Effects of feeding Italian ryegrass with corn on rumen environment,
nutrient digestibility, methane emission, and energy and
nitrogen utilization at two intake levels by goats
M. Islam
*,1, H. Abe, Y. Hayashi, F. Terada
Energy Metabolism Laboratory, National Institute of Animal Industry, Tsukuba Norin-danchi, Ibaraki 305-0901, Japan
Received 6 December 1999; accepted 22 March 2000
Abstract
This study was conducted to investigate the effects of corn addition to Italian ryegrass (IRG) (Lolium multi¯orumLam.) on rumen environment, nutrient digestibility, methane production and energy and nitrogen utilization by goats at two intake levels. Eight castrated Japanese goats were employed in two sequential digestion and metabolism trials. The goats were divided into two groups, offered two diets: Diet 1 consisted of 85% Italian ryegrass pellet (IRG) and 15% soybean meal; and Diet 2 consisted of 42.5% IRG, 7.5% soybean meal and 50% corn. The two intake levels were, high (1.6 times) and low (0.9 times) maintenance requirement of total digestible nutrient (TDN). Rumen ammonia nitrogen (NH3N) level of Diet 1 was
lower (p<0.05) than Diet 2. Ruminal pH was higher for Diet 1 (p<0.001) and ranged from 6.32 to 6.85. Diet 2 had higher (p<0.001) concentrations of butyric acid and total VFA but a lower (p<0.05) concentration of propionic acid. Rumen parameters were not signi®cantly affected by level of intake. Dry matter, OM, CF and EE digestibilities were signi®cantly higher for the Diet 2 while the CP digestibility was higher for Diet 1. Both diets had higher (p<0.001) digestibility when fed at lower level of intake. There was no difference (p>0.05) in energy losses as methane (CH4) and heat production between the
diets. Urinary energy loss (UE) as a proportion of digestible energy (DE) was higher (p<0.001) for Diet 1 and higher (p<0.01) for lower level of intake. Methane production (g 100 g per DDMI) was similar for both levels of intake. Retained energy (RE) was higher (306 vs. 297 Kcal) for Diet 2 than Diet 1. Nitrogen losses through feces and urine were lower (p<0.001) for Diet 2. Thus, retained N as a proportion of N intake and retained N as a proportion of digested N were higher (p>0.05) for Diet 2. The N loss/unit of N intake was signi®cantly lower (p<0.001) at the high level of intake although it had higher total N losses. Thus, supplementation of IRG diet with corn increased retained energy and retained N through reducing the energy and N losses. The high level of intake reduced the proportion of nutrient losses through feces, urine and methane. Supplementation of IRG with corn and soybean meal at the higher level of intake improved the ef®ciency of utilization of IRG and increased energy and nitrogen retention.#2000 Elsevier Science B.V. All rights reserved.
Keywords:Goat; Intake level; Corn; Italian ryegrass; Nutrient utilization
1. Introduction
Dietary manipulation can correct an unbalanced in energy and protein supply. Including N rich ingredi-ents could minimize the de®ciency of protein of the grass hay of 7.45% CP but no signi®cant in¯uence on
*Corresponding author. Tel.:81-0298-38-8655;
fax:81-0298-38-8606.
E-mail address: [email protected] (M. Islam).
1Present address: Bangladesh Livestock Research Institute
Savar, Dhaka 1341, Bangladesh.
N and energy retention was found (Khan et al., 1998). On the other hand, Keady and Mayne (1998) found no signi®cant effect of inclusion of concentrate energy on grass silage intake, feeding behavior and energy uti-lization. However, inclusion of 30% corn with alfalfa increased the energy and N utilization of the diets (Islam et al., 2000). Thus, it is anticipated that inclu-sion of corn and soybean meal with IRG might balance the energy and protein in the diets and improve the energy and N utilization through a more uniform pattern of fermentation in the rumen.
Increase in dietary feed intake as well as nutrient intake is one of the ways to increase in ef®ciency of animal productivity. The high feed intake may affect on rumen environment as well as nutrient digestibility. Studies on level of intake are relatively few for goat compared to sheep and cattle, and there is still a lack of information about energy and protein utilization at high and low levels of intake. Energy and N utilization at maintenance level (Terada et al., 1985) and the requirement for maintenance of Japanese goat (Itoh et al., 1978) have been reported earlier but the energy and N utilization at a high level of intake by goat are little known. Thus, the effects of high level of intake on the rumen environment, nutrient digestibility, and energy and N utilization in goats are needed. The objectives of this study were to determine the effects of inclusion of corn on the nutrient digestibility of IRG at high and low levels of feed intake. Energy and N partitions in goats fed on the IRG and soybean meal with or without corn were also determined.
2. Materials and methods
2.1. Diets
Diet 1 consisted of 85% IRG pellet and 15% soybean meal, while the Diet 2 was, 50% of corn, 42.5% IRG and 7.5% soybean meal. Two intake levels based on TDN requirement for metabolic body weight (W0.75) of goat were, low (0.9 times) and high (1.6 times) level maintenance requirement of the TDN obtained from Itoh et al. (1978).
2.2. Animals
Eight adult male Japanese goats with a mean weight 25.9 kg were used for two sequential digestion and
metabolism trials. The goats were randomly assigned to one of two groups, with mean body weights of 26.8 and 24.9 kg for groups A and B, respectively. In trial 1, the Diet 1 at high and low levels of intake was offered to the animals of groups A and B, respectively. Similarly, the Diet 2 at high and low levels of intake was offered to the animal groups in trial 2.
2.3. Metabolism trial
Metabolism trial for each diet was conducted for 21 days with a 7-day adjustment period and 7-day pre-liminary period prior to the trials followed by a 7-day collection period, which included 3 consecutive days for measurement for gas exchange. The daily allow-ances were weighed and fed in four equal proportions to the animals 4 times/day. Refusals if any, were collected and measured before the ®rst feeding of the day. Representative samples of feeds and refusals were taken, oven dried (608C for 48 h) and ground to pass through a 1 mm sieve for chemical analysis. The total feces and urine from each goat were collected and weighed prior to morning feeding. All the feces and 10% of the urine were preserved daily. Urine was collected in the urine bucket where 25 ml (1% of urine volume) of 20% H2SO4was placed before the collec-tion carried out. After total colleccollec-tion, feces and urine were mixed thoroughly and sub-sampled for N deter-mination. For further analysis, fecal samples were oven dried (608C for 48 h) and then ground similarly. Twenty millilitre of urine were weighed in a poly-ethylene ®lm, and freeze-dried for determination of GE using the method described by Itoh and Tano (1977).
2.4. Respiration chambers
2.5. Nutrient analyses
Analyses of DM, OM, EE, CF and CP of feeds, feces and urine were carried out using the methods described by AOAC (1984). Nitrogen free extract (NFE) was calculated by subtracting the sum of other proximate components from 100.
2.6. Collection and analyses of rumen liquor
Rumen liquor samples were collected from indivi-dual goats at 0 and 3 h post-feeding using stomach tube. The pH was then measured immediately after collection. The samples were then preserved in the freezer atÿ308C. The ammonia N of rumen liquor was determined following the method described by Conway (1957). The volatile fatty acids were analyzed using the Gas Chromatograph (YHP 5830A). Rumen samples were collected, preserved, and analyzed fol-lowing the method described by Islam et al. (2000).
2.7. Energy balance measurement
The energy values of sample of feed, feces and urine collected from the trials were used to calculate energy balance. Gross energy content of feed, feces and urine were determined using the values for heat of combus-tion by a bomb calorimeter (Shimadzu CA3P). Diges-tible energy was calculated as the difference between GE intake and fecal energy (FE) output. Metaboliz-able energy was calculated as the difference between DE intake and urinary energy (UE) and CH4output. Methane gas volume was converted to energy and mass values using the conversion factors 9.45 (Kcal lÿ1
) and 0.716 (g lÿ1
), respectively. An indirect estimation of heat production (HP) by measurement of gaseous exchange from the chamber was calculated
using the following formulae: HP (Kcal per day)-3.866O2 (l per day)1.200CO2 (l per day)ÿ0.518CH4 (l per day)ÿ1.431N (g per day in urine) described by Brouwer (1965). Retained energy (Kcal per day) was calculated using the equa-tion: ME-energy loss through heat production.
2.8. Statistical analyses
Statistical signi®cance was determined by analysis of variances with the dietary intake levels and diets as factors in a split plot design where main plot was diet and sub-plot was level of intake. Data were presented as least-square means of the diets and the intake levels. The standard error of means (S.E.) and signi®cance levels were also presented in respective tables. All the statistical analyses were carried out using general linear model procedure (GLM) of SAS (1994).
3. Results
3.1. Nutrient composition of feeds and diets
The nutrient composition of feeds and diets are presented in Table 1. Diet 1 contained higher CP and Diet 2 contained higher GE. Intake of DMI per metabolic body weight (W0.75) were higher (p<0.01) for goats on the Diet 1 than that for the Diet 2 (Table 2). The DCP intake also higher (p<0.001) on Diet 1 than Diet 2.
3.2. Rumen environment
The mean (0 and 3 h samplings) pH values of rumen liquor for goats on the diets at two intake levels are shown in Table 3 and the pH values were in between
Table 1
Nutrient composition (g kgÿ1DM, unless otherwise stated) of ingredients and diets
Feeds DM (g kgÿ1) OM CP EE CF NFE GE (Kcal kgÿ1DM)
IRG 910 901 76 24 297 504 4238
Corn 866 984 100 42 23 820 4562
Soybean meal 897 928 549 7 28 343 4783
Diets
Diet 1 908 905 146 21 258 481 4317
6.32 and 6.85 (Table 3). Between diets, a higher (p<0.01) pH value was on the Diet 1 but it was not affected by the intake level. Ammonia nitrogen of rumen liquor for Diet 1 was 133, which was lower than that for the Diet 2 (215 mg lÿ1
). The mean NH3N of rumen liquor at the higher level of intake was higher (p>0.05) than that at the lower level of intake con-sidering the diets. The NH3N concentration of rumen liquor increased (p<0.001) with inclusion of corn in the diet and the higher level of intake produced a higher rumen NH3N concentration. The mean con-centration of acetic acid in rumen liquor was higher when the goats consumed higher DM. Between the diets, a slight higher acetic acid concentration was on Diet 2 than Diet 1 (p>0.05). Propionoic acid concen-trations were in a narrow range among the intake levels but on the diets, a higher (p<0.05) value was on the Diet 1. Butyric acid concentration was slight higher (p>0.05) at the higher intake level. The Diet 2 produced signi®cantly higher (p<0.001) butyric acid than that for Diet 1 considering the intake levels. The mean of total VFA (mg dlÿ1
) was higher (p<0.01)
for Diet 2 than that for the Diet 1 and the higher level of intake produced a higher (p>0.05) total VFA (Table 3).
3.3. Diet apparent digestibility
Apparent digestibilities of the nutrient components were signi®cantly higher at the lower intake level (Table 4). Irrespective of the intake levels, signi®-cantly higher nutrient digestibilities were for Diet 2. The obtained DCP intake (g kg Wÿ0.75
) was higher (p<0.001) for Diet 1 than that for Diet 2 (Table 2).
3.4. Energy balance
Energy balances on the two diets at two levels of intake are shown in Table 5. Gross energy intake (Kcal per day) was higher (p<0.01) on Diet 1 than that for the Diet 2. The total energy losses through feces and urine were also higher (p<0.001) on Diet 1 than that for the Diet 2 and both the losses were higher (p<0.001) at the higher level of intake.
Table 2
Nutrient intake of goats fed different Italian ryegrass based diets at high and low level of intake
Diets S.E.a p Level of intake S.E. p
1 2 Diet 1 vs. Diet 2 High Low High vs. low
DM intake (g per day kgWÿ0.75) 52.7 44.1 1.96 * 61.0 35.8 1.93 ***
DCP intake (g kgWÿ0.75) 5.07 3.30 0.14 *** 5.04 3.32 0.12 ***
TDN intake (g kgWÿ0.75) 32.1 32.8 0.97 nsb 39.8 25.1 0.93 ***
aStandard error of least-square means. bNon-signi®cant (p>0.05).
*p<0.05; ***p<0.001.
Table 3
Mean rumen pH, NH3N and volatile fatty acid contents of goats fed different diets in two intake levels
Diets S.E.a p Level of intake S.E.a p
1 2 Diet vs. Diet 2 High Low High vs. low
pH 6.85 6.32 0.08 ** 6.58 6.59 0.08 ns
NH3N (mg l
ÿ1) 133 216 34.4 nsb 166 183 8.0 ns
Total VFA (m mol dlÿ1) 6.90 9.31 0.81 ns 9.01 7.21 0.66 ns
Acetic acid (mol%) 62.8 68.1 2.85 ns 67.7 63.1 3.17 ns
Propionic acid (mol%) 22.4 16.4 1.34 * 20.0 18.8 1.00 ns
Butyric acid (mol%) 7.5 11.7 0.55 ** 10.0 9.1 0.48 ns
aStandard error of least-square means. bNon-signi®cant (p>0.05).
3.5. Methane production
Daily CH4 emissions parameters are shown in Table 5. Irrespective of the diets, a higher (p<0.001) total CH4production (g per day per goat) was at high level of intake than the low level of intake, but the CH4 emission per digestible DM intake (g 100 g per DDMI) was almost similar at both the intake levels. The higher level of intake lost a higher total energy through CH4 (Table 5), but the energy loss through CH4per DMI was slight (p>0.05) lower at the high intake level (0.265 vs. 0.286 Kcal g per DMI).
Methane conversion ratio (MCR%, energy loss as CH4 per unit of GE intake) for diets 1 and 2 were 5.31 and 7.01%, respectively. The MCR value for Diet 2 was higher than that of Diet 1 (p<0.001), and the value for the lower level of intake was higher (p>0.05) than that for high level of intake.
Digestible energy and ME intake values were higher (p<0.001) at the higher level of intake but for the diets there were small differences (p>0.05) which favor Diet 1. Energy loss as heat production was higher (p<0.001) at high level of intake than the low level of intake and a non-signi®cance difference Table 4
Apparent digestibility (%) of diets of goats fed different Italian ryegrass based diets at high and low intake levels
Diets S.E.a p Level of intake S.E.a p
1 2 Diet 1 vs. Diet 2 High Low High vs. low
DM 64.2 74.7 0.54 *** 66.8 72.1 0.87 **
OM 66.1 76.6 0.59 *** 68.6 74.0 0.86 **
CP 68.1 63.2 1.44 nsb 62.5 68.7 1.49 *
EE 63.8 80.4 0.83 *** 70.8 73.4 0.39 **
CF 58.3 54.8 0.88 * 52.8 60.3 2.10 *
NFE 69.8 83.8 0.53 *** 74.6 79.0 0.60 **
aStandard error of least-square means. bNon-signi®cant (p>0.05).
*p<0.05; **p<0.01; ***p<0.001.
Table 5
Energy balance (Kcal per day) of goats fed two Italian ryegrass based diets at high and low intake levels
Diets S.E.a p Level of intake S.E.a p
1 2 Diet 1 vs. Diet 2 High Low High vs. low
Energy input and output
Gross energy intake 2681 2182 112 * 3075 1788 111 ***
Fecal energy 1016 590 55 ** 1076 530 57 ***
Digestible energy 1665 1592 59 nsb 1999 1258 54 ***
Urinary energy 120 80 3.5 *** 117 83 3.2 ***
Methane energy 140 151 7.4 ns 180 112 7.8 ***
Methane (g) 10.6 11.5 0.56 ns 13.6 8.5 0.59 ***
Methane (g 100 g per DDMI) 2.71 3.15 0.12 * 2.94 2.92 0.11 nsb
MCRc 5.31 7.00 0.25 ** 5.93 6.39 0.16 ns
Metabolizable energy 1545 1513 55.6 ns 1882 1175 52.5 ***
Heat production 1108 1056 30.7 ns 1203 961 28.3 ***
Retained energy 297 306 41.0 ns 500 103 30.2 ***
aStandard error of least-square means. bNon-signi®cant (p>0.05).
cMethane conversion ratio (% GE intake).
(p>0.05) was found among the diets. Diet 1 lost a higher energy as heat production than that for the Diet 2. The higher level of intake had a higher positive RE than the lower level of intake for both the diets. Irrespective of intake levels, the RE was higher (p<0.01) on Diet 2 than that for the Diet 1 (Table 5).
3.6. Energy partition
Energy partition calculations are shown in Table 6. Energy digestibility (DE/GE), metabolizability (ME/ GE) and the concentration of ME in the DM (Kcal Kgÿ1
DM, M/D) were higher for the Diet 2. The intake levels showed signi®cant changes on energy digestibility, metabolizability and ME per kg DM. Signi®cant variations for the energy digestibility (66 vs. 71) (p<0.01) and metabolizability (56 vs. 60) (p<0.05) and the concentration of ME in the DM (2448 vs. 2637 Kcal kgÿ1
DM, M/D) (p<0.05) values were found on intake levels and the values were higher at the low level of intake. Of the DE, the proportion lost as CH4were not affected by the diets and intake levels, but the proportion lost as urine was affected by the diets (p<0.001) and intake levels (p>0.05). The CH4loss was about 9% of DE for both intake levels. Diet 1 lost 8.5% of DE through CH4, where the Diet 2 lost 9.5%. The ME as a proportion of DE values were not affected (p>0.05) by the diets and intake levels
(Table 6). The energy lost as urine was 6.5% of the total DE at low intake level, while at the high intake it was 5.8%. Similarly, the urinary loss of DE was 7.2% for Diet 1 while, for the Diet 2, it was 5.1%. Of the DE, a slight higher (p>0.05) ME value was on the Diet 2 (85%) than Diet 1 (84%) and the ME/DE value at both intake levels were almost 85% (Table 6).
The proportion of ME lost as heat production was higher (p<0.001) at low level of intake than that at high level of intake (91 vs. 71%). The ME losses as heat production between the diets were almost similar. Diet 1 lost 80% of the ME for heat production while, the Diet 2 lost 81%. However, the RE of ME was slight higher (p>0.05) for Diet 1 (19.6%) compared to Diet 2 (18.8%).
3.7. Nitrogen balance
Major changes occurred in N balance with the diets and intake levels (Table 7). Nitrogen intakes (p<0.001), fecal nitrogen (FN) (p>0.05) and urinary nitrogen (UN) (p<0.001) output were higher for Diet 1 than those of Diet 2. The values were higher (p<0.001) for the higher level of intake. The amount of N digested was higher (p<0.001) on Diet 1 and the retained N was higher (p<0.01) for the Diet 1. Retained N/unit of N intake and the retained N/unit of N digested were slight higher (p>0.05) for Diet 2 Table 6
Partition of digestible energy (DE) and metabolizable energy (ME) of goats fed two Italian ryegrass based diets at high and low intake levels
Diets S.E.a p Level of intake S.E.a p
1 2 Diet 1 vs. Diet 2 High Low High vs. Low
Digestibility (DE/GE, %) 63 74 0.6 *** 66 71 0.9 **
Partition of digestible energy
Urine (%) 7.2 5.1 0.1 *** 5.8 6.5 0.2 nsb
Methane (%) 8.5 9.5 0.3 nsb 9.0 8.9 0.3 ns
Metabolizable energy (%) 84.2 85.4 0.4 ns 85.2 84.6 0.4 ns
Metabolizable energy
ME per kg DM (M/D Kcal) 2285 2801 25 *** 2448 2637 39 *
ME/GE (q %) 53 63 0.6 *** 56 60 0.9 *
Partition of metabolizable energy
Heat production (%) 80.3 81.2 2.0 ns 71 91 1.7 ***
Retained energy (%) 19.6 18.8 3.0 ns 29 9 1.7 ***
aStandard error of least-square means. bNon-signi®cant (p>0.05).
than that for the Diet 1. These values were signi®-cantly higher (p<0.001) for high level of intake con-sidering both the diets.
Of the N intake, FN loss was higher for Diet 2 (p>0.05) and for high level of intake (p<0.01) than that for the Diet 1 and for low level of intake, but the UN losses were higher for Diet 1 (58 vs. 52%,p<0.05) and for low level of intake (63 vs. 47%,p<0.001). How-ever, the total N loss was higher (p<0.0001) for the low level of intake (94%) than the high level of intake (84%). Between the diets, the total N losses were almost similar (90 and 89%).
4. Discussion
The effects of corn inclusion and levels of feed intake were studied on the basis of the parameters of nutrient digestibility, digestible nutrient intake, nutri-ent losses, and energy utilization and N utilization concerned. The statistical analyses did not show any signi®cant interactions between inclusion of corn and level of feeding. Hence, the effects of two factors are discussed separately.
4.1. Inclusion of corn
In this study the two diets were prepared on the basis of TDN requirement. The 15% soybean meal
was used to improve dietary protein of the IRG based Diet 1, and in Diet 2, corn was used 50%, which replaced both the IRG and soybean meal. Concentra-tion of NH3N, VFA of rumen liquor and ruminal pH were used to monitor rumen fermentation pattern. The pH values for both the diets were in optimum pH ranges for ®ber digestion (Orskov and Ryle, 1990) though the corn included diet reduced the rumen pH signi®cantly (p<0.01). This might be due to a higher starch content of the Diet 2. The mean concentration of NH3N for both the diets appeared to have been suf®cient to meet the requirements for N of rumen microbial population as they were above the higher of the minimum level of 50 mg lÿ1
for ®ber digestion of grass based diets that has been reported by Satter and Slyter (1974). Results showed that the diet with corn (Diet 2) decreased the pH and propionic acid, but increased NH3N, total VFA, acetic acid and butyric acids concentrations (Table 4). It was anticipated that the corn inclusion might increase in the propionic acid of the rumen liquor but inclusion of corn did not increase the concentration of propionic acid. Similar results were also found in the earlier study using different diets based on corn and alfalfa (Islam et al., 2000).
The higher (p<0.001) digestibility of DM, OM, EE and NFE were on the Diet 2, which suggested that corn inclusion in the IRG based diets has a positive effect on nutrient digestibility. This supports the results of Table 7
Nitrogen balance (g per day) of goats fed two Italian ryegrass based diets at high and low intake levels
Diets S.E.a p Level of intake S.E.a p
1 2 Diet 1 vs. Diet 2 High Low High vs. low
Intake 14.2 9.5 0.55 *** 14.9 8.8 0.54 ***
Feces 4.6 3.6 0.30 nsb 5.6 2.7 0.36 ***
Urine 8.0 4.7 0.36 *** 7.1 5.6 0.16 ***
Digested 9.6 5.9 0.33 *** 9.4 6.1 0.27 ***
Retained 1.6 1.2 0.05 ** 2.3 0.5 0.17 ***
Retained/intake (%) 10.3 11.4 1.03 ns 15.7 6.00 1.05 ***
Retained/digested (%) 15.4 18.6 1.46 ns 25.3 8.7 1.88 ***
Nitrogen partition
Fecal N/N intake (%) 32 37 1.0 ns 38 31 2.0 *
Urinary N/N intake (%) 58 52 2.0 * 47 63 2.0 ***
Total loss/N intake (%) 90 89 1.0 ns 84 94 1.0 ***
aStandard error of least-square means. bNon-signi®cant (p>0.05).
our earlier study (Islam et al., 2000) where increased digestibilities were found when corn included with alfalfa. The higher CP digestibility for Diet 1 can be explained that the effect of soybean meal that was included with IRG in the diet.
No differences (p>0.05) were found in DE and ME among the diets while the RE value was higher on Diet 2. The digestibility, metabolizability and ME per kg DM were higher on the corn included diet though the without corn diet had higher DE and ME (p>0.05) values. This evidenced that corn addition to IRG increased the energy utilization and thus a higher RE was available for the diet. Similar results were observed when corn was fed at different levels with alfalfa (Islam et al., 2000). The lower energy loss as urine (p<0.001) of Diet 2 than the Diet 1 supports the statement of Islam et al. (2000) that the dietary supplement of concentrate energy with ®brous energy source decreased energy loss as urine. The non-sig-ni®cant higher (p>0.05) CH4emission (g per day), and CH4conversion ratio (MCR, %GE intake) (p<0.001) on Diet 2 compared to the Diet 1 was due to corn addition. The signi®cantly higher (p<0.001) MCR value on the Diet 2 (7.01%) than Diet 1 (5.31%) (Table 5) could also be due to the effect of corn addition to IRG. The CH4per digestible dry matter intake (DDMI) were also signi®cantly different (p<0.001) between the diets and higher values were for corn-included diet. The higher CH4production on the corn-included diet is unknown. The corn-included diet supposed to be rich in readily available carbohy-drates that usually increase the propionic acid but the rumen parameters showed that the corn-included diet (Diet 2) in this study produced less propionic acid concentration than that of the diet without corn. The feeding of starch usually results in higher propionic acid concentration and therefore less CH4 (Murphy et al., 1982), while in this study inclusion of starch rich corn did not increase the propionic acid concentration. It might be due to restriction of feed intake at 0.9±1.6 times of maintenance requirement TDN. This sug-gested that inclusion of starch at near maintenance did not increase propionate production and the lower concentration of propionate resulted in higher CH4 production. The lower propionic acid concentration and higher CH4 supported the relationship between propionate and CH4(Orskov et al., 1991). The overall CH4production from IRG based diets were lower than
that of corn-included alfalfa based diets (Islam et al., 2000). In the alfalfa based diets the dietary ®ber and CP were obtained from legumes. The ®ber from leguminous sources is low digestible (Taminga, 1992) which was clearly found in the study of Islam et al. (2000). Comparing the CF digestibility values of IRG based diets with the alfalfa-based diets (56 vs. 36%), it is evident that the ®ber digestibility of IRG was higher than that of alfalfa which might have an effect on the reduced methane production in the IRG based diets. In addition to that the increased dietary protein of IRG based diets was from soybean meal, which might have an effect of the increased ®ber digestibility as well as reduced methane production.
4.2. Level of feed intake
Higher level of feed intake did not show any sig-ni®cant changes (p>0.05) on the rumen pH, NH3N, total VFA, propionic acid, butyric acid and acetic acid production. However, all the values obtained higher for the high level of intake. The nutrient digestibilities were higher at the low level of intake. Irrespective of diets, the CH4energy loss and MCR values were slight lower at high level of intake which suggest strong recommendation of using high level of feed intake in increasing the animal productivity.
The higher N losses as feces/unit N intake at the high level of intake might be due to the increased rate of passage. However, the lower N loss as urine and lower total N losses at the higher level of intake showed a higher absorption of N that resulted in a higher retained N/unit N intake and higher retained N/unit N digested.
for rumen microbes. Addition of readily fermentable carbohydrate at near maintenance level of diets may increase CH4production. This supported Bonhomme (1990) who found that an addition of readily fermen-table carbohydrates (e.g. cereal grain) to diets fed at maintenance levels causes a proliferation in the ciliate population. Ciliates are symbiotic with methanogens (Stumn and Zwart, 1986; Finlay et al., 1994) and the increase in CH4 production when grain is fed at maintenance may be due to an increase in hydrogen transfer between these microorganisms (Krumholz et al., 1983). The CH4parameters of this study evi-denced the observation as the CH4produced at with-out-corn diet was lower and the values were lower in high level of intake.
The digestibility, metabolizability and ME per kg DM values for both the diets were higher than those values for the goats consumed alfalfa and barley based diets reported by Prieto et al. (1990). This might be due to the energy of corn comprised of more either starch or digestible ®ber or starch ®ber mixture that showed higher digestible organic matter in the respec-tive diets (Tables 1 and 4). Partition of energy showed that the corn-included diet reduced urinary energy loss that strongly supported the previous results of Islam et al. (2000).
Of the N intake, proportions lost as urine and feces were affected by the diets, but the total losses were almost similar between the diets (89% vs. 88%). The reduced UN loss (Table 7) in the Diet 2 supports the results of the corn-included and alfalfa based diets of Islam et al. (2000). The slight lower losses in the Diet 2 resulted in a higher retained N/unit N intake and retained N/unit N digested. This high UN loss of Diet 1 resulted in an increase in the leaching NO3-N from animal source to surface, ground and as well as drinking water. Finally, the excess N may cause of environmental pollution as ammonia and nitrate in the manure (Yano and Nakajima, 1996). The trend of N losses and differences of N losses as feces were small among the intake levels whilst the differences were higher in N losses as urine. The 10% of total N losses recovered using high level of intake level and reducing the proportion of soybean meal by corn reduced the urinary N loss by 6%. Nitrogen digestibility was not much in¯uenced with the corn addition to IRG, but the total N losses recovered using corn with IRG. A high dietary N intake of Diet 1 using soybean meal resulted
in a higher urinary N loss. A higher urinary loss was also found in alfalfa alone (100%) diet where dietary N was signi®cantly higher (Islam et al., 2000). This suggesting that the dietary N requirement is needed to estimate clearly to reduce N excretion through feces and urine. Using diet with a higher dietary N may increase N excretion as well as increase N pollution. However, the positive effect of corn addition to the diet was found in urinary N excretion. The high level of intake showed higher values in total N losses as feces and urine but the rate was not higher on the high intake level. The N intake on high level was almost doubled. The fecal N loss showed similar trends of N intake between the low and high intake level while in urinary N losses, the trend was lower for the higher level of intake. Of the total N intake, the proportion lost as urine for the high and low levels of intake were, 47 and 63%, respectively. The values were much lower than the values for high and low levels of intake on alfalfa based diets (Islam et al., 2000). The retained N on low level of intake was small though the DCP intake was higher than the reported DCP value for maintenance (Itoh et al., 1978).
5. Conclusion
Acknowledgements
The ®rst author thanks to Japan Science and Technology Agency (JST) and Japan International Science and Technology Exchange Center (JISTEC) for the Award of Science and Technology Agency (STA) Fellowship to carry out the research at National Institute of Animal Industry, Tsukuba, Ibaraki, Japan.
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