Productive performance of Dorper sheep
S.W.P. Cloete
a, M.A. Snyman
b,*, M.J. Herselman
b aElsenburg Agricultural Development Centre, Private Bag X1, Elsenburg 7607, South Africa bGroo¯ontein Agricultural Development Institute, Private Bag X529, Middelburg 5900, South AfricaAbstract
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 produc-tion of slaughter lambs under the adverse condiproduc-tions 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
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 approxi-mately 4.5 million in the late 1960s to approxiapproxi-mately 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 *Corresponding author. Tel.:27-49-842 1113;
fax:27-49-842 4352.
E-mail address: [email protected] (M.A. Snyman)
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 para-meters 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 (Ack-ermann, 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 neces-sary attention.
This review focuses on various aspects of Dorper reproduction, such as sexual maturity, oestrus,
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 comprehen-sion.
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 com-ponent 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 8-monthly 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 repro-duction 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 bar-renness 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 Natural pasture Flushing treatments Coetzee (1964)
0.80 Natural pasture Flushing and super-ovulation Pretorius and Viljoen (1968)
0.91 Complete diet Accelerated lambing (8 months) Basson et al. (1969)
0.89 Natural pasture Accelerated lambing (8 months) Buitendag (1985)
0.97 Complete diet Accelerated lambing (8 months) Elias et al. (1985)
0.89 Natural pasture Annual lambing Cloete and De Villiers (1987)
0.81 Not given Annual lambing Eltawil and Narendran (1990)
0.90 Natural pasture Accelerated lambing (8 months) Manyuchi et al. (1991)
0.85 Irrigated pasture Accelerated lambing (8 months) Schoeman and Burger (1992)
0.92 Natural pasture Survey information Ackermann (1993)
0.75 Complete diet Accelerated lambing Schoeman et al. (1993b, 1995)
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 com-pared 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 a-seasonal. 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 litera-ture 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 Natural pasture Flushing treatments Coetzee (1964)
1.39 Natural pasture Control: flushing and super-ovulation Pretorius and Viljoen (1968)
1.73 Complete diet Accelerated lambing (8 months) Basson et al. (1969)
1.49 Natural pasture Accelerated lambing (8 months) Buitendag (1985)
1.40 Complete diet Accelerated lambing (8 months) Elias et al. (1985)
1.59 Natural pasture Annual lambing Cloete and De Villiers (1987)
1.14 Not given Maiden ewes: accelerated lambing Greeff et al. (1988)
1.58 Not given Mature ewes: accelerated lambing Greeff et al. (1988)
1.48 Not given Annual lambing Eltawil and Narendran (1990)
1.50 Not given Annual lambing Greeff et al. (1990)
1.56 Natural pasture Accelerated lambing (Carnarvon) Badenhorst et al. (1991)
1.36 Natural pasture Accelerated lambing (Tarka) Badenhorst et al. (1991)
1.29 Natural pasture Accelerated lambing (8 months) Manyuchi et al. (1991)
1.41 Irrigated pasture Accelerated lambing (8 months) Schoeman and Burger (1992)
1.17 Natural pasture Survey information Ackermann (1993)
1.08 Complete diet Accelerated lambing Schoeman et al. (1993b, 1995)
1.43 Natural pasture Control: super-ovulation Erasmus et al. (1994)
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; Schoe-man 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 approxi-mately 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 receiv-ing 500 IU PMS. Dorper ewes that were super-ovu-lated 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
ewes. In ewes subjected to natural service, a propor-tion of 0.475 of the potential embryos was recovered. Natural service after the application of prostaglandin
F2ato 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 ®g-ures found in the literature included 146.5 days (Jou-bert, 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 re-breeding.
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
dur-ing lactation did not markedly affect these ®gures. Vosloo et al. (1969) previously indicated that feeding level (high, medium or low) failed to reduce post-partum 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 com-mencement 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).
2.10. Lamb survival
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
compare favourably with overall levels of lamb mor-tality 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 varia-tion, 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.
2.11. Overall reproduction rate
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-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 Natural pasture Control: flushing and super-ovulation Pretorius and Viljoen (1968)
0.88 Complete diet Accelerated lambing (8 months) Basson et al. (1969)
0.84 Complete diet Accelerated lambing Elias et al. (1985)
0.91 Natural pasture Annual lambing Cloete and De Villiers (1987)
0.78 Not given Multiples: accelerated lambing Greeff et al. (1988)
0.90 Natural pasture Accelerated lambing (8 months) Manyuchi et al. (1991)
0.94 Irrigated pasture Accelerated lambing (8 months) Schoeman and Burger (1992)
0.95 Natural pasture Survey information Ackermann (1993)
0.88 Natural pasture Accelerated lambing (10 months) Van Niekerk (1998)
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 Reference
1.48a Complete diet Accelerated lambing (8 months) Basson et al. (1969)
1.40 Natural pasture Accelerated lambing (8 months) Buitendag (1985)
1.13 Complete diet Accelerated lambing (8 months) Elias et al. (1985)
1.30 Natural pasture Annual lambing Cloete and De Villiers (1987)
1.52a Natural pasture Accelerated lambing (Carnarvon) Badenhorst et al. (1991)
1.54a Natural pasture Accelerated lambing (Tarka) Badenhorst et al. (1991)
0.99 Natural pasture Accelerated lambing (8 months) Manyuchi et al. (1991)
1.70* Different systems Survey information Stafford and Hansson (1991)
0.99 Natural pasture Survey information Ackermann (1993)
0.89 Natural pasture Accelerated lambing (10 months) Van Niekerk (1998)
aRefers to the number of lambs weaned per ewe available per annum. The other estimates are based on the number of lambs weaned per
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 reproduc-tion 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 sub-sequent 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 perfor-mance 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 semini-ferous 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 209.4mm. The curvi-linear increase in testis size over time differed from a similar trend in Dohne Merinos (Schoeman and Com-brink, 1987). This difference between breeds was ascribed to maturity-type. Testis measurements (scro-tal 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
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<0.05) correlations were ob-served in some instances.
3. Live weight and growth
3.1. General
The performance recording schemes for South African mutton sheep emphasized weaning weight at ca. 100 days and early growth as selection objec-tives. Corrected 100-day live weight of Dorper ram and ewe lambs participating in performance testing (derived from data given by Campbell, 1989) showed a steady improvement over years (Fig. 2). This incline was probably mostly associated with an improved environment, and not necessarily genetic gains. Direct genetic responses to the selection for lamb weaning weight of Dorpers on natural pastures were compara-tively slow in the only long-term selection experiment that could be found in the literature (Neser et al., 1995), amounting to 0.087 kg per year. An even smaller gain was observed as far as maternal breeding values were concerned (0.016 kg per year). A regime of selection where ewe lambs were selected on wean-ing weight under pasture conditions and the 20 best ram lambs on weaning weight and post-weaning feedlot performance was found to be far less effective for the genetic improvement of weaning weight than direct selection (Neser et al., 1995). Direct genetic gains amounted to 0.030 kg per year, with no change in maternal breeding values.
This review will focus on lamb performance prior to weaning as well as post-weaning performance and mature live weight.
3.2. Pre-weaning lamb performance
widely different production systems in many cases. It is therefore not surprising that a large variation was observed as far as weaning weight of Dorper
lambs is concerned (Table 5). It is therefore appro-priate to rather concentrate on pre-weaning daily gain of lambs. The vast majority of ®gures from the
Fig. 2. Averaged adjusted 100-days live weight of ram and ewe Dorper lambs participating in performance testing in South Africa. Means were interpolated for years in which no data were available.
Table 5
Estimates of lamb weaning weight and pre-weaning growth rate (average daily gain) in Dorper sheep, as reviewed in the literature (in a chronological order)
Pre-weaning daily gain (kg per day) Weaning weight (kg)a Comment Reference
0.23±0.25 ± Docking trial on natural pasture Campbell and Bosman (1964)
0.23 24.7 (75) Complete diets Basson et al. (1970)
0.24±0.33 ± Natural pasture Pretorius (1970)
0.29 22.6 (77) Supplemented natural pasture Buitendag (1985)
0.27 41.3 (138) Natural pasture Cloete and De Villiers (1987)
± 22.1 (84) Not given Eltawil and Narendran (1990)
0.25 ± Natural pasture; Tarka Badenhorst et al. (1991)
0.21 ± Natural pasture; Carnarvon Badenhorst et al. (1991)
± 16.1 Natural pasture Inyangala et al. (1991)
± 16.4 Natural pasture Manyuchi et al. (1991)
± 28.0 (90) Various; survey information Stafford and Hansson (1991)
± 19.4 Natural pasture Inyangala et al. (1992)
0.26 18.2 (53) Cultivated pasture Schoeman and Burger (1992)
± 26.7 (100) Complete diets Schoeman et al. (1993b)
0.23±0.24 ± Super-ovulation trial on natural pasture Erasmus et al. (1994)
212 27.7 (117) Ewes on natural pasture; Namibia Van Niekerk (1998)
222 28.5 (117) Wethers on natural pasture; Namibia Van Niekerk (1998)
literature ranged from 0.24 to 0.28 kg per day. Given that the data were recorded under very extensive conditions in some cases, this rate of gain can be regarded as satisfactory. It also underlines the ability of the Dorper breed to thrive under sub-optimal con-ditions.
Dam age affected lamb pre-weaning gain in Dor-pers, the general pattern being an incline to a dam age of 4±6 years, followed by a decline (Cloete and De Villiers, 1987; Manyuchi et al., 1991; Schoeman and Burger, 1992). Ram or wether lambs were heavier and/ or faster growing than ewes (Campbell, 1963; Cloete and De Villiers, 1987; Inyangala et al., 1991; Man-yuchi et al., 1991; Schoeman and Burger, 1992). Twin lambs were lighter and slower-gaining than singles (Campbell, 1963; Cloete and De Villiers, 1987; Inyan-gala et al., 1991; Manyuchi et al., 1991; Schoeman and Burger, 1992). The growth rate of multiples reared as singles corresponded with that of singles in the study by Cloete and De Villiers (1987). Large differences were, on the other hand, discernible in the study of Manyuchi et al. (1991). Singles gained 0.255 kg per day, compared to 0.202 kg per day in twins reared as singles and 0.148 kg per day in lambs born and reared as twins.
Estimates of heritability for pre-weaning perfor-mance of Dorper lambs are scarce. The heritability of weaning weight was initially estimated at 0.25 by parent-offspring regression (Campbell, 1974). The corresponding paternal half-sib heritability estimate in a combined dataset of Dorper and Red Maasai lambs was 0.18 (Inyangala et al., 1990). Later analyses allowed the partitioning of genetic effects into direct additive and maternal components (Neser et al., 1995). Direct additive effects amounted to between 0.11 and 0.30 for the three lines included in the analysis of the latter authors, when expressed as a proportion of the overall phenotypic variance. Maternal effects corre-spondingly accounted for between 0.07 and 0.20 of the overall phenotypic variance.
Accurate estimates of genetic and environ-mental correlations for growth traits in Dorpers are scarce in the literature. Early work reported pheno-typic relationships, usable for the prediction of wean-ing weight in the current generation (Campbell, 1963, 1972; Campbell and Erasmus, 1967). These literature sources can be consulted for further infor-mation.
3.3. Post-weaning performance
When Dorper ewes are mated annually, it is usually attempted to market lambs directly from the ewes. Under accelerated lambing systems, where early re-breeding is a pre-requisite, it is necessary to subject lambs to early weaning. Dorper lambs weaned at 2±3 months subsequently grew at a rate of 0.230 kg per day, compared to growth rates of, respectively, 0.220 and 0.170 kg per day in Dohne Merino and Merino lambs (Basson et al., 1970). Dorper lambs that were weaned at an average age of 52.8 days and an average live weight of 18.2 kg, had a survival of 0.96 from weaning to 100 days of age (Schoeman and Burger, 1992). Post-weaning growth in these lambs was 0.206 kg per day to 100 days of age. Dorper lambs that were weaned at 100 days gained 0.180 kg per day from, approximately, 100±200 days, and 0.160 kg per day from, approximately, 200±360 days of age (Schoeman et al., 1993a). Dorper lambs were reported to grow at 0.180 kg per day from birth to slaughter, compared to 0.148 kg per day for Karakuls and 0.150 kg per day for Damaras (Von Seydlitz, 1996).
During of®cial post-weaning growth tests on nat-ural pasture, Dorper rams grew at 0.160 kg per day (Campbell, 1989). Comparable ®gures for other inter-nationally known breeds were: Suffolk ± 0.176 kg per day; Hampshire ± 0.144 kg per day; Ile de France ± 0.158 kg per day; Corriedale ± 0.164 kg per day. Average live weights of South African Dorpers at 6 months were 54.6 kg for rams and 47.8 kg for ewes (Campbell, 1989). Corresponding weights at approxi-mately 11 months were, respectively, 80.0 and 65.2 kg. These ®gures were substantially higher than those of Inyangala et al. (1991, 1992) for Dorper sheep in Kenya, being respectively, 21.1 and 24.5 kg at 6 months, as well as 33.7 and 36.5 kg at 12 months.
The ef®ciency of fat and protein deposition in growing Dorper sheep (Marais et al., 1991a), as well as compensatory growth (Marais et al., 1991b) were also studied. The sources cited can be consulted for further information in this regard.
3.4. Mature ewe body weight
natural pasture conditions (Cloete and De Villiers, 1987). Ewes maintained under accelerated lambing systems were reported to be somewhat lighter; 57.7 kg in the study of Greeff et al. (1988) and 61.3 kg in the study of Schoeman and Burger (1992). Pre-partum body weight of Dorper ewes in Egypt was 76.9 kg (Eltawil and Narendran, 1990). In the study of Man-yuchi et al. (1991), Dorper ewes weighed 51.6 kg after the birth of their lambs and 50.5 kg when their lambs were weaned. Ewes maintained on the Tarka experi-mental farm and mated two times per year weighed 69.8 kg at joining (Snyman, 1998 ± unpublished). The corresponding live weight recorded at the Carnarvon experimental farm was 62.9 kg.
Reproduction was affected by pre-joining live weight of ewes in the study of Cloete and De Villiers (1987), where annual lambing was practised. This relationship was stronger in young ewes (2 and 3 years of age) than in older ewes. No relationship between pre-joining live weight and litter size was found when Dorper sheep were subjected to an accel-erated mating regime (Schoeman and Burger, 1992). The repeatability of pre-joining live weight in Dorper ewes was estimated at 0.45 (Cloete and De Villiers, 1987).
4. Wool production
The Dorper is regarded as a non-wool breed, and commercial wool production does not form part of the selection strategies employed in the breed. The nature of the ¯eece cover is, however, regarded by some as important, as will be indicated later. Dorper ewes were, nevertheless, reported to produce 0.66 kg of greasy wool over an 8-month period, with a clean yield of 64.3% (Basson et al., 1969). These ®gures gave a clean wool production of 0.42 kg per ewe. The relative wool production of Merino ewes under the same conditions amounted to 5.3 kg greasy wool, 58.5% clean yield and 3.1 kg clean wool. Correspond-ing ®gures for Dohne Merino ewes were 4.1 kg, 52.4% and 2.1 kg, respectively. Dorper ewes that were mated two times a year, produced 0.41 kg of greasy wool per year at the Tarka experimental farm (Snyman, 1998 ± unpublished).
The phenotypic relationship of maternal ¯eece weight with progeny growth was negative (rÿ0.29)
in a small number of Dorpers ewes (Campbell, 1963). This aspect warrants further attention.
5. Milk traits
In early work, Bonsma (1944a) reported an average milk production of 1.22 kg per day over 77 days for 43 lactations of Dorset HornBlack-headed Persian ewes. The corresponding milk yields of purebred Black-headed Persian and Merino ewes were, respec-tively, 0.40 and 0.75 kg per day. Further work related milk yield ®gures to early lamb growth (Bonsma, 1944b). By regarding pre-weaning lamb growth (Table 5) as an indication of milk production, it can be deducted that present-day Dorper ewes are able to provide adequate nourishment for their progeny. The butterfat content of milk produced by Dorper ewes declined with 0.051% per day of lactation from 10 to 40 days post-partum (Schoeman et al., 1993b). After 10 days in lactation, ewes produced milk with a butterfat content of 7.1%. The corresponding ®gure after 40 days was 5.5%. On average, Dorper milk contained 5.6% protein and 4.6% lactose (Le Roux, 1969). Milk obtained from DorperBlack-headed Persian ewes was slightly higher in protein and lactose, 5.9 and 4.9%, respectively. Milk protein responded to supplementation with cottonseed meal in Dorper ewes, being 5.4% on the control diet and 5.9% on the cottonseed meal diet.
6. The production of lamb
(Carnarvon and Tarka) were combined, Dorper ewes weaned 48.0 (SE1.4) kg of lamb per ewe on a yearly basis, compared to 43.21.4 in Afrinos and 22.31.5 in Merinos (Snyman, 1998 ± unpublished). In a Saudi Arabian study, Dorper ewes also compared favourably with indigenous fat-tailed hair breeds (Eltawil and Narendran, 1990). Lamb production averaged 19.5 kg in Nadji ewes, 19.7 kg in Awassi ewes, 16.9 kg in Harri ewes and 20.4 kg in Dorper ewes. When related to post-partum ewe weights, the smaller Harri ewes were regarded as being the most ef®cient of the four breeds, with only minor differences between the other genotypes.
7. Slaughter traits
7.1. Slaughter weight and age
Dorper sheep are regarded as early-maturing and therefore they tend to put on fat at an early age. What is most obvious from Table 6, is the fact that slaughter weight was around 30±33 kg in earlier studies (Basson et al., 1970; Pretorius, 1970; Terblanche et al., 1973). In later studies, lambs were slaughtered nearer to 40 kg live weight (Brand, 1992; Snyman et al., 1996; Snyman, 1998 ± unpublished). This trend could be ascribed to selection within the breed for increased growth performance and against fat localization, resulting in a tendency towards a `drier' type (Nel, 1993; Campbell, 1995).
In South Africa, price premiums were paid for the highest grade lamb carcasses weighing between 18
and 22 kg. Dorper lambs tend to put on more localised fat at an earlier age and therefore at lower live weights than later maturing breeds. This is especially true under intensive or favourable environmental condi-tions, where Dorper lambs are slaughtered at lower live weights (32±35 kg) to avoid the carcasses being classi®ed as too fat. The later-maturing breeds have the advantage of producing carcasses with optimal fat thickness and distribution at a heavier live weight.
When slaughtered at a ®xed age, Dorper lambs reached slaughter weight earlier than woolled breeds. Dorper lambs reached a slaughter weight of 33.6 kg at an age of 131 days, compared to 137 days for Dohne Merinos and 176 days for Merinos (Basson et al., 1970). Snyman (1998 ± unpublished), accordingly found that Dorper lambs reached a slaughter weight of approximately 41 kg at 169 days of age, compared to 191 days in Afrinos and 339 days in Merinos. It is important to remember that marketing age is depen-dent upon a combination of live weight and body condition (fat depth and distribution). Differences in slaughter age reported by different authors in Table 6 can be ascribed to different environments and lambing systems. For example, results of Snyman et al. (1996) and Snyman (1998 ± unpublished) were based on data from surplus ewe and culled ram lambs raised under extensive conditions. Where Dorper, Afrino and Mer-ino lambs were compared (Snyman, 1998 ± unpub-lished), lambs born at two locations and in two seasons were included. Lamb data analysed by Brand (1992) and Van Niekerk and Steenkamp (1995) were, respec-tively, collected under natural pasture and feedlot conditions.
Table 6
Slaughter traits, dressing percentage and grading of Dorper lamb carcasses
Slaughter Dressing Percentage (%) Highest grade (%) Reference
Weight (kg) Age (days)
33.6 131 51.7 82.0 Basson et al. (1970)
31.0 92±125 50.1±52.6 56±79 Pretorius (1970)
32.0 136±238 47.0±50.2 ± Terblanche et al. (1973)
± ± ± 44±46 Boshoff (1986)
45.0 150 48.9±51.6 ± Brand (1992)
± ± 49.9±52.1 ± Strydom et al. (1995)
25±40 ± 40.7±51.1 ± Van Niekerk and Steenkamp (1995)
42.0 294 48.5 ± Snyman et al. (1996)
40.0 245 50.5 ± Snyman (1998 ± unpublished)
The advantage of Dorper lambs being marketed at an earlier age is that more ewes can be kept per hectare than ewes belonging to breeds with a similar lambing performance but a later marketing age of lambs (Sny-man, 1998 ± unpublished).
7.2. Dressing percentage and carcass traits
Dressing percentages of Dorper lambs reported in the literature (Table 6) are relatively constant at approximately 50% for a wide range of conditions. According to Van Niekerk and Steenkamp (1995), dressing percentage increased with slaughter age of lambs from approximately 40% when slaughtered at 25 kg live weight to approximately 50% when slaugh-tered at a live weight of 40 kg. Dorper lambs generally had higher dressing percentages than woolled breeds in all available comparative studies (Basson et al., 1970; Pretorius, 1970; Brand, 1992).
Carcass measurements reported since 1992 are summarised in Table 7. These can unfortunately not be compared to earlier measurements (Pretorius, 1970; Terblanche et al., 1973) due to different meth-ods of assessment. The V3±fat depth measurement (see Table 7 for de®nition) was used from 1981/1982 till 1994 to classify carcasses into various classes. Super was the top grade (V34±7 mm), followed by Grade 1 (too lean) and Grade 2 (too fat). Classi®cation of Dorper lamb carcasses (44±46% being awarded the highest grade) slaughtered during 1983±1985 at the major SA abbatoirs (Boshoff, 1986; Table 6) compares well with results obtained on the Carnarvon experi-mental station, where 36% of the carcasses achieved the highest grade (Snyman, 1998 ± unpublished; Table 6). Seasonal variation in environmental conditions
could most probably account for differences obtained between these two studies. Earlier work (Basson et al., 1970; Pretorius, 1970) recorded much higher percen-tages of lambs being awarded the highest grade. This could most probably be ascribed to the different classi®cation systems being in place.
7.3. Properties of lamb produced from Dorpers
Studies in which various carcass quality traits, such as muscle:bone:fat ratios among cuts, as well as traits such as ageing ability, palatability, tenderness, aroma, etc. of Dorper lamb were evaluated, are available in the literature (Webb et al., 1991; Casey, 1992; Webb and Casey, 1992; Webb et al., 1994a,b; Strydom et al., 1995; Von Seydlitz, 1996), and will not be elaborated upon further.
8. Skins
Dorper skins, known as glover skins, are highly regarded and sought after for processing into clothing leather (Terblanche, 1979). The leather quality of these skins is, however, poorly documented. Results of a study in which skins of 10 South African sheep breeds were evaluated for leather properties, indicated that Dorper skins were superior to woolled sheep skins, while they compared favourably with skins of the different indigenous hair sheep breeds (Snyman and Jackson-Moss, 1998).
9. Genotypes within the Dorper breed
Animals within the Dorper breed are classi®ed into different types, mainly according to their ¯eece cover
Table 7
Measurements recorded on Dorper lamb carcasses
Carcass length (cm) Hind leg measurementsa(cm) Fat depth measurementsa(mm) Reference
Circum-ference Length V1 V3 V5
± ± ± ± 3.3±5.6 ± Brand (1992)
90±103 ± 32±37 3.5±12.8 ± 1.0±5.8 Van Niekerk and Steenkamp (1995)
105 69 35 7.4 5.6 1.1 Snyman et al. (1996)
107 71 37 6.8 5.9 1.4 Snyman (1998 ± unpublished)
103 70 34 5.7 4.2 3.0 Snyman (1998 ± unpublished)
aDe®nitions: V1±Fat depth between the 3rd and 4th scaral vertebrae, 25 mm from the midline; V3±Fat depth between the 3rd and 4th
(Campbell, 1989). These types are a hair-type and a wool-type, with an intermediate (hair±wool)-type between them. Several perceptions as to the produc-tive and reproducproduc-tive potential of these types exist among breeders and farmers, with very limited scien-ti®c evidence to verify it. Studies comparing these types have therefore been done recently, in order to substantiate these perceptions (Van Niekerk and Steenkamp, 1995; Snyman, 1998 ± unpublished). In the former study, growth and carcass traits were evaluated under intensive conditions. The ef®ciency of production of hair- and wool-type Dorpers were evaluated under extensive conditions in the study of Snyman (1998 ± unpublished).
9.1. Reproductive performance of hair- and wool-type Dorper ewes
Snyman (1998 ± unpublished) maintained 110 hair-and 110 wool-type ewes under extensive conditions
at the Carnarvon experimental station. All ewes were hand-mated once a year during autumn and complete pedigree and performance records were kept. Young ewes were mated for the ®rst time at 7 months of age. There were no signi®cant differences between hair- and wool-type ewes with regard to any of the reproduction parameters (Table 8). It is further interesting to note that these ®gures correspond very well with other literature estimates summarised in Tables 1±4.
9.2. Growth and conformation traits of hair- and wool-type Dorper lambs
The growth performance till weaning of hair- and wool-type Dorper lambs born and raised under exten-sive conditions (Snyman, 1998 ± unpublished) is compared in Table 9. It is obvious that (as was the case with reproduction) there were no differences between types with regard to live weight and growth
Table 8
Mean (SE, where applicable) live weight and reproductive performance recorded for hair and wool Dorper ewes under extensive conditions
Trait Line
Hair Wool
Pre-mating live weight (kg) 55.3 (0.8) 53.8 (0.8)
Ewe fertility (ewes lambed per ewe mated) 0.85 0.82
Litter size (lambs born per ewe lambed) 1.54 1.54
Lamb survival (lambs weaned per lamb born) 0.91 0.91
Reproduction rate (lambs weaned per ewe mated) 1.20 1.16
Weight of lamb weaned per ewe mated (kg) 33.0 (0.9) 31.5 (0.9)
Table 9
Mean (SE) growth performance and ¯eece cover of hair and wool type Dorper lambs under extensive conditions
Trait Ram lambs Ewe lambs
Hair line Wool line Hair line Wool line
Live weight (kg) at:
42 days 16.3 (0.1) 16.2 (0.1) 15.2 (0.1) 15.2 (0.1)
100 days 31.3 (0.2) 31.1 (0.2) 28.6 (0.2) 28.8 (0.2)
Fleece coveraat:
Birthb 9.3 (0.4) 23.1 (0.4) 9.4 (0.4) 22.1 (0.4)
Weaningb 8.9 (0.4) 23.3 (0.4) 8.5 (0.4) 21.9 (0.4)
Condition score at weaning 27.0 (0.3) 27.0 (0.3) 29.0 (0.3) 29.0 (0.3)
Growth rate (kg per day) 0.265 (0.002) 0.263 (0.002) 0.242 (0.002) 0.242 (0.002)
aFleece cover and condition score were assessed on a linear scale ranging from 1 to 50.
traits. The ®gures also accorded very well with the literature estimates in Table 5.
9.3. Carcass and skin traits of hair- and wool-type Dorper lambs
Data from two studies comparing carcass traits of hair and wool Dorper lambs are available. In the ®rst study, hair-, wool- and hair±wool-type lambs were kept under intensive feedlot conditions from weaning and slaughtered at either 25, 30, 35 or 40 kg live weight (Van Niekerk and Steenkamp, 1995). In the other study, surplus hair- and wool-type lambs born and raised under extensive conditions (Snyman, 1998 ± unpublished) were slaughtered at approximately 40 kg live weight. Full carcass measurements, as described by Bruwer (1984), were taken in both trials. For the purpose of this review, only results from lambs slaughtered at 40 kg live weight were included as far as the study of Van Niekerk and Steenkamp (1995) was concerned.
The dressing percentage of wool lambs was higher than that of hair lambs in the study of Snyman (1998 ± unpublished). The opposite trend, albeit non-signi®-cant, was observed in the study of Van Niekerk and Steenkamp (1995). Carcass length and the length of the hind leg were longer in wool than hair lambs in the former study, which accorded with the study of Van Niekerk and Steenkamp (1995). With regard to
fat measurements, no signi®cant differences were observed between groups in either study. As grading is based primarily on V3 fat measurements, it is clear that no substantial differences occurred between types (Table 10).
The skins from hair Dorpers were slightly better than skins from wool Dorpers as far as some leather quality parameters were concerned (Snyman and Jack-son-Moss, 1998).
10. Conclusions
This review has shown that the Dorper is an adap-table sheep breed, capable of maintaining accepadap-table levels of production under a wide variety of condi-tions. There is clearly a lack of information on some aspects of Dorper production, including studies on ovulation rate, embryo survival as well as skin and pelt production. Moreover, the lack of genetic and envir-onmental parameters for Dorper sheep under different production systems is alarming. It is thus impossible to formulate a breeding plan based on scienti®c data at present. The judicious recording of production in experimental and commercial Dorper ¯ocks should thus receive high priority. Data obtained in this man-ner should be subjected to rigorous statistical evalua-tion, to assist in the formulation of well-de®ned selection objectives in a scienti®c breeding plan for the Dorper breed.
Table 10
Carcass measurements of wool and hair type Dorper lambs slaughtered at approximately 40 kg live weight
Trait Snyman (1998 ± unpublished) Van Niekerk and Steenkamp (1995)
Hair lambs Wool lambs Hair lambs Wool lambs
Number of observations 156 106 12 12
Carcass weight (kg) 19.2a(0.1) 19.7 (0.2) 20.2 19.3
Dressing percentage (%) 49.9a(0.4) 51.2 (0.4) 51.1 48.7
Slaughter age (days) 242 (5) 251 (6) ± ±
Carcass length (cm) 105.8a(0.4) 107.2 (0.5) 102.3 101.5
Hind leg length (cm) 36.3a(0.2) 40.0 (0.3) 35.7 37.3
Fat depth (mm)b:
V1 6.6 (0.4) 7.0 (0.4) 12.8 8.4
V3 5.8 (0.3) 6.0 (0.4) 5.7 5.5
V5 1.4 (0.1) 1.4 (0.1) ± ±
aSigni®cant (p<0.01) differences between hair and wool lambs (Snyman, 1998 ± unpublished).
bDe®nitions: V1±Fat depth between the 3rd and 4th sacral vertebrae, 25 mm from the midline; V3±Fat depth between the 3rd and 4th
Acknowledgements
We wish to acknowledge the assistance of collea-gues (Drs J.J. Olivier, P.R. King and Mr T.T. de Villiers) for technical and editorial suggestions during the preparation of the manuscript.
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