Nutritive value of some tropical feedstuffs for pigs. Chemical composition, digestibility and metabolizable energy content

Animal Feed Science and Technology, 28 (1990) 91-101

91

Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

Nutritive Value of Some Tropical Feedstuffs for Pigs. Chemical Composition, Digestibility and Metabolizable Energy Content FAUSTIN P. LEKULE*, HENRY JORGENSEN**, JOS]~ A. FERNANDEZ and ARNOLD JUST

National Institute of Animal Science, Foulum Research Centre, P.O. Box 39, 8830 Tjele (Denmark) (Received 6 December 1988; accepted for publication 29 May 1989)

ABSTRACT Lekule, F.P., Jorgensen, H., Fernandez, J.A. and Just, A., 1990. Nutritive value of some tropical feedstuffs for pigs. Chemical composition, digestibility and metabolizable energy content. Anita. Feed Sci. Technol., 28: 91-101. The chemical composition of some tropical feedstuffs and digestion coefficients obtained using pigs are given. Considerable variation was found in both chemical composition and content of metabolizable energy (ME) within some by-products, i.e. maize hominy feed, wheat bran, sunflower cake, cottonseed cake. On average for all feedstuffs a 2.2% decrease in digestibility of energy for each 1% increase in crude fibre was found (R2=0.73). Dry matter digestibility (DMD) is highly correlated with ME (or digestible energy) content and hence where DMD can be determined, the ME content can be predicted with reasonable accuracy for practical purposes (R 2= 0.83 ). Use of table values for the gross energy content of the feedstuff and DMD showed a promising equation with a R 2= 0.94 and residual standard deviation of 0.60 MJ or 4.1% of the average value. Inclusion of up to four chemical components (crude protein, crude fat, crude fibre and soluble carbohydrate) did not result in a better prediction equation than that obtained by using DMD or using table values.

INTRODUCTION

Many feedstuffs are produced in the tropics. Some of these feedstuffs are exported to Europe, where they are routinely analysed for quality control purposes. Such information, when obtainable, is useful to both the exporting and importing countries. Unfortunately, data on digestibility in pigs for many feeds *Present address: Department of Animal Science and Production, Sokoine University of Agriculture, P.O. Box 3004, Morogoro, Tanzania. **Author to whom all correspondence should be addressed.

0377-8401/90/$03.50

© 1990 Elsevier Science Publishers B.V.

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F.P. LEKULE ET AL.

of entirely tropical origin are insufficient or have been obtained at different times from different laboratories. The types of pig feeds used in the tropics vary greatly, and since many byproducts are used instead of cereals, the variation in nutritive values between and within feeds may be considerable. Determinations of metabolizable energy (ME) values are time-consuming and expensive, and the chemicals required are not readily available in many laboratories in the developing countries. The present study was carried out to show the variation in chemical composition and digestibility of feedstuffs originating from the tropics, and to develop regression equations for prediction of ME content from chemical analysis. MATERIALS AND METHODS

Seventy batches of 18 different feeds obtained during a period of 8 years from different parts of the tropics were chemically analysed and their digestibility determined by either the difference or the regression methods at The National Institute of Animal Science in Denmark. The basal diet used in the difference method consisted of 60% barley, 32% soya-bean meal, 8% meat-and-bone meal and minerals plus vitamins providing normally one-third to one-half of the daily ration, depending on the type of feedstuff tested. Five litters of six pigs each in the weight range 45-60 kg were used. One pig in each litter was fed on the basal diet alone; the other five pigs received five different test feedstuffs mixed with the basal diet. For protein-rich feedstuffs, the regression method was applied. Three litters in the weight range 45-60 kg were used. Within each litter, the six pigs were given the test feedstuff together with another feedstuff, usually a cereal or a by-product with low protein content, in six proportions. The pigs were given 1400 g, 1700 g and 2000 g per pig per day for the three periods (litters). The digestibility of nutrients and ME were calculated by multiple regression analysis according to the model:

y=bo +blXl +b2x2 +e where y-- digestible nutrient in total ration (g); bo-- intercept; bl -- digestibility coefficient of nutrient in basal feedstuff; xi = nutrient in basal feedstuff (g); b2 = digestibility coefficient of nutrient in test feedstuff; x2 = nutrient in test feedstuff (g); e = deviation from the regression line or error. The protein deposition on typical pig diets varies between 30 and 60% of digestible crude protein intake, therefore the ME values were adjusted to 50% protein deposition. The animals were kept in individual metabolic cages and faeces and urine were collected for 7 days after a preliminary period of 5 days and stored at 4 ° C. The urine was collected through urethral catheters under acid conditions (40 ml of 30% sulphuric acid). After the experiment, the collections were thor-

NUTRITIVE VALUE OF TROPICAL FEEDSTUFFS FOR PIGS

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oughly mixed and samples taken for chemical analysis as described by Fernandez et al. (1986). RESULTS AND DISCUSSION

The chemical composition of the feeds is presented in Table 1. The content of nitrogen-free extract (NFE) can thus be calculated as ( 1 0 0 - a s h - crude p r o t e i n - c r u d e f a t - c r u d e fibre) and the content of sugars as (soluble carboh y d r a t e - starch ). The corresponding digestibility coefficients of nutrients and ME content of the feeds are shown in Table 2. The average values of the feedstuffs are close to or similar to those documented by Gohl (1981), even though there is considerable variation in both chemical composition and content of ME within some of the feedstuffs, especially for the by-products. Within maize, there was a 7% difference between the lowest and highest contents of ME (Nos. 2 and 5) which, in part, can be explained by differences in crude protein and starch, showing that information on chemical composition can be useful for evaluation of a feedstuff. Maize hominy feed, owing to its variable fat content, showed a 10% difference between the highest and lowest ME contents (Nos. 16 and 17). Wheat bran was found to be highly variable in crude fibre content which partly explained the variation in ME. The amino-acid composition of the wheat bran showed a 19% difference between the two extremes; similar results were found by Batterham et al. (1980). Among the high-protein feedstuffs, sunflower cake and cottonseed cake had highly variable ME contents, especially because of a substantial variation in chemical composition (crude fibre in sunflower cake and crude fat in cottonseed cake). Cottonseed cake has been used as the main protein source in cassava meal-based diets with no toxic or other deleterious effects (Lekule, 1987) and the cottonseed cake was superior to sunflower cake because of its higher lysine content (Table 1). When formulating diets with cottonseed cake and sunflower cake, it is necessary to consider not only the level of dietary lysine, but also that the digestibility of the amino acids is lower than for soya-bean meal (Jorgensen et al., 1984; Tanksley and Knabe, 1984). The digestion of soluble carbohydrate (starch + sugars ) was in all cases nearly complete. Within the oil seeds (soya-bean meal, sunflower and cottonseed}, a large proportion of the soluble carbohydrate is sugars (Table 1) of which sucrose only constitutes a small fraction, the main part being oligosaccharides (Kuo et al., 1988). The pig does not possess any enzymes that can digest the oligosaccharides, but they may be digested by microbial fermentation in the hind gut. The energy absorbed from the hind gut is utilized only half as efficiently as that absorbed from the anterior digestive tract (Just et al., 1983). This implies that the energy digested from the oil seeds may be less efficiently used than that from cereals. The digestion coefficients were obtained with growing pigs, as they consume

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TABLE 1 Chemical composition of feeds ( % dry matter) No. Feedstuff

Ash Crude Crude Crude Soluble Starch NDF ADF GE Lysine Dry matter protein fat fibre carbo(MJ kg-~ (g 16g (%) hydrate DM ) N - ~)

1. 2. 3. 4. 5. 6 7 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49.

87.4 87.4 87.8 86.7 86.0 86.4 85.8 86.6 85.2 87.0 89.5 87.9 85.8 87.4 87.t 87.8 88.0 88.8 90.3 88.9 89.9 88.2 87.3 89.8 85.6 90.4 87.2 87.2 84.6 88.0 87.4 88.0 87.7 87.2 86.9 86.6 87.6 87.3 87.9 87.1 86.9 87.1 86.2 87.5 87.4 87.7 88.9 87 3 88.6

Maize Maize Maize Maize Maize Maize Maize Maize meal Maize meal Maize meal Maize bran Maize bran Maize hominy feed Maize hominy feed Maize hominy feed Maize hominy feed Maize hominy feed Maize-gluten meal Maize-gluten meal Maize-gluten meal Maize-gluten feed Maize-gluten feed Maize-gluten feed Maize germ Maize germ Maize germ Maize starch Maize starch Maize starch Cassava meal Cassava meal Cassava meal Cassava meal Cassava meal Wheat bran Wheat bran Wheat bran Wheat bran Wheat bran Wheatbran Wheatbran Wheat middlings Wheat middlings Soya-bean meal Soya-bean meal Soya-bean meal Soya-bean meal Soya-bean meal Soya-bean m'. -;

1.5 1.8 1.7 1.5 1.6 1.4 1.7 0.6 0.6 0.4 2.8 2.9 2.0 2.5 2.4 2.8 3.7 0.9 1.5 2.6 6.5 4.7 6.2 7.2 7.4 6.1 0.2 0.0 0.2 5.8 5.7 7.1 7.1 6.0 4.6 4.6 4.4 4.3 4.4 6.2 4.8 3.8 1.8 6.6 6.7 6.3 7.0 7.1 6.7

10.0 9.8 10.9 10.4 10.6 10.2 11.2 10.5 7.1 6.7 10.5 11.0 11.2 10.7 10.3 10.5 11.5 60.8 64.8 68.5 23.4 14.3 22.7 16.5 17.4 16.0 1.2 0.5 0.5 4.3 2.8 4.6 2.8 3.3 15.9 16.7 16.5 15.5 18.8 17.4 18.0 17.7 14.2 49.9 51.0 50.3 48.7 47.8 47.6

4.8 5.0 4.8 4.9 5.0 4.9 5.3 2.1 1.8 2.6 10.6 8.6 6.8 9.5 8.7 10.0 13.6 5.1 8.5 4.8 4.6 4.6 5.1 26.4 25.2 20.2 0.9 0.6 0.9 1.4 1.3 1.2 1.0 0.9 4.5 5.4 6.1 4.9 6.2 5.7 5.0 5.9 3.1 3.1 3.4 3.1 3.1 3.0 4.0

2.6 2.8 2.4 2.4 2.4 2.6 2.1 0.6 1.0 1.1 7.1 7.8 3.2 4.1 3.1 3.5 4.4 0.7 0.7 1.0 8.6 7.1 8.3 5.5 5.5 5.2 0.3 0.1 0.2 4.2 3.6 5.6 3.6 4.9 8.2 8.4 8.0 8.7 7.9 12.4 8.7 5.3 1.8 5.6 6.3 6.8 7.2 8.0 10.9

72.3 73.0 72.5 72.2 74.3 74.4 71.3 85.4 83.8 91.1 44.9 38.8 65.1 59.2 62.5 59.4 52.7 31.6 21.3 20.0 24.5 43.9 28.4 29.7 27.1 34.4 96.8 97.1 99.4 74.8 81.1 72.2 80.6 74.4 41.1 38.0 34.5 40.6 34.8 22.5 33.9 47.3 67.3 17.6 14.5 16.4 16.0 15.5 12.4

-70.4 71.3 -71.5 72.8 72.1 -87.1 86.9 -36.1 -54.0 57.4 53.6 40.6 -20.8 19.2 18.5 38.9 23.1 -23.3 27.1 -94.9 99.9 -78.6 -78.3 70.1 34.3 ---28.5 13.9 26.6 -55.0 2.4 -3.9 2.4 4.9 1.9

12.6 10.8

4.4 3.4

10.3 9.3 8.4

3.1 3.5 3.5

4.5 1.6

1.7 1.3

37.5

10.5

16.6 16.1 16.2 16.4

5.2 4.7 5.1 5.6

1.7 1.8 31.7 27.6 29.6

1.4 3.1 11.9 8.4 11.2

15.4 17.8

6.2 6.6

0.1

0.9

7.0 9.0 6.4 -33.1

5.3 7.8 4.9 5.9 11.8

27.8 46.3 34.0

9.7 15.0 12.1

8.8 11.6

3.0 9.3

12.1 17.2 17.0 19.5

9.7 12.7 9.8 16.3

18.83 18.50 18.90 18.72 18.97 18.64 19.20 18.40 18.68 18.15 20.25 19.74 19.61 19.69 19.24 19.72 21.15 22.96 23.56 23.41 18.99 19.06 19.30 22.57 22.93 21.80 17.33 17.53 17.89 16.76 16.22 16.77 15.94 16.67 19.00 19.21 19.40 18.83 19.44 19.44 19.15 19.10 18.57 19.59 19.65 19.56 19.51 19.60 19.98

2.8 3.2 3.0 3.0 2.6 2.9 2.9 2.0 2.8 2.8 4.2 3.9 3.7 3.6 3.6 3.7 4.4 1.7 1.8 1.7 2.8 4.3 2.9 5.0 3.1 5.1 3.5 --3.7 4.3 4.4 3.2 3.3 3.7 4.1 4.4 3.8 4.1 4.0 3.8 4.4 3.9 6.1 5.8 6.3 6.2 6.5 5.9

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NUTRITIVE VALUE OF TROPICAL FEEDSTUFFS FOR PIGS T A B L E 1 {continued) No. Feedstuff

Dry

matter

Ash Crude Crude Crude Soluble Starch N D F A D F GE Lysine protein fat fibre carbo( M J k g - I (g 16 g

(%) 50. 51. 52. 53. 54. 55. 56. 57. 58. 59. 60. 61. 62. 63. 64. 65. 66. 67. 68. 69. 70.

Sunflower cake Sunflower cake Sunflower cake Sunflower cake Coconut cake Coconut cake Coconut cake Cottonseed cake Cottonseed cake Cottonseed cake Cottonseed cake Cottonseed cake Palm cake Palm cake Sorghum Sorghum Sorghum

Dehulled rice Dehulledrice Dehulledrice Dehuned rice

90.5 90.3 88.3 87.3 89.1 90.2 94.4 93.9 90.4 91.4 92.3 89.2 94.4 89.6 87.5 87.1 87.3 86.8 87.4 87.2 85.4

hydrate 6.0 7.4 6.4 6.7 6.1 5.9 6.6 7.3 6.5 7.0 7.4 6.7 4.1 4.2 2.9 1.7 1.8 0.5 0.4 0.5 1.2

42.3 37.6 31.7 31.6 22.3 22.3 21.3 38.9 39.9 48.8 41.7 42.3 17.8 18.4 11.2 10.8 12.3 8.1 7.2 8.0 9.0

7.8 4.5 3.6 3.7 8.4 7.8 13.3 5.9 5.4 4.2 10.1 2.5 9.3 15.3 3.9 3.7 4.3 1.0 1.3 1.4 2.3

18.4 22.4 30.2 28.3 12.0 11.7 13.7 17.4 16.4 13.1 14.2 15.2 18.8 17.5 2.5 2.7 2.3 0.8 0.9 0.3 0.3

7.5 9.5 7.2 7.9 15.0 15.1 9.7 8.6 8.4 10.5 9.7 9.6 5.0 6.3 69.5 73.9 73.2 86.5 90.1 90.3 90.0

3.1 1.5 2.3 ---9.9 -2.9 2.1 1.6 2.0 3.1 2.5 -73.2 72.8 -89.0 91.6 85.5

32.2 33.7 45.0 41.7 --43.9 -32.7 22.5 25.0 30.7 66.6 55.9 -9.0 6.6 -0.4 1.4 1.1

23.1 27.8 35.9 32.4 --24.2 -21.8 16.9 19.9 22.2 42.7 38.3 -7.1 6.3 -0.7 0.9 0.6

DM)

N --1 )

20.59 20.28 19.80 20.21 19.14 19.57 21.08 20.02 20.25 19.65 20.67 19.66 20.15 21.29 18.45 18.37 19.09 18.28 17.66 17.88 18.06

3.1 3.5 3.4 3.8 2.9 2.6 2.5 3.8 3.5 4.2 4.4 3.7 2.5 3.6 2.5 2.4 -3.3 3.6 3.4 4.1

the main part of the feeds used in pig production. Therefore, the same feedstuffs could be expected to have higher digestion coefficients for sows as found by Fernelndez et al. (1986) in comparative studies with growing pigs and dry sows. Sows have a higher capacity for fermentation in the hind gut, especially in the gestation period when the feeding level is low. The results for different heat treatments of soya-bean meal (Table 3) are in agreement with those of Vandergrift et al. (1983) and van Weerden et al. (1985) who showed that the difference between toasted and untoasted soya-bean meal was greater when measured at the end of the small intestine than when measured over the total digestive tract, owing to an increased fermentation in the large intestine of nutrients from the untoasted soya-bean meal. The protein and amino acids that disappear from the large intestine have been shown to have little or no protein value for the pig, as their nitrogen is fully excreted in the urine (Just et al., 1981 ). The well-established negative influence of crude fibre (CF) on dry matter and energy digestibility was clearly demonstrated (Table 4). The influence was examined statistically by regression analysis, and for all feedstuffs there was a decrease in energy digestibility of 2.2% for each 1% increase in CF. Just (1982) found a 3.5% decrease in digestibility of energy when he investigated the influence of CF from cereals, and found also a 0.7% depression in the utilization of ME.

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F.P. LEKULE ET AL.

TABLE 2 Digestibility of n u t r i e n t s (To) a n d c o n t e n t of metabolizable energy Dry matter

No.

Feedstuff

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46.

Maize 87 Maize 86 Maize 91 Maize 89 Maize 92 Maize 87 Maize 88 Maize meal 95 Maize meal 95 Maize meal 95 Maize bran 62 Maize bran 67 Maize h o m i n y feed 85 Maize h o m i n y feed 81 Maize h o m i n y feed 84 Maize h o m i n y feed 79 Maize h o m i n y feed 80 Maize-gluten meal 92 Maize-gluten meal 92 Maize-gluten meal 89 Maize-gluten feed 65 Maize-gluten feed 66 Maize-gluten feed 63 Maize germ 74 Maize germ 71 Maize germ 70 Maize starch 96 Maize starch 97 Maize starch 97 Cassava meal 84 Cassava meal 85 Cassava meal 82 Cassava meal 86 Cassava meal 87 W h e a t bran 65 W h e a t bran 64 W h e a t bran 66 W h e a t bran 69 W h e a t bran 70 W h e a t bran 53 Wheatbran 64 W h e a t middlings 77 W h e a t middlings 88 Soya-bean meal 83 Soya-bean meal 84 Soya-bean meal 86

Organic matter

Crude protein

Crude fat

Crude fibre

NFE

Energy

Metabolizable energy ( M J kg -1 D M )

89 88 92 91 92 89 89 97 96 97 66 68 88 82 86 82 82 94 94 92 67 68 66 77 75 73 98 98 99 89 91 89 92 91 68 67 69 71 73 54 66 80 90 89 88 89

74 77 83 82 85 79 79 91 83 89 35 56 73 70 72 67 79 95 93 95 68 68 70 79 76 74 49 66 61 52 49 54 32 54 71 67 67 62 67 66 72 76 79 86 85 85

54 63 66 64 77 61 62 61 55 74 66 66 59 82 85 76 84 73 76 69 65 49 66 79 72 56 27 60 61 26 30 15 26 26 36 33 53 53 59 36 38 64 58 25 54 53

55 51 40 51 32 55 40 98 46 66 33 39 60 40 38 32 44 42 59 - 11 41 26 31 54 50 42 70 --38 52 40 53 42 9 12 20 24 26 17 9 26 30 67 79 85

94 93 96 95 95 93 94 99 99 99 75 74 94 86 90 87 84 97 99 91 71 73 69 78 79 82 99 99 100 95 97 96 97 97 76 78 78 81 81 64 74 87 94 97 94 97

86 87 90 89 91 87 87 96 95 97 65 67 85 82 85 80 82 94 93 92 67 67 66 78 75 69 97 97 99 86 88 86 90 90 65 64 66 68 71 54 64 78 88 86 87 87

15.89 15.75 16.64 16.31 16.92 15.86 16.40 17.36 17.42 17.31 12.90 13.04 16.40 15.69 16.07 15.49 17.09 19.65 19.99 19.38 12.14 12.32 12.21 17.08 16.70 14.60 16.65 16.93 17.60 14.24 14.24 14.24 14.32 14.32 11.94 11.85 12.35 12.,16 13.32 10.08 11.75 14.38 15.87 15.12 15.60 15.69

NUTRITIVE VALUEOF TROPICALFEEDSTUFFSFOR PIGS

97

TABLE 2 (continued) No.

Feedstuff

Dry matter

Organic Crude Crude matter protein fat

47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58. 59. 60. 61. 62. 63. 64. 65. 66. 67. 68. 69. 70.

Soya-bean meal Soya-bean meal Soya-bean meal Sunflower cake Sunflower cake Sunflower cake Sunflower cake Coconut cake Coconut cake Coconut cake Cottonseed cake Cottonseedcake Cottonseed cake Cottonseed cake Cottonseed cake Palm cake Palm cake Sorghum Sorghum Sorghum Dehulled rice Dehulled rice Dehulled rice Dehulled rice

82 83 80 63 58 48 54 76 71 70 56 56 61 57 53 61 67 88 87 89 96 96 96 95

85 86 82 66 59 50 55 78 73 71 58 59 64 59 55 63 68 90 89 91 97 98 98 97

85 85 83 78 81 70 75 68 57 56 73 68 78 76 68 48 58 71 69 76 84 89 82 86

49 51 46 63 62 70 87 75 75 73 70 82 70 95 50 78 74 50 51 53 44 55 58 64

Crude fibre

NFE

48 63 72 28 17 21 13 73 67 65 28 31 16 8 16 35 37 64 67 70 90 95 ---

91 92 88 72 65 55 66 84 81 80 53 57 57 46 56 76 81 96 95 96 99 99 99 99

Energy Metabolizable energy (MJ kg - 1 D M ) 83 85 81 64 60 49 56 75 70 60 59 60 64 64 56 61 66 87 86 88 96 97 97 96

14.94 15.27 14.89 12.17 11.17 9.00 10.45 13.88 13.20 13.95 10.85 11.33 11.33 12.14 10.00 11.95 13.55 15.72 15.49 16.35 17.34 16.81 17.05 17.11

TABLE 3 Effect of toasting on the digestibility and metabolizable energy content of soya-bean meal Toasting 1 Digestibility (%) time (min) Protein Fat Crude fibre Soya-bean Soya-bean Soya-bean Soya-bean

meal 2, not toasted meal, lightly toasted meal, heavily toasted meal, n o r m a l t o a s t e d

0 5 25 10

68 84 83 85

26 50 50 53

73 68 76 85

NFE

Energy

ME (MJ kg -~ DM)

95 96 93 96

75 85 84 87

13.22 15.19 15.18 15.69

~Toasting 102°C. 2For chemical composition, see Table 1, no. 46.

Energy content (DE, ME or net energy) is the major determinant of the nutritive value of a feedstuff and its assessment is therefore of great importance for diet formulation. Average values of the energy content of individual

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F.P. LEKULEET AL.

TABLE 4 Correlations (r) between chemical components, digestibility (DC) of dry matter and energy, and content of metabolizable energy (ME) in all feedstuffs (n = 70)

Crude fat Crude fibre Soluble carbohydrate DC dry matter DC energy ME

Crude protein

Crude fat

Crude fibre

Soluble carbohydrate

DC dry matter

DC energy

0.04 0.37 -0.76 -0.30 -0.26 -0.11

0.16 -0.38 -0.33 -0.33 0.00

-0.76 -0.86 -0.86 -0.82

0.77 0.76 0.57

0.99 0.91

0.91

feedstuffs can be obtained from the literature but, as shown in Tables 2 and 3, the chemical composition and therefore the energy content can vary considerably within the same feedstuff. Naturally, the best estimates are achieved by performing digestibility experiments but this is only possible, in the best of circumstances, with a very limited number of samples. The relationship between M E and DE in the data presented here was found to be: M E (MJ kg - 1 D M ) = 0 . 0 8 + 0 . 9 6 D E (MJ kg - 1 D M )

(R2=0.96, RSD = 0.47, CV=3.2)

(1)

The residual standard deviation (RSD) was 0.47 MJ or expressed relative to the average value as coefficient of variation (CV) 3.2%. The relation between M E and DE is very close and of the same magnitude as that found by Just (1982). From the official Danish values of ME (Cirkul~ere fra Statens Foderstofkontrol, 1987), the following equation was found: Measured ME (MJ kg -1 DM) =0.93+0.95Table M E (MJ kg -1 DM), (R2=0.88, RSD =0.85, CV=5.8)

(2)

Because of the above-mentioned variation in chemical composition and consequent variation in digestibility, Eqn. 2 is less accurate than Eqn. 1. An alternative approach emerges from analysis of the pooled data presented here. Of all the different combinations of equations, only a few, considered to be of practical interest, are presented. The digestibility coefficient (DC) of energy is closely related to that of dry matter (Table 2). For all feeds, the relationship can be expressed as: DC energy = 3.58+ 0.97 DC D M (R 2=0.99, RSD = 1.62, C V = 2.1 )

(3)

This finding is of practical importance, especially in the developing countries as determination of D M in feed and faeces is simpler than determination of gross energy values.

NUTRITIVE VALUE OF TROPICAL FEEDSTUFES FOR PIGS

99

Digested dry matter (DDM) is, as shown in Eqn. 4, not as good a predictor of M E as DE as would be expected from the close relationship between the digestibility of energy and DM (Eqn. 3): M E (MJ kg - 1 D M ) =2.01+0.016 D D M (g kg - 1 D M )

(R 2= 0.83,RSD = 1.03, CV = 7.0 )

(4)

The explanation is the variation in the chemical composition of digested dry matter {protein, fat or carbohydrate ). Inclusion of the variable crude fat (EE) in the equation improved the prediction considerably: M E (MJ kg -~ DM) = -0.45+O.O18DDM(g kg -~ DM)

+ 0.016EE (g kg -1 DM) (R2 =0.93, RSD =0.68, CV=4.6)

(5)

When using Eqn. 5, it is necessary to determine dry matter digestibility and to analyse the feedstuff for crude fat. Using table values of gross energy (TGE), to give an indication of gross energy concentration in the feedstuff, gives an equation just as good as using crude fat analysis M E (MJ kg -1 DM) = 1.06+ 0.91TGE×DC D M

(R 2= 0.94,RSD = 0.60, CV = 4.1 )

(6)

However, in most cases, digestibility values will not be available, and the ME content must be predicted from the chemical composition of the feedstuffs. Among the chemical components, CF was shown to have the highest correlation to the ME content (Table 4) and the relationship is shown in Eqn. 7: M E (MJ k g - ' D M ) = 1 6 . 8 1 - 0 . 0 3 1 C F (g kg -~ DM)

(R2= 0.68,RSD = 1.40, CV=9.5)

(7)

The high correlation of fibre content to DE or M E has been shown by Just et al. (1984), Fern~indez and Jorgensen (1986) and Morgan et al. (1987), among others. They also found that the best equations with two variables all included an estimate of fibre content, either crude fibre or neutral detergent fibre, and either gross energy or crude fat. In these data the best variables were found to be CF and crude protein (CP): M E (MJ kg -1 DM) =16.34-0.034CF (g k g - ' DM) +0.003CP (g kg -~ DM) (R2=0.73, RSD = 1.30, CV=8.9) (8)

Analysis of NDF was performed only in 49 samples as shown in Table 1. A prediction equation with these samples alone indicated that CF was slightly better as a predictor of M E than was NDF, which is in accordance with the results of Fern~indez and Jorgensen (1986). As a whole, the question of whether CF or N D F is the better indicator of M E is a matter of controversy and the reported results are conflicting in this respect (Just et al., 1984).

100

F.P. LEKULEETAL.

T h e best t h r e e - v a r i a b l e e q u a t i o n c o n t a i n e d drate ( S C ) :

CP, EE a n d soluble c a r b o h y -

ME ( M J kg -1 D M ) =3.36+0.016CP (g kg -1 D M ) + 0 . 0 2 9 E E (g kg -1 D M ) + 0 . 0 1 3 S C (g k g - 1 D M ) ( R 2 = 0.83, R S D = 1.04, C V - - 7.1)

(9)

I n c l u s i o n of up to four c h e m i c a l c o m p o n e n t s (CP, EE, CF a n d SC) resulted in an e q u a t i o n w h i c h was still n o t b e t t e r t h a n u s i n g table values as s h o w n in Eqn. 2. N o n e of t h e c h e m i c a l c o m p o n e n t s or c o m b i n a t i o n s used in this investigation were able to give a b e t t e r e s t i m a t i o n of the a m o u n t of M E t h a n t h e use of table values. E q u a t i o n 6 emphasizes the i m p o r t a n c e of inclusion of digestibility data. W h e n digestibility o f d r y m a t t e r is included, it will suffice to achieve a fairly a c c u r a t e a s s e s s m e n t of M E c o n t e n t .

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