Abdel Malik, A.M.(1) Thomson, E.F. Ahmed F.A. (2) and
Tambal A.A. (1)
International Centre for Agricultural Research in the
Dry Areas (ICARDA), Aleppo, Syria.
ABSTRACT
Two varieties of wheat straw mainly Hourani (H) and Sham 3 (S3) produced in years 1988 (Y1) and 1989 (Y2), were compared in terms of voluntary feed intake, digestibility and passage rate of their components in four mature Awassi male sheep for four periods in a Latin Square design. The results showed that the mean intakes of wheat straw were 71.5 for Hourani and 68.6 g/kg w 0‘75 for Sham 3 and 59.2 for year 1988 and 80.9 g/kg w 0‘75 for the year 1989. However, the intake of H2 was significantly (P< 0.05) higher than that of the other three treatments. There was no significant difference in dry matter digestibility between varieties, but both were increased with the supplementation of soybean meal. There was no significant difference in the passage rate between straw varieties and years, in experiment one.
Four varieties of barley straw (Arabic Abied, Er/Apam, C63 and Beecher) produced in two years (1988 and 1989) were compared for differences in voluntary feed intake, digestibility and passage rate of their components using two sets of Latin Square design with four Awassi male sheep for four periods. The results showed that the mean intakes of barley straw were 57.9, 56.4, 56.8 and 51.9 g/kg w 0‘75 for the four varieties Arabic Abied, Er/Apam, C63 and Beecher respectively and 28.1 and 82.4 g/kg w 0‘75 for the two years 1988 and 1989.
There was a little variation in the mean dry matter digestibility of the straws in the different treatments. There was no significant difference in passage rate between straw varieties and years.
Present address:
- Abnaee Est. for Agric. Trading Investment, Saudi Arabia.
- Animal Resources Research Corporation, P.O. Box 610, Khartoum, Sudan.
INTRODUCTION
Wheat is widely grown around the world. The straw, which is a residue of the crop, is an important feed for small ruminants, especially sheep. Throughout the world there has been a great deal of interest in increasing the use of cereal straw as feed for ruminant animals (Orr et al., 1985). Straw and other fibrous by products, which can be used as feed, are highly variable in nutritive value (Nicholson, 1984). Very small amount of the straw, of the nearly 230 million ha of wheat grown annually around the world, is used for animal production (Lesoing, et al., 1980).
Barley straw in the dry areas of West Asia is an important crop for sheep diets (Thomson, 1987). The feeding value of some varieties of wheat straw could be as high as those of some varieties of barley straw (Kernan et al., 1979). The main agricultural crop residues of the world are wheat, barley, oats, rye, rice and other fibrous by products (Theander and Aman 1984). White et a/.,1981 found that straw from small grains could be an important source of feed for ruminant maintenance if its nutritive quality could be improved.
The experiments reported here were carried out to evaluate the quality of wheat straw and barley straw and to determine its voluntary intake, digestibility and passage rate.
MATERIAL AND METHODS
Animals:
In Experiment 1, four mature male Awassi sheep were used. The average liveweight of the sheep was 53 kg.
In Experiment 2, eight mature male Awassi sheep were used. The average liveweight of the sheep was 55 kg.
Diets:
In experiment 1, straw from two varieties of wheat, namely Hourani (H) and Sham 3 (S3), harvested from the experimental plots of the ICARDA, for the years 1988 (Y1) and 1989 (Y2) was used. In experiment 2, straw from four varieties of barley, namely Arabic Abied (AA), ER/Apam (ER), C63 and Beecher (Be) harvested from the experimental plots of the ICARDA, for the years 1988 (Y1) and 1989 (Y2) was used. The straw was weed free and was groUnd mechanically through a screen to 2mm lengths before feeding to sheep.
Feeding and Management:
The animals were housed in individual cages. They were offered ad libitum chopped wheat straw in experiment 1 and barley straw in experiment 2. The straw was provided in equal amounts twice daily in the morning and afternoon. A mineral-vitamin mix was given at the rate of 20 gm/day/sheep. The sheep were weighed three times, at the start of adaptation period, before and after collection, for each feed. Returned feed and faeces were weighed for the last 7 days for each period and about 5% of the samples in experiment 1 and 10% of the samples in experiment 2 were taken for each day during the collection period. For each period, before collection, each sheep was given straw treated by chromium (20 gm) mixed with soybean meal on the first day only. Soybean meal supplement was given everyday before straw was offered and its amount depends on intake. Faeces were collected every 12 hours, at 08:00 a.m. and 08:00 p.m. for each sheep, unti1168 hours for determination of passage rate. Determination of digestibility and passage rate was measured during the last 7 days for each 28 days experimental period in experiment 2. Determination of digestibility was done indirectly by infusion of wheat straw in chromium in experiment 1 and barley straw in chromium in experiment 2. Temperature in the digestibility room was recorded daily, The amount of straw to be mixed with each diet was determined daily depending on i_ntake of the previous day and was calculated as follows:
If the returned feed was less than 5% in experiment 1 and 10% in experiment 2 of the amount offered, then 100 grams extra feed was added; if the returned feed was more than 10% in experiment 1 and 20% in experiment 2 of the amount offered, then the feed was reduced by 100 grams. If the returned feed was between 5-10% in experiment 1 and between 10-20% in experiment 2 of the amount offered, it was left unchanged. Soybean meal supplement was added to each diet to adjust the crude protein level to 7% in experiment 1. In experiment 2 there was no supplementation. Experiment 1 lasted 24 days with an adaptation period of 17 days while experiment 2 lasted 28 days with a preliminary period of 21 days.
Passage Rate Studies:
The procedure described by Uden et al., (1980) was used. Chemical Analysis:
Each sample of feed, feed refusals and faeces was dried in forced draught oven at 105 °C to constant weight for 24 hours. Then it was ground through a 2mm screen before analysis of Ash, ADF, NDF, CP,
IVDMD and IVOMD. The chemical method used for analysis has been described by Williams et al., (1988).
Statistical Analysis:
The design used was 4 x 4 Latin Square in experiment 1 and two sets of Latin Square designs in experiment 2. The data were subjected to GENSTAT statistical analysis of variance (Lawes Agricultural Trust, 1987).
RESULTS
The chemical composition of the four diets of wheat straw is shown in Table (1). The effect of the year on chemical composition of both varieties was significant (P< 0.05).
Table 1. Mean value (%) of the dry matter and chemical composition (%DM) of wheat straw used in experiment 1 as influenced by varieties and years.
Chemical composition (%) on dry matter basis
| Diets | DM(%) | CP | OM | ADF | NDF | Ash |
| Hyl | 93.5 | 1.5 | 91.5 | 48.8 | 82.4 | 8.5 |
| Hy2 | 92.6 | 4.9 | 90.4 | 35.9 | 72.1 | 9.6 |
| S3y1 | 93.3 | 1.8 | 91.0 | 48.7 | 83.3 | 9.0 |
| S3y2 | 92.6 | 5.5 | 90.1 | 32.6 | 70.1 | 9.9 |
| Means | 93.0 | 9.2 | 90.8 | 41.51 | 76.98 | 3.42 |
| S.E. | 0.147 | 0.272 | 0.273 | 0.806 | 0.709 | 0.217 |
| Soybean meal | 90.6 | 7.1 | 92.92 | 8.52 | 12.80 | 53.09 |
S.E. = Standard error of the mean.
Table (2) shows that in vitro dry matter digestibility for wheat varieties by years were 35.8, 46.8, 36.5 and 49.0% for (Hyl, Hy2, S3y1 and S3y2), respectively. There was a significant (P< 0.01) difference between the years, but the digestibility of the two varieties did not differ. The in vitro organic matter digestibility was significantly affected (P< 0.01) for varieties by years for all treatments.
Table 2. Mean value (%) of the dry matter digestibility (DMD) and organic matter digestibility (OMD) of wheat straw used in experiment 1.
| 1 (1988) | 35.8 36.5 | .36:1a | 1 (1988) | 29.0 30.9 | 29.9a |
| 2 (1989) | 46.8 49.0 | 47.9 b | 2 (1989) | 40.2 44.0 | 42.1″ |
| S.E. m 0.564 | S.E. m 0.721 | ||||
| Mean | 41.3a 42.8 a | 42.0 | Mean | 34.6a 37.4a | 36.0 |
Means in the same column and row with different superscripts are significantly different (P< 0.01).
Table (3) shows the mean changes in the intake (g/kg w 0.75) of the sheep during the experimental period. During the feeding period, the mean intakes of wheat straw were 71.5 and 68.6 for varieties Hourani and Sham 3 and 59.2 and 80.9 for the year 1988 and 1989. There was no significant differenCe between the two varieties in feed intake, but there was a significant difference (P< 0.05) between the years. The effect of the year on both varieties was significantly (P< 0.05) different, for all treatments. The intake of Hy2 was significantly (P< 0.05) higher than that of the other three treatments. The overall mean values for these intakes (g/kg w 0.75) are presented in table (3).
Table 3. Means intakes (g/kg w 0.75) of wheat straw by sheep for different varieties and years.
Intake Mean
Year S3
| 1 (1988) | 55.9 | 62.6 | 59.2a |
| 2 (1989) | 87.2 | 74.5 | 80.9″ |
| Mean | 71.5′ | 68.6a | 70.0 |
Means in the same column and row with different superscripts are significantly different (P< 0.05).
The apparent dry matter digestibilities of two varieties of wheat straw are given in table (4). There were no significant differences between straw varieties, but both of them were improved with supplementation of the soybean meal. The apparent digestibility of the second year was higher than the first year for both varieties. The maximum dry matter digestibility was 79.9% for variety S3y2 and the minimum was 74.0% for variety Hyl. There were no significant differences between treatments and there was no variation in the mean apparent dry matter digestibility by sheep on each treatment.
Table 4. Mean values (%) of dry matter digestibilities by sheep of
wheat straw varieties for different periods and years.
Period
| Diets | 1 | 2 | 3 | 4 | Mean |
| Hyl | 74.1 | 74.7 | 74.4 | 72.6 | 74.0′ |
| Hy2 | 77.5 | 78.5 | 78.2 | 79.0 | 78.8a |
| S3y1 | 78.0 | 75.2 | 74.2 | 75.6 | 75.8a |
| S3y2 | 77.4 | 79.2 | 81.4 | 81.6 | 79.9′ |
Means in the same column with the same superscripts are not significantly different (P< 0.05).
Table (5) shows passage rate of wheat straw during one period analysis. The concentration of chromium in the diet (Cr/PPM) was maximum in Hyl with maximum Cr excreted, however Hy2 was the minimum Cr/PPM. The maximum passage rate was 4.0% h. for Hy2 and the minimum was 1.8% h. for variety S3 y2. The concentration of Cr/PPM was observed for four treatments during one experimental period only, where Cr/PPM increased in all sheep until 48 hours and became maximum and then decreased gradually until 168 hours. The concentration of Cr/PPM was observed to be zero for all till 12 hours for each treatment, except treatment four (S3y2) which was 0.1 at 12 hours.
Generally, there was no significant difference .in the passage rate between straw varieties and years.
| Table 5. | Passage rate of wheat straw through the digestive tract of sheep. | ||
| Diets | Cr/PPM | Rate of passage | Excreted mg |
| % hour | |||
| Hyl | 5.0 | 2.5 | 1164.5 |
| Hy2 | 2.7 | 4.0 | 1139.8 |
| S3y1 | 3.8 | 3.2 | 1017.6 |
| S3y2 | 2.8 | 1.8 | 784.6 |
In experiment 2, the chemical composition of the eight diets of barley straw is shown in table (6). The effects of the year on chemical composition of four varieties were significant (P< 0.05).
Table 6. Mean value (%) of the dry matter and chemical composition of barley straw used in experiment 2 as influenced by varieties and years.
Chemical composition (%) on dry matter basis
| Diets | DM (%) | CP | OM | ADF | NDF | Ash |
| AAY1 | 93.7 | 1.9 | 89.7 | 51.4 | 84.8 | 10.3 |
| AYY2 | 92.8 | 6.4 | 89.9 | 30.0 | 93.9 | 10.1 |
| ERY1 | 93.6 | 2.0 | 90.3 | 52.4 | 85.5 | 09.7 |
| ERY2 | 93.2 | 5.4 | 90.0 | 34.1 | 71.7 | 10.0 |
| C63Y1 | 93.2 | 2.1 | 91.7 | 51.6 | 88.9 | 08.3 |
| C63Y2 | 93.0 | 6.7 | 89.9 | 34.9 | 70.0 | 10.1 |
| BEY1 | 94.0 | 1.6 | 91.2 | 53.5 | 86.1 | 08.8 |
| BEY2 | 93.4 | 4.4 | 90.2 | 39.0 | 77.0 | 09.8 |
| Mean | 93.4 | 3.8 | 90.4 | 43.4 | 79.7 | 09.6 |
Table (7) shows that the in vitro dry matter digestibility (IVDMD) for the four varieties by years were 34.0, 33.6, 34.2, 47.6, 45.3, 47.7 and 40.5% for AAY1, Eryl, C63y1, Beyl, AAY2, C63y2 and Bey2, respectively. There was a significant (P< 0.01) difference between the years, but the digestibility of the four varieties did not differ. The in vitro organic matter digestibility (IVOMD) the in vitro organic matter digestibility (IVOMD) followed the same trend. During the feeding period, the mean intake of barley straw as shown in table (8) were 57.9, 56.4, 54.8 and 51.9 for varieties AA, ER, C63 and Be,
respectively and 28.1 and 83.4 for year 1988 and 1989, respectively. There was no significant difference between the four varieties in feed intake, but there was a significant difference (P< 0.05) between the years. The effect of the year on four varieties was significant differences (P< 0.05) for all treatments. The intake of C63 was significantly (P< 0.05) higher than that of the other seven treatments in the second year.
Table 7. Mean value (%) of the IVDMD and IVOMD of barley straw Used in experiment 2 as influenced by varieties and years.
IVDMD (%)
| Year | AA | ER C63 | Be | Mean S.E. 0.950 |
| 1 (1988) 2 (1989) | 34.0 47.6 | 33.6 34.0 45.3 47.7 | 33.2 40.5 | 33.8a 45.3″ |
| S.E. m – 1.343 | ||||
| Mean | 40.8 | 49.4 41.0 | 36.9′ | 39.5 |
| Year | AA | IVOMD (%) ER C63 | Be | Mean S.E. 1.027 |
| 1 (1988) 2 (1989) | 28.7 42.5 | 27.7 28.3 39.4 42.0 | 27.0 35.5 | 27.9a 39.9″ |
| S.E. m- 1.452 | ||||
| Mean | 35.6a | 33.6a 35.2′ | 31.3a | 33.9 |
Means in the same column and row with different superscripts are significantly different (P< 0.01).
The overall mean values for these intakes (g/kg w 0.75) are presented in table (8).
Table 8. Mean intakes (g/kg w 0.75) of barley straw by sheep for Different varieties and in different years.
Intake
| Year | AA | ER C63 | Be | Mean S.E. m 2.08 |
| 1 (1988) 2 (1989) | 35.8 80.0 | 30.9 22.4 81.8 91.3 | 23.6 80.3 | 28.1a 83.4b |
| S.E. m — 2.08 | ||||
| Mean | 57.9a | 56.4a 56.8a | 51.9a | 55.7 |
Means in the same column and row with different superscripts are significantly different (P< 0.05).
The apparent dry matter digestibilities of the four varieties of barley straw are given in table (9). There were no significant differences between straw varieties, but all of them were better in the first year. The apparent digestibility of the first year was higher than the second year. The maximum dry matter digestibility was 77.7% for variety Beyl and the minimum was 73.1% for variety AAY2. There was no significant difference in apparent dry matter digestibility for all treatments. There was no variation in the mean apparent dry matter digestibility of sheep on each treatment. Beyl has a missing value in 3rd period.
Table 9. Apparent dry matter digestibility (%) of barley straw by sheep.
Period
| Diets | 1 | 2 | 3 | 4 | Mean |
| AAY1 | 71.4 | 78.7 | 67.2 | 77.3 | 73.7a |
| AAY2 | 78.1 | 70.5 | 77.1 | 66.5 | 73.1′ |
| ERY1 | 77.1 | 75.5 | 75.8 | 71.5 | 75.0a |
| ERY2 | 70.0 | 79.7 | 70.5 | 78.8 | 74.8a |
| C63Y1 | 79.8 | 69.0 | 78.2 | 71.4 | 74.6a |
| C63Y2 | 71.3 | 78.5 | 66.2 | 80.2 | 74.1′ |
| BEY1 | 71.3 | 80.3 | 80.0 | 77.1′ | |
| BEY2 | 80.6 | 70.9 | 78.0 | 68.9 | 74.6a |
| Means in the same column with significantly different (P< 0.05). | the same superscripts are not |
Table (10) shows the passage rate of barley straw during one period. The concentration of chromium in the diet (Cr/PPM) was maximum in C63Y1 with minimum Cr excreted. The maximum passage rate was 4.31% h. for C63Y1 and concentrations of Cr/PPM were only observed for eight treatments during one experimental period, where the maximum concentrate of 48, 36, 60, 48, 72, 60, 36 and 36 for varieties C63Y2, AAY1, BeY1, ERY2, C63Y1, ERY1, BeY2 and AAY2, respectively. Also Cr/PPM increased at the beginning, then decreased gradually until 168 hours.
Generally, there was no significant difference in the passage rate between straw varieties and years.
| Table 10. | Passage rate of barley straw through the digestive tract of sheep. | ||
| Diets | Cr/PPM | Rate of passage % hour | Mean |
| AAY1 | 3.96 | 1.25 | 880.7 |
| AAY2 | 2.74 | 2.87 | 757.2 |
| ERY1 | 4.02 | 1.69 | 774.4 |
| ERY2 | 2.72 | 2.77 | 946.8 |
| C63Y1 | 4.19 | 4.31 | 448.9 |
| C63Y2 | 3.59 | 3.27 | 1267.1 |
| BEY1 | 3.22 | 2.03 | 764.5 |
| BEY2 | 2.80 | 2.71 | 810.4 |
DISCUSSION
In experiment 1 the chemical composition of the same variety of wheat straw was affected by different years. These differences were highly significant. This might be attributed to the relationship between crude protein and rainfall. Whereas, crude protein content was high when rainfall decreased, but it •was low with increase in rainfall. This finding agrees with Rihawi and Treacher (1990) who reported that wide variations in rainfall from year to year have major effects not only on grain and straw yield but also on the yield and composition of the stubble remaining after harvest.
A highly significant difference in vitro dry matter digestibility was observed among varieties by years. This could be due to the chemical composition and nutritive value of straw. The finding also agrees with White et al., (1981) who reported that digestibility differences between cultivators and cultivars by year interaction were significant. The in vitro organic matter digestibility was significantly affected by variety and by year for all treatments. This appeared to be due to the proportions of wheat straw. This agrees with the findings of Kernan et al., (1979) who stated that wheat straws had significantly higher digestibility of organic matter levels than all the remaining cultivators studied.
Feed intake difference was not significant between the two varieties, but it was significantly different between years. This was explained by the protein content of straw. Bassette (1989) showed that among the variance components, years contributed most to total variance for protein percent.
Soybean meal supplementation had an apparent increase on dry matter digestibility, but this increase was not significant. This might be attributed to the level of soybean meal supplementation and also on the isonitrogenous level of the diets. This agrees with the findings of. A 1 Saghier and Compling (1991) who have recently reported that there was a tendency for digestibility of straw to increase when urea or soybean meal was given, but the effect was not significant. Also, Cecava et al., (1990) concluded that true digestibility was higher when sheep were fed soybean and other protein sources. There was an increase in passage rate of the straw varieties of the consecutive years, but this was not significant. This was probably due to a lower mean retention time in the rumen, which agrees with the findings of Bines and Davey (1970) who found that the rates of passage varied greatly between treatment different chopped barley straw (0.0, 20, 40 and 60) in passage rate through the entire alimentary tract.
In experiment 2 the chemical composition of the same variety of barley straw was improved in the second year, but the improvement was not significant. This could be due to the nutritive value of straw, because different varieties of different years did differ in crude protein.
This finding agrees with a report by Doyle and Panday (1990) who reported that straws differ in chemical composition and physical characteristics. Erickson et al., (1982) showed that the quality component of barley straw was influenced by the environment and year.
The interactions between varieties by years in in vitro dry matter digestibility were significantly higher for second year than first year. This might be due to the quality components of straws. This agrees to the findings of Rao (1989) who reported that cultivars did differ in crude protein and in vitro dry matter digestibility significantly by year cultivars interaction.
The in vitro organic matter digestibility was significantly affected by varieties with years for all treatments. This might be attributed to the chemical composition of straw. Pearce 2t al., (1979) showed that there was a wide variability in chemical composition and digestibility of cereal straws.
The voluntary feed intake of the barley straw was significantly different between varieties by years. This could not be fully explained, but it could be partly due to palatability. The findings of Rohweder et al., (1978) showed that neutral detergent fibre is a chemical array of choice to estimate intake, also dry matter intake (g/kg w 0.75) is inversely related to the neutral detergent fibre concentration, i.e. dry matter intake decreased as neutral detergent fibre increases.
The passage rate of the straw varieties was generally increased in the second year, but this was not significant. This was probably due to lower mean retention time in the rumen. Ganev et al., (1979) showed that the low rate passage of barley diet, during restricted feeding, results in appreciable amount of the supplements remaining in the rumens till 24 hours after feeding.
The interaction in apparent dry matter digestibility of barley straw between varieties by years was increased, but this increase was not significant. This could be due to the nitrogen content of the straws. White et al., (1981) showed that digestibility differences between varieties and cultivars by years interaction were significant. Also Erickson et al., (1982) reported that the straw quality components of barley straw components were influenced by environment and year.
CONCLUSION
The results in these experiments showed that the highest differences found in digestibility of straw varieties by years interaction, is attributed mainly to the environmental conditions (rainfall) that affected the nutritive value of crude fiber and crude protein.
Amongst straw varieties, barley straw was found to be more digestible than wheat straw. However, additional protein supplement i.e. soybean meal enhanced the feed intake by sheep.
ACKNOWLEDGEMENT
The senior author, A.A. Abdel Malik, was on a research scholarship gratefully granted by ICARCA. We acknowledge with thanks the assistance offered by the research staff, technicians and labourers during this period. The work is part of a thesis submitted by the senior author to the University of Gezira, Sudan, for the Degree of Ph.D.
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Authors:
Atif Mohamed Abdel Malik Euan F. Thomson
Faisal Awad Ahmed
Abdel Aziz Ahmed Tambal.
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