Intake, digestion and microbial protein synthesis in sheep on hay supplemented with prickly pear cactus [Opuntia ficus-indica (L.) Mill.] with or without groundnut meal

Small Ruminant Research 63 (2006) 125–134

Intake, digestion and microbial protein synthesis in sheep on hay supplemented with prickly pear cactus [Opuntia ficus-indica (L.) Mill.] with or without groundnut meal A.K. Misra b,∗ , A.S. Mishra a , M.K. Tripathi a , O.H. Chaturvedi a , S. Vaithiyanathan a , R. Prasad a , R.C. Jakhmola a a b

Division of Animal Nutrition, Central Sheep and Wool Research Institute, Avikanagar, Rajasthan 304 501, India Plant Animal Relationship Division, Indian Grassland and Fodder Research Institute, Jhansi-284003, UP, India Received 11 March 2003; received in revised form 17 February 2005; accepted 17 February 2005 Available online 19 October 2005

Abstract Prickly pear cactus [Opuntia ficus-indica (L.) Mill.] and roughage (Cenchrus ciliaris)-based diets with (OCG) or without (OC) an organic N source supplement (50 g groundnut meal) were compared to a roughage plus 200 g concentrate (CC)-supplemented diet. Intake, nutrient utilization, rumen fermentation, excretion of urinary purine derivatives and microbial N supply in Malpura hoggets were assessed. Opuntia cladodes contained DM 218 g/kg, CP 126 g/kg, NDF 466 g/kg and ash 172 g/kg of DM. Dry matter intake through cladodes was 237–243 g in opuntia-based diets. Dry matter intake was lowest (P < 0.02) in OC diets 61 g to that of 74 g/kg W0.75 in CC or OCG diets. Total tract apparent digestibility of DM, CP and GE were lower in OC diets than CC and OCG diets and these were not different between CC and OCG diets. DCP, DE and ME content and intakes were similar in CC or OCG diets, and were significantly higher than in OC diet. Urinary excretion of purine derivatives and microbial N supply were low in animals fed opuntia diets. Ruminal fluid pH increased due to opuntia feeding. Total N and NH3 -N in ruminal fluid was lower in OC diet. TVFA, acetate and butyrate were higher (P < 0.01) in CC diets, whereas propionate was similar in all three diets. It is concluded that opuntia cladodes and roughage diets require an additional supplementation of organic N source, which improve dry matter intake, apparent digestibility, nutritive value, plane of nutrition and ruminal N and NH3 -N. However, impaired microbial protein supply on opuntia diets needs further studies. © 2005 Published by Elsevier B.V. Keywords: Prickly pear cactus; Opuntia; Nutrient utilization; Purine derivatives; Microbial protein; Sheep

1. Introduction

∗ Corresponding author. Tel.: +91 517 2730128; fax: +91 517 2730833. E-mail address: [email protected] (A.K. Misra).

0921-4488/$ – see front matter © 2005 Published by Elsevier B.V. doi:10.1016/j.smallrumres.2005.02.014

Semi-arid and arid regions of South-east Asian countries are prone to drought. During this period both loss of life productivity and/or of animal life occur, mainly due to shortage of feed. To tackle the situation

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several measures e.g. transportation of straws and other crop residues from far off places, improvement of quality of existing feed resources and supplementary diets with meager quantity of concentrate are taken. Opuntia although available in semi-arid and arid regions is not fed to animals in south-east Asian countries. Opuntia [Opuntia ficus-indica (L.) Mill.] (prickly pear), an excellent natural source, is a fast growing xerophytic plant and well adapted to arid and hot environments. Dry matter yield from opuntia may exceed 2000 kg/ha (Muller et al., 1994), on uncultivated wastelands without any input. Opuntia has been used as a drought feed and as forage for cattle feeding since early 19th century (Griffiths, 1906; Woodward et al., 1915), in most instances it is still used as emergency feed during drought. However, the genus appears in great genetic diversity as it is widely used in human (fruits and green vegetables) and animal (fodder and forage) diets (Russell and Felker, 1987) in Mexico. Studies have indicated that the digestibility of opuntia cladodes is comparable with high quality hay (Shoop et al., 1977). The plant is extremely variable in its nutritive value, which depends mainly on species, variety, age of plant, season and plant part (Hanselka and Paschal, 1990). Nutritive value of various opuntia spp. was examined for animal feeding (Griffiths and Hare, 1906; Lehman, 1969; De Kock, 1980; Meyer and Brown, 1985; Retamal et al., 1987). Our previous experiments (Sirohi et al., 1997) have shown that opuntia from semi-arid regions in India contain CP 92 g/kg DM, which is higher than the commonly used dry roughages (straw, strovers and grasses) in ruminant feeding. Although opuntia feeding with conserved fodder maintained adult sheep, however, high N loss in urine led to negative N balance (Sirohi et al., 1997). Therefore, additional N source is needed. The present experiment was undertaken to study the effect of supplementing opuntia cladodes in Cenchrus ciliaris hay-based diets with or without groundnut meal as N source on rumen fermentation, intake, digestion, and urinary excretion of purine derivative in sheep. 2. Materials and methods 2.1. Study site The study was carried out at Central Sheep and Wool Research Institute, Avikanagar, located at 26◦ 17 N lat-

itude, 75◦ 28 E longitude and 320 m above sea level. The climate is typically semi-arid with yearly mean minimum and maximum temperatures of 6 and 41 ◦ C, respectively. The ambient temperature and relative humidity of the animal shed during experimental period were 9.0 ± 0.4 ◦ C and 43.0% minimum and 30.0 ± 0.8 ◦ C and 80% maximum, respectively. 2.2. Animals and feeding Twenty one 2- to 3-year-old Malpura breed rams (32.11 + 0.87 kg) were divided randomly into three groups based on comparable age and BW. The diet consisted of cenchrus (C. ciliaris) hay and chopped (5–8 cm) opuntia cladodes offered ad libitum. The opuntia cladodes were harvested from a newly established plantation, which had received farmyard manure in the preceding year. The control group (CC) was fed cenchrus hay ad libitum and 200 g concentrate mixture (barley 450 g/kg, wheat bran 250 g/kg, groundnut meal 280 g/kg, common salt 10 g/kg and mineral mixture 10 g/kg). The second group (OC) was fed cenchrus hay and chopped opuntia cladodes ad libitum. The third group (OCG) received cenchrus hay and opuntia ad libitum and 50 g groundnut meal to provide adequate protein (ICAR, 1998). Composition of diets is given in Table 1. Animals were housed individually in stalls. Roughage (hay and opuntia) and supplements were fed separately. Animals were permitted 10% roughage refusals. Animals were fed daily at 10.00 h, after discarding the orts of the previous day. Water was available freely twice a day at 9:30 and 13.30 h. Feeding experiment was continued for 45 days. 2.3. Metabolism trial A metabolism trial was conducted after 30 days of feeding, lasted for 7 days in metabolism cages with facility of quantitative collection of faeces and urine separately. Daily intake of feed and output of faeces and urine were recorded. Samples of feed offered, orts, faeces and urine voided were collected every morning. Dry matter in feed and faeces samples were determined daily by drying at 70 ◦ C to a constant weight. The dried samples of 7-day collection were pooled, ground through 1 mm screen and preserved for chemical analysis. Samples of faeces and urine (1/25) from individual animals were collected every morning for 7 days in

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Table 1 Composition of ingredients and diets Feed ingredients

Ingredient composition (g/kg fresh) Cenchrus + concentratea Cenchrus + opuntia Cenchrus + opuntia + GNMb

Concentrate mixture

Groundnut meal

Opuntia

Cenchrus hay

205 – –

– – 50

– 309 248

795 691 702

Chemical composition of feed ingredients (% DM) Dry matter 95.4 Crude protein 23.6 Neutral detergent fiber 56.5 Acid detergent fiber 13.8 Hemicellulose 42.8 Cellulose 9.0 Acid detergent lignin 3.8 Gross energy (Mcal/kg) a b

4.8

95.7 38.0 28.4 20.9 7.6 13.4 6.9

21.8 12.6 46.6 39.3 7.3 33.2 5.4

95.4 7.7 65.15 43.6 21.6 31.0 8.8

5.7

3.9

4.6

Concentrate contained: barley 450 g/kg; wheat bran 250 g/kg; groundnut meal 280 g/kg; common salt 10 g/kg; mineral mixture 10 g/kg. Groundnut meal.

a 500 ml Kjeldahl flask containing 25 ml concentrate sulfuric acid for N determination.

x values calculated for each sheep were converted to microbial N supply as follows:

2.4. Chemical analysis

Microbial N supply (g/day) =

Samples of roughage (cenchrus and opuntia), supplements, and faeces were analysed for ash and CP as per the standard procedures of AOAC (1995). The neutral detergent fiber (NDF) was determined by the procedure of Van Soest et al. (1991) without sodium sulfite and ␣-amylase, whereas ADF and acid detergent lignin (ADL) were determined according to Goering and Van Soest (1970). Energy content of feed, faeces and urine was estimated using a Ballistic Bomb Calorimeter (Gallenkemp, UK). Urinary purine derivatives viz., allantoin, xanthin and hypoxanthine, and uric acid were determined following the procedure as described in IAEATECDOC-945 (1997). The microbial protein absorbed (x, mmol/day) were calculated on the basis of purine derivative excreted (y, mmol/day) as follows (Verbic et al., 1990):

where 0.83 is the digestibility of microbial protein and 0.116 the ratio of purine N to total microbial N (Chen et al., 1992a).

y = 0.85x + 0.385LW0.75 where 0.85 is the recovery of absorbed purines as urinary purine derivatives and 0.385LW0.75 represents the endogenous contribution of purine excretion. The

70x 0.83 × 0.116 × 1000

2.5. Rumen fermentation Rumen liquor samples from experimental animals were collected at 0, 3, 6 and 9 h post-feeding, using stomach tube at the end of the feeding experiment. The pH was measured in whole rumen liquor immediately using a digital pH meter (pH 5652, EC India Ltd.). Rumen liquor samples strained with double layer of muslin cloth and 11 ml of preservative were added (5 ml of orthophosphoric acid plus 1 g of HgCl2 ) per 100 ml of strained rumen liquor (SRL) and stored frozen (−15 ◦ C) for quantification of total N (AOAC, 1995), NH3 -N (Conway, 1962) and total volatile fatty acids (TVFA; Bernett and Reid, 1957). Volatile fatty acids (acetate, propionate and butyrate) in SRL were determined on HPLC system (Shimadzu 10AD, Japan) as per standard procedure described by Canale et al. (1984).

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2.6. Statistical analysis

The group differences were compared by Duncan’s Multiple Range Test (Duncan, 1955).

Results obtained for intake, digestibility, plane of nutrition, urinary purine derivatives and microbial N supply were subjected to analysis of variance procedure of SPSS Base 10 (SPSS software products, USA), using a general linear model: Yij = µ + Di + eij , where µ is the general mean, Di the effect of ith diet (1–3) and eij the random error. The model used for rumen fermentation characteristics was as follows: Yijkl = µ + Di + Pj + (DPij )k + eijkl , where µ is the general mean, Di the effect of ith diet (1–3), Pj the effect of jth sampling period (1–4), (DPij )k the interactions among ith diet and jth sampling periods and eijkl the random error.

3. Results Opuntia cladodes were palatable and sheep generally ate them before eating roughage. The sheep fed opuntia consumed on average 1.2 kg daily in addition to cenchrus hay (Table 2). 3.1. Dry matter intake and apparent digestibility Dry matter intake and total tract apparent digestibility of DM, OM, CP and GE were lower (P < 0.05) in sheep fed OC diets than those on CC or OCG diets, which were similar (Table 2). The NDF and ADF digestibilities did not differ significantly among groups. Hemicellulose digestibility in OC and OCG was lower (P < 0.01) than in CC. However, OCG

Table 2 Feed intake, nutrient digestibility and nutritive value of diets containing cenchrus hay supplemented with concentrate (CC), opuntia (OC) or opuntia and groundnut meal (OCG) in sheep Items

Diets CC

Initial body weights (kg) Final body weights (kg) Dry matter intake (DMI, g/day) Cenchrus hay Opuntia Concentrate Groundnut cake Total DMI (g/kg W0.75 ) Diet digestibility (%) Dry matter Crude protein Neutral detergent fiber Acid detergent fiber Hemicellulose Cellulose Gross energy Nutritive value Digestible crude protein (% in ration) Digestible energy (kcal/kg DM) Metabolisable energy (kcal/kg DM)

29.8 30.2

OC 31.7 31.5

S.E.M.

P-value

0.86 0.97

1.01 0.95

OCG 31.8 31.0

752 – 191 –

547 243 – –

672 237 – 48

50.1 23.3

943 b 73.9 b

790 a 61.2 a

957 b 74.4 b

33.9 2.46

0.06 0.02

54.1 b 53.8 b 45.2 45.0 b 44.5 a 34.3 a 54.8 b

3.32 3.32 1.78 1.91 3.45 2.40 1.69

0.03 <0.01 0.98 0.06 0.01 <0.01 0.03

5.6 b 2501 b 2455 b

0.39 84.37 84.2

<0.01 0.03 0.02

53.9 b 48.7 b 46.1 35.5 a 60.8 b 45.9 b 48.3 b 4.6 b 2217 a 2150 ab

Values with different letter in a row differ significantly.

46.3 a 31.5 a 45.2 40.5 ab 38.7 a 50.54 b 45.0 a 2.8 a 1997 a 1915 a

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had lower (P < 0.05) cellulose digestibility than OC and CC, which exhibited the same digestibility values. 3.2. Nutritive value The OC diet had the lowest DE and ME content. However, the CC diet had middle values and which were similar (P > 0.05) in both OC and OCG diets. The DCP content of OC diet was lower (P < 0.05) than that of CC and OCG, which were statistically similar. The DE/DP ratio was higher (P < 0.05) in OC than in CC and OCG. 3.3. Plane of nutrition Intake of digestible DM, OM, CP and DE and ME were similar in CC and OCG diets but were significantly lower in OC diets (Table 3).

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3.4. Nitrogen balance Nitrogen intake was lower on the OC diet than CC and OCG diets. The N excretion was, however, similar in the three animal groups. Nitrogen balance was lower (P < 0.01) in OC than CC and OCG, which were similar. 3.5. Purine derivatives excretion and microbial protein supply Total purine derivative excretion was 4.39 mM/day in CC, however, these values were significantly reduced in opuntia fed groups (OC and OCG). Similarly, microbial protein supply was also higher (P < 0.05) in CC than in OC and OCG (Table 4). 3.6. Rumen fermentation characteristics Rumen fermentation characteristics are presented in Table 5. Ruminal fluid pH was higher in sheep fed

Table 3 Plane of nutrition of sheep fed with diets containing cenchrus hay supplemented with concentrate (CC), opuntia (OC) or opuntia and groundnut meal (OCG) in sheep Diets CC Digestible dry matter intake g/day g/kg W0.75

P-value

OCG

367 a 28.3 a

519 b 40.2 b

28.8 2.03

0.03 0.01

Digestible organic matter intake g/kg DM 562.3 ab g/day 530 b 41.5 b g/kg W0.75

510.3 a 403 a 31.2 a

617.3 b 591 b 45.9 b

18.43 30.42 2.16

0.04 0.02 <0.01

Digestible organic matter in rumen g/kg DM 366 b g/day 345 b 30.8 b g/kg W0.75

332 a 262 a 24.9 a

401 b 384 b 35.2 b

20.12 19.8 2.61

0.03 0.03 0.01

22 a 1.7 a

53 b 4.1 b

4.3 0.33

<0.01 <0.01

Digestible crude protein intake g/day g/kg W0.75

511 b 39.9 b

OC

S.E.M.

43 b 3.4 b

Digestible energy intake kcal/day kcal/kg W0.75

2095 ab 164 b

1588 a 122 a

2401 b 186 b

136.0 9.1

0.03 <0.01

Metabolisable energy intake kcal/day kcal/kg W0.75

2032 ab 159 b

1551 a 119 a

2358 b 182 b

134.2 9.03

<0.01 <0.01

75 b

45 a

4.9

0.01

DE/DP ratioa

49 a

Values with different letter in a row differ significantly. a DE/DP: ratio of digestible energy (kcal) and digestible protein ratio (g).

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Table 4 Nitrogen balance, urinary purines and microbial N supply in sheep fed with diets of cenchrus hay supplemented with concentrate (CC), opuntia (OC) or opuntia and groundnut meal (OCG) Diets

S.E.M.

P-value

CC

OC

OCG

Nitrogen (g/day) Intake Voided in faeces Voided in urine N retained

14.3 b 8.1 1.5 a 4.64 a

11.0 a 7.5 1.7 a 1.75 b

15.8 b 7.3 2.8b 5.80a

0.75 0.34 0.21 0.73

<0.01 0.66 0.02 0.01

N retention % of intake % absorbed

31.3 b 69.3

15.9 a 49.8

36.7 b 68.1

3.62 4.4

0.03 0.11

Urinary excretion of purine derivatives Allantoin (mM/day) Uric acid (mM/day) Xanthine and hypoxanthine (mM/day) Total purine derivatives (mM/day) Total purine derivatives (mM/kg W0.75 )

3.38 b 0.89 b 0.12 4.39 b 0.34 b

0.97 a 0.26 a 0.08 1.31 a 0.09 a

1.23 a 0.36 a 0.07 1.65 a 0.13 a

0.397 0.110 0.031 0.492 0.038

<0.01 0.02 0.79 <0.01 0.03

Purine derivatives absorbed (mM/day)

5.23 b

1.56 a

1.97 a

0.586

<0.01

17.5 a 6.29 a

15.1 a 4.97 a

1.04 2.71

0.05 0.05

Microbial protein supply g/day g/kg DOMI

44.8 b 15.2 b

Values with different letter in a row differ significantly.

with CC or OCG diets. OC diet had constantly higher (P < 0.01) ruminal pH at all sampling periods (Fig. 1). Total N content of ruminal fluid was highest in OCG diet. Total N concentration peaked at 6 h post-feeding in all diets and was maximum in CC diet (Fig. 2). OC diet had lower N concentration at all sampling hours. Ruminal NH3 -N concentration was lowest (P < 0.01) in OC diets. The maximum NH3 -N concentration was noted at 3 h post-feeding and declined sharply thereafter in

all diets. OC diet had constantly lower NH3 -N concentration at all sampling hours (Fig. 3). TVFA, acetate and butyrate concentrations were lower in opuntia diets but propionate concentration was similar among three diets. TVFA were different (P < 0.01) at four sampling periods and peaked at 3-h post-feeding in CC and OC diets compared to 6 h in OCG (Fig. 4). OCG diet had constantly lower TVFA at all sampling hours and this trend was similar for acetate. Ruminal propionate con-

Table 5 Rumen fermentation characteristics in diets containing cenchrus hay supplemented with concentrate (CC), opuntia (OC) or opuntia and groundnut meal (OCG) in sheep Fermentation characteristics

pH Total N (mg/dl) NH3 -N (mg/dl) TVFA (meq/dl) Acetate Propionate Butyrate

Diets

S.E.M.

CC

OC

OCG

6.8 a 62.2 ab 20.9 b 10.4 b 7.22 b 1.32 0.80 b

7.2 b 57.1 a 17.3 a 8.0 a 5.74 a 1.04 0.35 a

7.1 b 64.6 b 22.5 b 6.9 a 5.05 a 0.92 0.46 a

Values with different letter in a row differ significantly.

0.03 1.09 0.55 0.27 0.22 0.09 0.04

P-value Diet

Hours

Diet × hours

0.06 <0.01 <0.01 <0.01 <0.01 0.19 <0.01

0.01 <0.01 <0.01 <0.01 0.13 0.01 0.11

0.66 0.10 0.87 0.01 0.07 0.47 0.61

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Fig. 1. Ruminal pH of sheep on cenchrus hay supplemented with concentrate (CC), opuntia (OC) or opuntia and groundnut meal (OCG).

Fig. 2. Ruminal total N in sheep on cenchrus hay supplemented with concentrate (CC), opuntia (OC) or opuntia and groundnut meal (OCG).

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Fig. 3. Ruminal NH3 -N in sheep on cenchrus hay supplemented with concentrate (CC), opuntia (OC) or opuntia and groundnut meal (OCG).

tion in Brazil (Gillet, 1990) and Argentina (Guevara et al., 1999). Supplementation with opuntia cladodes increased milk production (Azocar and Rojo, 1992) in rangelands. Feeds and fodder are in short supply in many developing countries, the feed resources become scarce especially during drought. Thus, opuntia could be used in routine animal feeding even though it is poor in protein content, which varies from 55 to 113 g/kg DM (Gregory and Felker, 1992). Therefore, N supplementation should be emphasized to improve the nutritive value of opuntia diets (Sirohi et al., 1997; Ben Salem et al., 2002). Since opuntia is high in water content, it could meet water requirement also during

centration was different (P < 0.05) at four sampling periods. Propionate peaked at 3 h post-feeding and was maximum in OC followed by CC and OCG diets. It declined quickly between 3 and 6 h and then remained more or less constant from 6 to 9 h post-feeding. OC diet had constantly lower butyrate concentration at all sampling periods. Butyrate concentration was maximum at 3 h post-feeding in CC diets and reduced sharply in all diets.

4. Discussion The use of opuntia as supplement to native forage in dry season is common in goat meat produc-

Fig. 4. Ruminal total volatile fatty acids (TVFA) in sheep on cenchrus hay supplemented with concentrate (CC), opuntia (OC) or opuntia and groundnut meal (OCG).

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severe drought conditions. Opuntia cladodes used in this study contained DM 218 g/kg, CP 12.6% and NDF 46.6% DM and were higher than values reported in previous studies (Shoop et al., 1977; Retamal et al., 1987; Ben Salem et al., 1996; Sirohi et al., 1997). Gregory and Felker (1992) reported that forage clones of opuntia varied greatly in their protein content with some clones having 11% CP when other clones had only 6%. Reduced ruminal acetate in OC but similar propionate concentration in OC and CC diets indicated that opuntia is rich in readily available carbohydrates. Digestive disturbances were not observed in the current study. Dry matter and NDF contents of opuntia cladodes were high in the present study, which might have reduced their intake and apparent total tract nutrient digestibility in OC diet. N available in opuntia-containing diet (OC) was low. Stimulatory effect of amino acids, peptides and branched chain VFA on growth of rumen microorganisms (Huques and Thomson, 1984; Gorosito et al., 1985) and subsequent increase in nutrient digestibility is expected on OCG diet. Organic N supplements led to an increase in ruminal NH3 -N and sharply enhanced the net production of branched chain fatty acids (Broudiscou et al., 1999), but inorganic N supplements only increased NH3 -N (Balcells et al., 1993). Poor N utilization from opuntia cladodes reduced the nutritive value and thereby plane of nutrition in OC diet. However, groundnut meal supplementation improved these in OCG diet. The DCPI in OC diet was 50% of the recommended 40 g DCPI/day as maintenance requirement of adult sheep (INRA, 1978). Low DMI and apparent digestibility could be attributed to the depressed microbial activity due to lower ruminal NH3 -N, which might hamper fiber utilization in ruminants on opuntia diets (Preston and Leng, 1987; Ben Salem et al., 1996). Positive effect of organic N supplement, similar to this study, on apparent digestibility of opuntia-based diets was also found by Ben Salem et al. (2002). Nitrogen supply had probably enhanced microbial activity in the rumen and encouraged microorganisms to degrade more feed (Leng, 1990). High ruminal pH and reduced NH3 -N, TVFA and fractional VFA in opuntia-diets are contrary to previous studies (Ben Salem et al., 1996), which advocated that presence of spineless opuntia in the diet did not affect ruminal pH, increase ruminal NH3 -N, propionate and reduced acetate production, because spineless opuntia

are rich in easily fermentable carbohydrates. Normally reduced pH is expected with opuntia diets but it was not the case in this study as well as in others (Ben Salem et al., 1996). Increased ruminal pH in opuntia diets may be explained by the fact that consumption of opuntia had probably enhanced salivation resulting from the high levels of mineral salts (ash 150–250 g/kg DM) and abundance of mucilage in opuntia. Furthermore, the rate of consumption of opuntia would be less than concentrate or molasses. Although opuntia contained adequate CP but ruminal NH3 -N concentration was lower in OC diets. Opuntia cladodes fed animal may face deficiency of N and phosphorus, as it contains only 0.2% P (Gregory and Felker, 1992). Phosphorus deficiency is known to impair protein utilization and microbial protein synthesis (Petri et al., 1989; Ternouth and Sevilla, 1990). This mineral could also affect appetite and feed utilization (Ternouth, 1990). Low DMI and impaired apparent nutrient digestibility in OC diets may be the result of P deficiency in this study. Our results have also confirmed that N supplementation through groundnut meal (50 g/day) improved intake, diet digestibility, N balance and plane of nutrition. High urinary N excretion in OCG diets might be due to P deficiency caused by opuntia feeding. Sirohi et al. (1997) also reported higher urinary N loss on opuntia diets. The excretion of purine derivatives in urine is a widely accepted marker for estimating microbial protein synthesis in ruminants. A correlation between purine derivatives and duodenal flow of nucleic acid was reported in the literature (Chen et al., 1990; Balcells et al., 1991). The increase of DCP intake improves urinary purine derivative excretion, indicating higher duodenal flow of microbial protein (Balcells et al., 1993). Endogenous losses of purine derivatives increase with body weight (Chen et al., 1992a) and the intestinal supply of energy (VFA) and protein do not modify urinary excretion of purine N (Fujihara et al., 1987). In this experiment, live weight among the sheep were low and thus there was no significant effect on endogenous purine excretion. Although groundnut meal provision increased DCP intake in OCG sheep, but microbial protein supply was not improved as indicated by similar values of purine derivatives excreted in urine with OC and OCG. Efficiency of microbial N supply had linear correlation with either DMI or DOMI (Gomes et al., 1994). Microbial N supply values in sheep fed CC diet are close to those for the

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straw diets (12.8–15.8 g MN/kg DOMI) found in earlier experiments (Chen et al., 1992b; Susmel et al., 1994), in which sheep were given restricted intake of straw supplemented up to 40% DMI with barley or sugar beet pulp. Microbial N supply was very low in opuntia diets. High ash content and P deficiency in opuntia cladodes might have hampered microbial growth in rumen (Leng, 1990; Komisarczuk-Bony and Durand, 1991).

5. Conclusion Sheep offered opuntia in combination with cenchrus hay had low feed intake, apparent digestibility of DM, CP and energy, nutritive value, plane of nutrition and N balance. However, 50 g groundnut meal supplementation improved these in a way that the values were similar to cenchrus plus 200 g concentrate supplemented diet. Excretion of purine derivatives and microbial N as well as microbial protein supply was poor in sheep on opuntia diets. Opuntia feeding increased ruminal pH but decreased TVFA and fractional VFA. Supplemented groundnut meal (OCG) improved ruminal N and NH3 -N, whereas impaired microbial N supply needs further research to optimize P and other nutrient additives for better animal performance. The opuntia diets could be advantageous, when appropriate N supply is emphasized, as sheep may have similar digestion than those on common diets and may reduce considerably drinking water consumption.

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