Directory UMM :Data Elmu:jurnal:S:Small Ruminant Research:Vol36.Issue2.May2000:
Small Ruminant Research 36 (2000) 119±135
Productive performance of Dorper sheep
S.W.P. Cloetea, M.A. Snymanb,*, M.J. Herselmanb
a
Elsenburg Agricultural Development Centre, Private Bag X1, Elsenburg 7607, South Africa
Groo¯ontein Agricultural Development Institute, Private Bag X529, Middelburg 5900, South Africa
b
Abstract
The Dorper is a hardy South African composite breed, derived from a cross between the Black-headed Persian and the
Dorset Horn. Dorpers are regarded as early-maturing, and ewes lambed at an age of 1 year in one study. Age at ®rst lambing
was higher in other literature sources cited. The fertility of Dorper ewes was approximately 0.90 ewes that lambed per ewe
mated, with a litter size ranging from 1.45 to 1.60. The gestation length of Dorper ewes was approximately 147 days, while
they were reported to start cycling as soon as 52 days after parturition. The pre-weaning survival of Dorper lambs was cited at
approximately 0.90. Overall reproduction rate of Dorpers ranged from 0.99 to 1.40 lambs weaned per ewe mated, while it
exceeded 1.40 lambs weaned per ewe mated per annum under accelerated mating conditions. Dorper lambs gained from 0.24
to 0.28 kg per day under vastly different environmental conditions. When weaned early at 2±3 months of age, post-weaning
gains in excess of 0.18±0.20 kg per day were recorded. At slaughter, Dorper lambs had dressing percentages of approximately
50%. Two divergent genotypes in the breed (with a hairy or a woolly ¯eece cover) were evaluated under natural pasture
conditions. No conclusive advantage in favour of either genotype could be demonstrated as far as productive traits were
concerned. It was concluded that the breed adapts well to a wide variety of environmental conditions. In view of the scarcity of
estimates of genetic parameters for the breed, the maintenance and expansion of datasets suitable for this purpose should
receive high priority. # 2000 Elsevier Science B.V. All rights reserved.
Keywords: Dorper sheep; Reproduction; Growth; Carcass traits; Genotypes
1. Introduction
The need for a sheep breed suitable for the production of slaughter lambs under the adverse conditions of
the arid, extensive regions of South Africa resulted in
the formation of the Dorper breed in the early 1940s.
The founders of the new composite breed sought to
combine the hardiness of the Black-headed Persian
with the mutton production capability of the Dorset
*
Corresponding author. Tel.: 27-49-842 1113;
fax: 27-49-842 4352.
E-mail address: [email protected] (M.A. Snyman)
Horn (Campbell, 1989). The original crossings and
early history of the breed are documented well
(Nel, 1993). The hardiness and adaptability of the
Dorper led to a rapid increase in popularity (Marais
and Schoeman, 1990). Although exact Dorper
numbers are not known, the non-wool sheep numbers
in South Africa increased markedly from approximately 4.5 million in the late 1960s to approximately
7.0 million in the early 1990s (Abstract of Agricultural
Statistics, 1997). It is more than likely that an
expansion in Dorper numbers greatly contributed to
this increase, which was largely at the expense
of woolled sheep numbers (Fig. 1). The breed has
0921-4488/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 9 2 1 - 4 4 8 8 ( 9 9 ) 0 0 1 5 6 - X
120
S.W.P. Cloete et al. / Small Ruminant Research 36 (2000) 119±135
Fig. 1. Changes in the numbers of wool and non-wool sheep in the South African National sheep ¯ock over time.
grown to be the second largest in South Africa, and the
breeding stock have also been exported to other
countries (Terblanche, 1979). Today Dorpers are
found throughout southern and central Africa, in the
desert areas of North Africa and the Middle East as
well as on other continents, namely Northern America
and Australia.
The Dorper is able to withstand dehydration and
quickly replenish body weight losses when water
becomes available (Degen and Kam, 1992). This
capacity of Dorper sheep enables it to adapt to drier
regions where the availability of water proves to be a
limitation. The breed also adapts to temperate regions,
and has been extensively used in accelerated mating
systems (Basson et al., 1969; Manyuchi et al., 1991;
Schoeman and Burger, 1992). Dorper and Dorper
cross sheep were present on all the above average
sheep farms included in the survey of Stafford and
Hansson (1991) in Zambia.
Despite its popularity, scienti®c reports on Dorper
sheep are scattered over a number of scienti®c and
semi-scienti®c journals across the globe. Some of
these literature sources are not readily available for
all scientists. Moreover, estimates of the genetic parameters in the Dorper sheep breed are scarce. This
review attempts to present the bulk of information on
the production of Dorpers, while it will also include
the estimates of parameters that were found in the
literature.
2. Reproduction
2.1. General
In a comprehensive survey involving data of 130
Dorper farmers in the drier Karoo region of South
Africa and a total of 115 314 breeding ewes that were
maintained under different managerial regimes, lambs
born per ewe mated were estimated at 1.038 (Ackermann, 1993). District means ranged from 0.924 in
Prieska to 1.123 in Calvinia. It was estimated that only
36.1% of the respondents achieved lambing ®gures of
1.11 lambs born per ewe mated or higher. Given that
the production of lamb is the sole source of income in
a non-wool breed like the Dorper, it is evident that
reproduction needs to be maximized for maximum
economic returns. Little information is available for
changes in the relative reproductive performance of
the South African national ¯ock over time, but given
the increasing economic pressures on sheep farmers, it
is evident that reproduction should receive the necessary attention.
This review focuses on various aspects of Dorper
reproduction, such as sexual maturity, oestrus, gesta-
121
S.W.P. Cloete et al. / Small Ruminant Research 36 (2000) 119±135
tion and post-partum anoestrus. The de®nitions used
for the most commonly used reproductive parameters
will be presented at this stage, for ease of comprehension.
Ewe fertilityEwes that lambed per lambing
opportunity
Litter sizeLambs born per ewe that lambed
Lamb survivalLambs weaned per lamb born
Overall reproduction rateLambs weaned per ewe
mated (lambs weaned per ewe per annum, where
applicable under accelerated lambing systems)
Overall reproduction rate is a function of the component traits, namely ewe fertility, litter size and lamb
survival.
2.2. Sexual maturity
The Dorper is regarded as an early-maturing breed.
In early work, Joubert (1962) reported that Dorset
HornPersian ewes attained puberty at 399.7 days,
with a range between 195 and 872 days. Later work
reported substantially younger ages at ®rst oestrus.
Dorper maiden ewes exhibited their ®rst oestrus at an
age of 213 days and a live weight of 39 kg, while
Romanoff ewes were 228 days of age with a live
weight of 28 kg at their ®rst oestrus (Greeff et al.,
1988). Corresponding ®gures for Dorpers from the
study by Schoeman et al. (1993b) were an age of 8.14
months and a live weight of 50.8 kg. Under an 8monthly breeding cycle, Dorper ewes born in the
autumn were reported to conceive for the ®rst time
at their ®rst mating at an average age of 328 days and a
live weight of 45.9 kg (Basson et al., 1970). The
majority of ewe lambs that were born in winter (24/
250.96 of those available) conceived at an average
age of 252 days and a live weight of 44.7 kg.
Dorper ewes lambed for the ®rst time at an average
age of 346 days, compared to 363 days in Romanovs
(Greeff et al., 1988). Under an accelerated lambing
system, Schoeman and Burger (1992) found that
Dorper ewes lambed for the ®rst time at an average
age of 19.6 months. The ewe fertility of 208 Dorper
ewes mated to fertile rams at an age of 7 months was
0.58 (Snyman, 1998; unpublished), with a litter size of
1.16. Lamb survival averaged 0.79 and overall reproduction 0.53 in these ewes.
As far as rams are concerned, it was demonstrated
that epididimal sperm concentrations of Dorper lambs
rose markedly after an age of 140 days (Skinner,
1971). Mean sperm counts (109) were 0.1 at an
age of 112 days, 0.2 at 140 days, 16.6 at 168 days,
27.9 at 196 days and 40.6 at 365 days. From this it is
clear that Dorper ram lambs are capable of fertilizing
ewes from quite an early age.
2.3. Ewe fertility
Literature ®gures for ewe fertility are remarkably
consistent, being approximately 0.90 ewes lambed per
lambing opportunity in the majority of sources cited
(Table 1). Somewhat lower ®gures of respectively,
0.80 and 0.75, were reported in the studies of Pretorius
and Viljoen (1968) and Schoeman et al. (1993b). The
majority of ®gures is, however, consistent with barrenness percentages of approximately 6±7% reported
Table 1
Estimates of ewe fertility (ewes that lambed per ewe mated) in Dorper sheep, as reviewed in the literature (in a chronological order)
Estimate
Diet
Management
Reference
0.83±0.91
0.80
0.91
0.89
0.97
0.89
0.81
0.90
0.85
0.92
0.75
0.82
Natural pasture
Natural pasture
Complete diet
Natural pasture
Complete diet
Natural pasture
Not given
Natural pasture
Irrigated pasture
Natural pasture
Complete diet
Natural Pasture
Flushing treatments
Flushing and super-ovulation
Accelerated lambing (8 months)
Accelerated lambing (8 months)
Accelerated lambing (8 months)
Annual lambing
Annual lambing
Accelerated lambing (8 months)
Accelerated lambing (8 months)
Survey information
Accelerated lambing
Accelerated lambing (10 months)
Coetzee (1964)
Pretorius and Viljoen (1968)
Basson et al. (1969)
Buitendag (1985)
Elias et al. (1985)
Cloete and De Villiers (1987)
Eltawil and Narendran (1990)
Manyuchi et al. (1991)
Schoeman and Burger (1992)
Ackermann (1993)
Schoeman et al. (1993b, 1995)
Van Niekerk (1998)
122
S.W.P. Cloete et al. / Small Ruminant Research 36 (2000) 119±135
for New Zealand Romney sheep (Dalton and Rae,
1978). Ewe fertility of Dorpers compares favourably
to ®gures quoted for Australian Merinos (Knight et al.,
1975; Plant, 1984; Jordan et al., 1989), as well as
South African Merinos and Dohne Merinos (Fourie
and Cloete, 1993).
2.4. Qestrus cycle
Dorset HornBlack-headed Persian ewes were
reported to have an oestrus cycle of 16.9 days (Joubert,
1962). These ewes showed reduced seasonality compared to Merino ewes, which went into anoestrus for 1
month of the year (October), with very limited sexual
activity in 3 more months. The mean annual number of
oestrus cycles per ewe was 8.1 for Merinos and 16.6
for the Dorset HornBlack-headed Persian cross.
Both Dorper and Dohne Merino ewes were found to
have a 17.3-day cycle in subsequent work (Joubert and
Louw, 1964). Average cycle length of Dorper ewes
was similarly 17.3 days in the study of Boshoff et al.
(1975). This study suggested that the Dorper was
intermediate with regard to its seasonal expression
of oestrus activity. The Merino and Karakul were
found to be more seasonal, while the Black-headed
Persian and the Namaqua Afrikaner were more aseasonal. The peak level of activity of Dorper ewes
was, however, found to be higher than in the other
breeds. Pretorius and Viljoen (1968) reported mean
cycle lengths of 17.4 days for maiden Dorper ewes and
17.6 days for mature ewes. Corresponding values
recorded by Elias et al. (1985) were 16.6 and 17.6
days, respectively. The mean oestrus cycle length of
Dorper ewes was reported at 17.8 days in a group of
Dorper ewes where a commercial semen diluent was
placed in each uterine horn by laparoscopy, while
control group ewes had a mean cycle length of 18.4
days (Taljaard et al., 1991).
The average duration of oestrus was 33.3 h for
Dorset HornBlack-headed Persian cross ewes and
25.2 h for Merino ewes (Joubert, 1962). Depending on
the interval between oestrus recordings (every 4, 8 or
12 h), the duration of oestrus ranged from 28.0 to
35.1 h in Dorper ewes (Joubert and Louw, 1964). The
corresponding range in Dohne Merino ewes was 20.5±
26.6 h. More oestrus periods commenced during
nighttime than during daytime. In later work, the
average duration of oestrus was recorded at 36 h for
mature Dorper ewes and at 28 h for primiparous ewes
(Elias et al., 1985).
2.5. Litter size
Larger differences were observed between literature sources as far as litter size is concerned (Table 2).
A number of sources quoted litter size ®gures of below
Table 2
Estimates of ewe litter size (lambs born per ewe that lambed) in Dorper sheep, as reviewed in the literature (in a chronological order)
Estimate
Diet
Management
Reference
1.00±1.09
1.39
1.73
1.49
1.40
1.59
1.14
1.58
1.48
1.50
1.56
1.36
1.29
1.41
1.17
1.08
1.43
1.24
Natural pasture
Natural pasture
Complete diet
Natural pasture
Complete diet
Natural pasture
Not given
Not given
Not given
Not given
Natural pasture
Natural pasture
Natural pasture
Irrigated pasture
Natural pasture
Complete diet
Natural pasture
Complete diet
Flushing treatments
Control: flushing and super-ovulation
Accelerated lambing (8 months)
Accelerated lambing (8 months)
Accelerated lambing (8 months)
Annual lambing
Maiden ewes: accelerated lambing
Mature ewes: accelerated lambing
Annual lambing
Annual lambing
Accelerated lambing (Carnarvon)
Accelerated lambing (Tarka)
Accelerated lambing (8 months)
Accelerated lambing (8 months)
Survey information
Accelerated lambing
Control: super-ovulation
Accelerated lambing (10 months)
Coetzee (1964)
Pretorius and Viljoen (1968)
Basson et al. (1969)
Buitendag (1985)
Elias et al. (1985)
Cloete and De Villiers (1987)
Greeff et al. (1988)
Greeff et al. (1988)
Eltawil and Narendran (1990)
Greeff et al. (1990)
Badenhorst et al. (1991)
Badenhorst et al. (1991)
Manyuchi et al. (1991)
Schoeman and Burger (1992)
Ackermann (1993)
Schoeman et al. (1993b, 1995)
Erasmus et al. (1994)
Van Niekerk (1998)
S.W.P. Cloete et al. / Small Ruminant Research 36 (2000) 119±135
1.2, but the vast majority range from 1.45 to 1.60.
These ®gures compare favourably to ®gures reviewed
for New Zealand Romney ewes (Dalton and Rae,
1978), as well as Australian Merinos (Knight et al.,
1975; Jordan et al., 1989) and South African woolled
breeds (Fourie and Cloete, 1993). In a study where
Dorpers were maintained together with Merinos and
Dohne Merinos, respective litter size ®gures of 1.73,
1.39 and 1.41 were obtained (Basson et al., 1969).
Litter size of Dorper ewes was affected by ewe age,
multiple birth rate increasing to an age of 4±6 years,
followed by a tendency towards a decline (Cloete and
De Villiers, 1987; Schoeman and Burger, 1992). Ewes
born as multiples had a higher litter size than single
contemporaries (Cloete and De Villiers, 1987; Schoeman and Burger, 1992). The repeatability (estimated
as the simple correlation between paired records) of
litter size in Dorper ewes was computed at 0.32
(Schoeman and Burger, 1992).
2.6. Ovulation rate and embryo loss
Dorper ewes had an ovulation rate of 1.50 and
embryo losses of 0.66 in the study of Greeff et al.
(1990). Corresponding ®gures for Romanov ewes
were 3.33 and 1.15. More research on this topic
appears to be warranted.
2.7. Response of litter size and ovulation rate to
hormonal treatment
Litter size responded to exogenous pregnant mare
serum (PMS) in Dorpers. The administration of 500 or
750 IU PMS elevated litter size from 1.39 to approximately 1.70 in the study of Pretorius and Viljoen
(1968), while 250 IU PMS did not produce any effect.
Erasmus et al. (1994) similarly found that litter size
increased from 1.43 in control Dorper ewes to 1.60 in
ewes receiving 250 IU PMS and 1.88 in ewes receiving 500 IU PMS. Dorper ewes that were super-ovulated with follicle-stimulating hormone (FSH) had
18.2 corpora lutea compared to 6.7 corpora lutea in
ewes super-ovulated with 1250 IU PMS (Van Zyl
et al., 1987). Unovulated follicles amounted to,
respectively, 3.0 and 4.1, on respective treatments.
Only data of ewes that were super-ovulated with FSH
were thus considered further, owing to the small
number of fertilized ova recovered from PMS treated
123
ewes. In ewes subjected to natural service, a proportion of 0.475 of the potential embryos was recovered.
Natural service after the application of prostaglandin
F2a to the cervix of ewes resulted in a 0.668 recovery
rate. Surgical insemination by laparoscopy resulted in
a proportion of 0.933 of the potential embryos being
recovered.
2.8. Gestation length
The literature ®gures for the gestation length of
Dorper sheep are remarkably constant. Average ®gures found in the literature included 146.5 days (Joubert, 1962), 147.9 days (range 144±153 days; Joubert
and Louw, 1964) and 146.5 days (range 142±150 days;
Van Niekerk and Mulder, 1965). Gestation length of
Dorpers was consistently shorter than that of woolled
breeds when maintained together. Joubert and Louw
(1964) reported a mean gestation length of 150.5 days
(range 148±154 days) for Dohne Merinos, while Van
Niekerk and Mulder (1965) found a gestation length of
151.6 days (range 148±157 days) for Dohne Merinos
and 149.0 (range 145±154 days) for Merinos. In the
study of Elias et al. (1985), the length of gestation of
Dorpers ranged from 146.2 to 147.7 days, depending
on ewe age, litter size and lamb sex. When maintained
in an accelerated lambing system, the slightly shorter
gestation length of Dorpers may facilitate earlier rebreeding.
As far as the time of commencement of parturition
was concerned, it was demonstrated that 60% of
Dorper ewes started to lamb in the interval from
06:00 to 18:00, while 40% of parturitions commenced
between 18:00 and 06:00 (Joubert and Louw, 1964).
2.9. Post-partum anoestrus
Cross-bred Dorset HornBlack-headed Persian
ewes were recorded to start cycling 51 days after
parturition on average, with a range of 2±149 days
(Joubert, 1962). Post-partum anoestrus of Dorper ewes
depended strongly on the lambing season, being
approximately 123 days for ewes lambing in winter
and spring, 89 days for ewes lambing in summer and
62 days for ewes lambing in autumn (Joubert, 1972).
Widely different feeding levels (0.10 kg digestible
protein and 14.6 MJ digestible energy vs. 0.05 kg
digestible protein and 6.1 MJ digestible energy) dur-
124
S.W.P. Cloete et al. / Small Ruminant Research 36 (2000) 119±135
Table 3
Estimates of lamb survival (lambs weaned per lamb born) in Dorper sheep, as reviewed in the literature (in a chronological order)
Estimate
Diet
Management
Reference
0.85
0.88
0.84
0.91
0.78
0.90
0.94
0.95
0.88
Natural pasture
Complete diet
Complete diet
Natural pasture
Not given
Natural pasture
Irrigated pasture
Natural pasture
Natural pasture
Control: flushing and super-ovulation
Accelerated lambing (8 months)
Accelerated lambing
Annual lambing
Multiples: accelerated lambing
Accelerated lambing (8 months)
Accelerated lambing (8 months)
Survey information
Accelerated lambing (10 months)
Pretorius and Viljoen (1968)
Basson et al. (1969)
Elias et al. (1985)
Cloete and De Villiers (1987)
Greeff et al. (1988)
Manyuchi et al. (1991)
Schoeman and Burger (1992)
Ackermann (1993)
Van Niekerk (1998)
ing lactation did not markedly affect these ®gures.
Vosloo et al. (1969) previously indicated that feeding
level (high, medium or low) failed to reduce postpartum anoestrus in small groups of six Dorper ewes.
The treatments were chosen to result in respective live
weights of 106, 92 and 70% at the weaning of their
lambs, relative to a live weight of 100% at the commencement of feeding. The post-partum interval to the
®rst recorded ovulation was, however, reduced to 86
days in ewes on the high treatment compared to 119
and 124 days on the medium and low treatments. The
inter-lambing interval of Dorper ewes ranged from 6.2
to 7.7 months (Elias et al., 1985).
compare favourably with overall levels of lamb mortality expected in sheep-producing systems, as
reviewed in the literature (Dalton and Rae, 1978;
Alexander, 1984; Plant, 1984; Jordan et al., 1989;
Haughey, 1991). Moreover, lamb survival was found
to be largely independent of known sources of variation, including litter size (Cloete and De Villiers,
1987). The survival of lambs in the latter study was
0.92 for singles, as compared to 0.90 for multiples.
Corresponding ®gures from the study of Schoeman
and Burger (1992) were, respectively, 0.96 and 0.93.
2.10. Lamb survival
Literature sources suggest that Dorper ewes are
capable of weaning 0.99±1.40 lambs per ewe mated
(Table 4). This level of performance can be maintained
under harsh environmental conditions, on poor quality
natural pastures. The breed also adapts very well to
more intensive systems, achieving high overall repro-
Overall levels of lamb survival in Dorper sheep are
comparatively high, with the majority of literature
®gures being approximately 0.90 (Table 3). Given a
litter size of 1.45±1.60 for Dorper ewes, these ®gures
2.11. Overall reproduction rate
Table 4
Overall reproduction rate (lambs weaned per ewe mated) in Dorper sheep, as reviewed in the literature (in a chronological order)
Estimate
Diet
Management
1.48a
1.40
1.13
1.30
1.52a
1.54a
0.99
1.70*
0.99
0.89
Complete diet
Natural pasture
Complete diet
Natural pasture
Natural pasture
Natural pasture
Natural pasture
Different systems
Natural pasture
Natural pasture
Accelerated lambing
Accelerated lambing
Accelerated lambing
Annual lambing
Accelerated lambing
Accelerated lambing
Accelerated lambing
Survey information
Survey information
Accelerated lambing
a
Reference
(8 months)
(8 months)
(8 months)
(Carnarvon)
(Tarka)
(8 months)
(10 months)
Basson et al. (1969)
Buitendag (1985)
Elias et al. (1985)
Cloete and De Villiers (1987)
Badenhorst et al. (1991)
Badenhorst et al. (1991)
Manyuchi et al. (1991)
Stafford and Hansson (1991)
Ackermann (1993)
Van Niekerk (1998)
Refers to the number of lambs weaned per ewe available per annum. The other estimates are based on the number of lambs weaned per
ewe mated.
S.W.P. Cloete et al. / Small Ruminant Research 36 (2000) 119±135
duction ®gures (1.48 lambs weaned per ewe per
annum) under accelerated lambing systems (Table 4).
It is of interest to note that accelerated mating under
natural pasture conditions failed to improve reproduction conclusively above annual mating in experiments
(Olivier et al., 1990; Coetzer et al., 1995). In the
survey of Ackermann (1993), reproduction was,
accordingly, not signi®cantly related to mating regime
(continuous, annual or accelerated).
The repeatability of the number of lambs weaned
per ewe mated in Dorper ewes was estimated at 0.07
(SE0.03) by the intra-class correlation method
(Cloete and De Villiers, 1987). Selection in the current
¯ock should focus on the culling of ewes that failed to
rear a lamb, since ewes failing to rear a lamb at 2±3
years of age reared 0.150.02 fewer lambs in subsequent years than contemporaries that reared least
one lamb.
2.12. Longevity
Literature sources on the longevity of Dorper sheep
are scarce. Dorper ewes remained in the breeding ¯ock
for an average of 4.7 seasons in Zimbabwe, while
Mutton Merino ewes had 5.6 productive seasons
(Manyuchi et al., 1991). The longer ¯ock life of the
Mutton Merino ewes in this study contributed to a
higher overall lamb yield, despite inferior performance per ewe mated. This is obviously a topic where
more information is required.
2.13. Male reproductive traits
Testicular weight and the diameter of the seminiferous tubules of Dorper ram lambs markedly
increased with age (Skinner, 1971). At an age of
365 days, testis weight averaged 303.8 g, epididymus
weight averaged 54.1 g, and the diameter of the
seminiferous tubules averaged 209.4 mm. The curvilinear increase in testis size over time differed from a
similar trend in Dohne Merinos (Schoeman and Combrink, 1987). This difference between breeds was
ascribed to maturity-type. Testis measurements (scrotal circumference, testis diameter and volume) were
highly repeatable (>0.63) in Dorper rams (Schoeman
and Combrink, 1987).
When observed over a continuous 24 h period, 14
young Dorper rams joined to 50 oestrous ewes
125
served an average of 19.7 times, with a range from
12 to 30 (Schoeman et al., 1987). The mean number of
serves per ram per hour increased from 0.82 in
inexperienced rams to 1.6 and 2.9 serves per ram
per hour in subsequent tests. The repeatability of
the number of serves ranged from 0.10 to 0.69
between tests. Serving capacity within tests was not
conclusively correlated to either live weight, testis
measurements or plasma testosterone concentrations,
although signi®cant (p
Productive performance of Dorper sheep
S.W.P. Cloetea, M.A. Snymanb,*, M.J. Herselmanb
a
Elsenburg Agricultural Development Centre, Private Bag X1, Elsenburg 7607, South Africa
Groo¯ontein Agricultural Development Institute, Private Bag X529, Middelburg 5900, South Africa
b
Abstract
The Dorper is a hardy South African composite breed, derived from a cross between the Black-headed Persian and the
Dorset Horn. Dorpers are regarded as early-maturing, and ewes lambed at an age of 1 year in one study. Age at ®rst lambing
was higher in other literature sources cited. The fertility of Dorper ewes was approximately 0.90 ewes that lambed per ewe
mated, with a litter size ranging from 1.45 to 1.60. The gestation length of Dorper ewes was approximately 147 days, while
they were reported to start cycling as soon as 52 days after parturition. The pre-weaning survival of Dorper lambs was cited at
approximately 0.90. Overall reproduction rate of Dorpers ranged from 0.99 to 1.40 lambs weaned per ewe mated, while it
exceeded 1.40 lambs weaned per ewe mated per annum under accelerated mating conditions. Dorper lambs gained from 0.24
to 0.28 kg per day under vastly different environmental conditions. When weaned early at 2±3 months of age, post-weaning
gains in excess of 0.18±0.20 kg per day were recorded. At slaughter, Dorper lambs had dressing percentages of approximately
50%. Two divergent genotypes in the breed (with a hairy or a woolly ¯eece cover) were evaluated under natural pasture
conditions. No conclusive advantage in favour of either genotype could be demonstrated as far as productive traits were
concerned. It was concluded that the breed adapts well to a wide variety of environmental conditions. In view of the scarcity of
estimates of genetic parameters for the breed, the maintenance and expansion of datasets suitable for this purpose should
receive high priority. # 2000 Elsevier Science B.V. All rights reserved.
Keywords: Dorper sheep; Reproduction; Growth; Carcass traits; Genotypes
1. Introduction
The need for a sheep breed suitable for the production of slaughter lambs under the adverse conditions of
the arid, extensive regions of South Africa resulted in
the formation of the Dorper breed in the early 1940s.
The founders of the new composite breed sought to
combine the hardiness of the Black-headed Persian
with the mutton production capability of the Dorset
*
Corresponding author. Tel.: 27-49-842 1113;
fax: 27-49-842 4352.
E-mail address: [email protected] (M.A. Snyman)
Horn (Campbell, 1989). The original crossings and
early history of the breed are documented well
(Nel, 1993). The hardiness and adaptability of the
Dorper led to a rapid increase in popularity (Marais
and Schoeman, 1990). Although exact Dorper
numbers are not known, the non-wool sheep numbers
in South Africa increased markedly from approximately 4.5 million in the late 1960s to approximately
7.0 million in the early 1990s (Abstract of Agricultural
Statistics, 1997). It is more than likely that an
expansion in Dorper numbers greatly contributed to
this increase, which was largely at the expense
of woolled sheep numbers (Fig. 1). The breed has
0921-4488/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 9 2 1 - 4 4 8 8 ( 9 9 ) 0 0 1 5 6 - X
120
S.W.P. Cloete et al. / Small Ruminant Research 36 (2000) 119±135
Fig. 1. Changes in the numbers of wool and non-wool sheep in the South African National sheep ¯ock over time.
grown to be the second largest in South Africa, and the
breeding stock have also been exported to other
countries (Terblanche, 1979). Today Dorpers are
found throughout southern and central Africa, in the
desert areas of North Africa and the Middle East as
well as on other continents, namely Northern America
and Australia.
The Dorper is able to withstand dehydration and
quickly replenish body weight losses when water
becomes available (Degen and Kam, 1992). This
capacity of Dorper sheep enables it to adapt to drier
regions where the availability of water proves to be a
limitation. The breed also adapts to temperate regions,
and has been extensively used in accelerated mating
systems (Basson et al., 1969; Manyuchi et al., 1991;
Schoeman and Burger, 1992). Dorper and Dorper
cross sheep were present on all the above average
sheep farms included in the survey of Stafford and
Hansson (1991) in Zambia.
Despite its popularity, scienti®c reports on Dorper
sheep are scattered over a number of scienti®c and
semi-scienti®c journals across the globe. Some of
these literature sources are not readily available for
all scientists. Moreover, estimates of the genetic parameters in the Dorper sheep breed are scarce. This
review attempts to present the bulk of information on
the production of Dorpers, while it will also include
the estimates of parameters that were found in the
literature.
2. Reproduction
2.1. General
In a comprehensive survey involving data of 130
Dorper farmers in the drier Karoo region of South
Africa and a total of 115 314 breeding ewes that were
maintained under different managerial regimes, lambs
born per ewe mated were estimated at 1.038 (Ackermann, 1993). District means ranged from 0.924 in
Prieska to 1.123 in Calvinia. It was estimated that only
36.1% of the respondents achieved lambing ®gures of
1.11 lambs born per ewe mated or higher. Given that
the production of lamb is the sole source of income in
a non-wool breed like the Dorper, it is evident that
reproduction needs to be maximized for maximum
economic returns. Little information is available for
changes in the relative reproductive performance of
the South African national ¯ock over time, but given
the increasing economic pressures on sheep farmers, it
is evident that reproduction should receive the necessary attention.
This review focuses on various aspects of Dorper
reproduction, such as sexual maturity, oestrus, gesta-
121
S.W.P. Cloete et al. / Small Ruminant Research 36 (2000) 119±135
tion and post-partum anoestrus. The de®nitions used
for the most commonly used reproductive parameters
will be presented at this stage, for ease of comprehension.
Ewe fertilityEwes that lambed per lambing
opportunity
Litter sizeLambs born per ewe that lambed
Lamb survivalLambs weaned per lamb born
Overall reproduction rateLambs weaned per ewe
mated (lambs weaned per ewe per annum, where
applicable under accelerated lambing systems)
Overall reproduction rate is a function of the component traits, namely ewe fertility, litter size and lamb
survival.
2.2. Sexual maturity
The Dorper is regarded as an early-maturing breed.
In early work, Joubert (1962) reported that Dorset
HornPersian ewes attained puberty at 399.7 days,
with a range between 195 and 872 days. Later work
reported substantially younger ages at ®rst oestrus.
Dorper maiden ewes exhibited their ®rst oestrus at an
age of 213 days and a live weight of 39 kg, while
Romanoff ewes were 228 days of age with a live
weight of 28 kg at their ®rst oestrus (Greeff et al.,
1988). Corresponding ®gures for Dorpers from the
study by Schoeman et al. (1993b) were an age of 8.14
months and a live weight of 50.8 kg. Under an 8monthly breeding cycle, Dorper ewes born in the
autumn were reported to conceive for the ®rst time
at their ®rst mating at an average age of 328 days and a
live weight of 45.9 kg (Basson et al., 1970). The
majority of ewe lambs that were born in winter (24/
250.96 of those available) conceived at an average
age of 252 days and a live weight of 44.7 kg.
Dorper ewes lambed for the ®rst time at an average
age of 346 days, compared to 363 days in Romanovs
(Greeff et al., 1988). Under an accelerated lambing
system, Schoeman and Burger (1992) found that
Dorper ewes lambed for the ®rst time at an average
age of 19.6 months. The ewe fertility of 208 Dorper
ewes mated to fertile rams at an age of 7 months was
0.58 (Snyman, 1998; unpublished), with a litter size of
1.16. Lamb survival averaged 0.79 and overall reproduction 0.53 in these ewes.
As far as rams are concerned, it was demonstrated
that epididimal sperm concentrations of Dorper lambs
rose markedly after an age of 140 days (Skinner,
1971). Mean sperm counts (109) were 0.1 at an
age of 112 days, 0.2 at 140 days, 16.6 at 168 days,
27.9 at 196 days and 40.6 at 365 days. From this it is
clear that Dorper ram lambs are capable of fertilizing
ewes from quite an early age.
2.3. Ewe fertility
Literature ®gures for ewe fertility are remarkably
consistent, being approximately 0.90 ewes lambed per
lambing opportunity in the majority of sources cited
(Table 1). Somewhat lower ®gures of respectively,
0.80 and 0.75, were reported in the studies of Pretorius
and Viljoen (1968) and Schoeman et al. (1993b). The
majority of ®gures is, however, consistent with barrenness percentages of approximately 6±7% reported
Table 1
Estimates of ewe fertility (ewes that lambed per ewe mated) in Dorper sheep, as reviewed in the literature (in a chronological order)
Estimate
Diet
Management
Reference
0.83±0.91
0.80
0.91
0.89
0.97
0.89
0.81
0.90
0.85
0.92
0.75
0.82
Natural pasture
Natural pasture
Complete diet
Natural pasture
Complete diet
Natural pasture
Not given
Natural pasture
Irrigated pasture
Natural pasture
Complete diet
Natural Pasture
Flushing treatments
Flushing and super-ovulation
Accelerated lambing (8 months)
Accelerated lambing (8 months)
Accelerated lambing (8 months)
Annual lambing
Annual lambing
Accelerated lambing (8 months)
Accelerated lambing (8 months)
Survey information
Accelerated lambing
Accelerated lambing (10 months)
Coetzee (1964)
Pretorius and Viljoen (1968)
Basson et al. (1969)
Buitendag (1985)
Elias et al. (1985)
Cloete and De Villiers (1987)
Eltawil and Narendran (1990)
Manyuchi et al. (1991)
Schoeman and Burger (1992)
Ackermann (1993)
Schoeman et al. (1993b, 1995)
Van Niekerk (1998)
122
S.W.P. Cloete et al. / Small Ruminant Research 36 (2000) 119±135
for New Zealand Romney sheep (Dalton and Rae,
1978). Ewe fertility of Dorpers compares favourably
to ®gures quoted for Australian Merinos (Knight et al.,
1975; Plant, 1984; Jordan et al., 1989), as well as
South African Merinos and Dohne Merinos (Fourie
and Cloete, 1993).
2.4. Qestrus cycle
Dorset HornBlack-headed Persian ewes were
reported to have an oestrus cycle of 16.9 days (Joubert,
1962). These ewes showed reduced seasonality compared to Merino ewes, which went into anoestrus for 1
month of the year (October), with very limited sexual
activity in 3 more months. The mean annual number of
oestrus cycles per ewe was 8.1 for Merinos and 16.6
for the Dorset HornBlack-headed Persian cross.
Both Dorper and Dohne Merino ewes were found to
have a 17.3-day cycle in subsequent work (Joubert and
Louw, 1964). Average cycle length of Dorper ewes
was similarly 17.3 days in the study of Boshoff et al.
(1975). This study suggested that the Dorper was
intermediate with regard to its seasonal expression
of oestrus activity. The Merino and Karakul were
found to be more seasonal, while the Black-headed
Persian and the Namaqua Afrikaner were more aseasonal. The peak level of activity of Dorper ewes
was, however, found to be higher than in the other
breeds. Pretorius and Viljoen (1968) reported mean
cycle lengths of 17.4 days for maiden Dorper ewes and
17.6 days for mature ewes. Corresponding values
recorded by Elias et al. (1985) were 16.6 and 17.6
days, respectively. The mean oestrus cycle length of
Dorper ewes was reported at 17.8 days in a group of
Dorper ewes where a commercial semen diluent was
placed in each uterine horn by laparoscopy, while
control group ewes had a mean cycle length of 18.4
days (Taljaard et al., 1991).
The average duration of oestrus was 33.3 h for
Dorset HornBlack-headed Persian cross ewes and
25.2 h for Merino ewes (Joubert, 1962). Depending on
the interval between oestrus recordings (every 4, 8 or
12 h), the duration of oestrus ranged from 28.0 to
35.1 h in Dorper ewes (Joubert and Louw, 1964). The
corresponding range in Dohne Merino ewes was 20.5±
26.6 h. More oestrus periods commenced during
nighttime than during daytime. In later work, the
average duration of oestrus was recorded at 36 h for
mature Dorper ewes and at 28 h for primiparous ewes
(Elias et al., 1985).
2.5. Litter size
Larger differences were observed between literature sources as far as litter size is concerned (Table 2).
A number of sources quoted litter size ®gures of below
Table 2
Estimates of ewe litter size (lambs born per ewe that lambed) in Dorper sheep, as reviewed in the literature (in a chronological order)
Estimate
Diet
Management
Reference
1.00±1.09
1.39
1.73
1.49
1.40
1.59
1.14
1.58
1.48
1.50
1.56
1.36
1.29
1.41
1.17
1.08
1.43
1.24
Natural pasture
Natural pasture
Complete diet
Natural pasture
Complete diet
Natural pasture
Not given
Not given
Not given
Not given
Natural pasture
Natural pasture
Natural pasture
Irrigated pasture
Natural pasture
Complete diet
Natural pasture
Complete diet
Flushing treatments
Control: flushing and super-ovulation
Accelerated lambing (8 months)
Accelerated lambing (8 months)
Accelerated lambing (8 months)
Annual lambing
Maiden ewes: accelerated lambing
Mature ewes: accelerated lambing
Annual lambing
Annual lambing
Accelerated lambing (Carnarvon)
Accelerated lambing (Tarka)
Accelerated lambing (8 months)
Accelerated lambing (8 months)
Survey information
Accelerated lambing
Control: super-ovulation
Accelerated lambing (10 months)
Coetzee (1964)
Pretorius and Viljoen (1968)
Basson et al. (1969)
Buitendag (1985)
Elias et al. (1985)
Cloete and De Villiers (1987)
Greeff et al. (1988)
Greeff et al. (1988)
Eltawil and Narendran (1990)
Greeff et al. (1990)
Badenhorst et al. (1991)
Badenhorst et al. (1991)
Manyuchi et al. (1991)
Schoeman and Burger (1992)
Ackermann (1993)
Schoeman et al. (1993b, 1995)
Erasmus et al. (1994)
Van Niekerk (1998)
S.W.P. Cloete et al. / Small Ruminant Research 36 (2000) 119±135
1.2, but the vast majority range from 1.45 to 1.60.
These ®gures compare favourably to ®gures reviewed
for New Zealand Romney ewes (Dalton and Rae,
1978), as well as Australian Merinos (Knight et al.,
1975; Jordan et al., 1989) and South African woolled
breeds (Fourie and Cloete, 1993). In a study where
Dorpers were maintained together with Merinos and
Dohne Merinos, respective litter size ®gures of 1.73,
1.39 and 1.41 were obtained (Basson et al., 1969).
Litter size of Dorper ewes was affected by ewe age,
multiple birth rate increasing to an age of 4±6 years,
followed by a tendency towards a decline (Cloete and
De Villiers, 1987; Schoeman and Burger, 1992). Ewes
born as multiples had a higher litter size than single
contemporaries (Cloete and De Villiers, 1987; Schoeman and Burger, 1992). The repeatability (estimated
as the simple correlation between paired records) of
litter size in Dorper ewes was computed at 0.32
(Schoeman and Burger, 1992).
2.6. Ovulation rate and embryo loss
Dorper ewes had an ovulation rate of 1.50 and
embryo losses of 0.66 in the study of Greeff et al.
(1990). Corresponding ®gures for Romanov ewes
were 3.33 and 1.15. More research on this topic
appears to be warranted.
2.7. Response of litter size and ovulation rate to
hormonal treatment
Litter size responded to exogenous pregnant mare
serum (PMS) in Dorpers. The administration of 500 or
750 IU PMS elevated litter size from 1.39 to approximately 1.70 in the study of Pretorius and Viljoen
(1968), while 250 IU PMS did not produce any effect.
Erasmus et al. (1994) similarly found that litter size
increased from 1.43 in control Dorper ewes to 1.60 in
ewes receiving 250 IU PMS and 1.88 in ewes receiving 500 IU PMS. Dorper ewes that were super-ovulated with follicle-stimulating hormone (FSH) had
18.2 corpora lutea compared to 6.7 corpora lutea in
ewes super-ovulated with 1250 IU PMS (Van Zyl
et al., 1987). Unovulated follicles amounted to,
respectively, 3.0 and 4.1, on respective treatments.
Only data of ewes that were super-ovulated with FSH
were thus considered further, owing to the small
number of fertilized ova recovered from PMS treated
123
ewes. In ewes subjected to natural service, a proportion of 0.475 of the potential embryos was recovered.
Natural service after the application of prostaglandin
F2a to the cervix of ewes resulted in a 0.668 recovery
rate. Surgical insemination by laparoscopy resulted in
a proportion of 0.933 of the potential embryos being
recovered.
2.8. Gestation length
The literature ®gures for the gestation length of
Dorper sheep are remarkably constant. Average ®gures found in the literature included 146.5 days (Joubert, 1962), 147.9 days (range 144±153 days; Joubert
and Louw, 1964) and 146.5 days (range 142±150 days;
Van Niekerk and Mulder, 1965). Gestation length of
Dorpers was consistently shorter than that of woolled
breeds when maintained together. Joubert and Louw
(1964) reported a mean gestation length of 150.5 days
(range 148±154 days) for Dohne Merinos, while Van
Niekerk and Mulder (1965) found a gestation length of
151.6 days (range 148±157 days) for Dohne Merinos
and 149.0 (range 145±154 days) for Merinos. In the
study of Elias et al. (1985), the length of gestation of
Dorpers ranged from 146.2 to 147.7 days, depending
on ewe age, litter size and lamb sex. When maintained
in an accelerated lambing system, the slightly shorter
gestation length of Dorpers may facilitate earlier rebreeding.
As far as the time of commencement of parturition
was concerned, it was demonstrated that 60% of
Dorper ewes started to lamb in the interval from
06:00 to 18:00, while 40% of parturitions commenced
between 18:00 and 06:00 (Joubert and Louw, 1964).
2.9. Post-partum anoestrus
Cross-bred Dorset HornBlack-headed Persian
ewes were recorded to start cycling 51 days after
parturition on average, with a range of 2±149 days
(Joubert, 1962). Post-partum anoestrus of Dorper ewes
depended strongly on the lambing season, being
approximately 123 days for ewes lambing in winter
and spring, 89 days for ewes lambing in summer and
62 days for ewes lambing in autumn (Joubert, 1972).
Widely different feeding levels (0.10 kg digestible
protein and 14.6 MJ digestible energy vs. 0.05 kg
digestible protein and 6.1 MJ digestible energy) dur-
124
S.W.P. Cloete et al. / Small Ruminant Research 36 (2000) 119±135
Table 3
Estimates of lamb survival (lambs weaned per lamb born) in Dorper sheep, as reviewed in the literature (in a chronological order)
Estimate
Diet
Management
Reference
0.85
0.88
0.84
0.91
0.78
0.90
0.94
0.95
0.88
Natural pasture
Complete diet
Complete diet
Natural pasture
Not given
Natural pasture
Irrigated pasture
Natural pasture
Natural pasture
Control: flushing and super-ovulation
Accelerated lambing (8 months)
Accelerated lambing
Annual lambing
Multiples: accelerated lambing
Accelerated lambing (8 months)
Accelerated lambing (8 months)
Survey information
Accelerated lambing (10 months)
Pretorius and Viljoen (1968)
Basson et al. (1969)
Elias et al. (1985)
Cloete and De Villiers (1987)
Greeff et al. (1988)
Manyuchi et al. (1991)
Schoeman and Burger (1992)
Ackermann (1993)
Van Niekerk (1998)
ing lactation did not markedly affect these ®gures.
Vosloo et al. (1969) previously indicated that feeding
level (high, medium or low) failed to reduce postpartum anoestrus in small groups of six Dorper ewes.
The treatments were chosen to result in respective live
weights of 106, 92 and 70% at the weaning of their
lambs, relative to a live weight of 100% at the commencement of feeding. The post-partum interval to the
®rst recorded ovulation was, however, reduced to 86
days in ewes on the high treatment compared to 119
and 124 days on the medium and low treatments. The
inter-lambing interval of Dorper ewes ranged from 6.2
to 7.7 months (Elias et al., 1985).
compare favourably with overall levels of lamb mortality expected in sheep-producing systems, as
reviewed in the literature (Dalton and Rae, 1978;
Alexander, 1984; Plant, 1984; Jordan et al., 1989;
Haughey, 1991). Moreover, lamb survival was found
to be largely independent of known sources of variation, including litter size (Cloete and De Villiers,
1987). The survival of lambs in the latter study was
0.92 for singles, as compared to 0.90 for multiples.
Corresponding ®gures from the study of Schoeman
and Burger (1992) were, respectively, 0.96 and 0.93.
2.10. Lamb survival
Literature sources suggest that Dorper ewes are
capable of weaning 0.99±1.40 lambs per ewe mated
(Table 4). This level of performance can be maintained
under harsh environmental conditions, on poor quality
natural pastures. The breed also adapts very well to
more intensive systems, achieving high overall repro-
Overall levels of lamb survival in Dorper sheep are
comparatively high, with the majority of literature
®gures being approximately 0.90 (Table 3). Given a
litter size of 1.45±1.60 for Dorper ewes, these ®gures
2.11. Overall reproduction rate
Table 4
Overall reproduction rate (lambs weaned per ewe mated) in Dorper sheep, as reviewed in the literature (in a chronological order)
Estimate
Diet
Management
1.48a
1.40
1.13
1.30
1.52a
1.54a
0.99
1.70*
0.99
0.89
Complete diet
Natural pasture
Complete diet
Natural pasture
Natural pasture
Natural pasture
Natural pasture
Different systems
Natural pasture
Natural pasture
Accelerated lambing
Accelerated lambing
Accelerated lambing
Annual lambing
Accelerated lambing
Accelerated lambing
Accelerated lambing
Survey information
Survey information
Accelerated lambing
a
Reference
(8 months)
(8 months)
(8 months)
(Carnarvon)
(Tarka)
(8 months)
(10 months)
Basson et al. (1969)
Buitendag (1985)
Elias et al. (1985)
Cloete and De Villiers (1987)
Badenhorst et al. (1991)
Badenhorst et al. (1991)
Manyuchi et al. (1991)
Stafford and Hansson (1991)
Ackermann (1993)
Van Niekerk (1998)
Refers to the number of lambs weaned per ewe available per annum. The other estimates are based on the number of lambs weaned per
ewe mated.
S.W.P. Cloete et al. / Small Ruminant Research 36 (2000) 119±135
duction ®gures (1.48 lambs weaned per ewe per
annum) under accelerated lambing systems (Table 4).
It is of interest to note that accelerated mating under
natural pasture conditions failed to improve reproduction conclusively above annual mating in experiments
(Olivier et al., 1990; Coetzer et al., 1995). In the
survey of Ackermann (1993), reproduction was,
accordingly, not signi®cantly related to mating regime
(continuous, annual or accelerated).
The repeatability of the number of lambs weaned
per ewe mated in Dorper ewes was estimated at 0.07
(SE0.03) by the intra-class correlation method
(Cloete and De Villiers, 1987). Selection in the current
¯ock should focus on the culling of ewes that failed to
rear a lamb, since ewes failing to rear a lamb at 2±3
years of age reared 0.150.02 fewer lambs in subsequent years than contemporaries that reared least
one lamb.
2.12. Longevity
Literature sources on the longevity of Dorper sheep
are scarce. Dorper ewes remained in the breeding ¯ock
for an average of 4.7 seasons in Zimbabwe, while
Mutton Merino ewes had 5.6 productive seasons
(Manyuchi et al., 1991). The longer ¯ock life of the
Mutton Merino ewes in this study contributed to a
higher overall lamb yield, despite inferior performance per ewe mated. This is obviously a topic where
more information is required.
2.13. Male reproductive traits
Testicular weight and the diameter of the seminiferous tubules of Dorper ram lambs markedly
increased with age (Skinner, 1971). At an age of
365 days, testis weight averaged 303.8 g, epididymus
weight averaged 54.1 g, and the diameter of the
seminiferous tubules averaged 209.4 mm. The curvilinear increase in testis size over time differed from a
similar trend in Dohne Merinos (Schoeman and Combrink, 1987). This difference between breeds was
ascribed to maturity-type. Testis measurements (scrotal circumference, testis diameter and volume) were
highly repeatable (>0.63) in Dorper rams (Schoeman
and Combrink, 1987).
When observed over a continuous 24 h period, 14
young Dorper rams joined to 50 oestrous ewes
125
served an average of 19.7 times, with a range from
12 to 30 (Schoeman et al., 1987). The mean number of
serves per ram per hour increased from 0.82 in
inexperienced rams to 1.6 and 2.9 serves per ram
per hour in subsequent tests. The repeatability of
the number of serves ranged from 0.10 to 0.69
between tests. Serving capacity within tests was not
conclusively correlated to either live weight, testis
measurements or plasma testosterone concentrations,
although signi®cant (p