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THE EFFECT OF NUTRITION ON WOOL PRODUCTION, BODY MASS AND PLEAT DEVELOPMENT IN ADULT MERINO RAMS

 

M.J. HERSELMAN & B.R. KING

Grootfontein College of Agriculture, Middelburg, CP, 5900, South Africa

 

INTRODUCTION

The Merino is the most important wool sheep breed in South Africa and many research have been done on many aspects of wool production and some of the problems related to it. This includes work that was done between 1942 and 1954 at Grootfontein College of Agriculture to investigate the problem of blowfly strikes related to excessive pleat development. It was found that, although sheep with more pleats produced more wool, pleat development has a detrimental effect on reproduction rate, mortality and resistance against blowfly attacks (Nel, 1967). Because of the disadvantageous effects of excessive pleat development most breeders discriminate at the moment against pleats in their breeding programmes. It is known that nutrition influences pleat development and the aim of the present study was to illustrate the effect of nutrition on wool production and pleat development.

 

MATERIAL AND METHODS

This experiment was carried out in kraals at Grootfontein College of Agriculture. Sixty, 18 month old, Merino rams were obtained from the Tygerhoek Experimental farm in the South Western Cape. Rams were divided randomly into two groups. The experiment consisted of two phases which lasted eight and six months respectively (Table 1). As shown in Table 1, Group A was fed on a high and Group B on a low plane of nutrition during the first phase while Group B received the high plane and Group A the low plane during the second phase.

Table 1 Experimental design

  Phase 1 Phase 2
Group A High Plane Low Plane
Group B Low Plane High Plane

 

The composition of the two diets used, are shown in Table 2. At the beginning and end of each phase the animals were shorn and a score of body pleats or folds of the skin was taken with the help of a set of photographs which was developed in Australia. According to this score-card, points were awarded separately for development of pleats on the neck (0 - 6), body (0 - 5) and breech (0 - 6). Fleece samples at each shearing were taken for determining fibre diameter and clean yield. Body mass was recorded weekly. At the end of each phase a photograph was taken of each animal.

 

Table 2 Composition of the diets

  High Plane Low Plane
Maize meal 30 %  
Lucern 54 % 25 %
Fish meal 2 %  
Voermol Super 18 10 %  
Slaked lime 0.5 %  
Wheat Straw   70 %
NHCl 0.5 %  
NaCl 3 %  
Calorie 3000   5 %
Taurotec 17 g/100kg  

 

RESULTS AND DISCUSSION

Changes in mean body mass during both phases are depicted in Fig. 1. From Fig. 1 it is apparent that plane of nutrition had a drastic effect on body mass. After shearing at the end of phase 1 body mass was 83.9 and 42.8 kg for Groups A and B respectively. After the next 6 months (phase 2) body mass of the respective groups was 57.3 and 82.4 kg. In other words rams in Group A lost 31.7 % (26.6 kg) of their body mass during phase 2 while body mass of rams in Group B increased by 92.5 % (39.6 kg) during the same phase. From these results it is evident that animals which is in a bad condition recover rapidly once feeding conditions improves while the decrease in body mass of animals in a good condition is relatively slow when offered a sub-maintenance diet because energy requirements can be met by mobilising the high-energy con-taining fat depots.

 

[Figure 1 Changes in mean body mass of rams]

 

As indicated in Table 3, plane of nutrition also had a drastic effect on wool production and fibre diameter. In this regard, Group A produced 3.5 kg clean wool with a fibre diameter of 25.6 µ during phase 1 and Group B only 1.4 kg with a fibre diameter of 19.0 µ. In other words, rams on the high plane of nutrition produced 150 % more wool with a 34.7 % higher fibre diameter. These results is in accordance with work done by Grobbelaar & Wentzel (1989) who reported that strong wool merino wethers on a high plane of nutrition produced 184.4 % more wool than wethers on a low plane while fibre diameter was 40.6 % higher.

 

In South Africa many wool sheep types exist and therefore the wool production potential (WPP) of each type is often required. From the results on wool production in the present study it is evident that environmental influences makes it difficult to quantify the genetic potential for wool production of a specific type of sheep. The existence of environment-genotype interactions makes the interpretation of wool production data under specific conditions even more risky. Both wool production and body mass are affected by

Table 3 Body mass, clean wool production, fibre diameter and pleat scores of rams at the start of the experiment and after Phase 1 and 2 respectively.

  Group A Group B  
  Value %CV SE Value %CV SE  
START              
Body Mass (kg) 57.2 14.8 1.693 59.8 13.0 1.6609 NS
Clean wool (kg) 4.7 16.1 0.151 4.7 14.1 0.139 NS
Fibre diameter (µ) 19.4 5.9 0.228 19.2 7.8 0.31 NS
Total Pleats 10.1 26.7 0.539 10.1 27.4 0.576 NS
PHASE 1              
Body Mass (kg) 83.9 13.3 2.234 42.8 17.1 1.558 **
Clean wool (kg) 3.5 20.5 0.142 1.4 20.1 0.059 **
Fibre diameter (µ) 25.6 5.6 0.288 19.0 7.1 0.289 **
Neck Pleats 5.5 11.4 0.131 4.0 21.3 0.178 **
Body Pleats 3.8 17.6 0.133 2.4 20.9 0.104 **
Breech Pleats 3.8 22.1 0.170 2.4 20.9 0.104 **
Total Pleats 13.1 13.8 0.362 8.8 13.7 0.251 **
PHASE 2              
Body Mass (kg) 57.3 18.3 2.092 82.4 11.8 2.065 **
Clean wool (kg) 2.4 19.3 0.091 3.0 17.8 0.112 **
Fibre diameter (µ) 21.8 4.7 0.207 23.4 6.7 0.337 **
Neck Pleats 5.0 17.3 0.173 5.5 12.1 0.139 **
Body Pleats 3.1 23.3 0.145 4.5 17.7 0.165 **
Breech Pleats 2.7 23.4 0.125 3.8 25.2 0.198 **
Total Pleats 10.8 15.6 0.337 13.8 14.3 0.512 **

 

environmental changes and one possibility to overcome this problem is to scale wool production with body mass which in turn will express wool produc-tion as a percentage of body mass. Although both groups of rams in the present study had comparable genetic potentials for wool production, Group A produced 150% more wool than Group B during Phase 1. However, when WPP is defined by wool produced per unit of body mass, WPP of Group A was only 27.5% more than that of Group B. Furthermore, if wool produced per unit of body mass raised to the power 1.362 was used, WPP of Group A and B was identical. By further analysing the results of Grobbelaar & Wentzel (1989), it was necessary to raise body mass to the power of 1.325 to ensure similar wool production poten-tials for different groups. Although much more information on the scaling of wool production with body mass for different sheep breeds is needed, it can be assumed that wool production potential, defined as wool produced per unit of body mass, is a better way of comparing the genetic potential of different breeds under different environmental conditions.

The effect of plane of nutrition on neck-, body-, breech- and total pleat score is shown in Table 3 while changes in total pleat score are also depicted in Fig. 2.

 

[Figure 2 Changes in total pleat score]

 

From these results it is apparent that pleat development in Merino rams can be manipulated to a large extend by plane of nutrition in a relatively short period of time. This is also illustrated by the set of photographs (Fig. 3) taken from rams at the end of Phases 1 and 2. At the start of Phase 1 total pleat score for both groups was 10.1. After 8 months on a high plane of nutri-tion (Group A) total pleat score increased to 13.1 while that of Group B (low plane) decreased to 8.8. In contrast to the low scores for body- and breach pleats observed in rams on the low plane of nutrition during Phase 1, scores of neck pleats were relatively high on both planes of nutrition. After swapping the diets at the end of Phase 1, total pleat score of Group A decreased from 13.1 to 10.8 and that of Group B increased from 8.8 to 13.8. The relative small decrease in total pleat score observed in rams of Group A during Phase 2 can be explained by the fact that body mass and condition of these rams did not drop far enough. Although mean scores of neck pleats on both planes of nutrition and during both phase were relatively high, low neck pleat scores were observed in some individual rams. An interesting observation was made from the sets of photographs (Fig. 3) namely, that plane of nutrition had only a small effect on pleat development in rams with low scores for neck pleats. However, rams with a high score for neck pleats on a low plane of nutrition showed large development of pleats over the rest of the body when placed on a high plane of nutrition. Subsequently, the accuracy with which pleat development in rams can be estimated from pleat scores taken under dif-ferent feeding conditions was investigated by means of a correlation matrix for Group A (Table 4) and Group B (Table 5) respectively. In both groups a relatively high correlation coefficient was observed between scores of neck pleats taken at the end of Phase 1 and scores of neck-, body-, breech- and to-tal pleats taken at the end of Phase 2. In other words, if an animal has a low score for neck pleats it can be expected that pleat development over the rest of the body will be low irrespective of feeding conditions. On the other hand, it can be expected that animals on a low plane of nutrition, which display a high score for neck pleats but a low score for body- and breech pleats, will also develop excessive pleats over the rest of the body when changing to a high plane of nutrition.

 

SUMMARY

Plane of nutrition not only has a large effect on body mass and wool produc-tion but also plays a major role in the development of pleats. Wool production potential expressed as wool produced per unit of body mass is considered as a more suitable way to compare the genetic potential for fibre production of different wool sheep breeds under different environmental conditions. Body- and breech pleat development are much more susceptible to nutrition than neck pleats. Neck pleats, however, is a relative accurate parameter for pleat development under all environmental conditions.

 

Figure 3 Photographs taken at the end of Phase 1 (left) and Phase 2 (right) of some of the rams used in the present experiment. Ram No. 161 displayed relatively high pleat development in the neck on the low plane of nutrition and excessive pleat development over the entire body during Phase 2. Ram No. 005 with no neck pleats on the low plane of nutrition also displayed virtually no pleat development on the high plane of nutrition. Ram No. 339 first receive the high plane of nutrition and the extend to which pleats disappeared on the low plane of nutrition is clearly visible,

 

Table 4 Correlation matrix for pleat score of Group A

 

 

N1

M1

B1

TP1

N2

M2

B2

TP2

N1

1.00

-0.11

0.32

0.80

0.56

0.47

0.50

0.62

M1

 

1.00

0.90

0.37

0.04

-0.04

0.00

-0.00

B1

 

 

1.00

0.68

0.32

0.43

0.39

0.46

TP1

 

 

 

1.00

0.55

0.50

0.51

0.63

N2

 

 

 

 

1.00

0.37

0.40

0.68

M2

 

 

 

 

 

1.00

0.69

0.86

B2

 

 

 

 

 

 

1.00

0.89

TP2

 

 

 

 

 

 

 

1.00

 

 

Table 5 Correlation matrix for pleat score of Group B

 

 

N1

M1

B1

TP1

N2

M2

B2

TP2

N1

1.00

0.68

0.46

0.83

0.66

0.39

0.73

0.78

M1

 

1.00

0.52

0.86

0.36

0.58

0.61

0.66

B1

 

 

1.00

0.82

0.34

0.37

0.52

0.53

TP1

 

 

 

1.00

0.53

0.53

0.73

0.77

N2

 

 

 

 

1.00

0.07

0.69

0.80

M2

 

 

 

 

 

1.00

0.36

0.60

B2

 

 

 

 

 

 

1.00

0.88

TP2

 

 

 

 

 

 

 

1.00

 

where

N1 = Score of neck pleats at the end of Phase 1

M1 = Score of body pleats at the end of Phase 1

B1 = Score of breech pleats at the end of Phase 1

TP1 = Total pleat score at the end of phase 1

N2 = Score of neck pleats at the end of Phase 2

M2 = Score of body pleats at the end of Phase 2

B2 = Score of breech pleats at the end of Phase 2

TP2 = Total pleat score at the end of phase 2

 

REFERENCES

GROBBELAAR, P.D. & WENTZEL, D., 1989. Die invloed van voeding op wolproduksie en woleienskappe van genetiese sterkwol-merinoskape. Proc. S.A.S.A.P., 28.

NEL, J.E., 1967. The influence of flock composition on production and reproduction characteristics of Merino sheep. Univ. Stellenbosch, Stellenbosch (Afrikaans).


 

Published

Karoo Agric 5 (1), 3-7