Effect of different levels of berseem (
Trifolium
alexdrinum
) supplementation of wheat straw on some
physical factors regulating intake and digestion
Asit Das
a, G.P. Singh
b,*aICAR Research Complex, Sikkim Centre, Todong 737102 (Sikkim), India bNational Research Centre on Carnel, Jorbeer, Bikaner-334001, India
Received 24 April 1998; received in revised form 23 September 1998; accepted 17 March 1999
Abstract
Four ruminally fistulated cattle of about 31816 kg body weight were randomly distributed into four groups in an experiment based on 44 Latin square design. The four dietary treatments were: wheat straw ad lib without any supplement (I), supplemented with berseem at 15 (II), 30 (III), and 45 (IV) percent level. DMI was 3.95, 5.85, 7.28 and 7.08 kg; digestibility of DM was 39.85, 45.61, 52.97 and 47.52%; rumen content was 55.60, 68.45, 74.18 and 75.93 kg, or 18.09, 22.01, 23.37 and 23.22% of body weight; rumen fluid content was 48.62, 60.39, 65.20 and 68.01 kg; rumen pool size of DM was 6.02, 7.61, 7.92 and 7.66 kg; rumen pool size of particles larger than 1.18 mm (LP) was 2.38, 2.78, 2.80 and 2.55 kg; rumen pool size of particles smaller than 1.15 mm (SP) was 3.64, 4.91, 5.12 and 5.05 kg in Groups I, II, III and IV, respectively. Intake and digestibility increased significantly (p< 0.01), with increased level of berseem up to 30%, beyond which no further improvement was observed. Total rumen contents, rumen fluid content and pool sizes of DM increased significantly (p< 0.5) with berseem supplementation, level of berseem had no significant effect. Pool of LP and SP was similar in all the groups. Maximum rumen content was observed at 9, 9, 6 and 3 h post feeding in Groups I, II, III and IV, respectively. Rate of clearance of LP was 3.71, 6.71, 7.27 and 8.75; SP was 0.46, 0.83, 1.20 and 1.35; and communition rate was 3.45, 5.79, 5.92 and 7.37% hÿ1 in Groups I, II, III and IV, respectively. Rate of clearance of LP and rate of communition were significantly higher (p< 0.01) in berseem supplemented groups. Rate of passage (Kp) was 1.72, 1.88, 2.33 and 2.56% per hour.Kpincreased significantly (p< 0.01) with increased
level of berseem. From the results it is evident that rumen pool size of indigestible component, rather than rumen content, determines the intake. AsKdwas more thanKp, there was an overall
81 (1999) 133±149
*Corresponding author. Tel.: +91-151-523187; fax: +91-151-522183
E-mail address: [email protected] (G.P. Singh)
improvement of digestibility by 14, 33 and 19% in Groups II, III and IV, respectively, compared with Group I.#1999 Elsevier Science B.V. All rights reserved.
Keywords: Level of berseem; Berseem supplementation; Wheat straw; Cattle; Intake; Regulation; Digestion
1. Introduction
Wheat straw forms a major source of ruminant feed in India. Unfortunately, wheat straw is characterised by low intake and digestibility. Supplementation of poor quality roughage, including wheat straw, with green forages has been shown to increase intake (Woodward and Reed, 1995; Reed et al., 1990) or digestibility (Silva and Orskov, 1988; Ash, 1990; Bonsi et al., 1995) or both (Leng, 1990; Bird et al., 1994). However, type of basal diet (Mosi and Butterworth, 1985; Eliott et al., 1984), degradability characteristics of the supplement (Bates et al., 1988), level of supplement (Bonsi et al., 1994) as well as interactions between nutrients in feed ingredients (Brown et al., 1991) are important determinants of response to supplementation. Hence, specific study is required to know the effect of a particular supplement on intake and digestibility of the basal diet concerned.
Berseem (Trifolium alexdrinum) is a green leguminous fodder grown during winter. Berseem contains 15±20% CP and 4.1 kcal/g GE (Chauhan et al., 1980). It is highly palatable, fairly digestible and on sole feeding can support growth rate of 550 g/d (Chauhan et al., 1992) and milk production up to 10 kg/d. Berseem supplementation to wheat straw has been shown to increase in sacco dry matter degradability of wheat straw (Reddy et al., 1991). In practice, farmers in India feed wheat straw and berseem mixed together without considering the ratio. However, detailed information regarding the effect of different levels of berseem supplementation on digestion and intake of straw-based diet is not available. At the same time, prediction of likely effect on intake and digestion will be difficult without a better understanding of the processes, namely, rumenfil (Bosch et al., 1993), particle dynamics (Poppi et al., 1980) and passage rate (Oosting et al., 1993), which regulate intake. Hence, this experiment was undertaken to find out the level of berseem at which intake and digestion is maximum, with a better understanding of the physical factors regulating them.
2. Materials and methods
2.1. Animals and design
Activity Day
Adaptation 1±14
Rumen liquor sampling 15
Intake and digestion 16±22
Dacron bag analysis of feed sample 21±25
Rumen evacuation 26±31
Rumen evacuation on restricted feeding 32±35
Four dietary treatments were wheat straw alone (I), wheat straw supplemented with 15 (II), 30 (III), and 45% (IV) level of berseem. Supplement was offered once daily at 9 a.m. Clean and fresh drinking water was provided ad lib. The amount of supplement to be offered was determined from the record of previous day intake, to keep the level of berseem to the desired experimental level as far as possible.
2.2. Chemical composition of feed
Samples of wheat straw and berseem were taken daily during the last 21 days of each period. They were dried at 50±608C and analysed for dry matter (DM), ash, neutral detergent fibre (NDF), acid detergent fibre (ADF) and total nitrogen (N) content.
2.3. Digestion trial
During each period, a digestion trial of six-day collection (Days 17±22) was conducted to determine the intake and digestibility of diets.
2.4. Rumen evacuation
2.4.1. Rumen evacuation of animals of restricted feeding
During last 4 days of each experimental period, rumen evacuations were done on animals receiving restricted amount of feed. The animals were allowed to eat up to 12:00 hours. Each steer's rumen was evacuated once daily over 4 days, either on 12:00, 18:00 or 24:00 hours. There was a minimum interval of 30 h between emptying from any individual steer to overcome the effect of emptying on the repeatability of measurements. Total rumen contents were removed by hands, weighed, sampled and the remainder returned to the rumen. Two samples of 500 g were taken: the first one for separation into large (>1.18 mm) and small (>0.041 mm, <1.18 mm) particles and subsequent incubation into Dacron bags, and the second sample for analysis of chemical composition. The rate of turnover of large (LP) and small (SP) particles was measured from the logarithmic decline in rumen LP and SP pool.
2.5. Particle dynamics
Separation of rumen content samples was done through standard sieves of 1.18 mm (standard sieve no. 14; American Society of Agricultural Engineers, 1967) and Dacron cloth with a pore size of 0.041 mm. Hence, small particles passing this Dacron cloth were not included in the isolated small particles. Particles retained on sieves (1.18 mm) were referred to as large particles (LP), whereas particles passing through the sieves were considered small particles (SP).
Degradation characteristics of NDF fraction of whole rumen content, isolated SP and LP was measured through nylon bag incubation (Oosting, 1993). About 30 g (fresh) samples of rumen content, SP and LP were incubated in nylon bags (pore size 4141mm) for 6, 12, 24, 48, 72, 96, 120 and 336 h in the rumen of each animal, in duplicate, in another set of 4 animals fed on respective levels of berseem. Residues retained in nylon bags after 336 h incubation was considered to be truly undergradable fraction. After the removal of the bags at the end of each incubation time, the bags were rinsed under tap water till clean water started flowing from the bags. Each bag was dried in hot air oven at 708C. Residues remaining in bags were analysed for NDF.
2.6. Rumen fluid volume and liquid outflow rate
On Day 15 of each period, 30 g PEG-4000 was infused into the rumen and mixed thoroughly. Rumen fluid sample was collected 2, 4, 6, 8, 10, 12, 16 and 20 h after infusion of PEG. The samples were analysed for PEG in a spectrophotometer at 540 mm wavelength. Rumen fluid volume (RFV) and liquid out flow rate (Kl) was measured
according to the method of Hyden (1956).
2.7. Chemical analysis
method of Goering and Van Soest (1970). Hemicellulose was calculated as NDF minus ADF and cellulose as ADF minus acid detergent lignin (ADL).
2.8. Calculation and statistics
2.8.1. Pool size, rate of clearance (Kcl) and rate of passage (Kp)
Total rumen content, pool sizes of DM, NDF, SP, LP, IDM and INDF, rate of clearance (Kcl) and rate of passage were determined from rumen evacuation data, when rumen
evacuation was conducted on animals having free access to feed. Total rumen content was presented as the mean of six observations. Pool size of DM, NDF, SP, LP, IDM and INDF from rumen content and proportion of the respective component in rumen contents during each evacuation; mean value of six observations is presented. Input of DM was determined as mean DMI over 6 days, during which rumen evacuations were conducted. Input of NDF, IDM and INDF was calculated from mean DMI and proportion of the respective component in feeds.
Kcl(%/h) for DM was calculated as the intake of DM (g)/pool of DM in rumen/24 h
(Bosch et al., 1992). Similarly,Kclfor NDF was calculated using the respective values for
NDF. Kp(%/h) for DM and NDF was the reciprocal of mean retention time (MRT) of
IDM and INDF, respectively (Thiogo et al., 1992). MRT (h) for IDM was calculated according to the formula of Minson (1966):
MRT h Average weight of IDM in rumen g
Rate of intake of IDM g=h
Similarly, MRT for NDF was calculated using the respective values for INDF. Rumen fluid volume (RFV) and liquid outflow rate (Kl) was calculated from the logarithmic
decline in concentration according to the formula given by Hyden (1956).
2.9. Particle dynamics
Degradation characteristics of whole rumen NDF pool, isolated LP and SP, rate of clear-ance of LP and SP, and rate of communition (Kc) were calculated from the rumen evacuation
data when rumen evacuation was conducted on animals fed on restricted amount of feed.
2.10. Degradation characteristics
Potentially degradable fraction (D) and rate of degradation (Kd) of whole rumen NDF
pool, SP and LP was calculated according to the model of Orskov and McDonald (1979). Truly undegradable fraction (U) was estimated directly from the residues retained in nylon bags after 336 h incubation.
2.11. Rate of communition (Kc)
The rate of communition of large particles was calculated from the logarithmic decrease in rumen large particle pool in animals on restricted feeding and degradation
characteristics of large particle according to the model of Oosting et al. (1993):
ln LP t ln LP 0ÿKclt
whereKclis the rate of clearance (%/h) of rumen LP pool and (LPt) pool of LP at timet.
KcKclÿKd LP D DU
where Kc is the rate of communition (%/h), Kd(LP), D and U are the rate of
de-gradation, potentially degradable and truly undegradable fraction of rumen LP pool, respectively.
The model assumed that rumen LP pool comprised of two fractions: unavailable and available for degradation. It further supposes that undegradable and degradable fractions are intimately associated and rate of degradation is dependant on potentially degradable fraction as well as on the ratio of potentially degradable to total large particle (Robinson et al., 1986). The model supposes that increasing proportion of undegradable fraction has a negative impact on remaining potentially degradable fraction, perhaps by some form of shielding.
2.12. Statistical analysis
Data obtained in this experiment were analysed statistically according to Snedecor and Cochran (1967).
3. Results
3.1. Chemical composition of feed
Chemical composition of wheat straw and berseem is presented in Table 1. There was little variation in chemical composition of wheat straw across the experimental periods. However, CP content of berseem decreased and NDF content increased, gradually, with advancement of maturity. But these changes did not result in any significant period effect on intake or digestibility or factors regulating them.
3.2. Intake and digestibility
Total dry matter intake (DMI) increased significantly (p< 0.01) with increased level of supplementation up to 30% of level of berseem supplementation. However, 45% berseem supplementation did not show any effect on DMI as compared with 30% level of supplementation (Table 2). Similarly, intake of NDF increased significantly (p< 0.01) with increased level of berseem in the diet up to 30%; at 45% level of berseem, a declining tendency of NDF intake was observed.
animals in Group I, in addition to their respective quota of berseem. As a result, DMI within first 4 h increased linearly with increased level of berseem in the diet. Animals in Groups I, II, III and IV consumed 26, 34, 47 and 57% of their total DMI within the first 4 h period of offering. Animals in Group II consumed more straw than the animals in other groups in the second 4 h period as well. Animals in Groups I, II, III and IV
Table 1
Chemical composition of wheat straw and berseem Wheat straw Berseem
Periods
I II III IV
DM 85.09 10.93 12.16 14.80 16.44
Proximate principles(% DM)
OM 87.36 85.84 86.14 85.67 85.98
CP 3.28 20.83 17.69 15.86 14.42
CF 38.53 17.17 19.04 22.57 27.57
EE 1.45 2.64 2.48 2.41 2.01
Cell wall constituents(% DM)
NDF 81.36 43.93 45.87 49.12 54.12
ADF 56.56 36.21 38.72 43.66 46.56
Hemicellulose 24.80 7.72 7.12 7.47 7.57 Cellulose 36.16 23.55 25.89 25.10 27.51
Lignin 12.19 6.14 8.33 10.23 12.56
Table 2
Intake and digestibility on supplementation of different level of berseem in wheat straw dieta Group
I II III IV SEM
Intake(kg/day)
DM** 3.95 a 5.85 b 7.28 c 7.08 c 0.16
IDM** 1.52 a 1.89 b 2.01 b 2.36 c 0.064
NDF** 3.22 a 4.55 b 5.01 b 4.65 b 0.108
INDFb 1.27 1.52 1.55 1.77 0.004
Digestibility(%)
DM** 39.85 a 45.61 b 52.97 c 47.52 b 1.09 OM** 42.31 a 48.13 b 56.18 c 50.28 b 1.21 CP** 12.12 a 31.30 b 45.93 c 56.51 d 1.61 NDF** 32.97 a 37.59 b 45.41 c 37.73 b 1.10
ADF** 31.47 a 36.17 b 42.34 c 35.98 b 1.34
Hemicellulose** 36.42 a 41.50 b 53.47 c 46.78 b 0.81
Cellulose** 40.95 a 48.70 ab 51.57 b 47.98 ab 1.33 aValues followed by different letters in a row differ significantly.
bNon-significant;**p< 0.01.
had eaten, respectively, 64, 70, 70 and 77% of their total DMI, within the first 8 h of offering. Animals in all the groups consumed 90% of total DMI within 12 h of offering.
Digestibility of DM, OM, cell wall components and CP is presented in Table 2. Digestibility of DM, OM, NDF, ADF, HC and cellulose increased significantly (p< 0.01) up to 30% level of berseem supplementation, whereas, at 45% level of supplementation, digestibility of nutrients decreased. However, CP digestibility increased significantly (p< 0.01) with increased level of berseem in the diet.
3.3. Rumen pool size
Total rumen content and pool sizes of DM, NDF, IDM, INDF, LP and SP is presented in Table 3. Total rumen content, rumen fluid volume and pool of DM was significantly higher (p< 0.05) in berseem-supplemented groups, though the difference between different levels of berseem supplementation was non-significant. Similarly, rumen content as well as rumen fluid volume as percent of body weight also increased significantly (p< 0.05) due to supplementation of berseem. Level of berseem in diet did not affect these parameter significantly. However, NDF pool and IDM as well as INDF were not affected by berseem supplementation.
3.4. Diurnal variation in pool sizes
Diurnal variation in total rumen contents, pool of DM, NDF, IDM and INDF is presented in Table 4. Maximum rumen fill was observed at 3, 6, 9 and 9 h post feeding in
Table 3
Rumen pool sizes as affected by level of berseem in dieta
I II III IV SEM aValues followed by different letters in a row differ significantly.
bNon-significant;**p< 0.01.
Table 4
Diurnal variation of rumen pool sizes in animals fed different level of berseem in dieta
I II III IV SEM
Total rumen contents (kg) h post feeding
3** 55.0 a 66.3 ab 75.5 c 83.0 c 3.05
aValues followed by different letters in a row differ significantly. bNon-significant;**p< 0.01.
Groups IV, III, II and I, respectively. At around 18 h post feeding, the difference among different groups was non-significant. Similarly, the rumen DM as well as NDF pool were maximum at 6, 6, 9 and 9 h post feeding in Groups IV, III, II and I, respectively.
3.5. Particle dynamics
Degradation characteristics of rumen content, isolated LP, SP and rate of clearance of SP, LP and rate of communition are presented in Table 5, and distribution of SP and LP is illustrated in Fig. 2. Potential degradability of LP increased significantly (p< 0.01) with increased level of berseem in the diet. Potential degradability of SP and whole rumen NDF pool increased significantly (p< 0.01) with increased berseem level up to 30%. However, at 45% level of supplementation, potential degradability decreased for both SP and whole rumen NDF pool, difference being more marked in case of SP than whole rumen NDF pool. Rate of degradation of LP increased with increased level of berseem up to 30%; at 45% level of berseem, no further change was observed. Rate of degradation of SP reduced significantly (p< 0.01) in Group IV in comparison to control, whereas 15 and 30% levels of berseem increased the rate of degradation.
3.6. Passage from rumen
Rate of clearance (Kcl), rate of passage (Kp) and mean retention time (MRT) of DM and
NDF are presented in Table 6.Kclof DM increased significantly (p< 0.01) with increased
level of berseem up to 30%, beyond which no further change was observed. On the other hand, MRT decreased andKpincreased significantly (p< 0.01) with increased level of
berseem in the diet.
Table 5
Potentially degradable fraction (D), rate of degradation (Kd), isolated small and large particles, whole rumen
NDF pool, rate of clearance of large particle (LP) and small particle (SP), and rate of communition of large particlea
I II III IV SEM
D fraction(%)
LP** 25.20 a 40.02 b 48.11 c 49.44 d 0.34
SP** 36.48 a 41.94 c 45.90 d 39.08 b 0.36
Rumen NDF pool* 33.68 a 43.96 b 45.03 b 40.83 ab 2.06
Kd(%/h)
LP** 0.83 a 1.97 b 2.46 c 2.26 c 0.04 SP** 1.66 b 2.01 c 1.93 c 1.41 a 0.03 Rumen NDF pool* 1.54 a 2.07 b 2.15 b 1.84 b 0.10
Rate of clearance(%/h)
LP** 3.71 a 6.71 b 7.27 b 8.75 c 0.36
SPb 0.46 0.83 1.20 1.35 0.21
Kc(%/h)** 3.45 a 5.79 b 5.92 b 7.37 c 0.37 aValues followed by different letters in a row differ significantly.
Fig. 2. Diurnal variation of particle distribution in rumen as affected by the level of berseem in wheat straw diet.
3.7. Diurnal variation in passage rate
Within-day variation of passage rate is presented in Table 7. In this experiment, passage rate was determined for the periods of 0±9 h, 9±18 h and 18±24 h and grossly considered to be as the period of eating, rumination and idling, respectively, because the activity concerned was more in the respective period. Maximum passage was observed during eating in all the groups, except wheat straw alone fed group, where maximum passage was observed during rumination. However, the absolute amount passaged during rumination and idling was not different among the rations.
Table 6
Clearance rate (Kcl), mean retention time (MRT), fractional passage rate (Kp) and liquid outflow rate (Kl)a
I II III IV SEM
Kcl(%/h)
DM** 2.73 a 3.22 b 3.85 c 3.89 c 0.096
NDF* 2.85 a 3.40 b 3.67 b 3.76 b 0.14
MRT(h)
IDM** 58.33 a 53.24 b 42.98 c 40.20 c 1.01 INDF** 55.71 a 50.74 b 45.72 c 42.09 d 0.97
Kp(%/h)
DM** 1.72 a 1.88 b 2.33 b 2.56 b 0.047
NDF** 1.81 a 1.96 b 2.19 c 2.38 d 0.042
Klb 6.60 7.08 7.18 7.85 0.58
Intake(kg)
DM** 3.95 a 5.85 b 7.28 c 7.08 c 0.16
IDM** 1.52 a 1.89 b 2.01 c 2.36 c 0.064
NDF** 3.22 a 4.55 b 5.01 c 4.65 c 0.108
INDF** 1.27 1.52 1.55 1.77 0.004
aValues followed by different letters in a row differ significantly. bNon-significant;**p< 0.01.
Table 7
Variation in passage rate of INDF from the potentially removable INDF pool of rumen during eating (PEAT), rumination (PRUM) and idling (PID)a
I II III IV SEM
INDF intake(%)
PEAT** 35.96 a 46.18 b 59.93 c 67.74 c 3.08
PRUMb 46.32 33.26 26.73 23.24 8.73
PIDb 17.72 20.56 12.97 9.33 5.55
Passage(g)
PEAT** 462.5 a 713.3 b 930.3 b 1197.3 c 72.5
PRUMb 571.0 568.0 402.0 407.0 66.0
PIDNS 234.5 317.0 213.0 165.0 80.5 aValues followed by different letters in a row differ significantly.
4. Discussion
4.1. Intake and digestibility
Inclusion of berseem in the wheat straw based diet increased the total DM intake. Increased DM intake as a result of green legume supplementation has been reported by other workers (Mosi and Butterworth, 1985; McMeniman et al., 1988; Bird et al., 1994; Bonsi et al., 1994; Woodward and Reed, 1995). Findings of this experiment are in line with information available in the existing literature in general, but differ from the findings of Odowongo and Mugerwa (1980) and Ash (1990). Such variations in response can partly be attributed to the lower degradability of the supplement (Ash, 1990) and also to the presence of toxicant (Odowongo and Mugerwa, 1980) in the supplement. Berseem, on the other hand, is fairly degradable and contains no toxicant that is known to decrease intake.
Berseem supplementation up to 30% level increased digestibility of DM, OM, NDF, ADF, cellulose and hemicellulose; however, at 45% level of berseem supplementation, digestibility decreased. On the other hand, CP digestibility increased linearly with increased level of berseem in the diet, which is in line with the findings of Butterworth and Diaz (1970) and Mosi and Butterworth (1985). Increased digestibility as a result of forage supplementation has been reported by other workers (Juul-Nielson, 1981; Silva and Orskov, 1988; Bird et al., 1994; Bonsi et al., 1994). Maximum digestibility observed at 30% level of berseem supplementation suggests that 30% level of berseem in the diet provided all the essential nutrients critical for optimal microbial activity, viz., rumen NH3±N concentration (Eliott et al., 1984), peptides, essential minerals and vitamins
(Leng, 1990). In addition, berseem also provided fermentable cellulose and hemi-cellulose, which are known to promote fibre digestion (Silva and Orskov, 1988) by ensuring greater degree of colonisation of fibrolytic bacteria (Cheng et al., 1990) and fungi (Bauchop, 1979). Decrease in digestibility as a result of 45% berseem supplementation, as observed in this experiment, could be due to decreased mean retention time in the rumen, which means an increased rate of passage from the rumen (Oosting, 1993) as the green forages are bulky in nature (Bonsi et al., 1994).
4.2. Rumen pool size
Total rumen content was 18% of the body weight in animals fed on wheat straw alone; it increased up to 23% when supplemented with berseem. These values were higher than the values of 17.5% in cattle fed on either grass silage based diet (Bosch et al., 1993) or wheat straw based diet (Oosting, 1993), but lower than the values of 26% in early lactating cows (Hartnell and Satter, 1979). These values are similar to those observed by Chauhan et al. (1985) in buffalo fed on oat silage based diet supplemented with either concentrate or cowpea hay. They reported that gut content is 24%. It appears that ruminants fed on poor quality roughage, in the tropics, have higher rumen content than of those in the temperate region. Berseem supplementation increased the total rumen content and pool of DM and small particle. This indicates that intake is not limited by rumen capacity. Similar conclusion has also been drawn by other workers (Bosch et al.,
1992; Oosting, 1993). Similar pool size of indigestible components (IDM and INDF) in different groups having different levels of intake, as observed in this experiment, suggests that rumen pool of indigestible component determines the intake (Mertens and Ely, 1979).
Generally, after attainment of maximum rumen fill, it declined and reached a minimum value just before feeding. Maximum pool of DM was observed 6 h post feeding in Groups III and IV, and 9 h post feeding in Groups I and II (Table 4). Pool of NDF followed the same trend, but the difference between different groups was significant only at 6 h post feeding. The pools of IDM and INDF gradually decreased after they attained the maximum pool at 6, 6, 9 and 9 h post feeding in Groups IV, III, II and I, respectively. Increased passage rate observed with increased level of berseem in the diet due to its bulkiness (Bonsi et al., 1994) can partly be attributed to early attainment of maximum rumen pool.
4.3. Particle dynamics
The results indicate that LP and SP are not degraded in the same fashion. Increase in potential degradability and rate of degradation of LP with increased level of berseem in the diet could be attributed to increase in readily fermentable fibre content (Silva and Orskov, 1988). Potential degradability of whole rumen NDF, SP increased up to 30% level of berseem, beyond which a negative associative effect was observed. It seems that the decrease in potential degradability and rate of degradation at 45% level of berseem is due to decrease in potential degradability (PD) andKdof SP. The decreased PD andKdof
SP could be due to the fact that at 45% level of berseem, the rumen, microbes had enough substrate in rumen pool of host animal than the less preferably small particles, inside nylon bag when isolated from the rumen which ready to passage out of the rumen and substantial amount of digestion might had taken place before that. Rate of degradation of LP, barring wheat straw, was higher than SP in all the groups. This, in general, is in agreement that after attainment of critical particle size (1.18 mm) the feed particle do not remain in rumen for long (Poppi et al., 1980) and substantial amount of microbial digestion takes place before they attain that particle size.
4.4. Passage rate from rumen
rapidly lost after their formation (Moseley and Jones, 1984). In this experiment, rate of passage increased with increased level of berseem supplementation. Similar results have also been reported by other workers (Moran et al., 1983; Bamualim et al., 1984; Bonsi et al., 1994) when straw-based diets were supplemented with increased level of green forages. Increased passage rate as a result of increased level of berseem supplementation could probably be associated with the fact that berseem supplementation increased the ratio of cellulose/hemicellulose in the diet. Particles with higher cellulose content probably have a relatively higher functional specific gravity (Wales et al., 1990), which may explain increased passage rate with increased level of berseem in the diet.
In this experiment, no change in rumen pool size beyond 15% level of berseem was observed. Mean retention time decreased with increased level of berseem in the diet, as passage rate was measured as reciprocal of the mean retention time, in this experiment. Decreased mean retention time as a result of supplementation has also been reported by other workers (Moran et al., 1983; Bonsi et al., 1994). Though the passage rate of particulate matter increased with increased level of berseem supplementation, liquid outflow rate was not significantly different between treatments. This finding is contrary to that of Nsahlai (1991) and Bonsi et al. (1994), who reported that increased particulate passage rate results in increased liquid outflow rate. Nevertheless, a different pattern of particulate passage rate and liquid outflow rate has also been reported (Ulyatt et al., 1984).
4.5. Diurnal variation in passage rate
Difference in passage observed in this experiment, as a result of berseem supplementation, can be attributed to the increased rate of passage during eating. On an average, 36, 46, 60 and 68% of indigestible NDF ingested was lost from the rumen INDF pool, during eating, in Groups I, II, III and IV, respectively. The proportion of large particles in the rumen increased up to 3 h post feeding; then it gradually decreased and reached minimum just before feeding. Reduction in particle size was sharper in animals fed on higher level of berseem, indicating higher rate of communition that resulted in increased rate of passage as proportion of small particles in rumen was not significantly different among the rations. The act of eating has been shown to be accompanied by a marked increase in reticular and omasal contractions that might have elevated the rate of flow of digesta from the rumen (Balch, 1958). It is observed in this experiment that greater proportion of INDF is lost during eating with increased level of berseem in the diet. This change might have occurred due to increased rumination efficiency (Moseley and Jones, 1984). On an average, 462, 713, 930 and 1197 g of INDF was lost from the rumen within first 9 h of feeding in Groups I, II, III and IV, respectively.
Berseem supplementation increased the rumen fill, indicating that rumen capacity is not limiting intake. On an average, an increase of 23, 40 and 44% in DM intake was recorded as a result of 15, 30 and 45% berseem supplementation. Increased intake was accompanied by an increased rate of communition, which, in turn, increased the rate of passage. However, the increase in disappearance was more than the rate of passage. On an average, 19, 29 and 32% increase in clearance rate was observed in 15, 30 and 45% level of berseem supplemented groups, respectively. Respective values for increase inKpwas
8, 21 and 31%. Overall digestibility increased by 14, 33 and 19% in groups fed 15, 30 and 45% level of berseem, respectively. It is concluded that increased level of berseem supplementation up to 30% level to wheat straw based diet increases DMI and digestibility of wheat straw based diet.
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