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THE EFFECT OF EARLY GROWTH ENVIRONMENT OF DORPER LAMBS ON M. LONGISSIMUS DORSI AREA AT 16 MONTHS OF AGE

 

P.G. Marais, W.J. Olivier# & C.G. Stannard

Grootfontein Agricultural Development Institute, Private Bag X529, Middelburg (EC), 5900

#E-mail: Willem Olivier

 

INTRODUCTION

Some Dorper stud rams are subjected to relatively high and intensive feeding conditions early in life. In contrast to these rams, others are reared under natural veld conditions from birth. Producers have to choose between these two types of rams. Rams that were part of a veld ram test, for instance, are usually fed at higher levels for a period of a month or two before the ram sale. When these rams are put on sale together with rams that have been subjected to a high plane of nutrition throughout their lifetime, it is difficult to decide which ram is the better ram on the basis of phenotype alone. Despite having growth performance data available, the veld rams (rams kept under natural veld conditions) could still be at a disadvantage. It is claimed that the veld rams should have caught up to their intensively reared counterparts after two to three months on a higher nutritional level in terms of M. longissimus dorsi area. It is not clear if veld-reared lambs will catch up with lambs subjected to a higher plane of feeding during early growth.

 

The objective of this study was to determine if early growth environment has a carry-over effect on tissue measurements (muscle and fat) at a later stage in life and if lambs kept under veld conditions for a period of time during early growth, can compensate in terms of muscle and fat deposition when subjected to a higher plane of feeding for a subsequent period.

 

MATERIAL AND METHODS

This project was conducted at the Grootfontein Agricultural Development Institute with 48 weaned Dorper ewe lambs. At the start of the trial, all animals were weighed, drenched and inoculated against pulpy kidney and pasteurellosis. The lambs were divided into four groups on a stratified body weight basis. The experimental layout is summarised in Table 1.

 

Groups FF and FN were subjected to a high diet level (high protein and high energy) for an 8 months period under kraal conditions. Groups NF and NN were kept under natural grazing conditions for the same period. Acocks (1988) described the veld type as False Upper Karoo. After 8 months, the treatments of Groups FN and NF were changed, while the treatments of Groups FF and NN remained the same as during the first 8 months. Group FN was moved to the natural grazing and Group NF was moved to the feedlot. Feedlot lambs were group-fed on an ad libitum basis. The composition of the feedlot diet is summarised in Table 2. The trial started on the 6 February 2007 and during that time Grootfontein had exceptionally good rains, resulting in above average grazing conditions.

 

Table 1. Experimental layout

Group

Phase 1

(5 – 12 months of age)

Phase 2

(13 – 16 months of age)

Feedlot x Feedlot (FF)

Feedlot

Feedlot

Feedlot x Natural grazing (FN)

Feedlot

Natural grazing

Natural grazing x Feedlot (NF)

Natural grazing

Feedlot

Natural grazing x Natural grazing (NN)

Natural grazing

Natural grazing

 

Table 2. Composition of the feedlot diet

Composition

Percentage

Lucerne hay

46

Maize meal

35

Soya oil cake meal

10

Molasses meal

8

Feed lime

1

Estimated nutritional value

Crude protein

15.0

Energy (Total digestible nutrients)

66.4

Calcium

1.05

Phosphorous

0.25

 

Body weight of each lamb was taken every month after an overnight fasting period and on the same day the M. longissimus dorsi area and fat dept over the area was measured between the 3rd and 4th lumbar vertebrae with a Pie Medical 100 Falco Ultra Sonic Scanner. The same technician measured these characteristics over the entire trial period.

 

The least-squares means and standard errors for all the traits were obtained with the PROC GLM-procedure of SAS, and significance level between the different groups were obtained with the PDIFF-option under the PROC GLM-procedure of SAS (SAS, 2006). The initial body weight, muscle area and fat depth were included as a linear regression for subsequent measurements of these traits.

 

RESULTS AND DISCUSSION

The body weights and M. longissimus dorsi measurements (eye muscle area and fat depth) of the four groups are presented in Tables 3 to 5 and Figures 1 to 3 respectively.  The changes in the body weights and M. longissimus dorsi measurements (eye muscle area and fat depth) for the four groups are presented in Table 6.

 

The body weights of the feedlot groups increased with more than 35 kg during the first 8 months, which was higher (P<0.05) than the approximately 18 kg increase in the body weights of the natural grazing groups (Tables 3 and 6). This significant difference in body weight was observed from 6 months of age. There were no differences (P>0.05) between the body weights of the two feedlot groups, as well as between the two natural grazing groups during the first 8 months. During phase 2 the body weight of Group FN decreased with 2.2 kg, while that of Group NF increased with 12.0 kg (Table 6). During the same period, the body weights of the FF and NN groups increased by 6.1 kg and 7.2 kg respectively. It is thus evident from these results that the NF group outperformed the FF group over the same period in the feedlot. These responses could directly be attributed to the respective feeding levels. Compensatory growth is the ability of animals that were previously restricted with regard to feed or nutrient intake to outperform their contemporaries when given free access to good quality feed (Marais et al., 1991) and can be explained in terms of an increase in the efficiency of feed utilisation (Thompson et al., 1982). Olivier & Olivier (2005) also observed compensatory growth in Merino weaner lambs when the feeding levels improved.

 

 The eye muscle area of the feedlot groups increased with more than 17 cm2 during the first 8 months, which was higher (P<0.05) than the increase of the natural grazing groups (Tables 3 and 6). This significant difference in eye muscle area was also observed from 6 months of age.  During phase 2 the eye muscle area of Group NF increased with more than 10.0 cm2. It is interesting to note from Table 6 that despite the increase in body weight, the eye muscle area of Group FF did not change during phase 2. Furthermore, there was a slight increase in the eye muscle area of Group FN, despite the decrease in body weight of this group.

 

The fat depth of the feedlot groups increased with more than 4 mm from 5 to 12 months of age. This increase was higher (P<0.05) than the increase in fat depth of the natural grazing groups. During phase 2, the fat depth of the two groups (FF and NF) receiving the feedlot diet increased with more than 2 mm. From these results it is evident that feeding level had a direct influence on fat depth.

 

Meissner et al. (1977) found that compensatory growth changed the body composition, which suggested that less fat but more protein is deposited. This is also supported by Atti & Ben Salem (2008), which found that compensatory growth led to an increase in the lean content of a carcass and a reduction in fat. The results from this study concur with the findings in the literature. The fat depth of animals from Group NF increased only with 0.25 mm per 1 cm2 increase in muscle area compared to the increase of 3 mm per 1 cm2 increase for Group FF. This suggests that more protein and less fat were deposited in Group NF than in Group FF during phase 2, which is the result of the more efficient utilisation of nutrients (Marais et al., 1991).    

 


Figure 1. Body weight at different ages

 


Figure 2. Eye muscle area at different ages



Figure 3. Fat depth at different ages

 

Table 3. Body weight (± s.e.) of the four groups

Group

Phase 1 (months of age)

Phase 2 (months of age)

5

6

7

8

9

10

11

12

13

14

15

16

FF

23.5

± 0.8

31.1ab

± 0.5

34.3ab

± 0.7

42.1ab

± 0.9

46.3ab

± 1.2

46.3ab

± 1.0

51.0ab

± 1.2

59.4ab

± 1.4

60.8ab

± 1.5

62.1a

 ± 1.3

68.1abc

± 1.5

65.5abc

± 1.4

NF

22.9

± 0.7

24.9ac

± 0.5

28.8ac

± 0.6

32.4ac

± 0.9

35.4ac

± 1.1

34.7ac

± 1.0

36.5ac

± 1.2

41.6ac

± 1.3

43.7ac

± 1.4

48.7ac

± 1.2

53.5ad

± 1.4

53.7ac

± 1.3

FN

24.5

± 0.7

30.9cd

± 0.5

34.6cd

± 0.7

42.1cd

± 0.9

44.9cd

± 1.2

47.3cd

± 1.1

51.1cd

± 1.3

58.7cd

± 1.4

61.1cd

± 1.5

60.1cd

± 1.3

58.5bde

± 1.5

56.9bde

± 1.4

NN

23.2

± 0.7

24.8bd

± 0.5

28.6bd

± 0.7

31.9bd

± 0.9

35.9db

± 1.1

35.3bd

± 1.0

36.7bd

± 1.2

42.0bd

± 1.3

44.3bd

± 1.5

46.4db

± 1.3

48.1ce

± 1.5

49.2ce

± 1.3

abc Values in the same column with the same superscript differ significantly (P< 0.05)

 

Table 4. Eye muscle area of M. longissimus dorsi (± s.e.) of the four groups

Group

Phase 1 (months of age)

Phase 2 (months of age)

5

6

7

8

9

10

11

12

13

14

15

16

FF

10.0

± 0.6

17.5ab

± 0.6

18.0ab

± 0.7

22.5ab

± 0.8

25.0ab

± 0.6

26.7ab

± 0.8

28.2ab

± 0.8

28.9ab

± 0.9

29.3ab

± 1.0

28.9ab

± 0.6

30.3ab

± 0.7

29.2

± 1.1

NF

10.4

± 0.6

14.3ac

± 0.6

12.7ac

± 0.7

13.9ac

± 0.8

14.6ac

± 0.6

16.3ac

± 0.8

16.5ac

± 0.8

19.8ac

± 0.9

20.3ac

± 0.9

22.7ac

± 0.6

25.4ac

± 0.7

28.3a

± 1.0

FN

10.9

± 0.6

18.8cd

± 0.6

19.1cd

± 0.7

22.0cd

± 0.8

24.6cd

± 0.6

26.5cd

± 0.8

27.8cd

± 0.8

28.3cd

± 0.9

29.2cd

± 1.0

28.1cd

± 0.6

29.4cd

± 0.7

31.3ab

± 1.1

NN

11.1

± 0.6

13.2bd

± 0.6

12.9bd

± 0.6

15.7bd

± 0.8

15.5bd

± 0.6

17.1bd

± 0.8

17.5bd

± 0.8

21.5bd

± 0.9

20.2bd

± 1.0

21.0bd

± 0.6

23.1bd

± 0.7

26.6b

± 1.1

abc Values in the same column with the same superscript differ significantly (P< 0.05)

 

Table 5. Fat depth of M. longissimus dorsi (± s.e.) of the four groups

Group

Phase 1 (months of age)

Phase 2 (months of age)

5

6

7

8

9

10

11

12

13

14

15

16

FF

2.8

± 0.2

4.2

± 0.2

4.0

± 0.2

4.8ab

± 0.3

5.7ab

± 0.4

7.1ab

± 0.4

7.3ab

± 0.4

7.7ab

± 0.6

7.8ab

± 0.4

8.5ab

± 0.4

8.8ab

± 0.5

9.3ab

± 0.5

NF

3.1

± 0.2

4.1

± 0.1

3.6a

± 0.2

4.3ac

± 0.3

4.1ac

± 0.4

4.3ac

± 0.4

4.1ac

± 0.4

4.6ac

± 0.5

4.5ac

± 0.4

4.9ac

± 0.4

5.4ac

± 0.4

6.8ac

± 0.5

FN

3.6

± 0.2

4.0

± 0.1

4.4ab

± 0.2

5.9cd

± 0.3

6.1cd

± 0.4

7.3cd

± 0.4

7.6cd

± 0.4

7.8cd

± 0.5

8.5cd

± 0.4

8.9cd

± 0.4

8.6cd

± 0.4

8.2cd

± 0.5

NN

3.3

± 0.2

4.2

± 0.1

3.6b

± 0.2

3.9bd

± 0.3

4.1bd

± 0.4

4.4bd

± 0.4

3.8bd

± 0.4

4.6bdc

± 0.5

4.4bd

± 0.4

5.1bd

± 0.4

5.1bd

± 0.4

5.4bd

± 0.5

abc Values in the same column with the same superscript differ significantly (P< 0.05)

 

Table 6. The changes in the body weight, eye muscle area and fat depth of the M. longissimus dorsi (± s.e.) of the four groups

Group

Body weight change

Eye muscle area change

Fat depth change

Phase 1

Phase 2

Phase 1

Phase 2

Phase 1

Phase 2

FF

35.9ab ± 1.4

6.1abc ± 1.1

18.2ab ± 1.4

0.8ab ± 1.5

4.1ab ± 0.7

2.4a ± 0.7

NF

18.1ac ± 1.3

12.0ade ± 1.0

7.3acd  ± 1.3

10.7ac ± 1.3

1.3ac ± 0.7

2.7b ± 0.6

FN

35.2cd  ± 1.4

-2.2bdf ± 1.2

17.8ce ± 1.4

2.6cd ± 1.4

4.6cd  ± 0.7

0.4ab ± 0.6

NN

18.5bd ± 1.3

7.2cef ± 1.1

11.0bde ± 1.4

5.1bd ± 1.4

1.8bd  ± 0.7

0.9 ± 0.7

abc Values in the same column with the same superscript differ significantly (P< 0.05)

 

CONCLUSION

It is evident from the results that compensatory growth occurred in lambs when they are switched from a low to a higher feeding level. Furthermore, this compensatory growth will result in more muscle tissue being developed than fat due to an increase in protein deposits. Irrespective of feeding level, the differences in M. longissimus dorsi area between groups decreased towards the end of the experimental period. However, lambs reared on the higher feeding level early in life, retained their advantage over those lambs reared on a lower feeding level. The effect of improved feeding regime on fat depth was more pronounced than the effect on M. longissimus dorsi area.

 

REFERENCE

Acocks, J.P.H., 1988. Veld types of South Africa. Memoirs of the Botanical survey of South Africa 57, 1-146. Pretoria: Government Printers.

Atti, N. & Ben Salem, H., 2008. Compensatory growth and carcass composition of Barbarine lambs receiving different levels of feeding with partial replacement of the concentrate with feed blocks. Animal Feed Science and Technology 147, 265-277.

Marais, P.G., Van der Merwe, H.J. & Du Toit, J.E.J., 1991. The effect of compensatorary growth on feed intake, growth rate, body composition and efficiency of feed utilization in Dorper sheep. S. Afr. J. Anim. Sci. 21, 80-88.

Meissner, H.H., Hofmeyr, H.S. & Roux, C.Z., 1977. Similar efficiency at two feeding levels in sheep. S. Afr. J. Anim. Sci. 7, 7-15.

Olivier, W.J. & Olivier, J.J., 2005. Effect of feeding stress on the wool production of strong and fine wool Merino sheep. S. Afr. J. Anim. Sci. 35, 273-281

SAS, 2006. SAS Procedures Guide, Version 9.1.3. Cary, NC, SAS Institute Inc.

Thompson, E.F., Bickel, H. & Schürch, A., 1982. Growth performance and metabolic changes in lambs and steers after mild nutritional restriction. J. Agric. Sci. Camb. 98, 183-194.

 

Published

Grootfontein Agric 11 (2): 47-54