Effects of plant extract supplementation on rumen fermentation and metabolism in young Holstein bulls consuming high levels of concentrate

Animal Feed Science and Technology 137 (2007) 46–57

Effects of plant extract supplementation on rumen fermentation and metabolism in young Holstein bulls consuming high levels of concentrate M. Devant a,∗ , A. Anglada a , A. Bach a,b a

Grup de Recerca en Nutrici´o, Maneig i Benestar Animal, Unitat de Remugants, Institut de Recerca i Tecnologia Agroaliment`aries (IRTA), Barcelona 08193, Spain b Instituci´ o Catalana de Recerca i Estudis Avan¸cats (ICREA), Barcelona 08010, Spain Received 14 June 2006; received in revised form 6 September 2006; accepted 4 October 2006

Abstract Ninety male Holstein bulls were used in a complete randomized design to study the effects of a blend of plant extract (PE: cynarin, gingsen and fenugreek; Biostar® , Phytosynthese, France) supplementation on performance, rumen fermentation, and metabolism of Holstein bulls fed high-concentrate diets. Three treatments: control (CTR), supplementation with 32 mg/kg DM sodium monensin (MON, positive control), and supplementation with 2.8 g/kg DM of PE were tested. Animals were weighed (303 ± 3.6 kg of initial BW) and randomly distributed by BW in six pens. Concentrate and straw were both offered ad libitum. Animal body weight (BW), and group concentrate and straw consumptions were recorded every 3 weeks until the first animals reached the target slaughter weight of 460 ± 30 kg. Rumenocentesis was performed to all bulls at 63 days of study at 09:00 h to determine rumen pH, ammonia nitrogen, and volatile fatty acid concentrations. Blood samples from all bulls were taken at 7, 35, and 71 days of study at 09:00 h to determine cortisol, glucose, insulin, and leptin concentrations. At 84 days of study, when the first bulls reached the target BW, CTR bulls had lower (P<0.001) BW (428.1 ± 1.10 kg) than bulls supplemented with MON (435.6 ± 1.10 kg), however, the BW of PE supplemented bulls (432.6 ± 1.10 kg) did not differ from CTR or MON supplemented bulls. Neither monensin nor PE supplementation affected feed consumption, or feed efficiency. Rumen pH was lower (P<0.001) in MON and PE treatments than in CTR. Rumen molar concentrations of propionic acid Abbreviations: ADG, average daily gain; BW, body weight; CTR, control; DM, dry matter; MON, monensin; PE, plant extracts; VFA, volatile fatty acids ∗ Corresponding author. Tel.: +34 935 910 127; fax: +34 935 863 122. E-mail address: [email protected] (M. Devant). 0377-8401/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.anifeedsci.2006.10.003

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increased (P<0.05) in MON and PE bulls compared to CTR bulls. Bulls supplemented with PE had greater (P<0.05) serum insulin concentration than MON or CTR bulls. Cortisol serum concentration remained unchanged in the CRT treatment with time, in contrast to MON and PE treatments that elicited a decrease in cortisol serum concentration between 7 and 35 days of study and an increase thereafter. Leptin serum concentration increased (P<0.01) from 35 to 71 days of study; however, in MON bulls this increase was not as pronounced as in PE and CTR bulls. In bulls fed high-concentrate diets, plant extract supplementation had similar effects on growth, rumen fermentation, and cortisol serum concentration to monensin supplementation. © 2006 Elsevier B.V. All rights reserved. Keywords: Beef; Monensin; Plant extracts; Rumen; Leptin

1. Introduction Monensin is a monovalent carboxylic ionophorous polyether antibiotic produced by Streptomyces cinnamonensis that is active against parasites, Gram-positive bacteria and mycoplasmas (Butaye et al., 2003). In beef cattle, monensin has been widely used as a growth promoter (Goodrich et al., 1984). However, the use of monensin as a feed additive in the European Union is banned since January 2006 (EU 1831/2003). Plant extracts have been proposed as an alternative to antibiotics (Rhodes, 1996). Biostar® is a mixture of extracts from three plants: Cynara cardunculus subesp. scolymus, Eleutherococcus senticosus, and Trigonella foenum graceum. C. cardunculus subesp. scolymus (artichoke) is composed of cynarin, dicaffeoylquinic acid isomer, cynaropicrin, flavonoids (luteolin and cynarosid), chlorogenic and caffeic acids. E. senticosus (Siberian ginseng) contains unique steroidal saponins termed eleutherosides that are structurally similar to Panax ginseng (Chinese ginseng) ginsenoides (Bucci, 2000). T. foenum graceum (fenugreek) is rich in galactomannans, saponins, and 4-hydroxyisoleucine. Biological actions of artichoke, Siberian ginseng, and fenugreek plant extracts have been mostly studied in humans, and are mainly hypoglycaemic and hypocholesterolaemic (Briskin, 2000; Francis et al., 2002; Madar and Stark, 2002). However, few studies have been conducted to evaluate the effect of a mixture of these plant extracts on performance, rumen fermentation, and metabolism in beef cattle. The aim of this study was to evaluate the effect of the supplementation of this specific blend of plant extracts on performance and metabolism of Holstein bulls fed high-concentrate diets, contrasting the results with a negative (unsupplemented) and a positive (monensin) controls.

2. Materials and methods 2.1. Animals, treatments, and housing Ninety male Holstein bulls were used in a complete randomized design. Animals were weighed and randomly distributed by body weight (BW) in 6 pens (15 animals/pen). After 4 weeks of an adaptation period consuming the control concentrate bulls were weighed on two consecutive days and started the study with an initial BW of 303 ± 3.6 kg. The

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Table 1 Concentrate ingredients and chemical composition Item Ingredient composition on dry matter basis (g/kg) Corn Corn gluten feed Barley Soybean hulls Soybean meal Palm oil Calcium carbonate Salt Dicalcium phosphate Vitamin–mineral premixa

507 200 100 84 49 27 15 8 6 4

Chemical composition on dry matter basis (g/kg) Crude protein Ether extract Neutral detergent fibreb Ash

123 63 253 55

a

Vitamin–mineral premix per kg = 225,000 UI Vitamin A, 50,000 UI Vitamin D3, 1500 mg Vitamin E, 125 mg Vitamin B1, 500 mg Vitamin B2, 1.25 mg Vitamin B12, 1.25 g nicotinic acid, 7 g manganese oxide, 8.75 mg zinc oxide, 7.5 g iron carbonate, 2.5 g copper sulfate, 375 mg potassium iodide, 56 mg sodium selenite, 60 mg cobalt carbonate, and 37.5 g magnesium oxide. The MON concentrate was supplemented with monensin (32 mg/kg concentrate DM) and the PE concentrate was supplemented (2.8 g/kg concentrate DM) with a blend of artichoke (200–300 g/kg), Siberian ginseng (150–250 g/kg) and fenugreek (550–650 g/kg). b Assayed with heat-stable amylase and expressed inclusive of residual ash.

pens were then randomly assigned to treatments: control (CTR), monensin (MON), and a blend (Biostar® ) of plant extracts (PE), thus there were two pens per treatment. Biostar® is mixture of artichoke (200–300 g/kg), Siberian ginseng (150–250 g/kg) and fenugreek (550–650 g/kg). Concentrate and barley straw were offered ad libitum. Concentrate ingredient and chemical composition are presented in Table 1. Sodium monensin (Elanco Animal Health Inc., Indianapolis, IN) was included at the rate of 32 mg/kg DM in the MON concentrate, and Biostar® (Phytosynthese, France) was included at the rate of 2.8 g/kg DM to the PE concentrate to achieve the doses of 5 mg/100 kg of BW. Animals were housed in outdoor paved and covered pens in a commercial farm of the Cooperativa de Artesa (Lleida, Spain) and managed following the principles and guidelines of the IRTA Animal Care Committee. 2.2. Measurements and sample collection Animal BW, and pen concentrate and straw consumptions were recorded every 3 weeks until the first animals reached the target slaughter weight (460 ± 30 kg). After day 84 of the study, the first animals reached the target slaughter weight and this date was the end of the study, because animal density in the pens changed and this could affect performance of the remaining bulls. Bulls were weighed in two consecutive days (84 and 85 days of study). Rumenocentesis was performed to all bulls at 63 days of the study at 09:00 h during three consecutive days (30 animals/day) to avoid differences due to sampling time within day. Rumenocentesis was conducted with a 14-cm 14-gauge needle inserted into the ventral

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sac of the rumen approximately 15–20 cm caudal–ventral to the costocondral junction of the last rib. Rumen liquid pH was measured immediately after obtaining the sample. Also, 2 mL of rumen fluid were acidified with 2 mL of 0.2N HCl, and frozen until further NH3 N analysis. In addition, based on Jounay (1982), 4 mL of rumen liquid were mixed with 1 mL of a solution containing 2 g/L mercuric chloride, 20 mL/L orthophosphoric acid, and 2 g/L 4-methylvaleric acid (internal standard) in distilled water, and frozen until subsequent volatile fatty acids (VFA) analyses. Two blood samples were obtained by venipuncture of the jugular vein at 7, 35 and 71 days of the study at 09:00 h during three consecutive days (30 animals/day) to avoid differences due to sampling time within day. One blood sample (10 mL) was harvested without additives, whereas the second blood sample (5 mL) was harvested with sodium fluoride and potassium oxalate for subsequent glucose determination. Blood samples were centrifuged at 1500 × g at 4 ◦ C for 10 min to obtain serum. Serum and plasma samples were stored at −20 ◦ C until subsequent analyses of glucose, insulin, cortisol, and leptin. 2.3. Chemical analyses Feed samples were analysed for DM (24 h at 103 ◦ C), ash (4 h at 550 ◦ C), crude protein content using the AOAC (1990) method (988.05) adapted for an automatic distiller Kjeldhal (Kjeltec Auto 1030 Analyser, Tecator, Sweden) and using CuSO4 /Se as catalyst instead of CuSO4 /TiO2 , ether extract using the AOAC method (920.39) using petroleum ether for distillation instead of diethyl ether (AOAC, 1990), and neutral detergent fibre, with sodium sulphite and heat-stable alpha-amylase expressed inclusive ash (Van Soest et al., 1991). To determine rumen NH3 -N concentration, samples were centrifuged at 25,000 × g for 20 min and the supernatant was analysed as described by Chaney and Marbach (1962). Rumen VFA concentration was analysed with a polyethylene glycol terephtalic acid treated capillary column (25 m × 0.25 mm i.d., 0.25 ␮m film thickness, BP21, SGE, Europe Ltd., Barcelona, Spain) using a gas chromatograph (Carlo Erba Instruments chromatograph, CE 5300 HT, Milano, Italy) and an initial temperature of 100 ◦ C during 1 min, programmed at 8 ◦ C/min to 160 ◦ C held on 5 min. The injector and flame ionization detector temperatures were 250 and 280 ◦ C, respectively. Carrier gas was helium at 30 cm/s, and the injection was performed by split mode at a ratio of 1:30. Glucose plasma concentration was determined following the hexokinase/G-6-DH enzymatic method (Burrin and Price, 1985). Insulin serum concentration was determined using ELISA (kit no. 10-1131-01 Mercodia, Uppsala, Sweden). Cortisol serum concentration was determined using an immunoassay technique (DRG-Cortisol ELISA EIA-1887, DRG Instruments, Germany). Leptin serum concentration was only analysed in blood samples corresponding to 35 and 71 days using a radioimmunoassay (Multi-Species leptin RIA kit, ref XL-85K, Linco Research, Missouri, USA), previously validated for use with bovine serum (Minton et al., 1998; Gabai et al., 2002). 2.4. Statistical analyses Average daily gain (ADG), and metabolism data were analysed using a mixed-effects analysis of variance (ANOVA) with repeated measures. The statistical model included initial

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BW as a covariate, and treatment, time, and the interaction between treatment and time as fixed effects, and bull nested within pen as random effect to account for any potential dependencies between animals within pen. Time was considered a repeated factor and for each analysed variable, the interaction of bull within pen nested within treatment (the error term) was subjected to three variance–covariance structures: compound symmetry, unstructured, and autoregressive order one. The variance–covariance matrix that yielded the smallest Schwarz’s Bayesian criterion was considered to be the most desirable structure. Multiple comparisons among treatment means were assessed by a Tukey’s test. Concentrate and straw consumption, and feed efficiency data were analysed as described above but using pen as random effect. Leptin data were analysed as described above but without subjecting the time effect to any variance–covariance structure (as there were only two measures for each animal). Initial BW, BW at 84 days, and rumen fermentation data were analysed as described for ADG without the time effect (as there were no repeated measures), and pen as random effect. Insulin serum concentration data were transformed to a log scale to achieve a normal distribution. The means presented herein correspond to non-transformed data, however, S.E. and P-values correspond to the ANOVA analyses using log-transformed data.

3. Results Data of one animal receiving the PE treatment were removed from the database used for the statistical analyses because during the last weeks of study the bull lost weight (−1.6 kg/day) and after slaughter a massive tissue jaundice and a fatty liver were observed. 3.1. Animal performance Performance data are presented in Table 2. After 84 days of study, when the first bulls reached the target BW, CTR bulls had lower (P<0.001) BW (428.1 ± 1.10 kg) than bulls supplemented with monensin (435.6 ± 1.10 kg), but the BW of PE supplemented bulls (432.6 ± 1.11 kg) did not differ from that of CTR or MON supplemented bulls. Consequently, ADG from 0 to 84 days of study tended (P=0.10) to be lower for the CTR bulls (1.48 ± 0.029 kg/d) compared to the MON bulls (1.57 ± 0.029 kg/d). At 84 days of the study a total of 6, 8, and 6 bulls reached the target BW for CTR, MON, and PE treatments, respectively. No statistical differences between treatments were observed in group concentrate and straw consumptions, and concentrate conversion efficiency (Table 2). Both, ADG decreased (P<0.001) and group concentrate consumption increased (P<0.01) with days of study, and as a consequence, the concentrate conversion efficiency (ADG to concentrate intake ratio) decreased (P<0.001) with days of study. 3.2. Rumen fermentation Rumen fermentation data are presented in Table 3. Average rumen pH was greater (P<0.01) in CTR animals (6.52 ± 0.068) than in MON (6.08 ± 0.068) or PE (6.12 ± 0.068). Average rumen NH3 -N concentration was not affected by treatment. Neither monensin nor PE supplementation affected total rumen VFA concentration, molar proportions of butyrate,

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Table 2 Performance and carcass parameters of Holstein bulls as affected by monensin or a plant extract blend supplementation Item

BW Initial (kg) Final (kg) ADG (kg/day) Concentrate intake (kg DM/day) Straw intake (kg DM/day) Concentrate efficiency (kg/kg)

Treatmenta

S.E.b

CRT

MON

PE

302.8 428.1 b 1.48 b 7.47

304.8 435.6 a 1.57 a 7.67

303.2 432.6 ab 1.54 ab 7.72

1.64

1.43

0.199

0.206

P-valuec T

Time

T×time

1.58 1.10 0.029 0.236

0.60 <0.001 0.10 0.76

– – <0.001 <0.01

– 0.48 0.83

1.47

0.127

0.51

0.60

0.57

0.199

0.0043

0.63

0.01

0.87

Means with different letters (a and b) within the row are statistically different. a CRT = control, MON = supplemented with monensin (32 mg/kg concentrate DM), PE = supplemented (2.8 g/kg concentrate DM) with a blend of artichoke (200–300 g/kg), Siberian ginseng (150–250 g/kg) and fenugreek (550–650 g/kg). b S.E. = standard error of the means. c T = treatment effect, time = time effect, T×time = interaction between treatment and time.

isobutyrate, isovalerate, and valerate. However, monensin and PE supplementation numerically (P=0.11) decreased rumen molar proportion of acetate and increased (P<0.05) rumen molar proportion of propionate compared to the CRT treatment. Consequently, the acetate to propionate ratio in the rumen fluid was greater (P<0.05) in the CTR (1.20 ± 0.115) than in the MON (0.82 ± 0.115) or PE (0.84 ± 0.115) animals. Table 3 Rumen fermentation parameters of Holstein bulls as affected by monensin or a plant extract blend supplementation Item

Treatmenta

S.E.b

P-valuec

CRT

MON

PE

pH NH3 N (mg/100 mL) Total VFA (mM)

6.52 a 0.51 88.4

6.08 b 0.62 93.2

6.12 b 0.47 102.2

0.068 0.091 10.1

<0.001 0.488 0.673

VFA (mol/100 mol) Acetate Propionate Butyrate Isobutyrate Isovalerate Valerate Acetate to propionate ratio

49.2 44.2 b 4.2 0.4 0.9 0.9 1.20 a

42.9 51.1 a 4.1 0.2 0.9 1.0 0.82 b

41.5 52.4 a 4.1 0.3 0.8 1.1 0.84 b

2.68 2.40 0.26 0.10 0.06 0.15 0.115

0.112 0.047 0.970 0.655 0.578 0.790 0.049

Means with different letters (a and b) within the row are statistically different. a CRT = control, MON = supplemented with monensin (32 mg/kg concentrate DM), PE = supplemented (2.8 g/kg concentrate DM) with a blend of (200–300 g/kg), Siberian ginseng (150–250 g/kg) and fenugreek (550–650 g/kg). b S.E. = standard error of the means. c Treatment effect.

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Item

Treatmenta

S.E.b

CRT

Glucose (mg/dL) Insulind (␮g/L) Cortisol (ng/mL) Leptin (ng/mL)

MON

PE

7 days

35 days

71 days

7 days

35 days

71 days

7 days

35 days

71 days

91.6 0.7 13.3 –

93.1 0.5 13.3 4.2

84.9 1.9 11.0 4.9

94.0 0.6 17.9 –

93.7 0.7 12.2 4.3

82.5 2.3 17.2 4.6

92.9 0.8 15.1 –

96.0 0.9 8.1 3.8

97.7 2.9 20.4 4.8

1.25 0.12 1.35 0.32

P-valuec T

Time

T × time

0.13 <0.001 <0.001 0.82

<0.001 <0.001 <0.001 <0.001

0.06 0.94 <0.001 <0.01

a CRT = control, MON = supplemented with monensin (32 mg/kg concentrate DM), PE = supplemented (2.8 g/kg concentrate DM) with a blend of artichoke (200–300 g/kg), Siberian ginseng (150–250 g/kg) and fenugreek (550–650 g/kg). b S.E. = standard error of the means. c T = treatment effect, time = time effect, T×time = interaction between treatment and time. d Data have been log transformed to achieve a normal distribution. Means in the table are not log-transformed means, however, S.E. and P-values correspond to the ANOVA analyses conducted with log-transformed data.

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Table 4 Serum and plasma metabolite concentrations of Holstein bulls as affected by monensin or plant extract blend supplementation

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3.3. Serum metabolites Serum metabolite concentrations are presented in Table 4. The interaction effect treatment and time tended (P=0.06) to be significant for glucose plasma concentration (Table 4). Glucose plasma concentration increased (P<0.05) in PE treatment from 7 to 35 days of study but it remained constant in the CRT and MON treatments. Bulls supplemented with PE had greater (P<0.001) insulin serum concentrations (1.6 ± 0.04 ␮g/L) than MON (1.2 ± 0.04 ␮g/L) or CTR bulls (1.1 ± 0.04 ␮g/L). In addition, insulin serum concentrations increased (P<0.001) from 35 to 71 days of study (Table 4). An interaction (P<0.001) between treatment and time on cortisol serum concentration was observed (Table 4). Cortisol serum concentration remained unchanged in the CRT treatment with time, in contrast to MON and PE treatments that elicited a decrease in cortisol serum concentration between 7 and 35 days of study and an increase thereafter. Leptin serum concentrations increased (P<0.001) in all treatments between 35 and 71 days of study. However, an interaction between treatment and time (P<0.001) on leptin serum concentrations was observed: leptin serum concentrations increased 17 and 28% in the CRT and PE treatments, respectively, whereas with MON treatment serum leptin concentration only increased 8% between 35 and 71 days of study (Table 4).

4. Discussion In the present study, monensin supplementation improved animal growth by 6%, but had no effect on feed intake and resulted only in a numerically better concentrate conversion efficiency. Page (2003) reviewed different studies conducted with beef cattle evaluating monensin supplementation and concluded that monensin improved 10% ADG and 12% feed conversion efficiency. In contrast, Bergen and Bates (1984) concluded that beef fed high-concentrate diets only improved feed conversion efficiency as result of a decrease in feed consumption. Explanations whereby MON increases animal growth and efficiency have been focused on rumen fermentation (Schelling, 1984). Main described effects of monensin on rumen fermentation have been explained partially by the reduction of Gram-positive bacteria in the rumen (Russell, 1987), and are the increase of propionate production, the decrease in methane production (McGinn et al., 2004), and the decrease of ammonia N in the rumen (Yang and Russell, 1993; Surber and Bowman, 1998). In addition, it has been described that monensin supplementation increases rumen pH (Surber and Bowman, 1998) due to an inhibition of lactate-producing bacteria (Dennis et al., 1981; Nagaraja et al., 1982), and to a reduction of intake variation and feed consumption (Chiriase et al., 1991; Larson et al., 1991). In the present study bulls supplemented had lower rumen pH and no effect was observed on rumen NH3 -N concentration compared to CTR bulls. There is no clear explanation for the observed lower rumen pH in MON bulls compared to CTR bulls, but it could be due to a greater numerical concentrate consumption and lower straw consumption of MON bulls compared to CTR bulls. With the low rumen NH3 -N concentration values observed in the CTR diets, monensin seems not to have an effect on rumen NH3 -N concentration. In agreement to the present study, Campbell et al. (1997) reported no differences in rumen

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NH3 -N concentration in steers consuming an 86% dry-rolled corn and low CP (12.5%) diet with or without monensin (33 mg/kg diet). Few data are available describing monensin effects on serum metabolites and their relationship with animal performance. In agreement with previous experiments (Theurer et al., 1990; Duff et al., 1994), monensin supplementation did not significantly affect blood glucose and insulin concentration. Greater ADG observed in MON treatment bulls may be related to increase cortisol levels, as Verde and Trenkle (1987) observed greater cortisol serum levels in fast-growing cattle than in slow-growing cattle. In the present study, leptin serum concentration increased with BW coinciding with the increase of insulin and cortisol with BW (Table 4). The observed increase in insulin serum concentration with BW (Table 4) has been previously reported (Duff et al., 1994; Matsuzaki et al., 1997). This increase in insulin serum concentration with BW may be due to age (Trenkle, 1970; Trenkle and Topel, 1978; Martin et al., 1979), to carcass fatness (Trenkle and Topel, 1978), or to the increase in feed consumption (Lapierre et al., 2000). In addition, obesity in cattle has been associated with basal hyperinsulinemia and insulin resistance (McCann and Reimers, 1986). Glucocorticoids and insulin had additive effects stimulating the secretion of leptin (Chilliard et al., 2001). However, in MON bulls the increase of leptin serum concentration with BW was not as pronounced as in PE and CTR bulls. Levy and Stevens (2001) reported that, in vitro, monensin was able to block leptin secretion from the adipocytes providing a possible an explanation for the lower leptin serum concentration increase as BW increased observed in the MON compared with CTR or PE animals. The potential capacity of monensin to modulate leptin secretion could be a non-discussed mode of action that could explain, partially, the improvement of feed efficiencies observed in finishing beef cattle supplemented with monensin (Bergen and Bates, 1984; Page, 2003). In this study, in monensin supplemented bulls a numerical improvement of efficiency was observed as consequence of an enhanced growth in contrast to the CTR bulls. No previous data are available of the effect of the blend of PE used in the current study on animal performance. However, some studies have been conducted with plants containing sarsaponins and saponins which are also present in ginseng and fenugreek, respectively. Growth of steers has been reported to improve when supplementing sarsaponin, a steroidal saponin extracted from Yucca schidigera (Zinn et al., 1998). In contrast, effects of sarsaponins and saponins on feed consumption are contradictory. Some studies have reported increases (Zinn et al., 1998), whereas others (Hussain and Cheeke, 1995) have reported a decrease from 2 to 3%, and others (Hristov et al., 1999) did not find any effect of Y. schidigera (rich in sarsaponins and saponins) supplementation on feed consumption. The numerical improvement in ADG observed in the present study in animals supplemented with PE could be partially explained by its effect on rumen fermentation. Rumen mode of action of the blend of PE could be similar to that of monensin due to the gingseng and fenugreek saponin content. Saponins, contained in fenugreek, have antimicrobial properties, and suppress the growth of ciliate protozoa, peptidase-producing bacteria, and cellylolytic bacteria in the rumen (Francis et al., 2002) which are normally acetate-, but not propionate-producers (Wallace et al., 1994). The antiprotozoal effect of saponins is due to their capacity to form irreversible complexes with the cholesterol present in the protozoal cell membranes, causing cell lysis (Francis et al., 2002). This antiprotozoal effect could explain the reduction of rumen

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NH3 -N concentration observed in different studies conducted with saponins in vivo (Hussain and Cheeke, 1995; Hristov et al., 1999) and in vitro (Lila et al., 2003; Busquet et al., 2006), which was not observed in the present study. However, as mentioned before, with the low rumen NH3 -N concentration values observed in the CTR diets, PE supplementation seems not to have an effect on rumen NH3 -N concentration. In agreement to the present study, some studies reported that saponins supplementation increased propionate and decreased acetate proportion (Hussain and Cheeke, 1995; Hristov et al., 1999; Lila et al., 2003; Busquet et al., 2006). The lower rumen pH in bulls supplemented with PE compared to CTR bulls could also be explained by the numerical greater concentrate consumption and lower straw consumption, however, saponins effects on rumen pH are contradictory. In accordance to the present results, Hristov et al. (1999) observed a lower rumen pH when heifers were supplemented with Y. schidigera (rich in sarsaponins and saponins) compared with the control heifers. Busquet et al. (2006) studied the effect of different plant extracts on in vitro rumen fermentation and also reported a decrease in pH when fenugreek was tested. In contrast, Hussain and Cheeke (1995) feeding Y. schidigera to steers did not observe any effect on rumen pH. Effects of PE on serum metabolits have been mostly studied in humans. A hypoglicaemic effect of PE has been described in humans (Briskin, 2000; Francis et al., 2002; Madar and Stark, 2002), for this reason a decrease throughout the study in plasma glucose concentration in bulls supplemented with PE was expected. Different mechanisms have been proposed as possible explanations for the hypoglicaemic PE effects. Madar and Stark (2002) described in rats a chronically greater serum insulin levels due to the stimulation of pancreatic ␤-cells probably due to the 4-OH-Ile fenugreek content. The increase in insulin serum levels with PE supplementation has been described in other studies (Broca et al., 1999, 2000 cited by Madar and Stark, 2002). Greater insulin serum concentrations observed in the PE bulls, compared to MON bulls could explain the greater leptin serum concentrations observed at 71 days of study (approximately at 415 kg of BW) in contrast to MON bulls. If serum leptin concentrations are related to animal growth and efficiency, this might explain that PE bulls grew more than CTR but less than MON bulls, eventhough PE effects on rumen fermentation were close to those of MON.

5. Conclusions The supplementation of the blend of plant extracts (200–300 g/kg artichoke, 150–250 g/kg Siberian ginseng, and 550–650 g/kg fenugreek) in bulls fed a high-concentrate diet is a plausible alternative to monensin supplementation because it has similar effects on growth, rumen molar proportion of propionate, and cortisol serum concentration.

Acknowledgements This research was made possible by the financial contribution of Phytosynthese (France). The authors thank Salvador Maluquer, Joan Fornos, and Joan Potrony from Cooperativa d’Artesa, N´uria and Marta from IRTA-Unitat de Remugants, and the Chemical Departments of IRTA and UAB for their assistance.

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