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

 

#V.N. Shivambu, J.H. Hoon, M.A. Snyman & B.R. King

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

#E-mail: VN Shivambu

 

 

INTRODUCTION

High-concentrate diets are routinely fed to cattle and sheep to capitalise on more rapid and less expensive gains than can be accomplished with forage alone. Feeding high-concentrate diets to young animals typically has resulted in higher quality carcasses with improved palatability characteristics compared to carcasses produced with forage-based systems (Van Soest, 1982). Feeding high levels of concentrates to sheep has shown to increase the growth rate, increase dressing percentage and improve carcass quality and tenderness (Haddad & Husein, 2004).

 

Feedlotting is a common practice on most sheep farms. However, different opinions exist with regard to the ratio of roughage to concentrate in sheep feedlot diets. The cost and availability of raw materials such as lucerne hay and maize often dictate the decisions of the producer with regard to the inclusion rate of roughages and concentrates. Different opinions also exist among farmers, advisors, feed companies, etc. with regard to the advantages and disadvantages of different roughage to concentrate ratios in sheep feedlot diets.

 

Ferreira et al. (2002) compared the production efficiency of Mutton Merino lambs and Boer goat kids receiving either a low or a high energy feedlot diet and reported that the average daily gain of Mutton Merino lambs on the low energy diet was lower than for those on the high energy diet. However, there was no significant difference between the average daily gains of Boer goat kids on high or low energy diets. The Mutton Merino lambs on the high energy diet had higher feed conversion efficiency than those on the low energy diet, regardless of the time spent in the feedlot. It was further reported that the cold carcass weight of the animals on the high energy diet was higher than the animals on the low energy diet. Abdullah & Hussein (2007) reported that different energy levels in the diet significantly affect the total feed intake, metabolisable energy and the average daily gain of black male goat kids. The kids fed the medium energy level diets had the highest total feed intake, followed by the low energy level and then the high energy level. Higher metabolisable energy was recorded for medium energy level diets, followed by the kids fed low energy diets, while kids that were fed high energy diets had the lowest metabolisable energy. Crude protein intake and average daily gain also followed the same trends as those of total feed intake and metabolisable energy. However, no differences in total cold carcass weights among the kids were observed between the dietary energy levels. The increased levels of dietary energy affect intermuscular fat percentage in an increasing order. Higher energy diets resulted in higher total fat and subcutaneous fat percentage but lower muscle to fat ratios (Abdullah & Hussein, 2007).

 

Lucerne is one of the most important hay crops and the most important roughage source in feedlot diets in South Africa and is normally self-produced by farmers, whilst maize is normally the most important concentrate source in feedlot diets. However, both raw materials can be expensive and difficult to obtain in some years (Brand et al., 1991). The most economical energy level in a finishing diet for sheep may differ in accordance with various factors. When the price of the diet and the efficiency of feed conversion at different roughage to concentrate ratios are known, the lowest feed cost per unit of live weight and/or carcass weight increase can be calculated. Therefore, the aim of this project was to determine the effect of energy level in feedlot diets on growth and carcass characteristics of Merino lambs.

 

MATERIAL AND METHODS

Ninety weaned Merino lambs were used in this study. At the start of the trial before the animals entered the facility, a standard animal health program was followed. 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 oilcake 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 every Monday at 08:00 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. The water troughs were cleaned daily in order to provide clean fresh water to the lambs.


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

Ingredient

Diet

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

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

2.25

 

As the group reached an average body weight of 44 kg, the animals 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, 2006).

 

RESULTS AND DISCUSSION

Diet energy level contributed significantly (P<0.05) to variation in live body weights measured weekly. During Week 2 of feeding, there were no significant differences in body weights observed among the groups. Significant differences were, however, observed amongst most of the groups from Week 4 onwards. The growth curves of the different treatment groups are illustrated in Figure 1 and their regression equations are presented in Table 2. Lambs receiving the diet with the 70% roughage level took two weeks longer to reach the predetermined slaughter weight of 44 kg when compared to the other groups. All the groups followed more or less the same trend with regard to their respective growth curves. The slaughter traits of the six groups are presented in Table 3.

 


Figure 1. Growth curves of the different treatment groups


Table 2. Regression equations and R2-values for the growth curves of the different treatment groups

Group

Equation

R2-values

 20%

y = 1.55x + 22.83

0.9692

 30%

y = 1.75x + 23.26

0.9914

 40%

y = 1.56x + 23.51

0.9920

 50%

y = 1.58x + 23.44

0.9871

 60%

y = 1.40x + 25.00

0.9587

 70%

y = 1.24x + 25.10

0.9746

 

Diet energy level contributed significantly (P<0.05) to overall variation in carcass yield, hind leg length (outside) and hind leg circumference, fat depth and kidney fat. The 70% diet differed (P<0.05) from the other diets for most of the slaughter traits. The carcass yield and carcass weight of lambs on the high energy diets were higher than on the low energy diets (P<0.05). This is consistent with the results reported by Haddad & Husein (2004). They studied the effect of dietary energy density on growth performance and slaughtering characteristics of fattening Awassi lambs and observed that lambs fed a high energy diet had a higher (P<0.05) dressing percentage compared to lambs fed a low energy diet. The effect of diet energy levels on carcass classification is summarised in Table 4.

 

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

Group

Grade A2 (%)

(Fat 1-4 mm)

Grade A3 (%)

(Fat 4-7 mm)

Grade A4 (%)

(Fat 7-9 mm)

Grade A5 (%)

(Fat 9-11  mm)

20%

0.00

53.33

40.00

6.67

30%

0.00

86.67

6.67

6.67

40%

6.67

46.67

40.00

6.67

50%

26.67

26.67

40.00

6.67

60%

13.33

73.33

13.33

0.00

70%

21.43

71.43

7.14

0.00

 

Seventy-one percent of the animals in all the groups were graded into A2 and A3 grades and 29% of the lambs were graded into A4 and A5 grades. Lambs in the high energy groups (20% and 30% roughage level) had zero carcasses graded as A2, while lambs in the low energy groups (60% and 70% roughage level) had zero carcasses graded as A5 carcasses.


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

 

Trait

Group

20%

30%

40%

50%

60%

70 %

Slaughter weight (kg)

42.01 ± 1.00

42.39 ± 1.00

41.13 ± 1.00

42.88 ± 1.00

41.03 ± 1.00

41.43 ± 1.00

Carcass weight (kg)

19.48a ± 0.20

19.27a ± 0.20

19.61a ± 0.20

19.31a ± 0.20

18.80b ± 020

18.87b ± 0.30

Carcass yield (%)

44.10a ± 0.40

44.58a ± 0.40

44.23a ± 0.40

42.58b ± 0.40

43.18b ± 0.40

42.41c ± 0.50

Hind leg, inside length (cm)

49.11 ± 0.70

49.35 ± 0.70

50.92 ± 0.70

50.68 ± 0.70

49.76 ± 0.70

49.62 ± 0.70

Hind leg, outside length (cm)

40.83a ± 0.50

38.45b ± 0.50

40.71a ± 0.50

41.12b ± 0.50

40.36a ± 0.50

40.32a ± 0.50

Hind leg circumference (cm)

67.19a ± 0.40

65.20b ± 0.40

67.14a ± 0.40

67.63a ± 0.40

67.46a ± 0.40

66.64c ± 0.50

Carcass length (cm)

108.45a ± 0.60

108.35a ± 0.60

109.47b ± 0.60

110.13b ± 0.60

109.98b ± 0.60

108.80a ± 0.70

Fat depth 1 (mm)

7.63 ± 1.80

10.67 ± 1.80

9.07 ± 1.80

6.35 ± 1.80

7.11 ± 1.80

6.69 ± 1.80

Fat depth 2 (mm)

8.42a ± 0.60

6.26b ± 0.60

8.36a ± 0.60

6.65b ± 0.60

6.22b ± 0.60

6.45b ± 0.60

Fat depth 3 (mm)

7.12a ± 0.50

6.84a ± 0.50

7.63a ± 0.50

6.95a ± 0.50

6.14a ±0.50

5.27b ± 0.60

Fat depth 4 (mm)

4.39 ± 0.30

4.43 ± 0.30

4.35 ± 0.30

3.50 ± 0.30

3.72 ± 0.30

3.49 ± 0.40

Fat depth 5 (mm)

3.91a ± 0.40

4.31a ± 0.40

4.41a ± 0.40

3.55a ± 0.40

3.68a ± 0.40

1.90b ± 0.50

Kidney fat (kg)

1.34a ± 0.20

0.61b ± 0.20

0.77b ± 0.20

0.78b ± 0.20

0.56b ± 0.20

0.55b ± 0.20

Abdominal fat (kg)

0.93 ± 0.20

0.75 ± 0.20

0.74 ± 0.20

0.79 ± 0.20

0.62 ± 0.20

1.09 ± 0.20

abc Values with different superscripts differ significantly (P<0.05)


Total feed intake and weight gain, average daily gain (ADG), feed conversion ratio (FCR) and days till slaughter of the six groups are summarised in Table 5. Diet energy level influenced the ADG and FCR of the animals. The animals in the higher energy groups (lower roughage levels) in general had better ADG and FCR than the lower energy groups (higher roughage levels). The results of this study concur with the results reported by Haddad (2005) that increasing the concentrate portion of fattening diets increased ADG and improved feed efficiency as well as carcass characteristics of growing Baladi kids. He further observed a linear increase in ADG with an increasing level of dietary concentrates. Other researchers observed similar results in weight gain and ADG for sheep (Fluharty & McClure, 1997).

 

Table 5. Total feed intake and weight gain, average daily gain, feed conversion ratio and days till slaughter of the six groups

Group

Feed intake

kg DM

Total weight gained (kg)

Average daily gain (g/animal/day)

Feed conversion ratio

Days till slaughter

20%

1627.12

238.4

189.2 ± 14.4

6.8

84

30%

1459.24

249.6

227.9 ± 14.4

5.8

73

40%

1571.32

224.6

194.5 ± 14.4

7.0

77

50%

1854.50

263.5

209.1 ± 14.4

7.0

84

60%

1666.98

187.2

162.1 ± 14.4

8.9

77

70%

1771.39

228.9

177.7 ± 14.9

8.3

92

 

 

CONCLUSION

From the results of this study it can be concluded that differences in the energy levels of feedlot diets had an effect on growth rates, slaughter traits and feed conversion ratio of Merino lambs. High energy diets improved the average daily gain and feed conversion ratio compared to the high roughage diets. However, roughage levels of below 30% can lead to increased incidents of acidosis, resulting in a decrease in animal performance and profitability. Further trials will be conducted using lambs from other breeds (Dorper, Dohne Merino) to determine the effect of different energy levels in feedlot diets on the same traits that were measured in this trial. A computer model to determine the most economical energy inclusion level in feedlot diets for lambs will be developed after completion of the trials with the other breeds.

 

REFERENCES

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

Brand, T.S., Cloete, S.W.P., Franck, F. & Van der Merwe, G.D., 1991. Wheat-straw as roughage component in finishing diets of growing lambs. S. Afr. J. Anim. Sci. 21(4), 184-188.

Ferreira, A.V., Hoffman, L.C., Schoeman, S.J. & Sheridan, R., 2002. Water intake of Boer goat and Mutton Merinos receiving either a low or high energy feedlot diet. Small Rumin. Res. 43, 245-248.

Fluharty, F.L. & McClure, K.E., 1997. Effect of dietary energy intakes and protein concentration on performance and visceral organ mass in lambs. J. Anim. Sci. 75, 604-610.

Haddad, S.G., 2005. Effect of dietary forage: concentrate ratio on growth performance and carcass characteristics of growing Baladi kids. Small Rumin. Res. 57, 43-49.

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

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

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

 

Published

Grootfontein Agric 11 (2): 55-64