep will have to be continually studied and
documented throughout future research work so that appropriate husbandry
can be maintained in the interests of productivity and welfare in this species
which is woven into the fabric of world-wide animal farming.
REFERENCE
Fraser, A.F., 1968. Reproductive Behaviour in Ungulates. Academic Press, London and
New York, 202 pp.
SECTION I ι
Sexual Behaviour
MATING ACTIVITY AND ITS RELATIONSHIP TO REPRODUCTIVE
PERFORMANCE IN MERINO SHEEP
D.G. FOWLER
New South Wales Department of Agriculture, CSIRO, Blacktown, N.S.W. (Australia)
ABSTRACT
Fowler, D.G., 1975. Mating activity and its relationship to reproductive performance in
Merino sheep. Appl. Anim. EthoL, 1: 357—368.
Mating activity was observed directly on 22 flocks of Merino sheep at five locations
spread over several hundred kilometres. The flocks were subjected to differences in
nutritional, seasonal, climatic and topographic influences and varied in size, and in the
age and weight of ewes and rams. Each flock was joined with rams for mating under
paddock conditions.
In the first series of observations there were 16 flocks at five locations and it was found
that the sum of interservice intervals for all ewes, T, during an observation period was
highly correlated with the total number of services Ν (r> 0.89, Ρ < 0.005).
This report is confined to an analysis and interpretation of this relationship and the
second series of observations form part of the analysis.
In the second series of observations, six different flocks of Merino ewes in two differ-
ent environments were used to study the relationship between mating activity and repro-
ductive performance. Each flock was joined under paddock conditions and studied by
direct observation. It was found that the sum of interservice and intermount intervals for
ewes were highly correlated with the number of pregnancies (r > 0.87, Ρ < 0.05). The
ratio T/N was found to be highly correlated with the number of foetuses for both mounts
(r = 0.88, Ρ < 0.05) and services (r = 0.88, Ρ < 0.05).
The variables Τ and Ν are thus closely related to each other over a wide range of envi-
ronments and their ratio, T/N accounts for the major proportion of the variation in the
fertility of six different flocks of Merino sheep in two different environments. These
results offer the possibility of the prediction of fertility in Merino sheep.
INTRODUCTION
The mating behaviour of domestic sheep under field conditions with mini-
mal interference has not been examined although many millions of sheep are
joined with rams for mating under these conditions each year.
Studies of mating behaviour in which oestrus has been induced with exo-
genous hormones (Lindsay and Robinson, 1961 a and b; Lindsay, 1966 b;
Lindsay and Ellsmore, 1968; Fletcher and Lindsay, 1968; Blockey and
Cumming, 1970) or where rams and ewes are in pens (Hulet et al., 1962 a
2
and b; banks, 1964; Pepelko and Clegg, 1965; Lindsay, 1965,1966 a;
Beamer et al., 1969; Bermant et al., 1969) or where rams are removed from
the flock each night (Mattner et al., 1967; Mattner and Braden, 1967;
Braden, 1971) may bear little relationship to natural mating under paddock
conditions. Removing rams from the flock influences the length of oestrus in
ewes (Hulet et al., 1962 c; Parsons and Hunter, 1967; Parsons et al., 1967)
and intensifies the initial mating activity that occurs when rams are reintro-
duced to the flock (Hulet et al., 1962 a; Blockey and Cumming, 1970).
In this study, particular emphasis has been placed on the average interser-
vice and intermount intervals of time for ewes because they can be measured
under field conditions without interfering with the flock. Also, during pre-
liminary examination of the Series 1 data, it was found that the sum of inter-
service intervals was very closely related to the number of services obtained
from many different flocks over a wide range of environments.
Analysis and interpretation of this relationship then commences and it is
postulated that the average interservice and intermount intervals may be
directly related to fertility. The average interservice interval for ewes is known
to increase as the number of services increases (Pepelko and Clegg, 1965) and
a relationship between number of services and fertility has been suggested
(Gerasimov, 1957; Mattner and Braden, 1967). The second series of observa-
tions were designed to examine the relationship between the interservice and
intermount intervals and fertility. The results offer the possibility of explaining
the variation in reproductive performance as it is determined at mating which
would enable the prediction of fertility.
SERIES 1
Methods
From March, 1971 to May, 1973, the mating activity of flocks of Merino
sheep was observed at four locations throughout New South Wales (Fig.l).
At a fifth location in March, 1964 (Mattner et al., 1967), data were collected
in an identical way to that collected here and is included in the present study.
Sheep
Flocks were joined with one, two or three Merino rams for 5 weeks. Each
flock was mated with a different ram or different groups of rams whose age
varied from 2 to 6 years. Flock size varied from 50 to 400 ewes and the
average age of ewes varied from 2 years in some flocks to 8 years in others.
The average weight of ewes varied from 32 kg in some flocks to 45 kg in
other flocks. Pastures on which the flocks were grazing varied from very poor,
where there was almost zero feed, to rank where there was a superabundant
growth of green feed standing 60 to 80 cm high. Paddock size varied from 1
to 30 ha and meteorological conditions varied markedly.
Each ram was fitted with a "sire-sine" harness and crayon (Radford et al.,
3
Fig.l. Map of New South Wales showing the location of observation sites.
1960) and was individually identified with painted horns and a side brand.
Ewes were identified by means of an ear tag and by large numbers branded
on the side of the fleece.
Observations
Observations commenced at least 1 day after ewes and rams were joined.
At all times during observation, the sheep were in view of two or three ob-
servers in a mobile observation tower. Observations always commenced soon
after sunrise and continued uninterruptedly. The average duration of obser-
vation was 10.8 ± 2.7 (SE) h.
The ram and ewe involved in each mount and service were identified and
the time recorded. A mount was defined as having occurred when a ram
straddled the rear quarters of a ewe. A service was considered to have occurred
if mounting was accompanied by a distinct pelvic thrust followed immediately
by dismounting and a short period during which the ram displayed little
interest in the ewe but stood quietly, usually nearby the ewe, with his head
and neck extended and slightly lowered. When a ram mounted twice and
achieved intromission and ejaculation during the second mount, this was
defined as two mounts and a service. Mating activity was recorded directly
onto an event chart (Fig.2).
Statistical analysis
The following statistics were obtained from each event chart:
η = the number of services (or mounts) observed for any one ewe.
Ν = the sum of all services (or mounts) during the observation period.
t = the time interval between two successive services (or mounts) on any one
ewe.
t' = the sum of interservice (or intermount) intervals of time observed for
any one ewe.
4
EWE
35
20
19
Ν =10 SERVICES
Τ =975 MINUTES
L
06.00 12.00 18.00
TIME—*
PERIOD OF OBSERVATION
Fig.2. The pattern of mating activity that was observed on March 10th, 1971 at
Condobolin where one ram had been joined with 50 old ewes.
2000i
ONE RAM
0 500 100
N-SERVICES Ν-MOUNTS
Fig. 3. Showing the sample regressions of Τ on N. Within each ram number, the different
symbols refer to the different flocks studied in Series 1. Each flock has a pair of symbols,
one for services and the other for mounts.
5
Τ = the sum of all interservice (intermount) intervals for all ewes during an
observation period.
k = the number of ewes seen to be served or mounted during the observation
period.
Regression analysis and comparison of regressions (Williams, 1959) were
used to examine the data.
Results
There was a very close relationship between Τ and Ν for services ^nd
mounts, where flocks were joined with the same number of rams (Fig.3). The
relationship can be described by the general equation:
Τ = b + Nc
where Τ and Ν are defined and c and b are constants whose value depends on
the number of rams and whether the relationship is calculated from services
or mounts.
Regression coefficients and their standard errors, and the coefficients of
correlation (Table I) and the comparison of regression analysis (Table II)
show a general trend for the slopes of the regression of Τ on Ν to decrease as
the number of rams per flock increased.
Flocks having the same number of rams are markedly similar, despite the
very wide differences in the test situations from which the data were obtained.
Correlation coefficients were in excess of 0.73 (P < 0.05) for mounts and
0.89 (P < 0.005) for services.
DISCUSSION
A direct relationship between Τ and Ν is obvious. The closeness of the
TABLE I
Results on the regression analysis of Γ on Ν for both mounts and services
Mating Slope Intercept Correlation
activity ± SE ± SE
Services
1 ram 137.1 ± 17.4* -481 ± 175* 0.93**
2 rams 87.3 ± 13.8* —453 ± 256 0.89**
3 rams 51.1 ± 10.5* 199 ± 202 0.91**
Mounts
1 ram 34.1 ± 9.2* 157 ± 231 0.78*
2 rams 15.4 ± 4.5* 383 ± 332 0.73*
3 rams 30.4 ± 5.9* — 215 ± 373 0.92**
*P< 0.05; **P< 0.01.