Associative effects of supplementing barley straw
diets with alfalfa hay on rumen environment and
nutrient intake and digestibility for ewes
S.G. Haddad
*Department of Animal Production, Faculty of Agriculture, Jordan University of Science and Technology, P.O. Box 3030, Irbid 22110, Jordan
Received 18 February 2000; received in revised form 5 July 2000; accepted 16 August 2000
Abstract
The objectives of these experiments were to study the positive associative effects of supplementing barley straw-based diets with different levels of alfalfa hay on nutrient intake, rumen environment, and nutrient digestibility and to evaluate the minimal amount of alfalfa hay needed to produce such an effect
in ewes. In experiment one, 15 Awassi ewes (®ve ruminally ®stulated; body weight54 kg1:5)
were fed ®ve barley straw-based diets in a 55 Latin square design with 3-week periods. Dietary
treatments were as follows: diet 1, barley straw (no supplement), diet 2, barley straw supplemented with 1% urea (dry matter basis), diets 3, 4, and 5 barley straw supplemented with 150, 300, and 450 g of alfalfa hay, respectively. In experiment 2, the same experimental diets were fed to 50 ewes (10 ewes/diet) for 50 days in a complete randomized design. In experiment 1, dry matter intake (DMI) was increased (P<0:05) by the addition of alfalfa hay compared with diets that had no alfalfa. Metabolizable energy
intake (MEI) increased linearly (P<0:05) with the increasing amounts of alfalfa hay, being highest
(P<0:05) for diet 5. Diets that contained alfalfa hay had greater (P<0:05) dry matter (DM), organic matter (OM), neutral detergent ®ber (NDF), and crude protein (CP) digestibilities. The extent of barley
straw NDF digestibility was also increased (P<0:05) with the alfalfa addition (67 versus 60.5%).
Rumen ammonia and VFA concentrations were higher (P<0:05) in diets that contained alfalfa,
however, rumen pH was not affected by the diet (avg. 6.64). In experiment 2, the effect of alfalfa hay addition to barley straw-based diets had similar effects on DMI as observed in experiment 1. Straw
intake increased (P<0:05) with the 150 g addition of alfalfa hay compared with unsupplemented diet
(725 versus 650 gÿdper day) with no further improvement with the higher amounts of alfalfa. It seems
that the minimal amount of alfalfa hay needed to produce the positive associative effect on barley straw
is 150 g per day for maintenance diets of ewes.#2000 Elsevier Science B.V. All rights reserved.
Keywords:Straw; Alfalfa; Associative effects
87 (2000) 163±171
*Tel.:962-2-7095111/ext. 22220; fax:962-2-7095123. E-mail address: [email protected] (S.G. Haddad).
1. Introduction
Barley and wheat straws are the two major forage sources for ruminants in Jordan. However, the nutritive value of these crop residues is poor due to their higher concentration of both ®ber and lignin. Furthermore, if nutritive value is de®ned as the product of consumption and digestibility, then the low protein, high cell-wall content and high lignin concentrations of straws have important implications in animal nutrition (Anderson, 1978).
Improving digestibility and intake are the two major factors for improving the nutritive value of straws. Methods for improvements have largely dealt with physical (Welch, 1982), chemical (Haddad et al., 1995, 1998), and manipulation of forages (Klopfenstein et al., 1979). One way for improving straw utilization is to increase microbial activity by providing needed nutrients. Maeng et al. (1976) improved microbial growth rate and cellulose digestion in vitro when low levels of amino acids were added to the media.
Positive associative effects for alfalfa addition to low quality forages were observed on in vitro fermentation (Hunt et al., 1985), dry matter intake and NDF digestibility (Paterson et al., 1982; Brandt and Klopfenstein, 1986a) and animal gain (Brandt and Klopfenstein, 1986b). Similarly, positive associative effects of alfalfa±wheat straw combination diets fed to sheep were observed for NDF intake with no effect on DM and NDF digestibility (Ndlovu and Buchanan-Smith, 1985).
Many of the reported research on alfalfa±straw combination diets have dealt with the associative effects themselves rather than the minimal amount of alfalfa needed for such effects to occur. The objectives of these experiments were to study the associative effects of alfalfa hay addition to barley straw-based diets on rumen environment, DMI, and nutrient digestibility, and to evaluate the minimal amount of alfalfa hay needed to positively improve the utilization of barley straw by ewes.
2. Materials and methods
Barley straw and alfalfa hay used in experiment 1 and 2 were obtained from a local source and chopped using a hammer mill ®tted with a 15 mm screen. The chemical composition and the 48 h in sacco dry matter (DM) and neutral detergent ®ber (NDF) digestibility of the forages is shown in Table 1.
2.1. Experiment 1
Fifteen Awassi ewes (®ve ruminally ®stulated; body weight54 kg1:5) were
Diets were offered once daily. In diets 3, 4, and 5 alfalfa hay was offered prior to straw feeding. No barley straw was offered in these diets before the complete consumption of the hay. Amounts of barley straw offered and refused were recorded daily. Body weight was recorded weekly before feeding. Experimental periods were 21 days in which the last 6 days of each period were used for sample collection.
Forages used were sampled daily during the collection phase of each period. For the digestibility measurements, total fecal collection was carried out for 6 days, and a 10% representative sample was dried for further analysis. Composite samples of the forages and feces were oven-dried (608C), ground through 1 mm screen and ana-lyzed for crude protein (CP) (AOAC, 1984), amylase-modi®ed NDF (Van Soest et al., 1991), acid detergent ®ber (ADF), and permanganate lignin (Robertson and Van Soest, 1981).
Samples of ruminal ¯uid were collected on day 2 of each collection phase at 4 h intervals for 24 h. The pH was determined immediately using a portable pH meter and concentrations of VFA were determined by GLC (Erwin et al., 1961). Ruminal ammonia concentration was determined according to the procedure of Broderick and Kang (1980) using an autoanalyzer. Fractional rate of NDF digestion of wheat straw was measured using the in situ bag technique in which dacron bags containing 2 g of straw were incubated within the rumen of each ewe for 0, 6, 12, 24, 72, and 96 h. Prior to ruminal incubation, dried straw was ground through a 2 mm screen using a Wiley mill. After removal from the rumen and rinsing, all bags were dried at 608C and weighed. Contents were analyzed for ash-free NDF (Van Soest et al., 1991). The kinetics of ruminal NDF digestion and apparent extent of ruminal NDF digestion were calculated as described by Grant (1994).
2.2. Experiment 2
The objective of experiment 2 was to evaluate the effect of the experimental diets on dry matter intake (DMI) and body weight change in a longer-term study. In this experiment, 50 Awassi ewes were fed the same ®ve experimental diets as described earlier (10 ewes per diet) in a complete randomized design. The same experimental
Table 1
Chemical composition and 48 h in sacco digestibility of barley straw and alfalfa hay used in experiments 1 and 2 Barley straw Alfalfa hay
Dry matter (%) 91.5 89.3
Organic matter (% of DM) 89.9 88.5 Crude protein (% of DM) 4.6 17.8 Neutral detergent ®ber (% of DM) 81.1 43.2 Acid detergent ®ber (% of DM) 61.3 21.5 48 h in sacco digestibilitya
Dry matter 0.41 0.66
Neutral detergent fiber 0.43 0.44
approach used in experiment 1 for the determination of DMI and body weight change. The experimental period lasted for 50 days.
2.3. Statistical analysis
Data from experiment 1 were analyzed as a 55 Latin square using the general linear models procedure of SAS (1985). For experiment 2, means for the 50 days period were analyzed as a completely randomized design using the general linear models procedure of SAS (1985). Differences among treatment means, for both experiments, were detected by least signi®cant difference (SAS, 1985). Unless otherwise stated, signi®cance was declared atP<0:05 for both experiments.
3. Results
The chemical composition and the 48 in sacco digestibility of the forages used in both experiments are typical of those found in the Middle East area as shown in Table 1.
In experiment 1, barley straw intake was not affected (P<0:05) by the addition of
urea, however, it was increased (P<0:05) by the supplementation with alfalfa being
highest for the 150 g per day alfalfa diet as shown in Table 2. Dry matter intake increased by the supplementation of alfalfa being highest (P<0:05) for the 450 g per day (1125 g
per day) alfalfa diet compared with the other levels of alfalfa and the straw diets. Crude protein intake increased linearly (P<0:05) with the increasing levels of alfalfa
Table 2
Effect of the diets fed to ewes in experiment 1 on nutrient intake and body weight changea
Dietb
1 2 3 4 5 S.E.
Dry matter intake (g per day)
Straw 595 c 606 c 720 a 690 ab 675 b 35.6
Alfalfa 0 0 150 300 450 ±
Total 595 c 606 c 970 b 1001 b 1125 a 34.3 Organic matter intake (g per day) 535 c 544 c 864 b 892 b 1003 a 27.2 Crude protein intake (g per day) 25.9 d 66.1 c 62.3 c 86.1 b 109.2 a 5.3 Neutral detergent ®ber intake (g per day) 480 c 492 c 649 b 689 ab 740 a 30.1 Acid detergent ®ber intake (g per day) 364 c 371 c 472 b 486 ab 510 a 21.3 MEIc(Mcal per day) 0.89 d 0.90 d 1.37 c 1.63 b 2.01 a 0.1 Weight gain (kg) ÿ0.79 d ÿ0.65 d 0.61 b 0.95 ab 1.15 a 0.1
aMeans within row with different letters differ (P<0:05).
bDiet 1, barley straw (no supplement); diet 2, barley straw supplemented with 1% urea (DM basis); diets 3,
4, and 5 barley straw supplemented with 150, 300, and 450 g of alfalfa hay, respectively.
(109.2, 86.1, 62.3, and 25.9 g per day) in diets 5, 4, 3, and 1, respectively as shown in Table 2.
Metabolizable energy intake (MEI) showed a linear increase (P<0:05) with the
increasing level of alfalfa supplementation. Diet 5 had the highest (P<0:05) MEI
(2.01 Mcal per day) compared with the rest of the other levels of alfalfa (avg. 1.5 Mcal per day) and the unsupplemented diet (0.89 Mcal per day). Ewes fed the straw diet and the urea-supplemented straw diet lost weight (avg. 0.73 kg per experimental period). However, ewes fed the alfalfa supplements gained weight (avg. 0.9 kg per experimental period). The highest (P<0:05) weight gained (1.15 kg per experimental period) was
obtained with the 450 g per day alfalfa diet.
Dry matter digestibility of the diets was improved with the addition of alfalfa, being highest (P<0:05; 57.3%) for the 450 g per day alfalfa diet compared with diets 1 and 2
(avg. 43.1%) as shown in Table 3. The rest of the diets showed intermediate values (avg. 52.5%). Organic matter digestibility showed a similar response (Table 3). Neutral detergent ®ber digestibility was highest (P<0:05) for the diets that contained alfalfa
(avg. 54.7%) compared with the rest of the diets (avg. 49.5%) as shown in Table 3. Apparent CP digestibility increased linearly (P<0:05) with the increasing levels of
alfalfa in the diets, being highest for the 450 kg per day diet (60.7%) compared with the diet 1 (35.6%). The extent of wheat straw digestion was greatest (P<0:05) for the
alfalfa diets (avg. 67.7%) compared with the rest of the diets (avg. 60.6%) as shown in Table 3.
Rumen ammonia concentration increased (P<0:05) with urea and alfalfa
supple-mentation to straw, being highest (P<0:05) with the highest level of alfalfa used as
shown in Table 4. Total rumen VFA concentration increased (P<0:05) with the alfalfa
supplemented diets (avg. 88.9 mmol/l) compared with the rest of the diets (avg.
Table 3
Effect of the diets on total tract nutrient digestibility and digestive kinetics of barley straw ®ber in ewes used in experiment 1a Apparent crude protein 35.6 d 37.8 d 45.6 c 55.3 b 60.7 a 2.1 Digestive kinetics of barley straw Neutral detergent ®ber
Lag (h) 5.2 4.9 3.5 3.7 3.9 1.3
Rate (%/h) 1.65 b 2.05 a 2.17 a 2.20 a 2.18 a 0.4 Extent (%) 60.1 b 61.2 b 67.3 a 67.7 a 68.1 a 0.8
aMeans within row with different letters differ (P<0:05).
bDiet 1, barley straw (no supplement); diet 2, barley straw supplemented with 1% urea (DM basis); diets 3,
59.4 mmol/l; Table 4). Molar proportions of VFA and rumen pH were not affected by the diet as shown in Table 4.
In experiment 2, the effect of alfalfa hay addition to barley straw-based diets had similar effects on DMI, organic matter intake (OMI), crude protein intake (CPI), and neutral detergent ®ber intake (NDFI) as observed in experiment 1. Straw intake increased (P<0:05) with the 150 g addition of alfalfa hay compared with unsupplemented diet
(725 versus 650 gÿd) with no further improvement with the higher amounts of alfalfa as shown in Table 5.
Table 4
Effect of diets fed in experiment 1 on rumen environmenta
Dietb
1 2 3 4 5 S.E.
Ammonia (mg/l) 55 c 91 b 95 b 115 ab 136 a 13.5 Total VFA (mmol/l) 59.8 c 58.8 c 77.3 b 81.1 b 108.2 a 7.6 Molar proportions (%)
Acetate 74.5 72.6 75.3 69.6 66.9 7.5 Propionate 17.5 17.1 16.7 19.5 23.6 4.9 Butyrate 5.8 8.2 6.1 8.2 7.5 1.1
Others 2.2 2.1 1.9 2.7 2.0 0.7
Rumen pH 6.62 6.75 6.66 6.58 6.59 0.9
aMeans within row with different letters differ (P<0:05).
bDiet 1, barley straw (no supplement); diet 2, barley straw supplemented with 1% urea (DM basis); diets 3,
4, and 5 barley straw supplemented with 150, 300, and 450 g of alfalfa hay, respectively.
Table 5
Effect of the diets fed to ewes in experiment 2 on nutrient intake and body weight changea
Dietb
Initial weight (kg) 55.8 55.2 55.3 55.2 54.9 1.2 Final weight (kg) 51.2 d 53.8 c 56.1 b 57.8 ab 58.8 a 1.7 Weight gain (kg) ÿ3.6 e ÿ1.6 d 0.8 c 2.6 b 3.9 a 0.4
aMeans within row with different letters differ (P<0:05).
bDiet 1, barley straw (no supplement); diet 2, barley straw supplemented with 1% urea (DM basis); diets 3,
4, and 5 barley straw supplemented with 150, 300, and 450 g of alfalfa hay, respectively.
4. Discussion
Urea supplementation of straw did not affect intake or nutrient digestibility. The only associative effect of urea supplementation to barely straw was observed for the rate of NDF digestion. However, no overall improvement in ewe performance was observed. This is consistent with the ®ndings of Dias-Da-Silva and Sundstol (1986) who observed no difference in DMI, cellulose, and hemicellulose digestibilities of wheat straw supplemented with urea at feeding time.
In experiment 1, a positive associative effect of alfalfa addition to barley straw-based diet was observed on feed intake. This is consistent with the ®ndings of Hunt et al. (1987) who also observed a linear relationship between level of alfalfa in the diet and DMI and NDFI when similar diets were fed to sheep. The intake of straw was increased with the supplementation of 150 g per day alfalfa; however, no further improvement in straw intake was noted at the higher levels of alfalfa. These ®ndings are consistent with Hunt et al. (1988) who fed steers 100% wheat straw diets supplemented with 0, 25, 50, 75, and 100% alfalfa hay. These researchers observed that the highest straw intake was with the 25% alfalfa diet (lowest level of alfalfa used).
Dry matter and organic matter (OM) digestibilities increased linearly with the increasing levels of alfalfa. This is due to the higher digestibility of alfalfa compared with the straw (66.5 versus 41.3%, 48 h in sacco) as shown in Table 1. As the level of alfalfa increased, the alfalfa portion of the diet increased as well, which would ultimately increase DM and OM digestibility. At the same time, rate and extent of straw NDF digestion was increased with the alfalfa supplementation which would also explain the increase in DM and OM digestibilities. Lag time of barley straw NDF digestion was not affected by the alfalfa supplementation, which is consistent with the ®ndings of Haddad et al. (1998) using wheat straw.
The effect of alfalfa supplementation on rumen function is presented in Table 4. Rumen ammonia was increased with the increasing levels of alfalfa, which is primarily due to the higher CP intake. Total VFA were also higher due to the higher fermentability of the diets that contained alfalfa. Ruminal proportions of VFA and ruminal pH remained unaffected by the diet.
Experiment 2 was conducted to evaluate experiment 1 on a larger number of animals for a longer experimental period. The author felt that the Latin square design does not offer enough time in each period to accurately measure the effect of the experimental diets on DMI and animal performance. The results in experiment 2 were similar to those obtained in experiment 1; however, DMI, OMI and straw intake were higher in experiment 2 compared to experiment 1.
only a small quantity of alfalfa hay is needed to produce a positive associative effect for ewes fed barley straw diets.
5. Conclusion
No positive associative effects were observed for barley straw-based diets when supplemented with urea, however; alfalfa hay did produce such an effect. For ewes fed maintenance diets based primarily on barley straw, 150 g per day alfalfa hay was needed to promote positive associative effects for maximum straw intake.
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