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EFFECT OF SUPPLEMENTARY DIETARY CHROMIUM ON

DORPER LAMBS SLAUGHTERED AT TWO DIFFERENT WEIGHTS.

I. GROWTH AND CARCASS TRAITS

 

M.A. Snyman, B.R. King, W.J. Olivier & J.H. Hoon


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

E-mail: Gretha Snyman

 


INTRODUCTION

The need for a sheep breed suitable for the production of slaughter lambs under the adverse conditions of South Africa resulted in the establishment of the Dorper breed in the early 1940s (Cloete et al., 2000; Milne, 2000). The early fat deposition that occurs in Dorper lambs is a major constraint with regard to income from this mutton-producing enterprise due to downgrading of carcasses, resulting in a loss of income. In practice, too much fat deposition in Dorper lambs at a relatively early age force producers to market the lambs at a relative low body weight, especially during good seasons. This also applies to Dorper lambs in feedlots. On the other hand, the ability of Dorper ewes to store fat is essential for their adaptation to dry and harsh climates.

 

There are several possible ways to address this problem. Firstly, to select against animals with an early fat deposition; secondly, to do terminal crossbreeding with a late maturing sire breed and thirdly, through manipulation of the diet. The latter option would yield the easiest and fastest results, if a suitable substance that delays fat deposition could be identified. 

 

In pigs, dietary chromium, as chromium-picolinate, increased average daily gain and decreased fat deposition when fed at a level to provide up to 200 ppb chromium (Page et al., 1993). However, bio-availability of chromium contained in commercial feeds for ruminants is not known. Furthermore little is known about the relative bio-availability of the different chromium sources for ruminants. Performance responses observed to date are limited to work conducted with chromium-picolinate, high-chromium yeast, and chelated chromium (Committee on Animal Nutrition, National Research Council, 1997).

 

Kitchalong et al. (1993) reported decreased kidney, pelvic and heart fat and improved carcass yield grades in lambs fed chromium-picolinate in a diet based on corn-cotton seed hulls. However, Olsen et al. (1996) found no significant effect on average daily gain, feed intake, feed efficiency, carcass values or carcass composition among lambs fed cracked corn-alfalfa diets containing 0, 500 or 1000 ppb chromium-picolinate. Similarly, Kitchalong et al. (1995) found that supplementation of 0.25 mg Cr/kg DM as chromium-picolinate did not influence average daily gain, dry matter intake or nitrogen utilisation of female lambs (38 ± 2.7 kg body weight) that were fed a basal diet containing less than 1 mg Cr/kg DM for 85 days. In an experiment to evaluate differences in non-carcass components and wholesale cuts in fat-tailed Shal ram lambs fed a barley-based diet (12.2% crude protein) supplemented with chromium nicotinate or chromium chloride, Mostafa-Tehrani et al. (2006) found increased skin, head, liver and kidney weight, and decreased heart, heart fat and internal fat weight in lambs on the chromium nicotinate supplemented diet.

 

Samsell & Spears (1989), using low and high fibre diets containing 0.175 and 0.295 mg Cr/kg diet DM respectively, noted that supplemental chromium did not influence plasma glucose or insulin concentrations and did not affect plasma glucose clearance when lambs were given a glucose tolerance test. Pollard et al. (2001) on the other hand found enhanced protein synthesis and glucose uptake in primary bovine muscle cells. Williams et al. (1994), DePew et al. (1996), Sano et al. (1996), Gentry et al, (1999) and Juarez et al. (2005) did not record any significant effects of supplementary chromium on blood and plasma metabolites.

 

The work of Samsell & Spears (1989), Kitchalong et al. (1995), Sano et al. (1996) and Pollard et al. (2001) suggest that chromium supplementation exerts subtle effects on carbohydrate and lipid metabolism in sheep. The significance of these effects, however, is not clear. The aim of this study was to investigate the effect of different inclusion levels of chromium in high and low energy diets on growth rate, carcass traits and measurements, fat deposition and meat characteristics of Dorper lambs slaughtered at two different weights. Results on the growth and carcass traits will be reported here, while the meat characteristics will be reported in another article.

 

MATERIALS AND METHODS

Seventy-two Dorper weaner lambs (28.35±0.42 kg) were used in this study. The animals were divided on a stratified body weight basis into six groups of 12 animals each. The experimental layout is summarised in Table 1. Three of the groups received a high energy diet, while the other three groups received a low energy diet. For each of these two diets, three levels of chromium were added, namely high chromium level (250 g/ton = 500 ppm), low chromium level (100 g/ton = 200 ppm) and zero chromium level (0 g/ton). The source of chromium used was chromium yeast in the Bio-chrome 2000 ppm product (Alltech Inc.). The composition and nutritional value of the different diets are summarised in Tables 2 and 3 respectively. Basal chromium levels in the diets were not determined. The animals were fed pelleted diets in individual pens on an ad libitum basis. Six animals of each group were slaughtered at 38 kg body weight, while the other six animals were slaughtered at 44 kg body weight.

 

Table 1. Experimental layout

Group

Number of animals

Energy level  of diet

Level  of chromium

Animals slaughtered at 38 kg

Animals slaughtered at 44 kg

1

12

high

high

6

6

2

12

high

low

6

6

3

12

high

zero

6

6

4

12

low

high

6

6

5

12

low

low

6

6

6

12

low

zero

6

6

 

Table 2. Composition of the different diets

Ingredient

Low energy diet

High energy diet

Chromium level

Zero

Low

High

Zero

Low

High

Lucerne hay (%)

66.5

66.5

66.5

35

35

35

Maize meal (%)

12.5

12.5

12.5

50

50

50

Molasses meal (%)

8.0

8.0

8.0

6.0

6.0

6.0

Maize stover (%)

12.5

12.5

12.5

5.5

5.5

5.5

Salt (%)

0.5

0.5

0.5

0

0

0

Mutton gainer (%)

0

0

0

3.2

3.2

3.2

Buffer pack (%)

0

0

0

0.3

0.3

0.3

Bio-chrome 2000 ppm  (g/ton)

0

100

250

0

100

250

 

 

Table 3.  Nutritional value of the diets

Nutrient

Low energy diet (%)

High energy diet (%)

Crude protein

14.31

14.11

Moisture

3.44

3.90

Acid detergent fibre

27.68

18.41

Calcium

0.90

1.15

Phosphorus

0.28

0.29

Energy (Total digestible nutrients – Estimated value)

56.0

65.2

 

All animals were adapted in the individual pens for two weeks before the commencement of the trial on a diet consisting of milled lucerne, mixed with the low energy, zero chromium diet. Body weights of the lambs were recorded at the commencement of the trial, weekly during the trial period and finally on the day of slaughtering. The feed was weighed out weekly into plastic bags and animals were fed from the bags. Left over feed was recorded on a weekly basis in order to determine the feed intake and feed conversion ratio.

 

As soon as an animal reached its predetermined slaughter weight, it was fasted overnight for slaughtering the next day. The animals were slaughtered at the Grootfontein abattoir using standard slaughtering techniques. Animals were weighed before slaughtering, while warm carcass weight and amount of kidney and abdominal fat was recorded just after slaughtering. The carcasses were hung in a cooler at ± 2 °C for 48 hours. After 48 hours, the cold carcass weight and the following carcass measurements were taken as described by Bruwer & Naudé (1987), Bruwer et al. (1987a) and Bruwer et al. (1987b):

 

Carcasses were graded according to the South African classification system (Agricultural Product Standards Act; Act No. 1999 of 1990; Government Notice No. R. 1948, 26 June 1992). Carcass yield (dressing percentage), growth rate (average daily gain) from the start of the trial till slaughter, feed intake and feed conversion ratio were calculated for each animal from the recorded data.

 

General Linear Model (GLM) procedures of the SAS computer package (SAS, 2004) were used to identify fixed effects which contributed significantly to variation and to obtain least squares means of these effects for all traits analysed.

 

RESULTS AND DISCUSSION

The fixed effects, and interactions among these, included in the models are summarised in Table 4. Diet energy level contributed significantly (P<0.01) to overall variation in feed conversion ratio, carcass weight and carcass yield. Dietary chromium level did not have a significant influence on any of the traits. Slaughter weight significantly (P<0.01) influenced hind leg length and abdominal fat. Sex of the lamb had a significant effect on most of the traits, as indicated in Table 4. None of the interactions among these main effects were significant.

 

Table 4. Fixed effects included in the statistical model fitted for all traits

Trait

Diet energy level

(High, Low)

Chromium level

(High, Low, Zero)

Slaughter weight

(SW; 38 kg, 44 kg)

Sex (Ram, Ewe)

Actual slaughter weight (covariate)

Energy * Chromium level

Energy * Slaughter weight

Chromium * Slaughter weight

Energy * Chromium level * SW

Average daily gain

ns

ns

ns

**

-

ns

ns

ns

ns

Feed conversion ratio

**

ns

ns

**

-

ns

ns

ns

ns

Carcass weight

**

ns

ns

**

**

ns

ns

ns

ns

Carcass yield

**

ns

ns

**

ns

ns

ns

ns

ns

Hind leg length

ns

ns

**

ns

ns

ns

ns

ns

ns

Hind leg circumference

ns

ns

ns

**

ns

ns

ns

ns

ns

Carcass length

ns

ns

ns

ns

ns

ns

ns

ns

ns

Fat depth 1

ns

ns

ns

ns

ns

ns

ns

ns

ns

Fat depth 2

ns

ns

ns

**

ns

ns

ns

ns

ns

Fat depth 3

ns

ns

ns

ns

ns

ns

ns

ns

ns

Fat depth 4

ns

ns

ns

**

ns

ns

ns

ns

ns

Fat depth 5

ns

ns

ns

ns

ns

ns

ns

ns

ns

Abdominal fat

ns

ns

**

**

-

ns

ns

ns

ns

Kidney fat

**

ns

**

**

-

ns

ns

ns

ns

** P<0.01; ns = not significant

 

 

The effect of feed quality and chromium level on growth and carcass traits are summarised in Table 5. The average daily gain (ADG) of the lambs that received the high energy diet was 33.9 g/day higher (P>0.01) than that of the lambs that received the low energy diet. Feed conversion ratio was better on the high energy diet (5.11±0.24 vs. 6.85±0.24).

 

The carcass yield and carcass weight of lambs on the high energy diet was higher than on the low energy diet (P<0.01). Similar results were reported by Owens et al. (1993) and Díaz et al. (2002) where higher dressing values were observed for feedlot lambs that received higher concentrate diets than for lambs raised under veld conditions. Part of the difference in dressing percentage between these lambs was due to a smaller alimentary tract in the feedlot lambs fed concentrates. The veld-reared lambs, consuming herbage had larger alimentary tracts and thus lower dressing percentages.

 

Diet quality did not have a significant effect on carcass measurements or subcutaneous fat depth. The lambs that received the high energy diet had more kidney fat (P<0.01) than those on the low energy diet. Crouse et al. (1981) reported a higher fat deposition in lambs fed a high energy diet. 

 

The lambs receiving the low chromium level diet grew 42.86 and 16.46 g/day more than lambs receiving the high and zero chromium diets respectively. Carcass weight and carcass yield of lambs on the high chromium level diet were higher (P<0.01) compared to lambs on the low chromium level diet, but neither differed from the zero chromium diet. Neither carcass measurements, nor subcutaneous or internal fat deposition were significantly affected by supplementary dietary chromium level. These findings are in general agreement with those obtained for sheep (Kitchalong et al., 1993; Kitchalong et al., 1995; Olsen et al., 1996).

 

Table 5. Effect of diet energy and chromium levels on growth and carcass traits (± s.e.) of Dorper lambs

Trait

Energy level

Chromium level

 

High

Low

High

Low

Zero

Average daily gain (g/day)

273.11±10.30

239.24±10.14

233.09±12.71 b

275.95±12.41 b

259.49±12.41

Feed conversion ratio

5.11±0.24 a

6.85± 0.24 a

6.44 ±0.30

5.65±0.30

5.85±0.30

Carcass weight (kg)

20.29±0.17 a

19.26±0.17 a

20.25±0.21 b

19.42±0.21 b

19.65±0.21

Carcass yield (%)

51.68±0.43 a

49.07±0.42 a

51.62±0.53 b

49.54±0.52 b

49.98±0.51

Hind leg length (cm)

33.31±0.36

33.93±0.35

33.97±0.44

33.58±0.43

33.30±0.43

Hind leg circumference (cm)

70.04±0.48

69.07±0.48

69.28±0.60

69.53±0.58

69.85±0.58

Carcass length (cm)

97.25±0.67

98.21±0.66

98.97±0.82

96.72±0.81

97.48±0.80

Fat depth 1 (mm)

8.63±0.43

7.97±0.42

8.96±0.53

8.49±0.52

7.39 ±0.51

Fat depth 2 (mm)

6.79±0.37

6.65±0.37

7.05±0.46

6.82±0.45

6.29±0.45

Fat depth 3 (mm)

6.04±0.33

6.73±0.32

6.32±0.41

6.60±0.40

6.23±0.40

Fat depth 4 (mm)

4.44±0.24

4.08±0.24

4.65±0.30

4.00±0.29

4.11±0.29

Fat depth 5 (mm)

4.16±0.32

5.04±0.32

4.71±0.40

5.06±0.39

4.02±0.39

Abdominal fat (kg)

0.78±0.04

0.68±0.04

0.74±0.05

0.72±0.05

0.74±0.05

Kidney fat (kg)

0.44±0.03 a

0.32±0.03 a

0.34±0.04

0.37±0.03

0.39±0.04

a   Values with the same superscript differ significantly (P<0.01) between diet energy levels

b  Values with the same superscript differ significantly (P<0.01) between chromium levels

 

The effect of slaughter weight and sex on growth and carcass traits are summarised in Table 6. The only traits affected significantly by slaughter weight were hind leg length, kidney and abdominal fat. An increase in slaughter weight is usually marked by an increase in carcass fatness, which corresponds to the standard lamb growth pattern (Seideman et al., 1982; Díaz et al., 2002).

 

The rams had a higher average daily gain and a more favourable feed conversion ratio than the ewe lambs. It is generally accepted that male lambs grow faster than ewes because they utilise feed more efficiently (Seideman et al., 1982). Ewes had a ± 3 % higher carcass yield, which contributed to their higher carcass weights and measurements (P<0.01). The ewes also had higher subcutaneous as well as internal fat measurements (P<0.01) than the rams.

 

Table 6. Effect of slaughter weight and sex on growth and carcass traits (± s.e.) of Dorper lambs

Trait

Slaughter weight

Sex

38 kg

44 kg

Ewes

Rams

Average daily gain (g/day)

262.09±10.14

250.27±10.30

218.34±10.30 b

294.02±10.14 b

Feed conversion ratio

5.64±0.24

6.32±0.24

6.80±0.24 b

5.16±0.24 b

Carcass weight (kg)

19.11±0.30

20.43±0.30

20.40±0.17 b

19.14±0.17 b

Carcass yield (%)

48.70±0.74

52.05±0.73

51.97±0.43 b

48.79±0.42 b

Hind leg length (cm)

31.66±0.62 a

35.57±0.61 a

33.103±0.36

34.14±0.35

Hind leg circumference (cm)

68.14±0.84

70.96±0.82

71.43±0.49 b

67.67±0.48 b

Carcass length (cm)

95.27±1.16

100.19±1.14

98.10±0.67

97.37±0.66

Fat depth 1 (mm)

8.05±0.74

8.51±0.73

8.46±0.43

8.11±0.42

Fat depth 2 (mm)

5.83±0.65

7.61±0.63

7.60±0.37 b

5.84±0.37 b

Fat depth 3 (mm)

6.28±0.57

6.49±0.56

6.97±0.33

5.80±0.33

Fat depth 4 (mm)

3.96±0.42

4.55±0.41

4.93±0.24 b

3.59±0.24 b

Fat depth 5 (mm)

4.73±0.57

4.47±0.55

5.20±0.33

4.00±0.32

Abdominal fat (kg)

0.54±0.04 a

0.93±0.04 a

0.94±0.04 b

0.53±0.04 b

Kidney fat (kg)

0.29±0.03 a

0.47±0.03 a

0.51±0.03 b

0.25±0.03 b

a  Values with the same superscript differ significantly (P<0.01) between slaughter weights

b  Values with the same superscript differ significantly (P<0.01) between sexes

 

The effects of diet quality and chromium level on growth and carcass traits of the Dorper lambs slaughtered at 38 kg are summarised in Table 7. The lambs that received the high energy diet had a better feed conversion ratio, higher carcass weight, carcass yield and kidney fat (P<0.01), than lambs that received the low energy diet. None of the traits were significantly influenced by supplementary dietary chromium level.

 

Table 7. Effect of diet energy and chromium levels on growth and carcass traits (± s.e.) of Dorper lambs slaughtered at 38 kg

Trait

Energy level

Chromium level

High

Low

High

Low

Zero

Average daily gain (g/day)

277.09±14.33

247.09±14.33

234.77±17.56

269.78±17.56

281.72±17.56

Feed conversion ratio

4.81±0.34 a

6.47± 0.34 a

6.45 ±0.42

5.27±0.42

5.21±0.42

Carcass weight (kg)

19.62±0.34 a

18.60±0.36 a

19.64±0.39

18.94±0.38

18.75±0.39

Carcass yield (%)

50.11±0.84 a

47.30±0.88 a

50.16±0.96

48.28±0.95

47.67±0.97

Hind leg length (cm)

31.03±0.70

32.30±0.73

32.54±0.80

31.30±0.79

31.15±0.81

Hind leg circumference (cm)

69.32±0.95

66.97±0.99

67.64±1.09

68.71±1.07

68.07±1.09

Carcass length (cm)

94.10±1.31

96.44±1.37

97.63±1.50

93.28±1.48

94.90±1.51

Fat depth 1 (mm)

8.48±0.84

7.67±0.87

8.40±0.96

8.59±0.94

7.16±0.96

Fat depth 2 (mm)

6.01±0.73

5.65±0.76

6.28±0.83

5.76±0.82

5.45±0.84

Fat depth 3 (mm)

6.40±0.65

6.16±0.67

6.31±0.74

6.45±0.73

6.07±0.74

Fat depth 4 (mm)

4.41±0.47

3.51±0.49

4.14±0.54

3.60±0.53

4.14±0.54

Fat depth 5 (mm)

4.55±0.64

4.90±0.67

4.78±0.76

5.12±0.72

4.28±0.73

Abdominal fat (kg)

0.57±0.06

0.50±0.06

0.58±0.07

0.60±0.07

0.43±0.08

Kidney fat (kg)

0.36±0.04 a

0.22±0.04 a

0.32±0.05

0.30±0.05

0.25±0.05

a   Values with the same superscript differ significantly (P<0.01) between diet energy levels

 

The effects of diet quality and chromium level on growth and carcass traits of the Dorper lambs slaughtered at 44 kg are summarised in Table 8. As in the case of the lambs slaughtered at 38 kg, the lambs slaughtered at 44 kg that received the high energy diet had a better feed conversion ratio, carcass weight and carcass yield (P<0.01), than lambs that received the low energy diet. However, lambs on the low energy diet had higher subcutaneous fat measurements (P>0.01), which is contrary to what was expected. Lambs on the zero chromium diet had more abdominal fat than lambs receiving the high or low chromium diets.

Table 8. Effect of diet energy and chromium levels on growth and carcass traits (± s.e.) of Dorper lambs slaughtered at 44 kg

Trait

Energy level

Chromium level

High

Low

High

Low

Zero

Average daily gain (g/day)

269.15±14.78

231.39±14.33

231.77±17.56

282.13±17.56

237.26±17.56

Feed conversion ratio

5.41±0.35 a

7.23±0.34 a

6.43±0.44

6.03±0.42

6.50±0.42

Carcass weight (kg)

20.95±0.35 a

19.92±0.33 a

20.87±0.38

19.90±0.37

20.54±0.42

Carcass yield (%)

53.26±0.86 a

50.84±0.82 a

53.07±0.93

50.79±0.90

52.29±0.99

Hind leg length (cm)

35.59±0.72

35.56±0.69

35.40±0.78

35.86±0.75

35.46±0.83

Hind leg circumference (cm)

70.76±0.97

71.16±0.93

70.91±1.06

70.35±1.02

71.63±1.12

Carcass length (cm)

100.41±1.34

99.98±1.28

100.35±1.46

100.16±1.41

100.07±1.55

Fat depth 1 (mm)

8.77±0.86

8.26±0.82

9.51±0.93

8.40±0.90

7.63±0.99

Fat depth 2 (mm)

7.56±0.74

7.65±0.71

7.81±0.81

7.89±0.78

7.12±0.86

Fat depth 3 (mm)

5.68±0.66

7.30±0.63

6.33±0.72

6.75±0.69

6.39±0.76

Fat depth 4 (mm)

4.46±0.48

4.65±0.46

5.17±0.52

4.40±0.50

4.09±0.55

Fat depth 5 (mm)

3.77±0.65

5.17±0.62

4.65±0.71

5.01±0.68

3.76±0.75

Abdominal fat (kg)

0.99±0.06

0.86±0.06

0.90±0.07

0.83±0.07 b

1.05±0.07 b

Kidney fat (kg)

0.52±0.04

0.43±0.04

0.46±0.05

0.44±0.05

0.52±0.05

a   Values with the same superscript differ significantly (P<0.01) between diet energy levels

b  Values with the same superscript differ significantly (P<0.01) between chromium levels

 

The effect of diet quality and chromium levels on carcass classification of the Dorper lambs slaughtered at 38 and 44 kg are summarised in Tables 9 and 10 respectively. Neither energy nor chromium level had any significant effect on the classification of carcasses. From Table 9 it follows that 94.1 % and 88.8 % of lambs on the high and low energy diets respectively, slaughtered at 38 kg, were graded into the A2 and A3 grades. As far as the low chromium level diet lambs are concerned, 9.1 % of the lambs were leaner and 9.1 % of them were fatter than the A2 and A3 grades. No obvious trend was discernable among lambs slaughtered at 44 kg either.

Table 9. Effect of diet energy and chromium levels on distribution of carcasses over the carcass grades of Dorper lambs slaughtered at 38 kg

Traits

Grade A1 (%)

Grade A2 (%)

Grade A3 (%)

Grade A4 (%)

High energy

-

52.9

41.2

5.9

Low energy

5.6

44.4

44.4

5.6

 

High chromium

-

50.0

41.7

8.3

Low chromium

9.1

36.4

45.5

9.0

Zero chromium

-

58.3

41.7

 

 

Table 10. Effect of diet energy and chromium levels on distribution of carcasses over the carcass grades of Dorper lambs slaughtered at 44 kg

Traits

Grade A2 (%)

Grade A3 (%)

Grade A4 (%)

Grade A5 (%)

Grade A6 (%)

High energy

22.2

55.6

16.7

5.5

 

Low energy

5.5

38.9

38.9

5.6

11.1

 

High chromium

9.1

36.4

54.5

 

 

Low chromium

15.4

53.8

15.4

7.7

7.7

Zero chromium

16.7

50.0

16.7

8.3

8.3

 

CONCLUSIONS

Differences in the growth traits, carcass traits and measurements were mainly observed between the high and low energy diets, between slaughter weight groups and between the ewe and ram lambs. From the available results it can be concluded that supplementing of dietary chromium had no effect on growth rate, carcass measurements or fat deposition in Dorper lambs. These results are in accordance with the literature, which does not support a general recommendation for chromium supplementation in commercial sheep diets.

 

REFERENCES

Bruwer, G.G. & Naudè, R.T., 1987. An evaluation of the lamb and mutton carcass grading system in the Republic of South Africa. 3. Fatness score, conformation score and carcass mass as predictors of carcass composition. S. Afr. J. Anim Sci.17, 90-94.

Bruwer, G.G, Naudè, R.T., du Toit, M.M., &  Cloete, A., 1987a. An evaluation of the lamb and mutton carcass grading system in the Republic of South Africa. 2. The use of fat measurements as predictors of carcass composition. S. Afr. J. Anim Sci.17, 85-90.

Bruwer, G.G., Grobler, I., Smit, M. & Naudè, R.T., 1987b. An evaluation of the lamb and mutton carcass grading system in the Republic of South Africa. 4. The influence of age, carcass mass and fatness on meat quality characteristics S.Afr. J. Anim. Sci.17, 95-103.

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Grootfontein Agric 10 (1)