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Productive performance of hair and wool type Dorper sheep under extensive conditions
Small Ruminant Research 45 (2002) 17–23
Productive performance of hair and wool type Dorper sheep under extensive conditions M.A. Snyman∗ , W.J. Olivier Department of Agriculture, Grootfontein Agricultural Development Institute, Private Bag X529, Middelburg Cape 5900, South Africa Accepted 5 March 2002
Abstract The reproductive performance, growth, slaughter traits, and several conformation characteristics in Dorper sheep (hair and wool types) were evaluated under extensive conditions in the north-western Karoo region of South Africa. From 1993 to 2000, lambs of hair (n = 1070) and wool (n = 1044) type Dorper sheep, and corresponding reproductive records from 872 and 874, respectively, were analysed. There was no significant differences between hair and wool type lambs for body weight from 42 days till 12 months of age, and for pre- or post-weaning growth rate. The analysis of conformation tend to suggest that the hair type lambs were blockier with shorter legs, compared to the leggier appearance of the wool type lambs. This is also evident from the longer carcass length (108.5 vs. 107.2 cm) and hind leg length of wool type lambs compared to hair type lambs. With regard to other carcass traits, wool type lambs had heavier carcasses (19.6 vs. 19.2 kg) and higher dressing percentage (49.9 vs. 49.0%), though, fat measurements and carcass grades were similar. The ewes of the hair type were heavier at mating than wool type (57.4 vs. 56.4 kg). No differences were, however, observed for percentage of ewes lambed, lambs born, lambs weaned, survival rate of lambs or kg lamb produced per ewe per year. It was concluded that the economically important reproduction and growth traits were similar between the hair and wool types of Dorper sheep. Differences that do occur in some conformation and carcass traits will not effect the economic realisation from the different types. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Growth traits; Slaughter traits; Reproduction; Conformation traits
1. Introduction Mutton production is an important component of the agricultural sector in the extensive north-western sheep grazing areas of the Republic of South Africa. Due to the limited natural resources in these areas, it is important to increase the efficiency of mutton production within the limits of these resources. It is therefore essential that the most suitable type of sheep for these areas, in terms of adaptability and ∗ Corresponding author. Tel.: +27-49-842-1113; fax: +27-49-842-4352. E-mail address: [email protected] (M.A. Snyman).
profitability, be identified. Dorper sheep constitute a large proportion of the sheep numbers in these areas, and it is therefore obvious that the most profitable type within this breed should be identified. Animals within the Dorper breed are classified into different types according to coat cover, conformation or fat distribution. Several perceptions as to the productive and reproductive potential of these types remain among breeders and farmers. One of these is that Dorper sheep with a hairy coat cover, are more hardy and adapted, with a higher reproduction rate and ability to be marketed at an earlier age under extensive conditions than those Dorper sheep with a predominantly woolly coat cover. Results of growth and carcass
0921-4488/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 4 8 8 ( 0 2 ) 0 0 1 1 6 - 5
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M.A. Snyman, W.J. Olivier / Small Ruminant Research 45 (2002) 17–23
traits of hair/wool type and compact/larger frame type Dorper lambs under intensive conditions have been published (Van Niekerk and Steenkamp, 1995; Strydom et al., 1995). There is, however, no information available on the relative performance of hair and wool type Dorper sheep under extensive veld conditions, especially with regard to reproductive performance. In the present study, the reproductive performance, growth and slaughter traits, and several conformation characteristics in hair and wool type Dorper sheep were evaluated under extensive conditions.
2. Material and methods The flock was maintained under natural conditions at the Klerefontein Experimental Station near Carnarvon (30◦ 59 S, 22◦ 9 E) in the north-western Karoo region of South Africa, representative of the extensive low potential of the area. The natural pasture which varies from mixed grass and shrub veld to Karoo shrub veld has been described as arid Karoo (Acocks, 1988). The official grazing capacity is estimated at 5.5 ha per small stock unit. The climate is characterised by cold winters and hot summers. The average annual rainfall is 209 mm and occurs mainly during the autumn months. In July 1993, animals of the existing experimental Dorper flock at the Klerefontein Experimental Station were classed into two groups on the basis of their coat cover, i.e. either hair or wool type. Furthermore, 20 hair and 20 wool type young ewes were bought from the industry in 1994. These ewes formed the foundation of the two experimental flocks. Flock size was kept at 110 ewes each, for the hair and wool types. During the 1993 and 1994 breeding seasons, seven hair and wool type rams from various experimental flocks were used as sires, together with wool and hair type rams from the existing flock at Klerefontein. Thereafter, from 1995, only rams bred within the hair and wool flocks, were used as sires. The hair and wool ewes including their lambs were managed as one flock for the duration of the study. Animals kept under natural veld conditions did not receive any feed or mineral supplement. The routine inoculation, drenching and tick control program was followed.
The ewes were individually mated once a year during April. Replacement ewes were exposed to rams at 7 months of age, while replacement rams were used for breeding, the first time at 18 months of age. An age structure of five ewe and two ram age groups was followed, where 20% of older ewes and all but one or two rams were replaced with young ones each year. Ewes were not culled for poor reproductive performance, however, ewes with udder defects were culled. During the lambing season in September, the following data were recorded for each lamb: identification of the lamb, and its dam and sire, date of birth, birth weight, sex and birth status of the lamb and coat cover score. The body weight at 42 days and at weaning, condition score and coat cover score at 120 days of age were also recorded. At 6 months of age, various conformation traits were subjectively assessed for all lambs, on a linear scale ranging from 1 to 50. These included the general conformation of the head, chest width and depth, protrusion of chest between front legs, shoulders, hind quarters, hocks, front pasterns, hind pasterns, top line, slope of rump. The scale of assessment for these subjectively assessed traits are summarised in Table 1. All subjective assessments were done by the same person, in order to eliminate possible differences due to the Table 1 Linear scale of assessment for conformation traits and coat cover of 6 months old lambs Trait
Coat cover Condition score General conformation of the head Chest width and depth Protrusion of chest between front legs Shoulders Hind quarters Hocks Front pasterns Hind pasterns Top line Slope of rump
Scalea 1
25
50
Hairy Emaciated Poor
Mixture Average Average
Woolly Fat Ideal
Narrow
Average
None
Average
Wide and deep Much
Loose Narrow Poor Poor Poor Poor Sloped
Average Average Average Average Average Average Average
Ideal Well filled Ideal Ideal Ideal Straight Straight
a 1–10: poor; 11–20: below average; 21–30: average; 31–40: above average; 41–50: excellent.
M.A. Snyman, W.J. Olivier / Small Ruminant Research 45 (2002) 17–23
assessor. At the same time, the width of rump, width of hind leg from the side, length of hind leg from the side, body length, body depth, body height and testis circumference of ram lambs were measured objectively. During the subjective assessment at 6 months of age, ewe and ram lambs were classed and ewe lambs were selected for replacement. Correspondingly, 40–50 each of the hair and wool type ram lambs were selected for future use. Selection was based on weaning weight of the lambs. Animals with conformation defects or definite faults, such as short lower jaws, or lambs that were either too hairy or too woolly for their group, were earmarked to be slaughtered. These surplus lambs, as well as the ram lambs kept for future selection purposes, were weighed monthly until 12 months of age. Surplus ram and ewe lambs approaching a body weight of approximately 40 kg were slaughtered. The body weight and slaughter weight of lambs, fasted overnight was recorded. Carcass weight, dressing percentage and all carcass measurements included records based on the National Lamb Carcass Competition (Bruwer, 1984). Data from lambs born from 1993 to 2000 in the hair (n = 1070) and wool (n = 1044) flocks were available. The number of records for the growth traits are presented in Table 2. For body weight from 42 days till 7 months of age, body weights of all lambs were included, i.e. surplus as well as selected lambs. From 8 months of age, body weight data for surplus ram and ewe lambs not yet slaughtered, as well as the selected ram lambs, were included. Conformation traits from 1708 lambs (867 hair and 841 wool types)
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and slaughter traits from 816 lambs (430 hair and 386 wool types) were analysed. Least-squares procedures (SAS Institute, 1990) were used to analyse data for all growth, conformation and slaughter traits (Littell et al., 1991). The following mathematical model was used: Yijklmn = µ + yi + fj + sk + rl + am + (yf)ij + (ys)ik + (fs)jk + b1 AL + b2 FW + eijklmn where Yij klmn is the trait of the nth animal of the mth age of dam for the lth birth/rearing status, kth sex, jth flock and ith birth year, µ the overall mean, yi the fixed effect of the ith birth year, fj the fixed effect of the jth flock, sk the fixed effect of the kth sex, rl the fixed effect of the lth rearing status (birth status in the case of birth weight), am the fixed effect of the mth age of dam (years), (yf)ij the effect of the interaction between the ith birth year and the jth flock, (ys)ik the effect of the interaction between the ith birth year and the kth sex, (fs)j k the effect of the interaction between the jth flock and the kth sex, b1 the linear regression of the deviation from the mean of age of the lamb at recording (AL; except for birth weight), b2 the linear regression of the deviation from the mean of fasted body weight (FW; fitted only for all the slaughter traits), eij klmn the random error with zero mean and variance I σe2 . Data collected on the ewe flock from 1993 to 2000 include records on body weight before mating, number of ewes mated, number of ewes that lambed, number of lambs born, and number of lambs weaned. A total of 872 and 874 reproductive records were available for the hair and wool flocks, respectively.
Table 2 Least-squares means (±S.E.) of growth traits and coat cover score of hair and wool type Dorper lambs Trait
n
Hair
Birth weight (kg) Coat cover at birth 42-Day body weight (kg) 100-Day weaning weight (kg) Coat cover score at weaning Condition score at weaning Daily gain from birth to weaning (g/day) 5-Month body weight (kg) 6-Month body weight (kg) 7-Month body weight (kg) 9-Month body weight (kg) 12-Month body weight (kg)
2114 1887 2036 1985 1438 1438 1985 1730 1693 1570 636 421
4.06 9.7 17.6 30.1 14.2 24.9 246.6 33.6 36.9 38.5 48.2 64.4
Wool ± ± ± ± ± ± ± ± ± ± ± ±
0.03 0.2 0.1 0.3 0.6 0.5 3.4 0.3 0.3 0.3 0.8 1.1
4.12 23.1 17.5 30.0 35.9 28.3 245.5 33.6 36.7 38.3 47.8 63.5
P-value ± ± ± ± ± ± ± ± ± ± ± ±
0.03 0.2 0.1 0.3 0.6 0.5 2.4 0.3 0.3 0.3 0.8 1.1
0.038 0.000 0.201 0.489 0.000 0.000 0.414 0.933 0.311 0.336 0.303 0.079
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M.A. Snyman, W.J. Olivier / Small Ruminant Research 45 (2002) 17–23
Differences between the hair and wool flocks with regard to the percentage of ewes that lambed, percentage of lambs born per ewe mated or lambed, survival rate of lambs from birth till weaning and percentage of lambs weaned per ewe mated, were tested for significance employing the χ 2 procedure of SAS Institute (1990). Total weight of lamb produced per ewe per year (kg) was calculated as follows (Snyman et al., 1997): firstly, within each lambing season, individual lamb 42-day body weights and weaning weights were adjusted for variation in age to 42 and 120 days, respectively, followed by least-squares corrections for sex of the lamb. No corrections were made for birth status. Secondly, the corrected weights of all the lambs produced by each ewe in each lambing season were added together, in order to obtain total weight of lamb at 42 days and total weight of lamb weaned. For the analyses of variance for body weight before mating and total weight of lamb produced per ewe per year, the mathematical model included fixed effects due to flock, year and age of the ewe, and residual error (Littell et al., 1991).
presented in Table 2. Birth weight of wool lambs was significantly higher than that of the hair lambs. From Table 2, it is evident that no differences between hair and wool lambs were found for body weight recorded from 42 days till 12 months of age, nor for pre-weaning growth rate. Coat cover score at birth and weaning differed between hair and wool lambs (P < 0.01), and as expected the hair type lambs had a more hairy coat cover, and the wool type lambs a more woolly cover. Wool type lambs also had a higher condition score at weaning (28.3 vs. 24.9). Least-squares means for conformation of hair and wool type Dorper lambs are presented in Table 3. Hair type lambs had a better conformation than wool type lambs for chest width and depth, protrusion of the chest between the front legs, shoulders, hind quarters and width of the rump. Wool type lambs had a higher body height and length of hind leg, as well as better hocks and less sloped rumps, compared to the hair type lambs. There was no difference in general conformation of the head, width of hind leg, body length, body depth, front or hind pasterns or top line between lambs of the hair and wool types. These characteristics may have contributed to blockier hair type lambs with shorter legs, compared to the leggier appearance of the wool type lambs. These findings are in agreement with Van Niekerk and Steenkamp (1995), comparing carcass traits of hair, wool and hair/wool
3. Results and discussion Least-squares means of growth traits and coat cover score of hair and wool type Dorper lambs are
Table 3 Least-squares means (±S.E.) of conformation traits of hair and wool type Dorper lambs at 6 months of age Trait
Hair (n = 867)
General conformation of the head Chest width and depth Protrusion of chest between front legs Shoulders Hind quarters Width of rump (cm) Width of hind leg from the side (cm) Length of hind leg from the side (cm) Body length (cm) Body depth (cm) Body height (cm) Hocks Front pasterns Hind pasterns Top line Slope of rump Testis circumference (cm)
34.0 33.8 31.5 30.7 28.6 14.2 14.8 27.9 63.5 28.6 56.7 39.5 42.7 42.8 36.2 36.4 28.1
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.3 0.4 0.4 0.4 0.4 0.1 0.1 0.2 0.3 0.2 0.2 0.1 0.2 0.1 0.3 0.1 0.4
Wool (n = 841) 33.9 33.3 30.9 29.9 27.8 13.9 14.7 28.2 63.6 28.5 57.7 40.3 42.7 42.5 36.1 37.0 27.6
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.3 0.4 0.4 0.4 0.4 0.1 0.1 0.2 0.3 0.2 0.2 0.1 0.2 0.1 0.3 0.1 0.4
P-value 0.552 0.033 0.018 0.000 0.001 0.000 0.325 0.014 0.797 0.167 0.000 0.000 0.656 0.053 0.665 0.000 0.040
M.A. Snyman, W.J. Olivier / Small Ruminant Research 45 (2002) 17–23
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Table 4 Least-squares means (±S.E.) of slaughter traits of hair and wool type Dorper lambs Trait
Hair (n = 430)
Fasted body weight (kg) Carcass weight (kg) Age at slaughter (days) Dressing percentage Length of leg B1 (cm) Length of leg B2 (cm) Circumference of leg (cm) Carcass length (K2) (cm) V1-fat depth (mm) V2-fat depth (mm) V3-fat depth (mm) V4-fat depth (mm) V5-fat depth (mm)
40.1 19.2 264.1 49.0 37.8 49.2 72.7 107.2 6.5 4.9 5.6 3.0 1.3
± ± ± ± ± ± ± ± ± ± ± ± ±
0.3 0.1 3.4 0.1 0.1 0.2 0.1 0.1 0.3 0.2 0.3 0.1 0.1
Dorper lambs with hair type Dorpers that appear smaller, compared to their woolly counterparts. Testis circumference of hair type ram lambs measured at 6 months of age was larger (P < 0.05) than that for the wool type ram lambs (28.1 vs. 27.6 cm). Least-squares means of slaughter traits of hair and wool type Dorper lambs are presented in Table 4. Hair and wool type lambs were slaughtered at a live body weight of 40.1 and 39.8 kg, respectively. There was no difference in the age when hair and wool type lambs
Wool (n = 386) 39.8 19.6 266.3 49.9 38.6 49.8 73.0 108.5 6.7 5.2 5.8 3.0 1.3
± ± ± ± ± ± ± ± ± ± ± ± ±
0.3 0.1 3.6 0.2 0.1 0.2 0.1 0.1 0.3 0.3 0.3 0.1 0.1
P-value 0.059 0.000 0.338 0.000 0.000 0.000 0.012 0.000 0.200 0.044 0.178 0.962 0.590
reached slaughter weight, as is also evident from the growth performance in Table 2. In a study by Van Niekerk and Steenkamp (1995), carcass traits of hair, wool and hair/wool type lambs, kept under intensive feedlot conditions from weaning to slaughter at either 25, 30, 35 or 40 kg live weight, were compared. These results are in agreement with the present study. In contrast, the dressing percentage of wool type lambs was higher (P < 0.01) than hair type lambs in the present study. The higher dressing
Fig. 1. Distribution of hair and wool type lamb carcasses over the different grades.
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M.A. Snyman, W.J. Olivier / Small Ruminant Research 45 (2002) 17–23
Table 5 Reproductive performance of hair and wool Dorper ewes Trait
Hair ewes (n = 872)
Wool ewes (n = 874)
P-value
Body weight at mating (kg) Ewes lambed/ewes mated (%) Lambs born/ewe mated (%) Lambs born/ewe lambing (%) Survival rate from birth till weaning (%) Lambs weaned/ewe mated (%) Lamb at 42 days per ewe per annum (kg) Lamb weaned per ewe per annum (kg)
57.4 ± 0.3 85.89 128.56 149.67 96.92 116.17 20.4 ± 0.4 35.3 ± 0.8
56.4 ± 0.3 82.49 124.03 150.35 95.69 111.33 19.7 ± 0.4 33.9 ± 0.8
0.000 0.050 0.103 0.303 0.135 0.106 0.100 0.121
percentage recorded for wool lambs resulted in their heavier carcass weights (19.6 vs. 19.2 kg). Wool type lambs had longer carcass length and hind leg (B1 and B2) than hair type lambs in agreement with Van Niekerk and Steenkamp (1995) for B1 measurements. There was no significant difference in fat measurements for the wool and hair types. It therefore follows that there should be no difference in carcass grading between types, as grading is based primarily on V3-fat measurements. The distribution of hair and wool lamb carcasses over the various grades is presented in Fig. 1. From this figure, it is evident that there was no difference in grading between hair and wool lamb carcasses. Reproductive performance of hair and wool type Dorper ewes is presented in Table 5. Reproductive parameters for the first parity for the ewe lambs mated at 7 months of age are presented in Table 6 for all
young ewes mated, as well as for only young ewes that weaned a lamb(s). Body weight at mating was higher for hair type ewe than for wool type ewes (57.9 vs. 56.4 kg). No significant differences between groups were observed for percentage of ewes lambed, lambs born, lambs weaned, survival rate of lambs or kilogram of lamb produced per ewe per year. There was a trend for hair type ewes to reproduce 3–5% more than their wool type counterparts. Though not significant, a similar trend in reproductive performance was observed between hair and wool type ewes mated at 7 months of age. The growth and slaughter traits and reproduction of the two experimental flocks compared well with those reported in a literature review on productive performance of Dorper sheep (Cloete et al., 2000). Unfortunately, no other studies on the relative performance of
Table 6 Reproductive performance of young hair and wool Dorper ewes at their first parity Trait
Hair ewes (n = 237)
Wool ewes (n = 245)
P-value
All young ewes mated Body weight at mating (kg) Ewes lambed/ewes mated (%) Lambs born/ewe mated (%) Lambs born/ewe lambing (%) Survival rate from birth till weaning (%) Lambs weaned/ewe mated (%) Lamb at 42 days per ewe per annum (kg) Lamb weaned per ewe per annum (kg)
40.3 ± 0.3 67.09 76.79 114.47 95.06 63.29 10.0 ± 0.6 17.0 ± 1.07
39.6 ± 0.3 63.27 70.2 110.97 93.59 57.14 9.4 ± 0.6 15.7 ± 1.06
0.110 0.379 0.441 0.353 0.570 0.474 0.442 0.395
Hair ewes (n = 133)
Wool ewes (n = 128)
40.8 ± 0.4 17.7 ± 0.3 31.1 ± 0.6
40.3 ± 0.4 17.4 ± 0.3 30.4 ± 0.6
Young ewes that weaned a lamb(s) Body weight at mating (kg) Lamb at 42 days per ewe per annum (kg) Lamb weaned per ewe per annum (kg)
0.357 0.385 0.403
M.A. Snyman, W.J. Olivier / Small Ruminant Research 45 (2002) 17–23
hair and wool type Dorper sheep are available. However, the present findings are based on data collected over 8 years and a large number of records, therefore the findings of this study can be considered reliable. 4. Conclusion In terms of the economically important reproduction and growth traits, there were no differences between hair and wool types of Dorper sheep. Therefore, claims or perceptions in the industry as to the superior performance of hair type Dorper sheep under extensive conditions are not supported by these results. Differences that do occur, such as some conformation and carcass traits, will not have any effect on the economic realisation from the different types. References Acocks, J.P.H., 1988. Veld Types of South Africa, 3rd Edition. Memoirs of the Botanical Survey of South Africa No 57.
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Botanical Research Institute, Department of Agriculture and Water Supply, Pretoria, South Africa. Bruwer, G.G., 1984. Objective evaluation of the carcass grading system for lambs and sheep in R.S.A. M.Sc. Thesis. University of Stellenbosch, Stellenbosch, South Africa. Cloete, S.W.P., Snyman, M.A., Herselman, M.J., 2000. The South African Dorper sheep: a review of productive performance. Small Rum. Res. 36, 119–135. Littell, R.C., Freud, R.J., Spector, P.C., 1991. SAS System for Linear Models, 3rd Edition. SAS Institute, Inc., Cary, NC, pp. 137–198. SAS Institute, 1990. Procedures Guide, Version 6, 3rd Edition. SAS Institute, Inc., Cary, NC, pp. 325–340. Snyman, M.A., Olivier, J.J., Erasmus, G.J., Van Wyk, J.B., 1997. Genetic parameter estimates for total weight of lamb weaned in Afrino and Merino sheep. Livest. Prod. Sci. 48, 111–116. Strydom, P.E., Vermeulen, J.H., Nel, E., De Bruyn, J.F., 1995. Production and reproduction of two types of Dorper sheep (in Afrikaans). Research Report Available at the Dorper Sheep Breeders’ Society of South Africa, Middelburg, South Africa, 20 pp. Van Niekerk, W.A., Steenkamp, K., 1995. Comparison of three types of Dorper lambs (wool, hair and intermediate type) with regard to growth, feed and water intake, protein and fat metabolism (in Afrikaans). Dorper Sheep Breeders’ Society of South Africa, Middelburg, South Africa, 25 pp.
Productive performance of hair and wool type Dorper sheep under extensive conditions M.A. Snyman∗ , W.J. Olivier Department of Agriculture, Grootfontein Agricultural Development Institute, Private Bag X529, Middelburg Cape 5900, South Africa Accepted 5 March 2002
Abstract The reproductive performance, growth, slaughter traits, and several conformation characteristics in Dorper sheep (hair and wool types) were evaluated under extensive conditions in the north-western Karoo region of South Africa. From 1993 to 2000, lambs of hair (n = 1070) and wool (n = 1044) type Dorper sheep, and corresponding reproductive records from 872 and 874, respectively, were analysed. There was no significant differences between hair and wool type lambs for body weight from 42 days till 12 months of age, and for pre- or post-weaning growth rate. The analysis of conformation tend to suggest that the hair type lambs were blockier with shorter legs, compared to the leggier appearance of the wool type lambs. This is also evident from the longer carcass length (108.5 vs. 107.2 cm) and hind leg length of wool type lambs compared to hair type lambs. With regard to other carcass traits, wool type lambs had heavier carcasses (19.6 vs. 19.2 kg) and higher dressing percentage (49.9 vs. 49.0%), though, fat measurements and carcass grades were similar. The ewes of the hair type were heavier at mating than wool type (57.4 vs. 56.4 kg). No differences were, however, observed for percentage of ewes lambed, lambs born, lambs weaned, survival rate of lambs or kg lamb produced per ewe per year. It was concluded that the economically important reproduction and growth traits were similar between the hair and wool types of Dorper sheep. Differences that do occur in some conformation and carcass traits will not effect the economic realisation from the different types. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Growth traits; Slaughter traits; Reproduction; Conformation traits
1. Introduction Mutton production is an important component of the agricultural sector in the extensive north-western sheep grazing areas of the Republic of South Africa. Due to the limited natural resources in these areas, it is important to increase the efficiency of mutton production within the limits of these resources. It is therefore essential that the most suitable type of sheep for these areas, in terms of adaptability and ∗ Corresponding author. Tel.: +27-49-842-1113; fax: +27-49-842-4352. E-mail address: [email protected] (M.A. Snyman).
profitability, be identified. Dorper sheep constitute a large proportion of the sheep numbers in these areas, and it is therefore obvious that the most profitable type within this breed should be identified. Animals within the Dorper breed are classified into different types according to coat cover, conformation or fat distribution. Several perceptions as to the productive and reproductive potential of these types remain among breeders and farmers. One of these is that Dorper sheep with a hairy coat cover, are more hardy and adapted, with a higher reproduction rate and ability to be marketed at an earlier age under extensive conditions than those Dorper sheep with a predominantly woolly coat cover. Results of growth and carcass
0921-4488/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 4 8 8 ( 0 2 ) 0 0 1 1 6 - 5
18
M.A. Snyman, W.J. Olivier / Small Ruminant Research 45 (2002) 17–23
traits of hair/wool type and compact/larger frame type Dorper lambs under intensive conditions have been published (Van Niekerk and Steenkamp, 1995; Strydom et al., 1995). There is, however, no information available on the relative performance of hair and wool type Dorper sheep under extensive veld conditions, especially with regard to reproductive performance. In the present study, the reproductive performance, growth and slaughter traits, and several conformation characteristics in hair and wool type Dorper sheep were evaluated under extensive conditions.
2. Material and methods The flock was maintained under natural conditions at the Klerefontein Experimental Station near Carnarvon (30◦ 59 S, 22◦ 9 E) in the north-western Karoo region of South Africa, representative of the extensive low potential of the area. The natural pasture which varies from mixed grass and shrub veld to Karoo shrub veld has been described as arid Karoo (Acocks, 1988). The official grazing capacity is estimated at 5.5 ha per small stock unit. The climate is characterised by cold winters and hot summers. The average annual rainfall is 209 mm and occurs mainly during the autumn months. In July 1993, animals of the existing experimental Dorper flock at the Klerefontein Experimental Station were classed into two groups on the basis of their coat cover, i.e. either hair or wool type. Furthermore, 20 hair and 20 wool type young ewes were bought from the industry in 1994. These ewes formed the foundation of the two experimental flocks. Flock size was kept at 110 ewes each, for the hair and wool types. During the 1993 and 1994 breeding seasons, seven hair and wool type rams from various experimental flocks were used as sires, together with wool and hair type rams from the existing flock at Klerefontein. Thereafter, from 1995, only rams bred within the hair and wool flocks, were used as sires. The hair and wool ewes including their lambs were managed as one flock for the duration of the study. Animals kept under natural veld conditions did not receive any feed or mineral supplement. The routine inoculation, drenching and tick control program was followed.
The ewes were individually mated once a year during April. Replacement ewes were exposed to rams at 7 months of age, while replacement rams were used for breeding, the first time at 18 months of age. An age structure of five ewe and two ram age groups was followed, where 20% of older ewes and all but one or two rams were replaced with young ones each year. Ewes were not culled for poor reproductive performance, however, ewes with udder defects were culled. During the lambing season in September, the following data were recorded for each lamb: identification of the lamb, and its dam and sire, date of birth, birth weight, sex and birth status of the lamb and coat cover score. The body weight at 42 days and at weaning, condition score and coat cover score at 120 days of age were also recorded. At 6 months of age, various conformation traits were subjectively assessed for all lambs, on a linear scale ranging from 1 to 50. These included the general conformation of the head, chest width and depth, protrusion of chest between front legs, shoulders, hind quarters, hocks, front pasterns, hind pasterns, top line, slope of rump. The scale of assessment for these subjectively assessed traits are summarised in Table 1. All subjective assessments were done by the same person, in order to eliminate possible differences due to the Table 1 Linear scale of assessment for conformation traits and coat cover of 6 months old lambs Trait
Coat cover Condition score General conformation of the head Chest width and depth Protrusion of chest between front legs Shoulders Hind quarters Hocks Front pasterns Hind pasterns Top line Slope of rump
Scalea 1
25
50
Hairy Emaciated Poor
Mixture Average Average
Woolly Fat Ideal
Narrow
Average
None
Average
Wide and deep Much
Loose Narrow Poor Poor Poor Poor Sloped
Average Average Average Average Average Average Average
Ideal Well filled Ideal Ideal Ideal Straight Straight
a 1–10: poor; 11–20: below average; 21–30: average; 31–40: above average; 41–50: excellent.
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assessor. At the same time, the width of rump, width of hind leg from the side, length of hind leg from the side, body length, body depth, body height and testis circumference of ram lambs were measured objectively. During the subjective assessment at 6 months of age, ewe and ram lambs were classed and ewe lambs were selected for replacement. Correspondingly, 40–50 each of the hair and wool type ram lambs were selected for future use. Selection was based on weaning weight of the lambs. Animals with conformation defects or definite faults, such as short lower jaws, or lambs that were either too hairy or too woolly for their group, were earmarked to be slaughtered. These surplus lambs, as well as the ram lambs kept for future selection purposes, were weighed monthly until 12 months of age. Surplus ram and ewe lambs approaching a body weight of approximately 40 kg were slaughtered. The body weight and slaughter weight of lambs, fasted overnight was recorded. Carcass weight, dressing percentage and all carcass measurements included records based on the National Lamb Carcass Competition (Bruwer, 1984). Data from lambs born from 1993 to 2000 in the hair (n = 1070) and wool (n = 1044) flocks were available. The number of records for the growth traits are presented in Table 2. For body weight from 42 days till 7 months of age, body weights of all lambs were included, i.e. surplus as well as selected lambs. From 8 months of age, body weight data for surplus ram and ewe lambs not yet slaughtered, as well as the selected ram lambs, were included. Conformation traits from 1708 lambs (867 hair and 841 wool types)
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and slaughter traits from 816 lambs (430 hair and 386 wool types) were analysed. Least-squares procedures (SAS Institute, 1990) were used to analyse data for all growth, conformation and slaughter traits (Littell et al., 1991). The following mathematical model was used: Yijklmn = µ + yi + fj + sk + rl + am + (yf)ij + (ys)ik + (fs)jk + b1 AL + b2 FW + eijklmn where Yij klmn is the trait of the nth animal of the mth age of dam for the lth birth/rearing status, kth sex, jth flock and ith birth year, µ the overall mean, yi the fixed effect of the ith birth year, fj the fixed effect of the jth flock, sk the fixed effect of the kth sex, rl the fixed effect of the lth rearing status (birth status in the case of birth weight), am the fixed effect of the mth age of dam (years), (yf)ij the effect of the interaction between the ith birth year and the jth flock, (ys)ik the effect of the interaction between the ith birth year and the kth sex, (fs)j k the effect of the interaction between the jth flock and the kth sex, b1 the linear regression of the deviation from the mean of age of the lamb at recording (AL; except for birth weight), b2 the linear regression of the deviation from the mean of fasted body weight (FW; fitted only for all the slaughter traits), eij klmn the random error with zero mean and variance I σe2 . Data collected on the ewe flock from 1993 to 2000 include records on body weight before mating, number of ewes mated, number of ewes that lambed, number of lambs born, and number of lambs weaned. A total of 872 and 874 reproductive records were available for the hair and wool flocks, respectively.
Table 2 Least-squares means (±S.E.) of growth traits and coat cover score of hair and wool type Dorper lambs Trait
n
Hair
Birth weight (kg) Coat cover at birth 42-Day body weight (kg) 100-Day weaning weight (kg) Coat cover score at weaning Condition score at weaning Daily gain from birth to weaning (g/day) 5-Month body weight (kg) 6-Month body weight (kg) 7-Month body weight (kg) 9-Month body weight (kg) 12-Month body weight (kg)
2114 1887 2036 1985 1438 1438 1985 1730 1693 1570 636 421
4.06 9.7 17.6 30.1 14.2 24.9 246.6 33.6 36.9 38.5 48.2 64.4
Wool ± ± ± ± ± ± ± ± ± ± ± ±
0.03 0.2 0.1 0.3 0.6 0.5 3.4 0.3 0.3 0.3 0.8 1.1
4.12 23.1 17.5 30.0 35.9 28.3 245.5 33.6 36.7 38.3 47.8 63.5
P-value ± ± ± ± ± ± ± ± ± ± ± ±
0.03 0.2 0.1 0.3 0.6 0.5 2.4 0.3 0.3 0.3 0.8 1.1
0.038 0.000 0.201 0.489 0.000 0.000 0.414 0.933 0.311 0.336 0.303 0.079
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Differences between the hair and wool flocks with regard to the percentage of ewes that lambed, percentage of lambs born per ewe mated or lambed, survival rate of lambs from birth till weaning and percentage of lambs weaned per ewe mated, were tested for significance employing the χ 2 procedure of SAS Institute (1990). Total weight of lamb produced per ewe per year (kg) was calculated as follows (Snyman et al., 1997): firstly, within each lambing season, individual lamb 42-day body weights and weaning weights were adjusted for variation in age to 42 and 120 days, respectively, followed by least-squares corrections for sex of the lamb. No corrections were made for birth status. Secondly, the corrected weights of all the lambs produced by each ewe in each lambing season were added together, in order to obtain total weight of lamb at 42 days and total weight of lamb weaned. For the analyses of variance for body weight before mating and total weight of lamb produced per ewe per year, the mathematical model included fixed effects due to flock, year and age of the ewe, and residual error (Littell et al., 1991).
presented in Table 2. Birth weight of wool lambs was significantly higher than that of the hair lambs. From Table 2, it is evident that no differences between hair and wool lambs were found for body weight recorded from 42 days till 12 months of age, nor for pre-weaning growth rate. Coat cover score at birth and weaning differed between hair and wool lambs (P < 0.01), and as expected the hair type lambs had a more hairy coat cover, and the wool type lambs a more woolly cover. Wool type lambs also had a higher condition score at weaning (28.3 vs. 24.9). Least-squares means for conformation of hair and wool type Dorper lambs are presented in Table 3. Hair type lambs had a better conformation than wool type lambs for chest width and depth, protrusion of the chest between the front legs, shoulders, hind quarters and width of the rump. Wool type lambs had a higher body height and length of hind leg, as well as better hocks and less sloped rumps, compared to the hair type lambs. There was no difference in general conformation of the head, width of hind leg, body length, body depth, front or hind pasterns or top line between lambs of the hair and wool types. These characteristics may have contributed to blockier hair type lambs with shorter legs, compared to the leggier appearance of the wool type lambs. These findings are in agreement with Van Niekerk and Steenkamp (1995), comparing carcass traits of hair, wool and hair/wool
3. Results and discussion Least-squares means of growth traits and coat cover score of hair and wool type Dorper lambs are
Table 3 Least-squares means (±S.E.) of conformation traits of hair and wool type Dorper lambs at 6 months of age Trait
Hair (n = 867)
General conformation of the head Chest width and depth Protrusion of chest between front legs Shoulders Hind quarters Width of rump (cm) Width of hind leg from the side (cm) Length of hind leg from the side (cm) Body length (cm) Body depth (cm) Body height (cm) Hocks Front pasterns Hind pasterns Top line Slope of rump Testis circumference (cm)
34.0 33.8 31.5 30.7 28.6 14.2 14.8 27.9 63.5 28.6 56.7 39.5 42.7 42.8 36.2 36.4 28.1
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.3 0.4 0.4 0.4 0.4 0.1 0.1 0.2 0.3 0.2 0.2 0.1 0.2 0.1 0.3 0.1 0.4
Wool (n = 841) 33.9 33.3 30.9 29.9 27.8 13.9 14.7 28.2 63.6 28.5 57.7 40.3 42.7 42.5 36.1 37.0 27.6
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.3 0.4 0.4 0.4 0.4 0.1 0.1 0.2 0.3 0.2 0.2 0.1 0.2 0.1 0.3 0.1 0.4
P-value 0.552 0.033 0.018 0.000 0.001 0.000 0.325 0.014 0.797 0.167 0.000 0.000 0.656 0.053 0.665 0.000 0.040
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Table 4 Least-squares means (±S.E.) of slaughter traits of hair and wool type Dorper lambs Trait
Hair (n = 430)
Fasted body weight (kg) Carcass weight (kg) Age at slaughter (days) Dressing percentage Length of leg B1 (cm) Length of leg B2 (cm) Circumference of leg (cm) Carcass length (K2) (cm) V1-fat depth (mm) V2-fat depth (mm) V3-fat depth (mm) V4-fat depth (mm) V5-fat depth (mm)
40.1 19.2 264.1 49.0 37.8 49.2 72.7 107.2 6.5 4.9 5.6 3.0 1.3
± ± ± ± ± ± ± ± ± ± ± ± ±
0.3 0.1 3.4 0.1 0.1 0.2 0.1 0.1 0.3 0.2 0.3 0.1 0.1
Dorper lambs with hair type Dorpers that appear smaller, compared to their woolly counterparts. Testis circumference of hair type ram lambs measured at 6 months of age was larger (P < 0.05) than that for the wool type ram lambs (28.1 vs. 27.6 cm). Least-squares means of slaughter traits of hair and wool type Dorper lambs are presented in Table 4. Hair and wool type lambs were slaughtered at a live body weight of 40.1 and 39.8 kg, respectively. There was no difference in the age when hair and wool type lambs
Wool (n = 386) 39.8 19.6 266.3 49.9 38.6 49.8 73.0 108.5 6.7 5.2 5.8 3.0 1.3
± ± ± ± ± ± ± ± ± ± ± ± ±
0.3 0.1 3.6 0.2 0.1 0.2 0.1 0.1 0.3 0.3 0.3 0.1 0.1
P-value 0.059 0.000 0.338 0.000 0.000 0.000 0.012 0.000 0.200 0.044 0.178 0.962 0.590
reached slaughter weight, as is also evident from the growth performance in Table 2. In a study by Van Niekerk and Steenkamp (1995), carcass traits of hair, wool and hair/wool type lambs, kept under intensive feedlot conditions from weaning to slaughter at either 25, 30, 35 or 40 kg live weight, were compared. These results are in agreement with the present study. In contrast, the dressing percentage of wool type lambs was higher (P < 0.01) than hair type lambs in the present study. The higher dressing
Fig. 1. Distribution of hair and wool type lamb carcasses over the different grades.
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Table 5 Reproductive performance of hair and wool Dorper ewes Trait
Hair ewes (n = 872)
Wool ewes (n = 874)
P-value
Body weight at mating (kg) Ewes lambed/ewes mated (%) Lambs born/ewe mated (%) Lambs born/ewe lambing (%) Survival rate from birth till weaning (%) Lambs weaned/ewe mated (%) Lamb at 42 days per ewe per annum (kg) Lamb weaned per ewe per annum (kg)
57.4 ± 0.3 85.89 128.56 149.67 96.92 116.17 20.4 ± 0.4 35.3 ± 0.8
56.4 ± 0.3 82.49 124.03 150.35 95.69 111.33 19.7 ± 0.4 33.9 ± 0.8
0.000 0.050 0.103 0.303 0.135 0.106 0.100 0.121
percentage recorded for wool lambs resulted in their heavier carcass weights (19.6 vs. 19.2 kg). Wool type lambs had longer carcass length and hind leg (B1 and B2) than hair type lambs in agreement with Van Niekerk and Steenkamp (1995) for B1 measurements. There was no significant difference in fat measurements for the wool and hair types. It therefore follows that there should be no difference in carcass grading between types, as grading is based primarily on V3-fat measurements. The distribution of hair and wool lamb carcasses over the various grades is presented in Fig. 1. From this figure, it is evident that there was no difference in grading between hair and wool lamb carcasses. Reproductive performance of hair and wool type Dorper ewes is presented in Table 5. Reproductive parameters for the first parity for the ewe lambs mated at 7 months of age are presented in Table 6 for all
young ewes mated, as well as for only young ewes that weaned a lamb(s). Body weight at mating was higher for hair type ewe than for wool type ewes (57.9 vs. 56.4 kg). No significant differences between groups were observed for percentage of ewes lambed, lambs born, lambs weaned, survival rate of lambs or kilogram of lamb produced per ewe per year. There was a trend for hair type ewes to reproduce 3–5% more than their wool type counterparts. Though not significant, a similar trend in reproductive performance was observed between hair and wool type ewes mated at 7 months of age. The growth and slaughter traits and reproduction of the two experimental flocks compared well with those reported in a literature review on productive performance of Dorper sheep (Cloete et al., 2000). Unfortunately, no other studies on the relative performance of
Table 6 Reproductive performance of young hair and wool Dorper ewes at their first parity Trait
Hair ewes (n = 237)
Wool ewes (n = 245)
P-value
All young ewes mated Body weight at mating (kg) Ewes lambed/ewes mated (%) Lambs born/ewe mated (%) Lambs born/ewe lambing (%) Survival rate from birth till weaning (%) Lambs weaned/ewe mated (%) Lamb at 42 days per ewe per annum (kg) Lamb weaned per ewe per annum (kg)
40.3 ± 0.3 67.09 76.79 114.47 95.06 63.29 10.0 ± 0.6 17.0 ± 1.07
39.6 ± 0.3 63.27 70.2 110.97 93.59 57.14 9.4 ± 0.6 15.7 ± 1.06
0.110 0.379 0.441 0.353 0.570 0.474 0.442 0.395
Hair ewes (n = 133)
Wool ewes (n = 128)
40.8 ± 0.4 17.7 ± 0.3 31.1 ± 0.6
40.3 ± 0.4 17.4 ± 0.3 30.4 ± 0.6
Young ewes that weaned a lamb(s) Body weight at mating (kg) Lamb at 42 days per ewe per annum (kg) Lamb weaned per ewe per annum (kg)
0.357 0.385 0.403
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hair and wool type Dorper sheep are available. However, the present findings are based on data collected over 8 years and a large number of records, therefore the findings of this study can be considered reliable. 4. Conclusion In terms of the economically important reproduction and growth traits, there were no differences between hair and wool types of Dorper sheep. Therefore, claims or perceptions in the industry as to the superior performance of hair type Dorper sheep under extensive conditions are not supported by these results. Differences that do occur, such as some conformation and carcass traits, will not have any effect on the economic realisation from the different types. References Acocks, J.P.H., 1988. Veld Types of South Africa, 3rd Edition. Memoirs of the Botanical Survey of South Africa No 57.
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Botanical Research Institute, Department of Agriculture and Water Supply, Pretoria, South Africa. Bruwer, G.G., 1984. Objective evaluation of the carcass grading system for lambs and sheep in R.S.A. M.Sc. Thesis. University of Stellenbosch, Stellenbosch, South Africa. Cloete, S.W.P., Snyman, M.A., Herselman, M.J., 2000. The South African Dorper sheep: a review of productive performance. Small Rum. Res. 36, 119–135. Littell, R.C., Freud, R.J., Spector, P.C., 1991. SAS System for Linear Models, 3rd Edition. SAS Institute, Inc., Cary, NC, pp. 137–198. SAS Institute, 1990. Procedures Guide, Version 6, 3rd Edition. SAS Institute, Inc., Cary, NC, pp. 325–340. Snyman, M.A., Olivier, J.J., Erasmus, G.J., Van Wyk, J.B., 1997. Genetic parameter estimates for total weight of lamb weaned in Afrino and Merino sheep. Livest. Prod. Sci. 48, 111–116. Strydom, P.E., Vermeulen, J.H., Nel, E., De Bruyn, J.F., 1995. Production and reproduction of two types of Dorper sheep (in Afrikaans). Research Report Available at the Dorper Sheep Breeders’ Society of South Africa, Middelburg, South Africa, 20 pp. Van Niekerk, W.A., Steenkamp, K., 1995. Comparison of three types of Dorper lambs (wool, hair and intermediate type) with regard to growth, feed and water intake, protein and fat metabolism (in Afrikaans). Dorper Sheep Breeders’ Society of South Africa, Middelburg, South Africa, 25 pp.