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EFFECT OF ENERGY LEVEL IN LUCERNE (MEDICAGO SATIVA) HAY-BASED FINISHING DIETS ON CARCASS CHARACTERISTICS OF DOHNE MERINO LAMBS

 

V.N. Shivambu#, J.H. Hoon, W.J. Olivier & B.R. King

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

#E-mail: VN Shivambu

 

INTRODUCTION

Mutton production in the world is practiced in a large variety of environments under different production systems. The various environments and the different production systems have an effect on the performance of the animals. The main factors that affect economic mutton production in feedlots are a higher growth rate and feed conversion efficiency (De Sousa et al., 2012). In a feedlot, the diet used is responsible for the economic performance and among the dietary components, energy is the most limiting factor in production and can reduce daily weight gain. Sheep can have high productive indices when their nutritional requirements are met, especially in their first six months of life (De Sousa et al., 2012).  Feeding high concentrate diets to young animals has been shown to increase growth rate, carcass yield and carcass quality (Mahajan et al., 1976; Van Soest, 1982; Kochapakdee et al., 1994; Sheridan et al., 2003; Haddad & Hussein, 2004; Abdullah & Hussein, 2007; Shivambu et al., 2011; Shivambu et al., 2012). Nonetheless, roughage inclusion is required in feedlot diets to maintain normal ruminal function. Increased incidences of rumen acidosis, liver abscesses and erratic feed intake, resulting in decreased animal performance and profitability can be caused by inadequate roughage inclusion in the diets (Cranston et al., 2005).  Lucerne is one of the most important hay crops and the most important roughage source in feedlot diets in South Africa, whilst maize is normally the most important concentrate source in feedlot diets.

 

This article deals with the last in a series of three trials planned to determine the optimal roughage to concentrate ratio in feedlot diets of different breeds of lambs for economical mutton lamb production. Therefore, the aim of this study was to determine the effect of energy level in feedlot diets on growth and carcass characteristics of Dohne Merino lambs.

 

MATERIALS AND METHODS

Ninety weaned Dohne Merino lambs were used in this study. The animals were fasted overnight, tagged with individually numbered ear tags and the initial body weights were recorded. The lambs were then divided on a stratified body weight basis into six groups of 15 animals each and placed in different pens where they were group fed.

 

Six experimental diets with different energy levels were used. Maize and lucerne hay were used as the base ingredients in all the mixtures. The respective diets were equivalent with regard to crude protein, degradable and non-degradable protein, as well as the major minerals. Urea and cottonseed oil cake meal were used to balance the protein. The ingredients and chemical composition of the experimental diets are summarised in Table 1. The animals were allowed a one-week adaptation period on the diets. During this period, the lambs were supplied with lucerne hay on an ad libitum basis whilst the experimental diets were introduced gradually. Body weights of the lambs were recorded at the commencement of the trial and on a weekly basis during the trial period. The lambs were given feed daily and the leftover feed was weighed back and recorded weekly to determine the feed intake and feed conversion ratio on a group basis.

 

Table 1. Ingredients and chemical composition of the six experimental diets

 

Ingredients

Roughage level

20%

30%

40%

50%

60%

70%

Lucerne hay (%)

20.0

30.0

40.0

50.0

60.0

70.0

Maize meal (%)

62.1

54.6

46.1

38.1

30.0

20.5

Feed grade urea (%)

0.9

0.8

0.6

0.5

0.4

0.2

Cottonseed oil cake meal (%)

7.0

5.0

4.0

2.1

1.0

0.0

Molasses meal (%)

8.0

8.0

8.0

8.0

8.0

8.0

Feed lime (%)            

1.1

0.8

0.6

0.6

0.3

0.0

Salt (%)

0.3

0.3

0.3

0.3

0.3

0.3

Acid buffer (%)

0.6

0.5

0.4

0.0

0.0

0.0

Premix added to the balanced diet (%)

0.15

0.15

0.15

0.15

0.15

0.15

Chemical composition (calculated) 

Crude protein (g/kg)

140.4

139.9

139.4

140.3

141.2

143.5

Energy ME (MJ/kg)

10.82

10.48

10.12

9.77

9.41

9.03

Fat (g/kg)

32.9

30.8

28.4

26.2

23.9

21.4

Crude fibre (g/kg)

90.2

114.9

140.6

165.8

191.1

217.8

Calcium (g/kg)

8.8

8.6

8.7

8.6

8.7

8.8

Phosphorus (g/kg)

2.8

2.6

2.5

2.4

2.3

2.3

 

The Longissimus dorsi (rib eye muscle) area and fat depth were recorded and measured at the start and the end of the trial (before slaughter), using an Aloko Prosound 2 ultrasound scanner. The animals were slaughtered within one week after reaching an average body weight per group of 42 kg and were fasted overnight for slaughtering the following day. The animals were slaughtered at the Grootfontein abattoir using standard slaughtering techniques. Animals were weighed before slaughtering and the weight of the warm carcass, kidney fat and the abdominal fat were recorded just after slaughtering. The carcasses were hung in a cooler at 2 °C for 48 hours. The cold carcass weight was recorded after 48 hours and the following carcass and fat measurements were taken: 

 

Carcasses were graded (A1-A6) according to the South African Standard Chart classification system (Agricultural Product Standards Act; Act No. 119 0f 1990; Government Notice No. R. 1948, 26 June 1992). Carcass yield (dressing percentage) and growth rate (average daily gain) were calculated for each animal, while the feed intake and feed conversion ratio were calculated for each treatment group. Statistical analysis was done using the Proc GLM-procedure of SAS (SAS, 2009).

 

RESULTS AND DISCUSSION

The growth curves of the different treatment groups are illustrated in Figure 1. Diet energy level contributed significantly (P<0.05) to variations in weekly body weights. During the first few weeks of feeding, the body weight of the lambs subjected to the diet with the lowest roughage level was lower compared to the lambs subjected to the diet with the highest roughage inclusion level. However, from Week 7 the group receiving the lowest roughage diet started to gain weight faster than the group receiving the diet with the highest roughage level. This may be attributed to the digestive disorders experienced by the group receiving the diet with the lowest roughage level during the early days of the adaptation period. The same trend was observed in the study conducted by Shivambu et al. (2011) with Merino lambs.

 

 

Figure 1. Growth curves of the different treatment groups at different roughage inclusion levels

 

The growth rate of the group receiving the highest roughage level did not show a positive change from Week 10 until Week 13, probably due to the lower energy level of the diet. The group receiving the diet with the lowest roughage level showed a body weight increase from Week 4 until the animals were slaughtered. All the groups followed more or less the same trend with regard to their respective growth curves. However, the group receiving the diet with the highest roughage inclusion level showed better growth during the first few weeks of feeding. This is in agreement with the studies conducted by Shivambu et al. (2011; 2012) with Merino and Dorper lambs. The longissimus dorsi area and fat depth measurements are summarised in Table 2.

 

Table 2. The longissimus dorsi area (LDA) and fat depth (FD) measurements (± s.e.)

Roughage level

 

LDA at start of trial

(cm2) 

LDA at slaughter (cm2) 

Change in LDA

 (cm2)

FD at start of trial (mm)

FD at slaughter (mm)

Change in FD

(mm)

20%

4.19 ± 0.13

7.56 ± 0.15

3.36 ± 0.19

2.93 ± 0.01

5.33 ± 0.01

2.47a ± 0.02

30%

4.13 ± 0.13

7.53 ± 0.15

3.40 ± 0.19

3.07 ± 0.01

4.93 ± 0.01

1.87b ± 0.02

40%

4.23 ± 0.13

7.51 ± 0.15

3.29 ± 0.19

3.07 ± 0.01

4.80 ± 0.01

1.73b ± 0.02

50%

4.19 ± 0.13

7.82 ± 0.15

3.63 ± 0.19

3.00 ± 0.01

5.13 ± 0.01

2.13 ± 0.02

60%

4.10 ± 0.13

7.61 ± 0.15

3.51 ± 0.19

2.87 ± 0.01

4.80 ± 0.01

1.87b ± 0.02

70%

4.05 ± 0.13

7.46 ± 0.15

3.41 ± 0.19

2.93 ± 0.01

4.80 ± 0.01

1.87b ± 0.02

abValues in columns with different superscripts differ significantly (P<0.05)

 

The diets did not have a significant effect on the change in the longissimus dorsi area. However, significant differences were observed in the change in fat depth between the low roughage group (20%) and the 30%, 40%, 60% and 70% groups. The lambs in the lowest roughage inclusion level group had a higher fat change over the experimental period when compared to the other groups. The slaughter traits of the six groups are summarised in Table 3 while the effect of diet on distribution of carcasses over the different carcass grades is summarised in Table 4. Diet energy levels contributed significantly (P<0.05) to the variation in carcass yield, carcass weight, hind leg length (inside) and hind leg circumference, fat depth and abdominal fat.

 

Table 3. Slaughter traits (± s.e.) of the six groups

 

Roughage level

Trait

20%

30%

40%

50%

60%

70%

Slaughter weight (kg)

42.03 ± 1.13

42.12 ± 1.13

44.38 ± 1.13

42.85 ± 1.13

44.55 ± 1.13

44.49 ± 1.13

Carcass weight (kg)

18.92a ± 0.28

19.10a ± 0.28

19.68a ± 0.28

19.05a ± 0.28

19.03a ± 0.28

18.00b ± 0.28

Carcass yield (%)

47.68a ± 0.38

46.33bc ± 0.38

45.07d ± 0.38

46.93abc ± 0.37

47.30ab ± 0.38

45.99cd ± 0.38

Hind leg length inside (cm)

46.95a ± 0.54

46.75a ± 0.54

45.47 ± 0.54

46.13 ± 0.54

44.78b ± 0.54

46.32a ± 0.54

Hind leg length outside (cm)

37.14 ± 0.45

36.96 ± 0.45

35.96 ± 0.45

36.76 ± 0.45

36.30 ± 0.45

36.40 ± 0.45

Hind leg circumference (cm)

59.53ac ± 0.61

60.51 ± 0.60

62.07b ± 0.60

61.69b ± 0.60

60.92ab ± 0.60

58.82c ± 0.60

Carcass length (cm)

104.85a ± 0.77

106.89 ± 0.77

106.86 ± 0.77

105.93 ± 0.76

107.03b ± 0.77

105.63 ± 0.77

Fat depth 1 (mm)

5.81a ± 0.59

7.73b ± 0.59

6.80 ± 0.58

6.38 ± 0.58

5.50a ± 0.58

6.5 ± 0.58

Fat depth 2 (mm)

5.16a ± 0.59

6.42 ± 0.59

6.86b ± 0.59

5.21a ± 0.58

5.85 ± 0.59

5.52 ± 0.59

Fat depth 3 (mm)

5.98 ± 0.67

7.24a ± 0.67

6.27 ± 0.66

7.60a ± 0.66

5.56b ± 0.66

5.33b ± 0.66

Fat depth 4 (mm)

3.90ac ± 0.45

3.95ac ± 0.45

4.40a ± 0.45

3.86ac ± 0.44

2.57b ± 0.45

2.92bc ± 0.45

Fat depth 5 (mm)

3.24a ± 0.57

5.21b ± 0.57

4.76 ± 0.56

5.50b ± 0.56

4.93b ± 0.56

3.93 ± 0.56

Kidney fat (kg)

0.52 ± 0.04

0.57 ± 0.04

0.59 ± 0.04

0.50 ± 0.04

0.47 ± 0.04

0.49 ± 0.04

Abdominal fat (kg)

0.57 ± 0.05

0.69a ± 0.05

0.66a ± 0.05

0.68a ± 0.05

0.51b ± 0.05

0.59 ± 0.05

abcdValues with different superscripts in rows differ significantly (P<0.05)

 

Table 4. Effect of diet on distribution of carcasses over the different carcass grades

Roughage level

Grade A2 (%)

Grade A3 (%)

Grade A4 (%)

Grade A5 (%)

20%

5

8

1

1

30%

0

11

2

2

40%

2

8

5

0

50%

4

5

5

1

60%

4

10

0

1

70%

6

5

4

0

 

From Table 4 it follows that the group receiving the 30% roughage inclusion level diet produced the most carcasses with Grade A3 classification when compared to the other groups. However, 52% of the carcasses from all the groups were graded as A3, with only 5.6% graded as overfat (A5). Average daily feed intake, feed conversion ratio, average daily gain and days until slaughter of the six groups are summarised in Table 5.

 

Table 5. Average daily feed intake, average daily gain, feed conversion ratio and days until slaughter of the six groups

Roughage level

Average daily feed intake/group

(kg)

Feed conversion ratio (FCR)

Average daily gain (g)

Days until slaughter

20%

18.8

5.39

186.8

76

30%

20.2

6.79

175.3

90

40%

20.8

6.40

196.6

92

50%

21.1

6.87

175.6

90

60%

20.5

6.61

171.5

97

70%

21.1

7.31

149.2

104

 

Diet energy level had an effect on feed intake, feed conversion ratio and number of days until slaughter. In this study, it is evident that the feed conversion ratio of the lambs fed the low roughage diet (20%) was better than those fed the high roughage diet (70%). This is in agreement with the study conducted by Shivambu et al. (2012) with Dorper lambs where it was also found that the highest energy level diet had the better feed conversion ratio. These results may be attributed to the greater energy density and lower neutral detergent fibre content present in the low roughage diet, because lambs fed this diet needed smaller quantities of dry matter to meet the nutritional requirements. Lambs fed the diet with a low roughage content had a higher average daily gain when compared with the lambs receiving the diet containing a high roughage content. These results are similar to the observations of Sheridan et al. (2003) on Mutton Merino lambs fed a diet containing high energy and low energy levels. The period of time spent in the feedlot was also influenced by the diet. Lambs fed the lowest roughage diet required less time (76 days) in the feedlot to reach the predetermined slaughter weight when compared with the lambs that received the highest roughage diet (104 days). This is in agreement with the study conducted by De Sousa et al. (2012) who reported that lambs fed a higher energy density diet required less time in the feedlot to reach the slaughtering live weight when compared with lambs that received the lower energy density diet. 

 

CONCLUSION

The ratio of roughage to concentrate in the feedot diet has an impact on the performance of lambs. From the results of this study it can be concluded that differences in the energy levels of the feedlot diets had an effect on weekly body weights, average daily gain, feed conversion ratio, fat depth and some of the slaughter traits, but not on the change in the longissimus dorsi area. Lambs subjected to diets with low roughage inclusion levels perform on average better than those receiving diets with high roughage inclusion levels. 

 

REFERENCES

Abdullah, Y.A. & Hussein S.M., 2007. Effect of different levels of energy on carcass composition and meat quality of male black goat kids. Livestock Sci. 107, 70-80.

Cranston, J.J., Krehbiel, C.R., McBeth, L.J. & Ball, R.A., 2005. Effects of roughage level and FibrozymeTM supplementation on performance and carcass characteristics of finishing beef steers. p. 1–6. http://www.ansi.okstate.edu/research2005rr/2005rr/05/05.htm

De Sousa, W.H., Cartaxo, F.Q., Costa, R.G., Cezar, M.F., Cunha, M.G.G., Filnho, J.M.P. & Dos Santos, N.M., 2012. Biological and economic performance of feedlot lambs feeding on diets with different energy densities. R. Bras. Zootec., 51(5), 1285-1291.

Haddad, S.G. & Husein, M.Q., 2004. Effect of dietary energy density on growth performance and slaughtering characteristics of fattening Awassi lambs. Livestock Prod. Sci. 87, 171-177.

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SAS Institute Inc., 2009. SAS OnlineDoc® 9.2. Cary, NC, SAS Institute Inc.

Sheridan, R., Ferreira, A.V. & Hoffman, L.C., 2003. Production efficiency of South African Mutton Merino lambs and Boer goat kids receiving either a low or a high energy feedlot diet. Small Rumin. Res. 50, 75-82.

Shivambu, V.N., Hoon, J.H., Snyman, M.A. & King, B.R., 2011. Effect of energy level in lucerne (Medicago sativa) hay-based finishing diets on carcass characteristics of Merino lambs. Grootfontein Agric 11(2), 55-59.

Shivambu, V.N., Hoon, J.H., Olivier, W.J. & King, B.R., 2012. Effect of energy level in lucerne (Medicago sativa) hay-based finishing diets on carcass characteristics of Dorper lambs. Grootfontein Agric 12(1), 15-23.

Van Soest, P.J., 1982. Nutritional Ecology of the Ruminant. United States of America. Your Town Press, pp 10-12.

 

 

Published

Grootfontein Agric 13 (1)