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Citation of this paper

Effects of nitrogen supplementation of acorns (Quercus coccifera) on in vitro fermentation, intake and digestion by lambs

N Moujahed, A Moujahed-Raach*, C Ben Mustapha*, H Bel Heni* and C Kayouli

Institut National Agronomique de Tunisie, 43 Av. Ch. Nicolle, Tunis Mahragène, 1082, Tunisia
*Ecole Supérieure d'Agriculture de Mateur, Mateur, Tunisia
nizar.moujahed@laposte.net

Abstract

The effects of Nitrogen (N) supplementation of kermes oak acorns on in vitro gas production (experiment 1) and on intake and digestibility by lambs (experiment 2) where investigated.

In experiment 1, seven simulated diets composed of a mixture of 200 mg of oat-vetch hay and 100 mg of acorns as basal diet (control diet: HA) were evaluated. Diets included the basal diet above plus several levels of urea (1%, 2% and 3% of basal diet OM, respectively HAU1, HAU2 and HAU3) and amounts of ground soybean meal to give equivalent amounts of N as the 3 urea diets (HASb1, HASb2 and HASb3). The kinetic of in vitro gas production from incubated diets was determined using the calibrated glass syringe technique. In experiment 2, four Barbarine lambs (aged about 6 month, initial average BW 26 kg) were used in 4x4 Latin squares design to study the effect of the type of N supplementation on intake and digestion of diets containing acorns. Experimental diets provided oat-vetch hay ad libitum plus either processed barley (HB) or shady-dried processed acorns (HA). The HA diet was supplemented with either 10 g of urea (HAU) or with an iso-nitrogenous amount of soybean meal (HASb). Every experimental period comprised 21 days for adaptation and 7 days for measurements. Feed and water intakes, apparent digestibility of OM, CP and CF and N balance were determined.

The level 3% of urea (HAU3) resulted in higher (P<0.05) total gas production than 1% urea (respectively 65.7 and 63 ml), but no differences were observed among soybean diets. Levels of urea did not affect in vitro fermentation, but added soybean meal increased (P<0.01) gas production of acorns diet comparatively to control and urea diets. Protein sources did not affect total diet and hay DM intake or OM and CF digestibility. The acorns diet (HA) exhibited a lower (P<0.01) N digestibility (32%) than the three other diets, which were similar (mean value 54.7%). Retained N was negative in HA. The highest N retention values (P<0.01) were noted with HB and HASb, which were similar (mean value 1.7 g day-1).

Keywords: Acorns, digestibility, gas production, intake, lambs, nitrogen, Quercus coccifera


Introduction

In Tunisia, many local non-conventional feed resources are available during the year. In addition to crop residues and by-products, a growing interest is given to some forestry products including shrub foliage and fruits in small ruminants feeding. Acorns from Oak trees, mainly Kermes oak (Quercus coccifera) and Cork oak (Quercus suber) are abundant in Tunisian coastal-forestry regions. The maturation of acorns from kermes oak is biennial. They reach morphological maturity at the end of autumn and greatest percentage of trees bear fruits in November (Elena-Rossello et al 1993). Acorns are generally harvested by farmers from October to December and fed to goats, or marketed or traditionally conserved (Kayouli and Buldgen 2001).

Acorns are a cost-effective energy source for small ruminants (Kayouli and Buldgen 2001) and can reduce the need for barley in the diet (Al Jassim et al 1998). Recently, the effect of replacing some or all barley with acorns from Kermes oak in concentrate on in vitro fermentation in goats was reported (Moujahed et al 2005b). Metabolisable energy (ME) content calculated from gas production was higher for barley than for acorns (2484 and1767.4 kcal kg-1 DM, respectively). In addition, these results suggested that acorns from kermes oak could replace 50% of barley in concentrate supplementing vetch-oat hay basal diet. Beyond this level, in vitro gas production deceased; this may reflect deceased microbial activity. Al the previous studies reported clearly that in spite of their relatively high energetic level, acorns are low in nitrogen (CP ranged from 30 to 40 g kg-1 DM). This work was designed to examine the effects of the type and level of N supplementation (from urea and soybean) on in vitro fermentation, intake, digestibility and N balance in lambs.


Material and methods

Plant material

For the in vitro trial, Acorns (Quercus coccifera) were harvested in the forestry region of Bizerte (North of Tunisia, humid climate). Acorns from several trees were harvested in November and December 2002 and mixed to make a sample. Dry matter (DM) was determined at 105°C in a forced-air oven and the samples were dried at 40°C during 48 h and then ground to pass through a 1 mm screen and stored for chemical analysis and in vitro determinations. In the in vivo trial, acorns were harvested in the forestry region of Nefza (North of Tunisia, sub-humid climate) during November and December 2003. They were air-dried in the shade for one month (82% DM). Oat-vetch hay (70% oat and 30 % vetch at sowing) was produced at the region of Mateur (North of Tunisia, humid climate) in 2003. It was chopped to avoid selection and loss from troughs. Urea (46.6% N) and soybean meal (46.24% CP) were used as N supplements.

Diets, animals, experimental designs and measurements
Experiment 1: In vitro effect of acorns nitrogen supplementation

Seven simulated diets consisting of a mixture of 200 mg of oat-vetch hay and 100 mg of acorns as basal diet (control diet: HA) were studied. Experimental diets included HA, HA with added urea (1%, 2% and 3% of basal diet OM, respectively HAU1, HAU2 and HAU3) or added ground (1 mm screen) soybean meal to give equivalent amounts of N as the three urea diets (respectively HASb1, HASb2 and HASb3). Urea (46.6% N) was added as solution, while soybean meal replaced a part of the hay. Diets mixtures were made of component ground feeds using a mixer. .

The in vitro gas production technique described by Menke and Steingass (1988) was used to measure gas production from diets. Rumen liquor was collected from four adult local goats fitted with rumen cannula (average live weight: 44.5 kg). Goats were housed in individual pens and received 70 g kg-1LW0.75 of a ration composed of 70% of oat-vetch hay and 30% of commercial concentrate on dry matter (DM) basis twice per day. Duplicate samples of 300 mg DM from each experimental diet were introduced into pre-warmed (40°C) calibrated 100 ml glass syringes before injection of 30 ml of ruminal liquor: buffer mixture (1:2 v/v) into each syringe. Syringes where incubated in a warm bath (39 °C) and gently shaken every 30 min during the first 10 hours of incubation. Gas production was recorded after 1, 2, 4, 6, 12, 24, 36, 48, 72 and 96 h periods. For each diet, measurements were carried out during 3 successive experimental periods. Gas volumes were fitted using the exponential model of Ørskov and McDonald (1979): GP=a+b(1-e-ct), where: GP is the gas production at time t; 'a' is the immediate gas production; 'b' is the fraction with slower gas production; 'c' is the rate of gas production and 'a+b' is the total gas production. Parameters were calculated using a Non Linear procedure (SAS 1985).

Experiment 2: In vivo effect of nitrogen supplementation

Four male Barbarine lambs aged 6 months (initial average BW 26 kg) were used in a 4x4 Latin square. Animals received 200 g of commercial concentrate and oat-vetch hay ad libitum for one month before the beginning of the experiment in order to equalize their body condition. They were housed individually in metabolism cages. Four experimental diets containing supplied oat-vetch hay ad libitum were evaluated. The first diet included 200 g of processed barely (HB). The second diet included 200 g of processed acorns (HA). The later was supplemented with 10 g of urea, which represents 2% of OM intake (HAU) or with 63 g of soybean meal (HASb). Diets HAU and HASb were is-onitrogenous. Urea and soybean meal were mixed with acorns. Every experimental period lasted 28 days (21 days for adaptation and 7 days for measurements). Diets were offered in two equal meals (08:00 and 16:00) daily. Feed and water intakes and apparent diet digestibilities of OM, CP and CF and N balance were determined during the 7-day measurement period. Animals had free access to fresh water and were weighed at the start and the end of each measurement period.

Amounts of offered and refused hay, acorns and water were weighed daily during the measurement period. Daily samples of hay and acorns refusals (20%) were taken and bulked separately. Total daily fecal output for each animal, collected before the morning meal, was weighed, sampled (10%) and pooled for the 7- day collection period. Fecal samples were stored at -10°C. A daily collection of urine was made. About 100 ml of 10% H2SO4 solution was added to the urine container. A 10% urine aliquot collected daily from each animal was stored at - 10°C pending N analysis. Portions of individual pooled samples of refusals and faeces were dried in a forced-air oven (40°C), ground through a 1 mm screen, and stored for later analysis. Drinking water consumption was recorded daily during the 7-day measurement period.

Laboratory analysis

Dry matter (DM) content of food, refusals and feces was determined by drying in a forced-air oven at 105°C for 24 h. Feed, refusals and faeces were analyzed for ash (550°C, 6 h), CF using the Weende procedure and CP by the Kjeldahl method (AOAC 1984) as 6.25 x N (ID7.015). NDF, ADF and ADL exclusive of residual ash (respectively NDFom, ADFom and ADLom) were analyzed in offered feeds as described by Goering and Van Soest (1970). Urinary N was determined by the Kjeldahl method. Total tannin content of acorns was analyzed using the procedure described by Julkunen-Tito (1985). Briefly, aqueous acetone (70%) was used to extract tannins from 200 mg samples of air-dried acorns during 24h at 4°C. After centrifugation (3000 r/mn), the floating part was mixed with a Folin-Ciocalteu solution and Na2CO3 (20%). Total tannins were measured colorimetrically using a spectrophotometer at 720 nm. Results were expressed as g of equivalent tannic acid per /kg DM.

Statistical analysis

The General Linear Model procedure (GLM) of SAS (1985) was used to analyze data. In the in vitro trial, the model included effects of diet, incubation and diet x incubation. In the in vivo trial, model included effects of diet, animal and period. Duncan's multiple range test was used to compare treatment means.


Results

Chemical composition and in vitro gas production characteristics of feeds

Chemical composition of feeds is presented in Table 1.

Table 1.   Chemical composition of feeds and in vitro incubated diets (g kg-1 DM)

Item

Acorns

Oat-vetch hay

Barley grains

Soybean meal

HA

HB

HAUa

HASba

DM

816

856

860

881

838

844

836

867

Ash

24

66

66

75

65

66

65

62

CP

44

52

106

462

58

83.4

112.5

112.5

NDFomb

382

413

277

106

390

365

390

354

ADFom

174

263

58

59

227

195

227

197

ADLom

70

42

15

2

48

32

48

46

TTc

36

-

-

-

-

-

-

-

a The average of the urea or soybean diets.

b Exclusive ash.

c TT: Total tannins expressed as g equivalent tannic acid/kg DM.

Feeds are generally low in ash. The lowest value was found in acorns (24 g kg-1 DM). Oat-vetch hay was highest in fibre (NDFom and ADFom) and acorns presented highest proportion of lignin (ADLom: 70 g kg-1 DM). CP was lowest in acorns (44 g kg-1 DM) and highest in soybean meal (462 g kg-1 DM). Barley exhibited a moderate CP content (106 g kg-1 DM). Total tannin content of acorns was relatively low (36 g kg-1 DM). All incubated diets were similar in ash content. CP content ranged from 58 in HA to 112.5 g kg-1 DM in HAU and HASb. Acorns (HA) and urea (HAU) diets had higher fibre contents (NDF and ADF) than barley (HB) and soybean (HASb) diets.

Data on in vitro gas production of feed are reported in Table 2. Total cumulative gas production (a+b) was high with barley and soybean (respectively 84.9 and 87.4 ml), moderate with acorns (66.5 ml) and relatively low with hay (60.6 ml). The rate of gas production (c) was highest in soybean (0.11 h-1) and lowest in hay (0.05 h-1).

Table 2.  In vitro gas production characteristics of feeds

Parametersa

Acorns

Hay

Barley

Soybean

a (ml)

b (ml)

c (h-1)

a+b (ml)

-4.4

70.5

0.063

66.5

-1.3

62

0.05

60.6

-1.9

86.8

0.1

84.9

-1.1

88.5

0.11

87.4

aa, b and c are constants in the equation: GP= a + b(1-e-ct), where GP is the gas production at time t, a is the immediate gas production, b is the fraction of the slowly gas production, c is the rate of gas production; and (a+b) is the total gas production.

Gas production from diets

Gas production parameters for individual diets are reported in Table 3.

Table 3.  Effects of Acorns N supplementation on in vitro gas production parameters of diets

Diets

a (ml)

b (ml)

a+b (ml)

c (h-1)

HAU1

-1.8

64.8b

63b

0.0506

HAU2

-1.8

66. 5ab

64.7ab

0.0506

HAU3

-2.4

68.1a

65.7a

0.0508

SEM

0.242

0.85

0.699

0.001

P

ns

< 0.05

< 0.05

ns

HASb1

-0.55

67.8

67.2

0.0554

HASb2

-1.13

68.5

67.4

0.0583

HASb3

-0.6

68.5

68.1

0.061

SEM

0.447

0.808

0.556

0.003

P

ns

ns

ns

ns

HA

-1.3AB

65.8B

64.5B

0.0572A

HAUb

-2B

66.5B

64.5B

0.0507B

HASbb

-0.76A

68.3A

67.6A

0.0577A

SEMc

0.221

0.483

0.385

1.47 10-3

P

< 0.05

< 0.05

< 0.01

< 0.05

aa, b and c are constants in the equation: GP= a + b(1-e-ct), where GP is the gas production at time t, a is the immediate gas production, b is the fraction of the slowly gas production, c is the rate of gas production; and (a+b) is the total gas production.

a, b, c, A, B, C For the same column values with the same letter do not differ significantly, P probability.

b The average of parameters values for urea and soybean diets.

SEM: standard error of the mean.

The level 3% of urea (HAU3) gave higher (P<0.05) total gas production than 1% in AHU1 (respectively 65.7 and 63 ml). But no differences were observed between soybean diets (averaged 67.6 ml). Increasing the level of urea had no effect on in vitro fermentation. Protein supplementation of the basal diet increased (P<0.01) total gas production (a+b) of acorns diet as compared to control and urea diets (averaged 64.5, 64.5 and 67.6 ml, respectively in HA, HAU and HASb). Whatever their level, urea and soybean meal had no effect on the rate constant of gas production (c) of Acorns diets. This parameter was lower (P<0.05) in urea diet (0.05 h-1) than in control and soybean diets (0.057 h-1).

Feed and water intakes

Data on feed intake are reported in Table 4.

Table 4.  Feed intake and water consumption in lambs fed acorns dieta

 

HB

HA

HAU

HASb

SEMb

DM intake,g per day

 

 

 

 

 

  Hay

468

469

440

431

32.3

  Barley

172

0

0

0

0

  Acorns

0

104

126

146

33.4

  Total diet

640

573

574

632

91.3

DM intake, g kg-1 BW0.75

 

 

 

 

 

  Hay

40

40

38

37

3.4

  Acorns

0

9

11

12

2.7

  Total diet

55

49

49

54

2.7

Water consumed, g day-1

1770

1600

1600

1750

110

a HA: hay + acorns, HB: hay + barley, HAU: hay + acorns + urea, HASb: hay + acorns + soybean meal.

b SEM: standard error of the mean.

Neither acorns (compared to barley), nor supplementation with N or source of N had an effect on hay and total diet intake and water consumption. Although differences are not significant, highest values of total DM intake were observed in HB and HASb (mean value 636 g day-1) and lowest ones in HA and HAU (mean value 573.5 g day-1).

Apparent digestibility of diets

Diet digestibility coefficients are presented in Table 5.

Table 5.  Digestibility of diets in lambs fed acorns dieta

 

HB

HA

HAU

HASb

SEMb

Diet digestibility, %

 

 

 

 

 

  OM

60

59

51

62

6.4

  CP**

56a

32b

53a

55a

4.4

  CF

40.1

39.3

35.3

41.4

2.8

DOMi, g kg-1 BW0.75

29.7

27.6

22.6

34.1

6.4

DCPi, g kg-1 BW0.75

2.3a

1b

2.5a

2.8a

0.4

a HA: hay + acorns, HB: hay + barley, HAU: hay + acorns + urea, HASb: hay + acorns + soybean meal.

a, b means in the same line with different superscripts differ,  ** P< 0.01.

b SEM: standard error of the mean.

DOMi: Digestible organic matter intake.

DCPi: Digestible crude protein intake.

Digestibility values of organic matter and crude fiber were not significantly altered by acorns (compared with barley), N supplementation or N source. Crude protein digestibility was decreased (P<0.01) by substituting acorns for barley in the diet. Supplementation with N improved (P<0.01) N digestibility of the acorn diets, but no effect of N source was detected. Intake of digestible OM was not altered by energy source, N supplementation or N source; but intake of digestible N was increased (P<0.01) by supplemental N.

Nitrogen balance

Comparatively to acorns (HA), barley added to hay (HB) induced a higher N intake (P<0.01) (Table 6).

Table 6.  Nitrogen balance in lambs fed acorns dietsa

 

HB

HA

HAU

HASb

SEMb

N intake, g day-1**

7.6b

5.7c

9ab

9.6a

1.05

N excretion, g day-1

 

 

 

 

 

       Feces**

3.3b

3.9ab

4.1a

4.3a

0.42

       Urine**

2.8b

1.95b

4a

3.4a

0.72

N absorbed, g day-1**

4.5a

1.8b

4.9a

5.3a

0.79

N retained, g day-1**

1.5ab

-0.15c

0.9b

1.9a

0.48

a HA: hay + acorns, HB: hay + barley, HAU: hay + acorns + urea, HASb: hay + acorns + soybean meal.

a, b, c means in the same line with different superscripts differ significantly, ** P< 0.01.

b SEM: standard error of the mean.

Fecal and urinary excretions did not significantly differ between the two diets. While apparently absorbed and retained N were significantly (P<0.01) higher in barley diet. As expected, N intake was increased (P<0.01) by supplemental N, with similar fecal excretion and higher urinary losses. Adding N increased apparently absorbed and retained N (P<0.01). Supplemental N from soybean increased (P<0.01) to a higher level retained N than did urea (plus 1 g day-1).
 

Discussion

In vitro measurements

The increase of the level of urea supply increased moderately the extent (b and a+b) but not the rate of gas production in acorns diets. This effect may be due to a slight enhancement of fermentation of diet OM and cell walls. These results are consistent with those of Ben Salem et al (1995) who found a moderate but non-significant improvement in in vivo OM and crude fiber digestibility when Acacia cyanophylla was supplemented with urea. By another hand, the optimum use of ammonia-N by micro-organisms for microbial yield and cellulose digestion needs to be accompanied with available ATP from carbohydrates fermentation (Sauvant 1997) as the main motor for microbial yield (Demeyer 1991). Moujahed et al (2003) suggested that starch from acorns may have a slow degradation rate and this is supported by our comparison of feeds (Table 2). This could explain the effect of supplemental N noted in the present experiment. In addition, since acorns are very low in minerals (24 g kg -1DM), a deficiency in some minerals essential for microbial activity (e.g. S and P; Jouany et al 1995) may limit extent of fermentation. Although tannin content in acorns was not excessive (total tannins: 3.5% DM), tannins could have exerted negative effects on fermentation of all samples tested. With their affinity for proteins, tannins complex and precipitate them (Leinmüller et al 1991). In addition, tannins can reduce microbial cellulolytic activity by complexing enzymes and/or micro-organisms membranes (McLeod 1974). This may partially reduce proteolysis and result in an ammonia deficiency for ruminal microbes.

Compared with added urea, added soybean meal increased rate and extent of digestion as measured by gas production. These findings could be explained by a deficiency in amino acids and peptides, which might limit microbial yield and OM, cell wall (Kalmbacher et al 1995) and non structural carbohydrates (Knaus et al 2001) fermentation in urea diets. The added soybean meal may have itself contribute to the enhance of OM degradation (Knaus et al 2001) and improve energy supply for microbes (Carro and Miller 1997). In addition soybean meal supply has increased starch degradation by stimulating amylolytic microbes (Russell et al 1983).

Feed intake

Neither the source nor the level of supplemental N had an effect on intake of DM from hay or the total diet. This result dose not matches the gas production responses seen above or the positive effects of N supplementation often seen with forages (Faverdin et al 2003; Mahouachi et al 2003), since protein supplements generally increase forage intake (Preston 1986). Our results may be ascribed to the combined effects of physical and metabolic intake regulation. Indeed, the rumen could have been distended with all the studied diets and the chemical factors may have limited intake through absorption of fermentation end-products (Faverdin et al 1997), because animal metabolic demands were satisfied (Ærskov and Ryle 1990). Furthermore, the level of N supplementation may have been insufficient to meet the need for microbial fermentation. There was a trend for higher total DM intake with barley and soybean diets that could be explained by a better balance of nutrients for rumen microbes provided by barely and soybean or simply higher supply of digestible substrate.

No differences were observed in water intake among these diets. Water intake tended to parallel DM and OM intake. Generally, water consumption is correlated with feed intake (Chenost and Kayouli 1997).

Diet digestibility

Barley (HB) and acorns (HA) diets had similar OM and CF digestibility coefficients. Combined with intake data, this result indicates that at 30% of the diet, acorns could replace barley. This observation is in line with results of Moujahed et al (2005b). Those authors suggested that acorns could replace barley at 50% of the concentrate in vetch-oat hay basal diet as measured by gas production of incubated diets. Supplemental N from soybean or urea did not influence OM and CF digestibility of acorns diets. This contradicts both results of studies where N supplementation increased digestibility of low quality roughages (Moujahed et al 2000; Koeing et al 2002) and our gas production responses to supplemental N. Perhaps the amount of supplied N was low and not sufficient to improve digestibility. In addition, acorns tannins could have exerted a negative effect on digestibility because tannins are known to inhibit microbial and enzyme activities (Leinmüller et al 1991). Individual animal variations could be involved in the in vivo trial; in vitro observations are more repeatable. The closed and static in vitro system fails to consider digestive outflow, end-product absorption and post-ruminal digestion (Ellis 1978).

The acorns diet (HA) had a lower (P<0.01) CP digestibility than barley diet and digestibility was increased by N supplementation. Part of this was expected yet. Several studies have shown that soybean or urea supplements will increase CP digestibility of supplemented diets (Ben Salem et al 1995; Moujahed et al 2000; 2005a). No difference between the two sources of supplemental N was detected. These observations were not expected considering that acorns provide a considerable amount of energy (Al Jassim et al 1998, Kayouli and Buldgen 2004), but in line with in vitro observations by Moujahed et al (2005b) who found that ME content of acorns is lower than for barley. Consequently, the current results could be ascribed to a better energy to N balance for the diet without added N (HB). However, acorn tannins may have had negative effects. These secondary compounds could have protected part of protein in HASb (Leinmüller et al 1991) and reduced microbial (McAllister et al 1994) and enzyme activities (Griffits 1981).

Nitrogen balance

Nitrogen balance was negative with the basal diet (HA). Negative values are often found with low quality diets, particularly those containing tanniniferous feeds (Reed et al 1990; Moujahed et al 2000). Tannins reduce protein degradation (Leinmuller et al 1991) and absorption (Mc Leod 1974). These negative values are generally related to high faecal N losses (68.4 % of N intake). In the current study, N retention was low, due mainly to N intake (from 5.6 to 9.6 g day-1) relative to the need for growing lambs. Supplementation with both either form of N improved N retention by lambs as N intake and digestion were increased. Faecal N losses were high with the acorns diets (68.5, 45.6 and 44.9 of N intakes, respectively for HA, HAU and HASb). Lower than expected CP diegestibility with acorns diets may reflect a low degradation of CP in the rumen and absorption in the gat because tannin protein complexes were not fully hydrolysed in the gastro-intestinal tract reducing N absorption (Nunez-Hernandez et al 1991). The improvement from supplemental N might have been limited by tannin effects. Indeed, despite the better N and energy balance, we didn't observe any increase of N absorption. However, retained protein from soybean diet may be of a better quality than from urea diet, as supported by a higher numerical ratio of retention to absorption of N (35.8 and 18.4%, respectively).


Conclusions


Acknowledgments

In vitro results were presented in the Regional Workshop on Recent Advances in Goat Production Under Arid Conditions, FAO, DRC, 10-13 April 2006, Cairo, Egypt.


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Received 11 January 2007; Accepted 23 March 2007; Published 2 April 2007

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