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The effect of docking on growth, carcass quality, fat distribution

and reproductive performance of Namaqua Afrikaner Sheep

 

1M. A. Snyman, M van Heerden & B.R. King, 2J.A.N. Cloete


1Grootfontein ADI, Private Bag X529, Middelburg EC, 5900

2Carnarvon Experimental Station, Carnarvon, 8995

 


INTRODUCTION

Shelton (1990),  reported  that approximately one third of the world=s sheep population consists of fat tailed sheep. These sheep are characterised by the deposition of reserve fat in the tail. These types can have a high overall carcass fat content, of which up to 33% could be stored in the fat tail (Shelton et al., 1991). Consumers are now more diet conscious and are changing their eating habits in order to consume leaner meat. Therefore, the marketing of fat tailed sheep is becoming more difficult and the fat tail is considered as a waste product of the carcass.

 

From research results it is evident that Namaqua Afrikaner sheep are very hardy and adaptable under extensive conditions (Snyman et al., 1993; 1996a, 1996b). They are therefore ideally suited to the low potential north-western areas of the Northern Cape province, where many communal farmers are located. Many of these farmers keep Namaqua Afrikaner or other fat tailed sheep. The fat tails of these sheep - in which energy reserves are stored; Figure 1 - are the main reason why these animals are so hardy and adaptable. These same fat tails are also the reason why the carcasses of these sheep are identified at the abattoirs, and prices of up to R 3-00 less are paid per kg for fat tailed carcasses in comparison with other non fat tailed carcasses of  the  same fat grade (Snyman et al., 1996c).

 

Several authors (Joubert & Ueckermann, 1971;  Hofmeyr et al., 1974; Marai  et al., 1987; Shelton et al., 1991; Bicer et al., 1992) reported variable effects of docking on fat deposition and distribution over the carcass of docked fat tailed lambs. There is, however, no available scientific evidence of the effect of docking on the carcass quality or other production and reproduction traits of Namaqua Afrikaner sheep. As the fat stores in the tails of these animals contribute significantly to their hardiness, these effects should be clarified before any recommendations regarding docking could be made to farmers.

 

The aim of this project was to investigate what effect docking would have, firstly, on growth performance, slaughter traits and fat distribution over the carcass, and secondly, on reproductive performance of ewes which have been docked.

                                                                       

           

Figure 1. Fat tails of Namaqua Afrikaner lambs

 

MATERIAL & METHODS

 

Description of the experimental location

The study was conducted under natural conditions at the Klerefontein Ex­perimental Station near Carnarvon (30E 59'S, 22° 9'E) in the north‑western Karoo region of the Republic of South Africa. The experimental station is representative of the extensive low potential areas of the Karoo region. The natural pasture varies from mixed grass and shrub veld to karoo shrub veld and is described by Acocks (1988) as arid karoo. The official graz­ing capacity norm is estimated at 38 ha/LSU, which is approximately 5.5 ha per small stock unit. The climate is characterised by severe winters and hot summers. The average annual rainfall is 209 mm and occurs mainly during the autumn months.

 

Experimental animals

The Namaqua Afrikaner ewe flock (105 ewes) of the Klerefontein Experimental Station was used for this study. In April 1997, thirty additional ewes were mated. The lambs of these ewes, born during September 1997, were docked two days after birth with elastrator bands. Ram lambs were slaughtered at 40 kg body weight and compared to their counterparts with intact fat tails. The ewe lambs were allowed to reproduce for three lambing opportunities and their reproductive performance was evaluated.

 

Management practices and data recorded

All ewes were managed as one flock for the duration of the study. Lambs were also run together and managed as one flock. Animals were kept under natural veld conditions and received no supplementary feeding or any licks at any stage. The normal inoculation, drenching and tick control program was followed. The ewes were group mated once a year during April to 10% rams. Ewes were not culled on poor reproductive performance, only ewes with udder defects were culled.

 

During the lambing season in September 1997, the following data were recorded for each lamb : Lamb ID, Dam ID, date of birth, birth weight, sex and birth status of the lamb. Body weight at 42 days, weaning weight at 120 days of age and monthly body weight from 5 to 12 months of age were also recorded.

 

Twenty docked and 15 intact ram lambs were slaughtered as soon as they reached a body weight of approximately 45 kg. Upon reaching slaughter weight, lambs were fasted overnight and fasted body weight was recorded before slaughtering the next morning. Carcass weight, dressing percentage and all carcass measurements, as recorded for the National lamb carcass competition (Bruwer, 1984), were taken. The fat tails and all the fat around the tail region were removed and weighed as well.

 

The hind leg as well as two chops, one from the lumbar region and the other from the 9th to 10th rib area, were cut out and frozen for analyses of fat content. All the fat and meat of the hind leg and chops were trimmed from the bone after thawing of the cuts. The meat was weighed and minced twice. Afterwards, a weighed sample was freeze dried, minced again and then analysed for moisture, ash and protein content and ether extract (fat content).

 

Ewe lambs that were docked, were allowed to reproduce for three years (from 1999 to 2001). The reproductive performance of these ewes (n=21) was compared with that of the intact 1997-born ewes (n=20) over the same period. Reproductive data recorded include records on body weight before mating and after weaning, number of ewes mated, number of ewes that lambed, number of lambs born, number of lambs weaned, lamb survival rate and weaning weight of lambs. A total of 55 and 62 reproductive records were available for the intact and docked ewes respectively.

 

Statistical analysis

Body weight data from 132 intact and 45 docked lambs and slaughter data from 14 intact and 20 docked lambs (born during September 1997) were analysed with least‑squares procedures of SAS (Littell et al., 1991). A model including fixed effects for group, sex and birth/rearing status of the lamb and age of dam, as well as age at recording of body weight, was used to analyse body weights. For analyses of slaughter traits, slaughter weight was included as a co-variable.

 

Differences between the intact and docked ewes 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 CHI-SQUARE-procedure of SAS (SAS, 1990).

 

Total weight of lamb produced per ewe per year (kg) was calculated as follows : Firstly, within each lambing season,  weaning weight for all lambs was corrected to 120 days, 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 weaned. For the analyses of variance for body weight before mating and after weaning, as well as total weight of lamb produced per ewe per year, fixed effects for group, year and birth status of the ewe were included in the models. Least‑squares means for these traits were obtained with the PROC GLM-procedure of SAS (Littell et al., 1991).

 

RESULTS AND DISCUSSION

 

Body weights of intact and docked lambs from birth to 12 months of age are presented in Table 1 (weights for rams and ewe lambs from birth till 7 months; from 8 to 12 months of age, only weights for ewe lambs were given, as some of the ram lambs have already been slaughtered). From Table 1 it is evident that there was no difference in birth weight of docked and intact lambs, which was to be expected. However, intact lambs were heavier (P<0.05) than docked lambs at 42-days of age. From weaning till 12 months of age, no difference in body weight occurred between groups.

 

These results are in accordance with those reported by Joubert & Ueckermann (1971) who found no difference in weight gain and live weight from tail docking to slaughter weight at 100 days of age between 9 docked and 11 intact lambs obtained from crosses between Namaqua Afrikaner, Pedi and Blackhead Persian ewes and Namaqua Afrikaner rams. Similarly, Shelton et al. (1991) reported no effect of docking on growth rate of docked and intact Karakul and Karakul x Rambouillet lambs.


Table 1. Body weights of intact and docked lambs from birth to 12 months of age

 Trait

 Intact

n=132

 Docked

n=45

 P

 Birth weight (kg)

 4.41"0.08

 4.32"0.11

 0.387

 42-Day body weight (kg)

 15.7"0.3

 15.0"0.3

 0.027

 100-day Weaning weight (kg)

25.8"0.4

 25.1"0.5

0.122

 5 Month body weight (kg)

 30.4"0.5

 29.9"063

 0.390

 6 Month body weight (kg)

 32.6"0.5

 32.2"0.6

 0.527

 7 Month body weight (kg)

 35.0"0.5

 34.4"0.6

 0.296

 8 Month body weight (kg)

 35.5"0.8

 34.7"1.0

 0.357

 9 Month body weight (kg)

 37.0"0.8

 35.9"1.0

 0.225

 10 Month body weight (kg)

 41.5"1.0

 40.5"1.2

 0.318

 11 Month body weight (kg)

 42.0"0.9

 40.8"1.0

 0.190

 12 Month body weight (kg)

 43.9"0.9

 42.7"1.1

 0.223

 

Slaughter traits for intact and docked ram lambs are summarised in Table 2, while the moisture, ash and protein content and ether extract done on meat cuts of intact and docked lambs are summarised in Table 3.

 

From Table 2 it followed that docked lambs had significantly lower carcass weights than intact lambs (19.5"0.5 kg vs. 20.8"1.2 kg). This was due to the lower dressing percentage (48.7"1.0 % vs. 51.9"1.2 %) of docked lambs. Weight of the fat tail/fat around the tail differed between intact and docked lambs (1747.9"113.0 g vs. 556.7"95.6 g). It was obvious that docked lambs still accumulated some fat around the tail area (See figure 2). There was no significant difference in fat distribution over the carcass between docked and intact carcasses. The moisture, ash, protein and fat  content of meat cuts of intact and docked lambs also did not differ (Table 3).

 

Joubert & Ueckermann (1971) also reported a lower dressing percentage (49.7 % vs.52.2 %)  for docked vs. intact lambs. Other researchers reported the opposite (Marai  et al., 1987) or recorded no difference in dressing percentage (Epstein, 1961; Shelton et al., 1991; Bicer et al., 1992). Bicer et al. (1992) reported  no difference in subcutaneous fat of docked and intact Awassi lambs. Docked lambs, however, had a higher proportion of intramuscular fat than the intact lambs. Hofmeyr et al. (1974) also reported no difference in subcutaneous fat of docked and intact Karakul lambs.

 

Table 2. Slaughter traits for intact and docked ram lamb carcasses

Trait

Intact

n=14

Docked

n=20

P

 Carcass weight (kg)

20.8"0.5

19.5"0.4

0.004

Age at slaughter (days)

298"16.2

300"13.8

0.855

Dressing percentage

51.9"1.2

48.7"1.0

0.004

Length of leg B1 (cm)

44.1"0.8

44.9"0.6

0.269

Length of leg B2 (cm)

56.6"0.6

57.6"0.5

0.051

Circumference of leg (cm)

72.2"0.8

71.7"0.7

0.478

Carcass length (K2) (cm)

116.5"0.8

117.8"0.7

0.075

V1-fat depth (mm)

15.12"1.71

16.22"1.45

0.461

V2-fat depth (mm)

11.76"1.46

11.60"1.24

0.900

V3-fat depth (mm)

9.62"1.59

10.77"1.34

0.402

V4-fat depth (mm)

2.43"0.45

2.47"0.37

0.910

V5-fat depth (mm)

0.71"0.12

0.72"0.10

0.931

Omentum fat (g)

392.5"59.8

447.2"50.6

0.295

Kidney fat (g)

244.2"30.2

239.7"25.5

0.863

Fat tail (g)

1747.9"113.0

556.7"95.6

0.000

 


Table 3.  Moisture, ash and protein content and ether extract of meat cuts of intact and docked lambs

Trait

 Intact

n=14

 Docked

n=20

 P

 Moisture (%)

1.29"0.3

1.26"0.3

0.890

Ash (%)

3.0"0.3

3.2"0.2

0.464

Protein (%)

51.7"2.7

50.0"2.1

0.460

Fat (%)

43.3"3.1

45.1"2.5

0.498

 

 

 


 

Figure 2. Docked Namaqua Afrikaner lambs

 

Reproductive performance of intact and docked ewes over three lambing opportunities are presented in Table 4. From Table 4 it is evident that intact ewes had a higher body weight than docked ewes. The were no significant differences in reproductive performance between groups. However, differences that do occur, will have an influence on profitability. Docked ewes had a 6 % higher conception rate, a 9 % higher lambing percentage and a 16.5 % higher weaning percentage than intact ewes. Docked ewes also had a lower percentage of still births and their lambs had a higher survival rate from birth to weaning. Individual weaning weights of lambs did not differ between docked and intact ewes.

 

Shelton (1990) also recorded a higher percentage of docked ewes lambing (P<0.05), while docked ewe lambs also lambed at a younger age than intact ewe lambs. This could most probably be ascribed to the fact that rams found it easier to mate with the docked ewes (Figure 3). He furthermore found no significant difference in ewe body weights, survival rate or growth of the lambs between docked and intact Karakul ewes over a period of six years.

 

Table 4. Reproductive performance of intact and docked ewes over three lambing opportunities

 

 

Intact ewes

n= 55

Docked ewes

n=62

 P

 Body weight at mating (kg)

 49.2"1.4

 47.6"1.2

 0.387

Body weight after weaning of lambs (kg)

 52.9"2.0

 50.1"1.6

 0.281

 Ewes lambed / ewes mated (%)

 90.9 %

 96.8 %

 0.182

 Lambs born / ewe mated (%)

 145.5 %

 154.8 %

 0.612

 Lambs born / ewe lambing (%)

 160 %

 160 %

 0.984

 % Still born lambs

 7.3 %

 3.2 %

 0.489

 Survival rate from birth till weaning (%)

 90.8 %

 93.6 %

 0.490

 Lambs weaned / ewe mated (%)

 125.5 %

 141.9 %

 0.537

 Weaning weight of individual lambs (kg)

 29.9"0.4

 29.8"0.4

 0.840

 kg Lamb weaned / ewe/ annum

 36.5"3.5

 41.4"4.1

 0.330

 

 

                

 

Figure 3. Docked and intact Namaqua Afrikaner ewes

 

CONCLUSION

 

From the results of this study it is evident that docking of Namaqua Afrikaner lambs after birth did not influence growth rate, carcass traits or fat distribution over the carcass. Ewes that have been docked tended to have a higher reproductive rate than intact ewes, most probably due to rams being better able to service docked ewes. There was no evidence that docking of Namaqua Afrikaner ewes influenced their hardiness during the trial period.

 

REFERENCES

 

ACOCKS, J.P.H., 1988. Veld types of South Africa. 3rd.Ed, Memoirs of the botanical survey of S.A., No 57. Botanical Research Institute, Dept. of Agric. and Water Supply, Pretoria, South Africa.

BICER,O., PEKEL, E. & GUNEY, 1992. Effect of docking on growth performance and carcass characteristics of fat -tailed Awassi ram lambs. Small Ruminant Research, 8 : 352-357

EPSTEIN, H., 1961. The development and body composition of docked and undocked fat tailed Awassi lambs. .J Exp Agric. 29 : 110-118

HOFMEYR, H.S., MANAZCYNSKI, I., MEISSNER, H.H., FRANK, E. & GERHARD, K.E., 1974.   The influence of docking on carcass composition,  subcutaneous fat distribution and voluntary food intake in fat-tailed Karakul lambs. Agroanimalia  6 : 1-6

JOUBERT,  D.M. & UECKERMANN, L., 1971. A note on the effect of docking on fat deposition in fat tailed sheep. Anim. Prod. 13 : 191-192

LITTELL, R.C., FREUD, R.J., SPECTOR, P.C., 1991. SAS-system for linear models, 3rd  Ed., Cary, NC : SAS Institute. Inc. pp. 137-198

SAS Institute. Inc., SAS Procedures Guide, Version 6, 3rd Ed., Cary, NC : SAS Institute. Inc., 1990. pp. 325-340

MARAI, I.F.M., NOWAR, M.S., BAHGAT, L.B. & OWEN, J.B., 1987.  Effect of docking and shearing on growth and carcass traits of fat tailed Ossimi sheep. J. Agric Sci Camb. 109 :  513-518

SHELTON., M., 1990. Influence of docking fat tail (Karakul) sheep on lamb production. Small Ruminant Research 3 : 73-76

SHELTON, M., WILLINGHAM, T., THOMPSON, P. & ROBERTS,  E.M., 1991. Influence of docking and castration on growth and carcass traits of fat-tailed Karakul, Rambouillet and crossbred lambs.   Small Ruminant Research  4 :  235-243

SNYMAN, M.A., HERSELMAN, M.J. & CLOETE, J.A.N.,  1996c. Carcass characteristics of Namaqua Afrikaner lambs. Congress DAB-SASAS, Pilansberg, 1-4 Oktober

SNYMAN, M.A., OLIVIER, J.J. & CLOETE, J.A.N., 1993. Productive and reproductive performance of Namaqua Afrikaner sheep. Karoo Agric 5(2) : 21-24

SNYMAN, M.A., OLIVIER, J.J., & CLOETE, J.A.N., 1996a. Economic comparison of Namaqua Afrikaner sheep with other breeds during drought. Congress DAB-SASAS, Pilansberg, 1-4 Oktober

SNYMAN, M.A., OLIVIER, J.J., OLIVIER, W.J. & CLOETE, J.A.N., 1996b. Production and reproduction potential of Namaqua Afrikaner sheep. Congress DAB-SASAS, Pilansberg, 1-4 Oktober

 

 

Unpublished Dissertation

 

BRUWER, G.G., 1984. Objective evaluation of the carcass grading system for lambs and sheep in R.S.A. M.Sc. treatise, University of Stellenbosch, Stellenbosch, South Africa.

 

Published

Grootfontein Agric Vol 5 No1 2002 (7-11)